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Патент USA US2410657

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Patented Nov. 5, ‘1946
2,410,657
2,410,657
ANTENNA SWITCG SYSTEM
William D. Hershberger, Haddon?eld, N. 3., as
signor to Radio Corporation of America, a cor
poration of Delaware
Application September 25, 1941, Serial No. 412,291
3 Claims. (Cl. 250-—11)
1
2
This invention relates to antenna switching
systems, and especially to an improved antenna
switching system which alternately connects the
the accompanying drawing, in which Figure 1 is a
schematic circuit diagram of one embodiment of
the invention; and Figure 2 is a circuit diagram
antennas of a pair of directive antennas to a
of a preferred embodiment of the invention.
radio device and which distinctively indicates the
Similar reference characters indicate similar ele
operative antenna. The instant invention is an
ments in the drawing.
improvement over the one described and claimed
A pair of antennas l, 3, which are preferably
in applicant’s U. S. Patent 2,189,549, which is as
directive, are connected by a transmission line
signed to the same assignee as the instant ap
5. A- radio device ‘I is connected‘by a line 9 to
plication.
10 an electrically symmetrical point I l on the trans
The system disclosed in the patent depended
mission line. The point of symmetry may coin
primarily upon short circuiting, conductively or
cide with the geometrical mid-point between the
electronically, the transmission lines connecting
antennas, or the point may be displaced there
a pair of antennas to a radio device. The short
from provided it is at a point at which substan
circuits were arranged alternately at quarter wave 15 tially equal currents would flow for equal currents
points on either side of the common line to the
in the antennas.
device so that first one, then the other, of the
A variable diiferential capacitor I3, having a
antenna lines offered a high impedance to cur
grounded rotor I5 and a pair of high potential
rents to (or from) the inoperative antenna, while
plates i'l', it is'connected as follows: The high
a matched impedance was offered to currents to 20 potential plates are connected respectively to
(or from) the operative antenna.
high potential points located on the transmission
'VWhile the system of the said patent is suitable
line 5 an odd number of quarter wave lengths, of
for certain installations, in some arrangements it
the applied antenna currents, on opposite sides
has been found preferable to use reactors in place
of the point H of electrical symmetry. These
of- conductive shorting means. One suitable re 25 points are indicated as A and B on the diagram.
actor proved to be a variable di?erential capac
The rotor plate is driven by a motor 2|, which
itor which was continuously varied so that a
may also drive a cam operated switch 23. The
very high reactance may be o?ered to the an
switch may be ‘connected to a cathode ray tube
tenna currents in ?rst one, then the other, of the
or left-right indicator to indicate which of the
antenna‘ transmission lines by applying the re
30 antennas l, 3 is operative.
active connection at quarter wave points. In one
use of the instant invention, the residual react
ance of the smaller di?erential capacitor un
balanced the line to the operative antenna, this
e?ect may be neutralized by shunting the residual 35
reactance with a suitable reactance of opposite
sign so that the combination is resonant and,
therefore a high shunt impedance.
The mode of operation is as follows: When the
di?erential capacitor l5, l1 offers the minimum
reactance to the antenna currents, the point A
is effectively short circuited. Owing to the proper
choice of the length of the transmission line C
between H and A, a short circuit at A is trans
formed into a high impedance at point H, look
ing toward A. At the time when point A is short
It is one of the objects of the invention to pro
circuited to ground, the maximum reactance of
vide improved means for antenna switching. An 40 the then smaller capacitor l5, l9 appears between
other object is to provide a variable differential
point B and ground viewed through a correspond
capacitor for connecting alternately antennas
ing transmission line D between l9 and B. If
having diiierent directive characteristics to a
this reactance is large enough, it will have no
radio device and for indicating which of said
effect upon the antenna currents in the trans
antennas is operative. Another object is to pro 45 mission line conected to antenna 3. As the motor
vide an antenna switching system with a vari
turns the rotor plate I 5, the reactance of the
able capacitor operating continuously to pro
capacitors l5, H and l5, ill will vary so that first
vide short circuiting reactances for ?rst one, then
one, then the other, becomes a maximum. The
the other, of a pair of antenna transmission lines
antennas l , 3 are thus alternately effectively conand for minimizing the effect of residual capac 50 nected to and disconnected from the radio device
ity reactances in the unshorted line. An addi
and at the same time the cam driven switch oper
tional object is to provide a motor driven vari
ates to apply suitable currents to the indicator
able capacitor with a low impedance connection
from which designates the operating antenna.
to ground.
