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Патент USA US2406876

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Sept. 3,1946.
Filed May 29, 1942 «
4 sheets-sheet 1
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CHESTER 5. Mfrs, c/f?.
Sept. 3, 1946.
Filed May 29, 1942r
4 sheets-sheet 2
Sept" 3, 1946»
Filed May 259,I 1942
4 Sheets-Sheet 3
BYpW/f Ü? Mw@
Sept. 3, 1946.
Filed May 29, 1942
4 Sheets-Sheet 4
CHESTER B. Mfrs, de,
Patented Sept. 3, 1946
Chester B. Watts, Jr., East Orange, N. J., assigner
to Federal Telephone and Radio Corporation,
a corporation of Delaware
Application May 29, 1942, Serial N0. 444,988
16 Claims.
( Cl.' Z50-_11)
This invention relates to directive antenna
structures and more particularly to such systems
for producing the radiation patterns of Fig. 3
with the antenna apparatus of Fig, l;
as are employed for the instrument landing of
Fig. 5 diagrammatically represents another
suitable antenna arrangement;
aircraft. The invention is considered to be equal
ly adaptable to transmitting and receiving pur
Fig.> 6 is a schematic block diagram of a circuit
poses and, in this connection may be useful in
for feeding the antenna structure of Fig. 5 to
radio locating systems-especially where discrim
yield substantially the radiation characteristics
ination as to elevation angles of low magnitude
is of particular importance.
It is an object of the invention to provide an im
proved and safer instrument landing system.
shown in Fig. 3;
Figs. 7, 9 and 11 are graphical plots of signal
10 strength as a function of the elevation angle for
further illustrating features of the invention; and
Another object is to provide such a system
wherein small deviations up or down from the true
Figs. 8, 10 and 12 are schematic block diagrams
glide path will be characterized by relatively large
signal strength.
A more specific object is to provide means for
of appropriate circuits yielding substantially the
radiation characteristics shown in Figs. 7, 9 and
11 respectively.
Antenna structures of the so-called vertical
type are known for use in connection with set
ting up radiation fields suitable for instrument
throughout the region from zero elevation angle
landing purposes. Referring to Fig. 1, it has here
to a substantial fraction of the angle at which 20 tofore been proposed that the antenna for defin
the iirst major lobe occurs.
ing a glide path by the equi-signal principle
In accordance with a feature of the invention,
should comprise two antennae A, B disposed one
I provide means for radiating a vertically direc
above the other.
radiatingr a vertically directional pattern char
acterized by relatively weak signal strength
tional pattern (suitable for use as one of two over
According to the system heretofore proposed,
lapping patterns of an equi-signal glide path ra 25 the higher antenna A is fed with a signal repre
diation) and including an undesired lobe of lower
senting a “too low" airplane position (preferably
elevation than the first (i. e. lowest) useful lobe
a carrier modulated with 90 c. p. s.) while the
of said pattern but having a maximum magni
lower antenna B is fed with a “too high” signal
tude less than four percent of the maximum sig
(preferably a carrier modulated with 150 c. p. s.) .
nal strength of said ñrst useful lobe.
30 The two patterns thus produced overlap and ef
In accordance with another feature of the in
fectively intersect along several conical surfaces,
vention, I provide means for radiating~ a verti
where the axes of said conical surfaces are con
cally directional pattern characterized, in the ele
sidered as passing vertically and symmetrically
vation angle region about the desired glide path,
through antennae A and B.
by a signal strength which varies with elevation 35
In order better to compare these two diiîerent
angle 0 roughly in accordance with the following
patterns, radiation signal strength R. has been
plotted as a function of the elevation angle 0 in
Klcos @fi-cos (Ice-00)]
Fig. 2.
In the case illustrated by this ñgure, it
was assumed that the ratio a:b of the respective
40 elevations (with respect to ground) of antennae
where K and Ic are constants and 6o is less than
A and B was such that each lobe I0 of radiation
twenty-five degrees (positive or negative).
due to antenna B comprises a total elevation angle
Other objects and further various features of
equivalent to that comprehended by lobes ll, Il',
novelty and invention will hereinafter be pointed
out or will become apparent to those skilled in the 45 ll", etc. of radiation due to antenna A. With
this type of system, if maximum radiation due to
art from a reading of the following specification
each óf vantennae A and B is substantially equal
in connection with the drawings included here
(as illustrated by the lobes ID and Il), the first
with. In said drawings
l2 of radiation due to antenna A with
Fig. 1 diagrammatically represents an antenna
that due to antenna B, occurs at an angle well
structure suitable for use in accordance with the 50 above that at ywhich the first maximum of radi
ation due to .antenna A occurs. This circum
Figs. 2 and 3 are graphical plots of signal
stance is significant in that, for a given antenna
strength R as a function of e (the elevation angle)
height, the glide path angle is too large; or, con
for illustrating features of the invention;
versely, for a desired glide angle, the antenna
Fig. 4 is a schematic block diagram of a circuit 55 height must be unnecessarily large. In addition
to this fact, there are further intersections I3, I4
for angles very close to that represented by in
tersection I2. Since each intersection represents
an angle which landing instruments aboard an
aircraft may indicate as an appropriate glide an Ul
gle, intersections I3 and le may be sources of
considerable confusion to a pilot.
It is accordingly necessary in this type of
system to increase the magnitude of current fed
antenna B with respect to that fed antenna A a
substantial amount so as to produce a “swamp
fore, the overall 15G-cycle radiation pattern will
be seen to have substantially zero radiation for
these small angles as well as substantially zero
slope (i. e. rate- of increase oí radiation per de
gree elevation) . Thereafter, between 2 and 3 de
grees this radiation will markedly increase (due
to the rapid divergence of the two curves after
the one due to antenna A passes its maximum
and starts to decrease).
