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Патент USA US3064263

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Nov. 113., 1962
F. R. DICKEY, JR
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3,064,254
MONOPULSE RADAR WITH LINEAR ERRORv VOLTAGE
Filed Oct. 16, 1956
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INVENTOR.
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FRANK R. DIOKEY JR.
dww?
A TTORA/E)’
United States Patent U” EQQ
1
3,@64,Z54
Patented Nov. 13, 1962
2
3,064,254
MONOPULSE RADAR WITH LINEAR ERROR
VOLTAGE
Frank R. Dickey, Jr., Dewitt, N.Y., assignor to the United
States of America as represented by the Secretary of
the Army
Filed Oct. 16, 1956, Ser. No. 616,357
4 Claims. (Cl. 343-113)
menopause system wherein the discrete outputs from the
two antennas A and B are heterodyned by the output from
a common oscillator O. The output from the respective
mixers MA and MB are applied to respective IF ampli
?ers RA and RB and the outputs of the IF ampli?ers are
compared in a linear phase detector D to produce a
voltage proportional to the phase difference between the
output of the two receivers. The phase relationship exist
ing between the respective input and output voltages of
This invention relates to searching and tracking radar 10 antennas A and B may be readily shown by means of
systems and more particularly to a monopulse type radar
FIG. 2 which represents the equivalent circuit of the two
system.
'similar antennas having mutual coupling therebetween
The monopulse technique in radar consists in deriving
designated by ZM and respective input impedances ZA
sufficient information from a single pulse by multiple,
and 23. The respective induced antenna voltages VA and
simultaneously acting receiving channels to determine
completely both the angular position and range of the
15 VB are assumed to be equal except for the phase dif
ference 95, that is
target. In one well- known system employing two antenna
feeds and two receivers, the azimuth error correction sig
nal is obtained by comparing the phase difference between
the’ outputs of the two receivers. The phase difference 20 In terms of the antenna load impedance Z1“. the antenna
between the voltages induced in the two antennas will
loop impedance Z and the mutual impedance ZM, the two
vary linearly with the target angle but, due to the cross
antenna output voltages EA and EB may be derived by
coupling between the antennas, the voltage signals derived
.simple circuit analysis and shown to be
from the output of the antenna feeds and detected in the
receivers will not have this linear relationship. Due to 25
(2)
this factor, inaccuracies in the error correction signal
derived from the phase comparison of the two received
signals will result in erroneous target indications.
and
It is therefore an object of the present invention to ‘pro
vide an improved phase-comparison monopulse radar 30
system having a linear error correction voltage.
It is another object of the present invention to provide
an improved phase-comparison monopulse radar system
wherein the phase errors due to the mutual coupling be
35
tween the antenna feeds are effectively eliminated.
The factors shown in the brackets ‘of Equations 2 and 3
It is another object of the present invention to provide
are functions of the phase difference ¢ due to the effect
an improved phase-comparison monopulse radar system
of the mutual coupling ZM which causes undesirable
wherein greater accuracy of the angular location of a
phase errors.
>
target with respect to the bore sight axis is achieved.
In FIG. 3 there is shown the improvement comprising
Briefly, the present invention is directed to a mono
the present invention which compensates and corrects for
pulse phase-comparison system wherein the error cor
the effects of the coupling between the antenna feeds A
rection signal is a function of the phase difference between
and B. Referring now to FIG. 3, the voltage outputs
the signal voltages induced in two antennas having a pre
EA and EB from respective mixers MA and MB are com
“[7]
scribed mutual impedance ZM therebetween and each
bined in a ?rst adder or sum circuit 10 and a ?rst sub
having a loop impedance Z. Means are provided for 45 tractor or difference circuit 12 to provide the respective
maintaining the error voltage proportional to the phase
sum and difference voltage signals E=EA+EB and
difference between the signals derived from the respective
A=EA—EB. Such adder and subtractor circuits are well
outputs of the antennas. Such means include means for
known in the art and no further description thereof is
producing respective sum’ and difference signals of the
believed necessary. The sum signal output from adder
antenna output signals and means for altering the ampli 50 circuit 11} is applied to an attenuating and phase shifting
tude and phase of the sum signal by the factor
circuit 14 which is adapted to alter or, in effect, multiply
the amplitude and phase of the sum signal Z=EA+EB
by a factor
Z
Also included are discrete means for producing respective
voltage signals equal to the sum of the altered signal
and the difference signal, and equal to the difference of
the altered signal and the difference signal.
