Патент USA US2410657код для вставки
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.