Thus the resultant radiation of the 15G-cycle or
“too high” signal will present substantially the
characteristics of curve Il in Fig. 3, while the 90
ing” lobe l5 of radiation. It will be noted that
cycle or “too-low" radiation, being due to antenna
the 90-cycle radiation pattern due to antenna A
A alone, will have the simple substantially hali
intersects lobe l5 of the 15G-cycle pattern at only
sine slope of curve l, l', 1” in the same iigure.
one point in the ñrst 20 degrees namely, at point 15
The curves of Fig. 3 represent radiations from
Ikfà, near the maximum of the first lobe Il.
an array like Fig. 1 where the elevation ratio
However, although any diiiiculty of confus
arb is 3 so that at low angles there are three lobes
ing intersection i6 with further adjacent inter
of radiation due to antenna A lfor each lobe due
sections of the radiations due to both antennae
to antenna B. Curves 'i-l'-'i”, il, &--%’-‘9", and
A and B has been removed, certain other diiiî
il relate to a system wherein the “too high”
.culties are presented 'by this type of radiation.
signal current in B, the “too high” signal cur
For example, it will be noted that the differences
rent in A, and the “too low” signal current Yin
between radiation l5 due to antenna B and radia
A are proportional to the values 1, 1A?, and 1 re
tion ll due to antenna A for angles of elevation
spectively. Curve 8 represents the “too high”
lower than the glide path are relatively small as
signal component from antenna BÍ. . Curve
compared with corresponding differences at ele
9--9’--9” represents the “too high’y component
vationV angles just above the correct glide path.
from antenna A. Curve Il represents the re
This condition is considered undesirable in view
sultant I “too-high” pattern of slow-rise form.
of the fact that a pilot will not be sumciently
Curve 'l-‘i’-1” represents the simple pattern oi
warned of deviations below the latter. A safer - the “too-low” signal as radiated from antenna
glide path should be characterized by relatively
A only. Point I-ß is the intersection of vcurves Il
great differences in amplitude of the two types
of radiation for deviations below the glide plane,
so that there will be no danger of running into
high ground obstacles as a result of miscalculat
ing the true glide path. Furthermore, a safe
glide path should exhibit the feature illustrated
by lobes il and l5 of presenting no false glide
paths for angles which may reasonably be con
fused with the true glide angle.
In accordance with the invention, these desir
able features may be realized by producing the
“too high” radiation pattern as a vector sum of
two or more elementary radiation patterns from
two or more antennae of different heights above
the ground. In accordance with a specific fea
ture of the invention two elementary radiation
patterns to be combined have their strengths pro
portioned to make their slopes about equal at or
and 'a'.
Curves l1’ and Il” are slow-rise curves
produced from the same array but with the cur
rent proportions adjusted to 111/511 and 1:2/511
respectively instead of 111/311 as in curve il.
It will be noted that intersection I8 is formed
from one rapidly falling curve l and onerapidiy
rising curve Il and that therefore, deviations
above or below the correct glide plane will be
characterized by abnormally large signal recep
tion. It is further to be noted in connection
with the arrangement illustrated in Fig. 3, that
the next intersection i9 of the two signals char
acterized by these two types of radiation occurs
at an elevation angle well above the true glide
plane. There will accordingly be little or no
danger in this >case of a reasonable pilot mis
taking the true glide plane.
A relatively simple circuit for simultaneously
near the zero point and are oppositely phased. 5.0
obtaining the two types of radiation in Fig. 3 is
Thus the resultant “too high” pattern produced
by combining them has a substantially zero slope
shown in Fig. 4. This circuit is designed for pro
ducing an equisignal glide path wherein devia
at or near zero and is therefore delayed in rising
tion below the true glide plane is detected by a
, to its ñrst large maximum value. Such a pattern
predominance of one steady signal and deviation
may for convenience be referred to as a slow-rise 55 above is characterized by a predominance of an
other steady signal. In the form shown, a car
-A glide path system having a “too high” pattern
rier frequency fu is supplied from a common
of the slow-rise type may be constructed with_
source Ztl and fed to one terminal of a conjugate
a two-antenna-element structure of the nature
network. 2i of the type disclosed in the U. S.
shown in Fig. 1 by applying to antenna A not 60
Patent 2,147,807 to A. Alford. In accordance
only the usual 90-cycle signal but in addition some
with the teachings or" the said patent, network
15G-cycle signal (exactly like that supplied to
2i serves to supply equal amounts of carrier en
antenna B but in phase opposition thereto). 1n
ergy into two transmission lines 22, 2e for sep
other Words, considering the radiation pattern of
arate modulation by the respective signals F1
the 15G-cycle signal, the radiation thereof will
and F2 (which may be 9i) and 150 c. p. s. respec
be modified considerably due to an effective can
tively). Also in accordance with the said pat
cellation of radiations from antennae A and B
ent, this modulation is preferably effected by
for very small elevation angles in the vicinity of
continuously' varying the tuned states of a pair of
zero elevation. In accordance with the inven
tion the magnitudes of the 15S-cycle signal corn 70 coupled sections 2i, 25 associated respectively
with lines 22 and ‘23. The “too-low” signal (oon
ponents fed toV antennae A and B are such that,
when plotted, the two curves are substantially
tangent at the lowest elevation angles, say be
tween zero and 1 degree. Upon combining these
two 'components for effective subtraction, there
sisting of carrier .modulated by the iXi-cycle sig
nai F1) is then fed from line 22 to one terminal
of another conjugate network 26, and the diag
75 onally opposite terminal thereof is similarly con
nected to line 23 to receive the “too-high” sig
nal (consisting of 15G-cycle or Fz-characterized
carrier). Other terrminals of network
connected respectively to antenna A and
ing network 21. Between the terminals
work 26 connected to antenna A and to
26 are
of net
line 23,
there is a phase reversal element 28 (e. g. a trans
the simple ñrst embodiment above taken for illus
tration, the power radiated at 6° is
(1.33)2+(1) 2:2.78
and the power radiated along the glide path is
(.55)2+(.55)2=.6 Thus the wastage ratio is 4.6.
By slightly varying the ratio of the “too high”
mission-line transposition) for assuring that none
signal currents fed to antennae A and B the
of the “too high” or E12-characterized signals will
be fed into line 22 and, conversely, that none of 10 elementary patterns corresponding to patterns 8
and 9-9’--9” will become less accurately tan
the "too low” or .F1-characterized signals will be
gent and the combined pattern will change from
fed into line 23. Amplitude control means 29 is
the form shown in curve I1 to the form shown
provided in the line supplying the signal F2 to
in curve l1’ or I7".
network 26, whereby the amount of signal F2 to
If for example the 150-cycle-modulated cur
be radiated from antenna A may be controlled 15
rents are fed to antennae B and A in the ratio
with respect to the amount of signal F1 radiated
1:1/5 (instead of 1:1/3 as before) the elementary
?therefrom.Y .As explained above, antenna B is
pattern due to antenna A will be of smaller am
fed with only one signaland, in the form shown,
plitude than curve 9--9’--9” and therefore the
it is connected to line 23 so as to radiate carrier
characterized with F2 modulation. For purposes 20 combined pattern l1’ instead of having a zero
slope at the origin will start rising immediately.
of controlling the magnitude of radiation from
If such a pattern I1' is substituted for pattern
antenna B with respect to that from antenna A,
I'l (the pattern 'I-1’-1” being retained without
suitable amplitude control means 3i! are pro
change for the “too low” signal) the resulting
vided in its supply line.