For a better understanding of the invention together
with other and further objects thereof, reference is had
to the following description taken in connection with the
accompanying drawings in which:
FIG. 1 is a block schematic diagram of a prior art
monopulse phase-comparison system;
FIG. 2 illustrates schematically the equivalent antenna
feed circuit of the prior art system shown in FIG. 1; and
FIG. 3 is a block schematic diagram illustrating the
60 where this factor is a complex number having an absolute
value which expresses the required amplitude ratio and
having an angle which expresses the required phase shift
and where, as explained above, ZM is the value of the
‘mutual impedance between the two antennnas and Z is
the respective loop impedance of the two antennas. The
values ZM and Z, of course, may be measured or derived
in any conventional manner well known in the art. As
shown, the altered sum signal is respectively combined
with the diiference signal A=EA~EB in a second adder
70 circuit 16 and in a second subtractor circuit 18. The
present invention.
'
outputs of second adder circuit 16 and second subtractor
,FIG. 1 illustrates a conventional’ phase-comparison
circuit 18 are respectively applied to IF ampli?ers RA
3,064,254
4.;
3
changed in amplitude and phase by the factor
and RB, and the output of the IF ampli?ers are compared
in linear phase detector D as shown.
The network 14 may consist of an attenuator and a
phase shifter connected in cascade or it may consist of
and the difference A-=EA—EB should be changed in
amplitude and phase by the factor
ZM
a single network designed to provide both the desired
change in amplitude and the desired value of phase shift.
Furthermore, if the absolute value of the factor discussed
above, is greater than one, it may be necessary to place
1‘ 2
the network in the output of subtractor 12 instead of in
Since
only
the
phase,
not
the amplitude, of the output
the output of adder 10. For convenience in making ad 10
is
of
interest,
the
actual
requirement
is that the gain and
justments it may be desirable to place a network in each
phase shifts of the sum and difference channel differ in
of the two locations.
accordance with the factor
The theory of operation of the present invention is
based on the fact that the voltage VA and VB induced in
antennas A and B, respectively, are derived from EA and 15
EB by linear transformation independent of the phase
angle q). This can be shown by utilizing the relationship
set forth in Equations 1, 2, and 3. Let S represent the
quantity
20
52
Z
_Z_M>”
1——
Z
As shown in FIG. 3, the sum and difference signals
E=EA+EB and A=EA—EB are derived respectively from
adder circuit 10 and subtractor circuit 12. The desired
output signals are obtained by sending the sum (EA+EB)
through the network 14 having a transfer function given
by the factor
V
and let U represent the quantity
25
Z
“7M
in
Now, by adding and subtracting Equations 2 and 3 we
have
Z
30 and then deriving another sum and difference signal by
means of second adder circuit 16 and second subtractor
(4)
circuit 18. By such addition and subtraction, the signals
applied to phase detector D from the IF ampli?ers RA
and RB will be in phase with VA and VB, respectively.
(5)
35 The same result is achieved if the ?rst sum and difference
VA
,
’
VB
signals are sent through networks having transfer func
.
tions given respectively by
VB 6
vA
these values may be substituted in Equations 4 and 5
for e-i" and eat”, and as a result we have
1+gZiI and 1—ZZAI
40
and
before being applied to adder circuit 16 and subtractor
circuit 18.
Although the linearizing circuits shown in FIG. 3 are
added after the mixer stages MA and MB, that is, at the
From Equation 6 the value of VB in terms of VA may be
IF level, it is to be understood of course that the lineari
45 zation circuits described hereinabove may be added at
readily derived as follows:
the RF level before the mixer stages. Well known mi
EA+EB _
VB _
crowave hybrid circuits such as magic-tees would be
~s ( 1 _ U) VA
(8)
used in this case.