A preferred embodiment of the invention is
The invention will be described by ‘referring to 55 illustrated in Fig. 2, in which a transmitter 25
2,410,657
4
and receiver 21 are both connected. One suit
able means for connecting both devices to the
antenna is described in a copending application,
Serial No. 184,354, ?led, January 11, 1938 by Irving
W011i and William D. Hershberger. In practice,
the residual reactance of the smaller capacitor
may be large enough to unbalance the operative‘
transmission line. The residual capacitive re
actance is neutralized by connected stub lines 29,
35 which are connected to the points A and B 10
and are adjusted to a length just su?icient to pro
vide a suitable reactance of the sign opposite to
the residual reactance so that the combination is
application of the currents is accomplished by
applying a short circuiting reactor to the trans
mission line connecting the antennas at a point
thereon a quarter wave length from the point
at which the radio device is connected. Any
undesired residual reactance is neutralized or
tuned out by shunting a suitable reactance of
the opposite sign across the residual reactance.
The reactor may be a motor driven differential
variable capacitor provided with supplemental
grounding means to minimize variations in the
electrical resistance of the bearings.
I claim as my invention:
1. An antenna switching system including in
parallel-resonant at the frequency of the antenna
currents. Thus at point B, at the instant position 15 combination a pair of antennas, a transmission
line connecting said antennas, a radio device,
of the rotor, the stub line 3! and the capacitor l5,
l 6, viewed through its connecting line D, are res
onant and are a high shunt impedance which has
substantially no effect on the antenna currents to
or from the operative antenna 3. At the same 20
means connecting said radio device to an elec
instant the larger capacitor l5, ll effectively
trically symmetrical point on said line, a pair of
differential reactors connected respectively be
tween ground and points spaced an odd number
of quarter wave lengths from said symmetrical
short circuits the line so that the effect of the
stub 2?, is negligible.
point and including a common rotatable mem
ber, means for increasing first one then the
‘ In one arrangement, which was operated at a
other reactance of said reactors at the operating
carrier frequency of about 500 megacycles per 25 frequency of said device and supplemental ?xed
second, the ground connection of the rotor plate
capacitive means rotatable with said common
i5 through the motor bearings 2! was insufficient.
rotatable member for minimizing the impedance
A disc
several inches in diameter, was at
between said common rotatable member and
tached to the rotor assembly. The disc was
ground.
spaced approximately a hundredth of an inch 30
2. An antenna switching system including in
from a similar disc 35 which was mounted ?x
combination a pair of antennas, a transmission
edly and was grounded. The capacity reactance
line connecting said antennas, a radio device,
of this path to ground proved low enough to
means connecting said radio device to an elec
eliminate the dif?culties of the uncertain ground
trically symmetrical point on said line, a pair
through the motor bearing. The reactor device 35 of differential reactors connected respectively
is preferably located within a grounded housing
between points spaced an odd number of quarter
35].
wave lengths from said symmetrical point and
One suitable cathode ray indicator connection
is illustrated in Fig. 2. The cathode ray tube 31
ground and including a common rotatable mem
ber, means for increasing ?rst one then the other
is provided with de?ecting elements 39 which 40 reactance of said differential reactors, means for
are biased by a battery 1H. The bias is applied
balancing out the smaller reactance so that the
in synchronism with the variation of the capaci
larger reactance oiiers an e?ective short circuit
tor by employing the cam switch 23 which is
and the smaller reactance offers high impedance
connected in the biasing battery circuit. The
at the operating frequency of said device and
choke coils 43 and the capacitors 1&5 keep the 45 supplemental ?xed capacitive means rotatable
biasing currents and the signaling currents sepa
with said common rotatable member for mini
rated.
mizing the impedance between said common ro
Thus the invention has been described as an
tatable member and ground.
antenna switching system in which currents from
3. A system according to claim 1 including
a transmitter are applied alternately to ?rst one, 50 means operated in synchronism with said react
then the other antenna of a pair antennas, or
ance increasing means for indicating which an
the currents from the antennas may be applied
tenna is operative.
alternately to a radio receiver. The alternate
WILLIAM D. HERSHBERGER.
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