In the embodiment above described as a ñrst 25 system will be a little better than the first em
bodiment in respect of lowness and power wast
age ratio but a little less desirable in sharpness.
More speciñcally for this second embodiment rep
resented by curves I‘l’ and 'l-'V-'I" the low
9-9’-9” (representing the “too high” signal
energy from the antenna A) had such an inten 30 ness is !3.2% per wave length of height, the
illustration, it was assumed for simplicity, that
patterns 8 and T_T-1" each had an intensity of
one unit while the elementary radiation pattern
wastage ratio is 3.4 and the sharpness angle
sity as to be substantially tangent to pattern 8
for two to one signal ratio is about 0.65 degree.
(representing the “too high” signal energy from
If on the other hand the A antenna’s share of
the antenna B). This latter assumption required
the 150-cyc1e-modu1ated signal is raised instead
that pattern 9--9’--9" be about 1/3 the ampli
tude of pattern 8 since the spread between two 35 of lowered, so that the current ratio is 1:2/5 for
this signal, the resulting embodiment will be
successive nulls of pattern 9-9’-9" was about
slightly less advantageous in respect to lowness
’,/3 the corresponding spread for pattern 8. These
of glide path _for a given antenna height as well
simple assumptions led to the postulation of cur
as in respect to the power wastage, but the
rent strengths proportionate to 1:1/3r1 as above
will be improved. More specifically for
set forth.
such third embodiment (having a 1:2/5z1 propor
The two intersecting patterns H and T_T-7”
tion for the “too high” current in antenna A the
which result from these simple assumptions prove
“too high” current in antenna B and the “too
to be reasonably useful from the most essential
low” current in antenna B respectively) the pat
standpoints. Considering ñrst the important cri
terns will correspond to curve il” and curve
terion of how low a glide angle can be defined " T_T-ï”. It can be computed that these pat
with a given antenna height, it will be seen from
terns give about 12.6 percent lowness per wave
Fig. 3 that a glide angle can be established at
length of height, a power wastage ratio of 5.5, and
3.25". Now the curves of this ligure are based
a sharpness of about .47 degree.
upon antenna heights a and b of about 7.2 wave
In. accordance with the invention, the lowness
lengths and 2.4 wave lengths respectively. Thus
per wave length of height can be increased by
if the percentage of lowness of the glide
be taken as I3Q() times the reciprocal of the
path elevation in degrees (so that a glide
of 3° has 100% lowness while a glide path
of 6°
providing for the “too low” signal, in lieu of .the
conventional half-sine pattern ’I-«T-V' a modi
fled pattern which will cause the intersection de
fining the glide plane to occur at smaller angles
has only 50% lowness) the simple embodiment 55 for given antenna heights. This modified half
above described gives 92.4% lowness for an over
sine is illustrated in Fig. ’7 as the curve 130. Curve
all height of 7.2 wave lengths or 12.8% lowness
4B is the resultant of a vectorial addition of some
per wave length of height.
radiation from both antennae A and B in a phase
relationship similar to that required to produce
Considering next the sharpness of the glide
path, this may usefully be deñned by the number 60 the slow rise type of curve (such as curves il, I "I",
I1” in Fig. 3 and curve lil in Fig. 7) but with the
of degrees divergence downward from the true
relative magnitude greatly altered. To produce
glide path required to yield a two-to-one intensity
the slow-rise type of pattern previously described
ratio between the 150 and 90 cycle signals. Using
this criterion, itwill be seen from Fig. 3 that at 65 the amplitudes of the two elementary 15G-cycle
radiations are so adjusted that in the low angle
275° the 90-cycle-modulated signal has an inten
region below 11/2" or 2° they are roughly equal and
sity of about 0.78 while the 150-cycle-modulated
in the region near the glide angle the slower vary
signal has an intensity of about 0.39. Thus since
ing radiation from the lower antenna B is pre
the glide path I8 is at 3.25", the sharpness is ap
dominant so that around the glide angle the
proximately 0.5 degree.
resultant 15G-cycle radiation may be said to con
Finally, consideration may be given to the
sist o1" the 150-cycle radiation from B minus the
power wastage which will be roughly indicated
15G-cycle radiation from A. To produce the
by the ratio of the maximum power radiated in
modified half-sine curve 40 for the 90-cycle signal
any one direction oil the glide path to the power
on the other` hand the elementary 90-cyc1e pat
radiated along the glide path. In the case of »
tern from antenna A should predominate over
therefore adjusted to >effect a- 50% current‘mag
nitude reduction.
The Frsignal is usedto produce? curve 4l! by
of the 90-cycle radiation from A minus the 90
directly connecting line 22 to terminal 46’ of netcycle radiation from B. For convenience the for
work ¿lliy and also through appropriatev ampli
mer procedure of combining radiations to yield a a tude control means` A8 to terminal 44' of net
slow-rise pattern consisting of Bradiation minus
work 44. As above indicated, curve 4l] was obv-`
Aradiation may bey hereinafter referred to as a
tained by a reversed subtraction involvingranti
normal subtraction proces-s, and the latter proce
phasal radiation of the F1 signal from both the;
dureV of combining radiations to yield a modiñed
antennae. Th-e phase reversalk element in both
half-sine pattern consisting of. A radiation minus.
networks 'it and ¿ill are- therefore so disposed'
B radiation may be referred to as a reversed sub
that the'Fl signal isïconveyed to both‘ antenna
thaty from B so-thatzaroundtheglide anglefthe-î
resultant S30-cycle radiation may beisaid to consistf
traction process.