Substituting this value for VB in Equation 7 and solving
While there has been described what is at present con
for VA we arrive at the following equation:
>
1
50
‘,
VA=W[(EA+EB) (1+ U) T (EA-EB) (1- UN
(9)
Inasmuch as
without departing from the invention, and it is, there
55
_z_L
Z
S=1~ U2
where
60
d
LEM
UZ
phase difference between the respective signal voltages
induced in two antennas having a prescribed mutual im
dance Z, means for maintaining the error voltage propor
VA—§—Z—L[:(EA+EB)(1+7)+(EA—EB)(1—7>]
(10)
ZM
ZM
tional to the phase difference between the signals derived
65 ‘from the respective outputs of said antennas comprising:
means for producing respective sum and difference sig
nals of said output antenna signals, means for multiply
In a similar manner it can be shown that
Z
fore, aimed in the appended claims to cover all such
changes and modi?cations as fall within the true spirit
and scope of the invention.
What is claimed is:
1. In a monopulse phase-comparison system wherein
the error correction signal voltage is a function of the
pedance ZM therebetween and each having a loop impe
we have
__ Z
\sidered to be the preferred embodiments of this inven
tion, it will be obvious to those skilled in the art that
various changes and modi?cations may be made therein
Z
z
Z
VB=§Z[(EA+EB>(1+—M —<EA-EB>(1——Z“-‘):|
(11)
70
It is apparent from Equations 10 and 11 that to ob
tairi the results desired, the sum 2=EA+EB should be 75
ing the amplitude and phase of said sum signal by the
factor
in
and discrete means for producing respective voltage sig
3,064,254
5
nals equal to the sum of said multiplied signal and said
dilference signal, and equal to the difference of said
6
plying the amplitude and phase of said sum and difference
signals by the factors
multiplied signal and said di?erence signal.
2. In a monopulse system wherein the relative phase
of respective signals induced in two similar antennas
varies linearly with the target angle relative to the bore
sight axis, means in circuit with the output Signals of
said antenna for maintaining the linearity of said induced
signals comprising: a ?rst adder circuit for producing
1-l—Z7M and 1-—€ZM
respectively, and means for respectively adding and sub
tracting said multiplied sum and said multiplied dif
ference signal.
'
4. In a monopulse phase-comparison system wherein
the error correction signal voltage is a vfunction of the
the sum signal of the antenna output signals, a ?rst sub 10 phase difference between the signal voltages induced in
tractor circuit for producing the difference signal of the
two antennas having a prescribed mutual impedance
antenna output signals, a network responsive to the sum
ZM therebetween and each having a loop impedance Z,
signal and having a transfer function given by the factor
means for maintaining the error voltage proportional
to the phase difference between the signals derived from
15 the respective outputs of said antenna comprising: means
for producing respective ‘sum and difference signals of
said output antenna signals, a ?rst network responsive
to said sum signal and having a transfer function given
by the factor
where ZM is the mutual impedance between both anten 20
nas and Z is the loop impedance of each antenna, a
a second network responsive to said diiference signal and
second adder circuit ‘for producing the sum signal of the
having a transfer function given by the factor
output of said network and said difference signals, and
a second subtractor circuit for producing the difference
.214
signal of the output of said network and said difference 25
2
signal.
3. In a monopulse phase-comparison system wherein
the error correction signal voltage is a function of the
phase diiference between the signal voltages induced in 30
two antennas having a prescribed mutual impedance ZM
therebetween and each having a loop impedance Z, means
‘for maintaining the error voltage proportional to the
phase difference between the signals derived from the
respective outputs of said antennas, said means compris~
means for producing the sum signal of the outputs of
said ?rst and second networks, and means ‘for producing
the difference signal of the outputs of said ?rst and sec
ond networks.
.
References Cited in the ?le of this patent‘
UNITED STATES PATENTS
2,147,810
Alford _____________ __ Feb. 21, 1939
ing: means for producing respective sum and difference
2,687,520
Fox ____ __v _________ __ Aug. 24, 1954
signals of said output antenna signals, means for multi
2,713,164
Baum :_..____,,__.._____v___ July 12g 195‘
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