The curves illustrated in Fig. 'ï'relateto a two
element antenna array as illustrated in Fig. l,
elementsin such manner thatY one is‘in phase:
opposition with respect to thek other. Since thef
magnitude of theFl signalsupplied to antennal
wherein. antenna A is disposed at> anelevationof. 15: Bis toy be one half that of the same signal sup5.y Wave lengths while antenna B Y is V2.2 wave
plied to antenna A, amplitudecontrol means 48
lengths above the ground. At. 330 megacycles,
is so adjustedas tol eifect a 50%-reduction' in F1
these. heights are 4.5 meters and 2 meters. The
modulatedcarrier currentv magnitude. With re-elementary radiation. pattern from antenna A
spect to'the'F2 signal current fed antenna B,
alone is therefore> a half-sine curve consistingof
which current has Ybeen considered as of unit
a series of lobes such as 5 occurring alternately
magnitude, theF1 signal fed antenna A is three
inphase opposition atperiods-of about 5.8°. The
quarters this value, and that fed to antennal B
elementary radiation pattern from antenna B
is three-eighths thereof. Accordingly, ampli- alone is characterized by somewhat fatter lobes E5
`control means t9 is included in line 22 prior
havingv a periodicity of about 13.1°. Curve
to its branch connections to networks 44 and 46.
4 l '--4 I'is a slow-rise pattern similar to curve Il”
When control means 49‘ is adjusted in accord
ofFig. 3. In the system represented in Fig. '7,
ance‘with this three-quarters factor, it is clear
curve lll is characterized by the F2 signal and is
bothI antennae will be supplied with signals
obtained by radiating the same at unit magnitude
from antenna B and` substantially half unit mag 30 F1: and F2 in correct proportion and phase simul
taneously to produce‘the F1 signal in accordance
nitude in opposed phase relationship from an
withi radiation curve fili andthe F2 signal in ac
tenna A, while the F1 signal is fedy to antenna A
cordance with curve 1H.
in three-quarters unit magnitude andto antenna
It will be observed that inherent in the oper
B in phase opposition `to that fed antenna A and
atsubstantially half the magnitude of the latter, ‘
that is, about three-eighths unit magnitude.
The result of' both these normal and reversed
subtraction processes with respect to signals‘Fi
ation of the circuits of' Figs. 4 and 8 above de
scribed, is the undesirable feature', due to the
arrangement of network 26er 46, that for eachY
watt of power supplied to antenna A for radia-`v
tion, approximately one watt is dumped `or lost
and F2 will be observed as yielding, a pair of
curves ¿lli and lll which are well separated from 40 in the balancing network (e. g. network 2l of
Fig..4 or network 55A of Fig. 8). Such ineffi
ciency may be avoided while still yielding sub-Y
stantially the same type of radiation characintersection point of curves ¿El and ¿li more near
teristics as above described. in connection with`
ly approaches the maximum of curve 5 whereby a
more desirable glide angle of approximately 3.7° is 45 Figs. 3 and 4. To accomplish this, the antennav
structure of Fig. 1 should be. replacedby an an
obtained with the above-indicated antenna di
tenna structure of the nature shown in Fig. 5
mensions at the specified carrier frequency. This
eachother for substantialïarcs both sides of the
glide angle. It will further be observedthat the
represents a lo‘wnes-s of 16.2% per wave lengthoi
height. The sharpness is about .5 degree, i. e.
practically the same as before. It is to be noted,
connected as shown in Fig. 6. This alternate an
tenna structure comprises an additional radiat
. ing element so that there are in all three antennae
A, B', and B” dispo-sed one above the other. An
tennae A andB’ may be relatively close to each.
other but vnot so rclose as to exhibit undesirable in
teraction. If the elements A and B have directiv
power on co-urse to maximum power in any one 55 ity in themselves, they may be tilted orV displaced
horizontally (perpendicular to the flight path) so
direction off cour-se is a little less than 1:12.
each may have its null aimed at rthe other to
An appropriate circuit for obtaining the radia
decrease interaction even with the antennae quiteV
tion patterns illustrated in Fig; 7 is shown in Fig.
close t0 each oth-er-or at least at nearly the
8, wherein the common carrier frequency source
same height. In order to obtain substantially
2O and modulator means Zê and 25 for modulating 60
however, that this improvement as to lower glide
angle for given antennae heights has been gained
at the expense of radiating eñîciency, for, with
the arrangement according to Fig. '7, the ratioof,
carrier with the signals Fi and F2, respectively,
will be recognized. In order to produce curve 4l,
line 23 is directly connected to antenna B .through
the effects shown in Fig. 3, the elevations- of
one arm of a conjugate network Afl, and to-an
Thus the arrangement is approximately equiv
alent to that’shown in Fig; 1, as‘will be clear.
tenna A by way of appropriate amplitude> control
means 455 and another conjugate network d6.
Since it'was necessary in the production of curve
4i that the F2 signal be supplied to antennae A and
antennae A and B' may be almost alike and the
mean height of antennae A and B’ is made equal
to the height computed for antenna A in Fig. 1.
A circuit for feeding the array of Fig. 5 to
produce effects similar to those produced by the
circuit of Fig. 4 is shown in Fig. 6 wherein the
B in reversed phase relation, the phase reversal
>element 4l of network 46 is included in the arm 70 common carrier source 2i] and modulators 24
and 25 will be recognized. Since antennae A
thereof adjacent antenna Aand line
In the
and B' are sufficiently spaced so as to have rel
assumed case, the magnitude of F2-modulated Sig
atively little interaction, there is no need for a
nal fed toantenna A is one half unit (where a
fur-ther‘conjugate network. The Fi-character
unit represents .the magnitude of the F2 signal fed
to antenna B). Amplitude control means ¿55 is 75 izedsignalmay- therefore, lbe fed- directly- to an-V
tenna A and the 1lb-characterized signal direct
ly to antennae B’ and B” in appropriate am
plitude relation as controlled by amplitude con
trols 3|, 32. Again in order to obtain the de
sired effective subtraction in connection with
radiation of the F2-characterized signal, the line
feeding antenna B’ includes a phase reversal ele
ment 33.
Instead of considering the array of Fig. 5
as being merely an approximate equivalent of
Fig. 1 (an approximation which is valid only if
antennae A and B’ have nearly the same heights),
the array may be more rigorously analyzed as
comprising one pair of antennae B’, B” used
for radiating the “toohigh” signal in accord
ance with a slow-rise type of pattern and one
above the ground, antenna B’ is at 1.5 meters
elevation, and antenna >B” is at one meter, the
curves shown in Fig. 9 result for an operating
frequency of 330 megacycles.
In this iigure, curve 50, representing radiation
of the F2 signal, is a composite of radiation from
all three of the antenna elements, and curve 5|,
representing radiation of the Fi signal, is formed
by using the upper two antennae A and B’. In
order to ensure that oscillations of curve 50 sub
sequent to the initial rise thereof occur so safely
above those of curve 5| as not to permit an
intersection of these two curves except at point
52 (for the glide angle), curve 50 has a com
ponent of radiation from the lowest antenna ele
ment B” of a magnitude approximately 2.4 times
unit magnitude. Due to the fact that radiator
B” is but a meter from the ground, lobes of
radiation therefrom are relatively fat and have
a periodicity of the order of 30°. Thus curve 50
is prevented from intersecting curve 5| for sub
stantially that range of elevation angles. In
order to promote a steepness in the first rise of
curve 50, the F2 signal is supplied to antenna B’
in substantially 1.1 current magnitude and t0
antenna A in unit magnitude and opposed phase
relation with respect to its supply to the lower
two antenna units B’ and B".
In order to ensure that the ñrst lobe of curve
further lone antenna used for radiating the “too
low” signal in accordance with a conventional
half-sine pattern. 4When computing the radia
tion patterns o-n this basis, the actual heights
of B’ and B” may be used in plotting the slow
rise radiation pattern of the F2 or “too high”
signal, and the actual height of antenna A may
be used in plotting the conventional pattern of
the Fi or “too low” signal.
In a preferred embodiment of the invention the
form of array shown in Fig. 5 is proportioned
with antennae B” and B' at heights of 2.17 and
6.5 meters respectively and the 150-cycle-modu
lated 330 megacycle “too high” signals are fed 30 5| representing radiation of the F1 signal, will be
into these antennae with current strengths of 1
of substantial magnitude and at the same time
unit, and 2/5 units respectively, thus producing
in order to prevent subsequent lobes thereof from
for this signal a slow-rise pattern exactly like
attaining such magnitudes as may be likely again
curve 17" of Fig. 3. The A antenna used for
to intersect with curve 50, the former is com
radiating the 90-cycle-modula|ted 330 megacycle
posed of two components radiated from the upper
“too low” signal in this system is 7.5 meters
two antenna elements A and B’ in aiding phase
high thus giving a conventional pattern of sub
for their lowest elevation lobes. In the form
stantially half-sine form, similar to the pattern
shown, curve 5| is the resultant of Fi signal cur
l, l', “l”, but narrowed so that its first null is
rent of 0.7 unit magnitude supplied to antenna
at 31/2" instead of 4°. If this signal is fed into 40 A and 0.3 unit magnitude supplied to antenna
antenna A with a current strength of 1 unit the
B’. The resultant of such radiation of the Fi
“too low” pattern will be practically the same as
and F2 signals is thus seen to define a reasonably
curve '1_-T_T’ except for the narrowing above
low glide angle (3.7") for a given maximum arimentioned. Thus, no special set of curves are
tenna height (4.5 meters at 330 megacycles, i.e.
shown to illustrate this embodiment since curves
5 wave lengths). It is quite clear from an in
il" and ‘|-1’--'|” of Fig. 3 may (by disregard
spection of the trend of curves 50 and 5| for
ing the calibrations in degrees) be regarded as
larger elevation angles that these two curves will
rough illustrations of the general form of the
not intersect one another to form a confusing or
radiation patterns of this embodiment. The in
secondary glide path until some abnormally large
tersection of the two patterns of this embodiment 50 angle, of the o-rder of 25 to 30 degrees, is reached.
occurs very nearly at 3°, thus giving a somewhat
An appropriate circuit for supplying the three
lower glide path than the patterns of Fig. 3.` The
antenna elements A, B’ and B" simultaneously
antenna height assumed, however, is substan
to generate radiation patterns 50 and 5|, is
tially higher (e. g. 8.2 wavelengths) than in the
shown in Fig. 10 wherein the circuit for produc
case of Fig. 3. The percentage of lowness per
ing the F1 and F2 modulated carriers will be rec
wave length of antenna height is therefore only
ognized from the several foregoing circuit dia
about 12.2% being thus slightly less than for
grams, In the form shown, the B12-characterized
Fig. 3.
carrier is supplied in a line 53, and the Fi-char
It will be observed that in all of the above
acterized carrier in a line 54. Line 53 is Con
described radiation conñgurations, false courses 60 nected to one terminal of a conjugate network
are bound to occur at elevation angles within
55, and the latter serves to relay the F2 signal
about three times the glide angle defined thereby.
in unit current magnitude to antenna A, as will
As indicated above, this condition is not ordi
be clear. As indicated, the supply of the F2 sig
narily serious, for a reasonable pilot will nor
nal to antenna A is in reversed phase relation;
mally be able to distinguish between a proper 65 accordingly, the phase reversal element 56 of net
glide angle of about 3° and a false one three
work 55 is in the arm thereof joining antenna
times as steep. However, in order unmistak
A and line 53. The F2 signals are also simul
ably to deñne a glide angle without there being
taneously supplied to antenna B’ through ap
any secondary or false angles at anywhere near
propriate amplitude control means 51 and an
the proper magnitude, I propose to employ three
other conjugate network 58, and to antenna B"
vertically disposed radiating elements to produce
through amplitude control means 59. As indi
patterns substantially as shown in Fig. 9. To
cated, the supply of F2 signals to antenna B’
this end, an antenna structure of the nature
is at 1.1 unit magnitude; accordingly, amplitude
shown in Fig. 5 may be employed. In a specific
control means 51 is adjusted to eiïect this am
case wherein antenna A is disposed 4.5 meters
plification. In the same way, amplitude control
means 59 ís set to efîect a 2.4 increase in mag:
nitude of the F2 signals supplied to antenna B”.
The F1 signals are supplied to antennae A and
B' simultaneously by branchesV of line 54 con
Y nected respectively to terminals oi networks 55
and 58, which'terminals are opposite those at
which the F2 signals are furnished.
In order to
effect the appropriate proportioning of these sig
nals with respect to the above-mentioned unit
current magnitude, amplitude control means El]
and El are included in the respective branches of
line '51E connected to conjugate networks 55 and
53. In order to produce the curve 5i of Fig. 9,
control network Si] is adjusted to eiTect a reduc
tion in Fi-signal current to 0.7 unit magnitude,
and control network 6I is adjusted to eiiect a 'ren
glide plane.
In order to illustrate an alternate method of
supplying the radiating elements with appropri
ate mixtures oi the two Vsignals Fi and F2 for
radiation in accordance with the invention, the
form of circuit arrangement shown in Fig. 12 is
used to illustrate how this alternate method may
be adapted to produce the radiation patterns oi
Fig. l1. In accordance with this form, signal Fi
modulates a first carrier fi, >and the signal F2
modulates a second carrier f2. Appropriate mix
ing means vare provided for radiating the two
signals F1 and F2 in accordance with the inven-`
tion, Vand when an aircraft is equipped with re
duction thereof to 0.3`unit magnitude.
In connection with the radiation patterns of
Fig. 9, it will be noted that the comparatively
great >degree of .freedom from false glide angles
ceiver means having suñicient band width of
response -to vcomprehend both carriers fi and f2,
it is clear that the original characteristic signals
F1 and F2 may be detected and then separately
has been obtained with a substantial sacrifice in
radiating eniciency, for, in that case, the ratio
of power on course to maximum power olii course
path-indicating signals.
is of the order of 1:14. Actually, however, much
closer false courses may be tolerated and in ac
cordanceV with a further embodiment, this ehi»
ciency expression is vastly improved and at the
same time, the glide angle is still further re
duced for the same maximum antenna height.
This latter embodiment produces the radiation -
characteristics of Fig. 11 by means of a circuit
such as shown in Fig. 12. The antenna structure
for producing these patterns is substantially the
will be impossible for a reasonable pilot to mis
take this second ’coursefat 12° ior the proper
same as that required to produce the patterns
of Fig. 9 with the. exception that the middle
antenna element'B’ is at twice its former height,
that is, three meters for the assumed case of 330
Radiation oi the F1
megacycle operation.
characterized carrier is of the form shown by
curve ‘652, and the Fzwsignal radiation is repre
sented by curve
The latter is, as in the case
of Fig. 9, formed as the resultant of radiation
from all three antenna elements in the same
discriminated as by filter means to derive glide
In the form shown, the carrier f1 modulated by
signal F1 is supplied in a line ffiä having three
branches leading respectively'to antennae A, B',
and B”. The ñrst of these branches includes a
phase reversal element Sii and ñlter means 6l
passing only the signal supplied in line 65, that
is, the carrier fi together with the F1 side-bands.
The second branchihcludes vamplitude control
means 'Sil and another iilter @8 passing the same
frequencies as filter 8l. The 'third branch in
cludes merely amplitude control means l0. As
explained above, the fi carrier and its Fi side
bands are supplied to`antenna A in unit current
magnitude, to antenna B’ in 1.1’times unit mag-'
nitude, and to antenna B” in 2.4 times unit
magnitude. Amplitude control means 58 and 'lll
are Yappropriately adjusted with respect to each
cther’and Atothe magnitude of current supplied
to antenna A to lsecure this proportioning of
current‘magnitud'es, as will be clear.
The f2 carrier as modulated by the signal F2
is supplied ina line 'H having two branches
magnitude and phase relation proportions as '
above-‘considered for Fig. 9. Curve V52, however, 45 connected respectively to the upper'antenna ele
is formed by a so-called reversed subtraction
process >of the nature above described in con
nection with curve il@ in Fig. 7. In the form
shownthe F1 signal is supplied te antenna A in
twice vthe unit current magnitude and to antenna
B’ in unit magnitude and opposed phase relation
with respect to the F1 signal fed antenna A.
-The result oi this reversed subtraction (curve
ments A and B’. The i'lrst 'of these branches in
cludes amplitude control means ’E2 and a ñlter
network 'ld lpassing only the frequencies present
in line "M_ rI‘he' other branch Vincludes a phase
reversal element ‘i3 and another filter 'E5 similar
to filter lli. YCarriers f1 and f2 are preferably
relativelyclose to each other `in the frequency
spectrum, ‘and their Yproximity is governed by
the ability ‘of `iilters 6l ande?) to discriminate
radiation having a shorter periodicity than that 55 against the frequencies present in line li and by
the converse ability of filters "M and 'l5 to dis
of radiation due to the highest antenna element
criminate against the frequencies presentïin line
(see lobe Gil). lIîhus, if radiation of this lobe
$5. Amplitude control means l2 is adjusted to
d2 were controlled to be approximately the same
reffect an ampliñcation oi substantiallytwice the
maximum magnitude as that of lobe ed, it follows
that the intersection deñning the glide angle 60 unit current magnitude. When this adjustment
is made, it is clear that the circuit of Fig. 12
will be lower than the corresponding intersection
will be effective to radiate simultaneously in
which would result from use of Vthe simple lobe
accordance with “curves S2 and §53 substantially
64. Also it is evident that the reversed sub
as shown in Fig. 1l.
traction gives a greater sharpness than would be
It is to be noted in connection with the embodi
obtained by use of the simple lobe Gli.
ment shown in Fig. 12 that it has been possible
It is to benoted that the second lobe of curve
to avoid the above-noted ine'îiiciency (due to a
62 is of greater magnitude than the ñrst. This
power dumping) arising out oi >the usefof a num
factor, _while detrimental from the standpoint of
ber of conjugate networks and that relative lit
power wastage ratio, clearly in no way affects
the sharpness or unmistakability of the proper 70 tle additional apparatus'is necessary. If desired,
the carriers fi and `;f2 may be maintained in sub
glide course. The nrst false course as set up by
stantial alignment with respect to each other by
the second intersection of curves §32 and ‘53 oc
means of appropriate frequency stabilization
curs at virtually 12°, that is, ‘almost four times
means lâ associated with both "the respective
the proper glide angle. It is considered that even
under the most adverse headwind conditions, it 75 sources of carriers `irland f2 whereby the total
E2) will he seen to produce a first lobe of Fi
band-Width required for the system may be‘made
subtraction process, that the proportioning of the
a minimum.
component of this signal radiated from the lower
antenna element with respect to the component
of this signal radiated from the upper element
of the forms shown in Figs. 4, 8 and 10 to give Ul occurs in a preferred relationship. More speciñ
patterns such as illustrated in Figs. 3, 7 and 9.
cally for the F1 signals the ratio of the current
Similarly, the principle (described in connection
in the lower element to that in the upper should
with Figs. 5 and 6) of using two separate anten
be C’ divided by the corresponding height ratio,
nae close together instead of one antenna fed
where C’ is between 0 and 0.75. The preferred
with two signals, may be applied to all the em
somewhat narrower limits for C’ are between 0
bodiments illustrated as having two signals ap-`
and 0.60.
It will be clear that the form of feeding ar
rangement shown in Fig. 12 maybe used in place
plied to one element of an array.
It will be noted that some of the above de
Although this invention has been described in
connection with transmitting apparatus, it is not
scribed embodiments have fairly low radiating
to be interpreted as limited to that type 0f use
efiîciency as .. measured byY the power wastage
ratio; butin many cases this decrease in e?ciency
may be justified by the very substantial improve
ment in the sharpness and in the maximum 90
to'150 cycle signal ratio observable below the
glide plane. In the case of the radiation pattern 20
shown in Fig. 11, for example, the efiiciency
power ratio dropped only to 117.6. It is particu
larly to be emphasized that at the very reasonable
operating wave length of 330 megacycles the re»
sults shown, for example, in Fig. 11 were ob
tained with a maximum antenna height of 4.5
meters, that is, about 14.5 feet.
From an examination of all of the figures
graphically showing radiation patterns in ac
cordance with the invention, it will be observed
that the slow-rise type of curve formed by what
has been termed a normal subtraction process
(e. g. curve M in Fig. '7) is generally S-shaped
for V,angles up to and in the neighborhood of the
glide path; the lower end of the S commencing ,
sometimes with a> Zero slope (e. g, curve I1),
sometimes with a small downward slope (e. g.
curve Iï”) and sometimes with a small upward
but ratherit is adaptable both to transmitting
and receiving purposes. In the latter case, it may
find utility in radio locating systems of the type
wherein radiations emitted (or reñected) from a
plane are received on two receivers (or on one
A-N-keyed receiver) making use of the equality
of two reception patterns for determining the
direction of the plane.
While I have particularly described my inven
tion in connection with systems producing tone
l» modulated signals for an equi-signal course, it is
clear that its principles are equally adaptable to
other known course-defining systems, such as
for example, the well-known aural indicating sys
tem wherein the two patterns defining the glide
course are alternately radiated in accordance
with a keyed pattern. vIn connection with the
above-described circuits keying means may be
substituted for the modulators. Furthermore,
in keying systems the use of power dumps may
be altogether avoided by merely switching over
the antennae so that in one key position they
receive the relative powers above described for
signal F2, and in the other position they receive
slope (e. g. curve Iï’). Roughly the S-shaped
the relative powers described for signal F2. Un
form of the curve resembles the first half cycle 40 der such conditions, the keying means may be
of a cosine curve; and to a fair approximation
said to couple the antennae to the transmitter in
the shapes 0f the various possible forms of so
called “slow-rise” curves shown and described
hereinabove may be conveniently defined by the
cosine function
one relation (i. e. with one set of amplitudes)
“in respect of one signal” while coupling the
same antennae thereto in a different relation “in
K[cos flo-cos (R04-00)]
respect of a second signal.” Likewise, in the
earlier described illustrations of feeding the an
tennae in accordance with the invention by the
where K, lc and 0o are constants. If this expres
sion is used to describe the shapes of the slow
use of a common carrier separately modulated
in two branch lines in accordance with two sig
rise pattern, the preferred shapes can be said 50 nals, it may also be said that the antennae are
to be those corresponding to a value of 0o be
coupled to the common carrier source in one rela
tween +20° and --20°. If on the other hand
tion “in respect of a first signal,” and in another
the slow-rise patterns are to be considered as
relation “in respect of a second signal.”
made up of a slowly periodic elementary curve
Although I have described my invention in de
from which there is subtracted a smaller more 55 tail in particular connection with the preferred
rapidly periodic elementary curve, then the pre
forms illustrated, it is to be understood that many
ferred forms of such slow-rise patterns may be
modifications, additions and omissions may be
said to be those whose initial slope is roughly be
made fully within its scope, as defined by the
tween -i-l/g the slope of the slowly periodic ele
appended claims.
mentary curve and -1/2 this slope. Generally 60
What is claimed is:
speaking, satisfactory results may be obtained
1- Glide path apparatus suitable for instru
when the ratio of Fz-signal amplitudes in the
ment landing of aircraft, comprising a first an
lower antenna element B> with respect to ampli
tudes of the F2 signal in the upper antenna ele
ment A is C times the inverse ratio of respective
elevations of these elements above ground, where
C is between 0.7 and 1.9. In other words the F2
signal current ratio (i. e. of the lower element
to the upper) is C times the ratio of the height
of the upper element to that of the lower ele
tenna means and a second antenna means dis
posed one generally above the other, a first
wave-translating means operating at a predeter
mined carrier frequency, means coupling said
first and said second antenna means to said
wave-translating means, a second wave-translat
ing means also operating at said frequency, and
means coupling said second wave-translating
Preferred conditions, however, call for
means solely to said first antenna means.
slightly stricter limits of C as between O. 8 and 1.6.
2. Apparatus according to claim l wherein said
It will further be observed in connection with
ñrst antenna means is disposed above said second
the above described figures, in which the F1 sig
antenna means.
nal was formed by what is termed as a reversed .75
3. Apparatus according to claim 1 wherein said
to said ñrst antenna means more energy than
said second signaling meansl but said second sig
naling means being adapted toY feed to said sec
ond antenna means more energy than said first
signaling means, whereby said iirst antenna radi
first antenna means is disposed above said second
antenna means and wherein said first antenna
means includes-two antennae, one of said two
antennae »being »connected to said last-delined
coupling means, and the other of said antennae
ates predominantly energy characterized by said
being connected to said first-defined coupling
first> signal and said second antenna radiates pre
dominantly energy characterized by said second
4. Apparatus according «to claim 1 wherein said
first antenna means is disposed above said sec
ond antenna means and further wherein said iirst
antenna means includes two antennae, >one of
signal. »
8. Glide path antenna apparatus suitable for
instrument landing of aircraft, comprising a first
antenna means and a second antenna means dis-V
said two antennae being connected to said last
posed one generally above the other and above
deiìned coupling means and the other of said
a ground, a wave-translating means, and means
antennae being connected to said first-defined
coupling means, said two antennae being less 15 coupling said nrst and said second antenna
means Yto said wave-translating means, said cou
spaced with'respect to each other than the spac
pling _means including amplitude control means
ing between Veither of said two antennae and said
coupling said first >antenna means to said wave
translating means in a first energy transfer rela
second antenna means.
5. Glide path apparatus suitable for instru
ment landing of aircraft, comprising a first an
20 tion and amplitude control means `coupling said
tenna means and a second antenna means dis
posed one generally above the other, a ñrst wave
translating means operating .at a given modula
tion frequency, means coupling said ñrst and said
second antenna means to said wave-translating
second antenna means to said wave-translating
means in a seco-nd energy transfer relation, and
thetwo amplitude control means being adjusted `
so that the ratio of magnitude of said first energy
transfer relation to that of said second energy
transfer relation is of the same order of magni
tude as the ratio of the elevation above said
ground o-f said second antenna vmeans to that of
means, a second wave-translating means oper
ating ¿at a modulation frequency different from
said given'frequency and means coupling only said
first antenna means to said second wave-translat
ing means, said first-mentioned coupling means
including means coupling said first wave -translat
ing >means to said first antenna means in a first
energy transfer relation and means coupling said
first wave-translating means to said second an
tenna'means in a second energy transfer relation
said first antenna means.
V9. Apparatus according to claim 8 wherein the
two amplitude control means are adjusted so that
the ratio of the magnitude of said energy transfer
relations is between .7 and 1.9 times the ratio of
the elevation of said seco-nd antenna means to
Vthat of Ysaidiìrst antenna means.
l0. Glide path antenna apparatus suitable for
instrument landing of aircraft, comprising a ñrst
differing in‘phase from said -iîrst energy transfer
Vt. Glide path apparatus Vsuitable for instru
antenna means and a second antenna means dis
posed one generally above the other and above a
ment landing of aircraft, comprising a ñrst an
ground, a wave-translating means, :and means
tenna means and a second antenna means dis
coupling said first and said second antenna means
posed o-negenerally above the other, añrst wave
translating means, means co-upling said iii-st and
said second-antenna means to said wave-translat
ing means in substantially opposite phase, a sec
ond wave-translating means, and means coupling
said first antenna means and said second >an
tenna means to said second wave-translating
means'in substantially opposite phase, said ñrst
to said wave-translating means, said coupling
means including amplitude control »means cou
pling said first antenna means to said wave
translating means in a first energy transfer rela
tion and amplitude control means `coupling said
second antenna means to said wave-translating
means in a second-energy transfer relation, and
the two vamplitude control means being adjusted
mentioned coupling means »including means cou
pling said first wave-translating means to said 50 so »tnat the magnitude of said first energy trans
fer relation with respect to said second energy
transfer relation is such that _for smallelevation
angles above said ground the magnitude of the
first antenna means in a first energy transfer
relation and means coupling said first wave
translating means to said second antenna means
in-a second energy transfer relation different in
magnitude and phase from said firstV energy
characteristic curve `of saidV first antenna means
substantially equals that of said second antenna
transfer relation, said second-mentioned coupling
:11. Apparatus according to claim 1 wherein
means including means coupling >said second
said `first antenna means comprises two radiating
wave-translating lmeans to said first' antenna
elements spacedone above the other, wherein said
means in a third energy transfer relation and
means coupling said second wave-translating 60 first-mentioned coupling means includes means
coupling said first wave-'translating means to one
means to said second antennameans in a fourth
of said radiating elements ina first energy trans
energy transfer relation different in Imagnitude
fer >relation kand means coupling said ñrst wave
and phase Vfrom both said third energy transfer
transiating imeans to the other of said radiating
relation and said second energy transfer relation.
'7. Glide path apparatus suitable for instru
ment landing of aircraft, comprising a first an
tenna means and a second antenna lmeans dis
' posed one generally above the other, ñrst signal
ing means for feeding said first andrsecond an
tenna means in substantially opposite -phase with 70
elements rinia secondenergy transfer relation, and
furtherY lwherein said second-mentioned coupling
means inoludes’means coupling said second wave
translating' means toA one of said radiating ele
naling means for feeding said first land seco-nd
ments in _a vthird energy transfer relation and
meansk `coupling said second wave-'translating
means .to said other radiating element Vin* a fourth
cnergytransîer relation, said first energy transfer
antenna means in substantially opposite :phase
' relation Lbeing .of `substantially opposite-phase 'to
energy characterized byra first signal, .second sig
said ssecond V'energy transfer relation »and said
said first signaling means'being adapted to feed 75 thirdienergy `transfer relation'being of substan
with energy characterized by a A’second signal,
tially opposite phase to said fourth energy trans
fer relation.
12. Glide path antenna apparatus for operation
at a given carrier frequency and suitable for in
strument landing of aircraft, comprising a ñrst
antenna means, a second antenna means, and a
third antenna means disposed one generally above
the other and spaced with respect to each other
at least a half Wave-length at said operating fre
the combined characteristic of both said antenna
means is of the general. form of the function
[cos lio-cos (ICH-00)]
where 0 is the elevation angle, and k and 0o are
constants, 0n being between +20° and -20°.
14. Glide path antenna apparatus suitable for
instrument landing of aircraft, comprising a ñrst
antenna means and a second antenna means dis
quency; a first wave-translating means; means 10 posed one generally above the other, a wave
coupling said wave-translating means to said first
antenna means in a first energy transfer relation,
to said second antenna in a second energy trans
fer relation, and to said third antenna means in
a third energy transfer relation, all said energy
transfer relations being different; a second wave
translating means; and means coupling said sec
ond Wave- “anslating means to said first antenna
translating means operating at a predetermined
carrier frequency, means coupling said first an
tenna means and said second antenna means to
said wave-translating means in respect of a ñrst
signal at said carrier frequency, a further means
coupling substantially only said first antenna
means to said wave-translating means in respect
of a second signal at said carrier frequency,
means in a fourth energy transfer relation and
15. Glide path antenna apparatus according to
to said second antenna means in a fifth energy 20 claim 14, wherein said wave-translating means
transfer relation different from said fourth en
ergy transfer relation.
13. Glide path antenna apparatus suitable for
instrument landing of aircraft, comprising a first
antenna means and a second antenna means dis
posed one generally above the other and above a
ground, a wave-translating means, and means
coupling said first and said second antenna means
includes keying means, said first-mentioned cou
pling means being responsive to said keying
means to couple said first antenna means and
said second antenna means to said wave-trans
25 lating means in respect of said ñrst signal, said
further coupling means being responsive to said
keying means to couple substantially only said
first antenna means to said wave-translating
means in respect of said second signal.
to said wave-translating means, said coupling
means including means coupling said ñrst an 30
16. Glide path antenna apparatus according to
tenna means to said wave-translating means in a
claim 14, wherein said first-mentioned coupling
first energy transfer relation and means coupling
means includes modulating means operating in
said second antenna means to said wave-translat
accordance with said first signal, and wherein
ing means in a second energy transfer relation,
said further coupling means includes modulating
said ñrst and said second energy transfer rela 35 means operating in accordance with said second
tions being of substantially opposite phase and of
such magnitude with respect to each other that
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