US2395870A - Impedance switching device - Google Patents

Description

j March 5, 1946. M. E. HIEHLE ,87O

IMPEDANCE SWITCHING DEVICE Filed Dec. 7, 1942 Inventor: Michael E.Hieh|e,

h j W His Attobney Patenta& Mar. 5, 1946 23255370 IMPEDANCE SWITCHING DEVICE Michael E. Hiehle, Schenectady, N. Y., asslgnor to General Electric Company, a corporation of New York Application December "l, 1942, Serial No.-468,120

(Cl. rus-44) 2 Claims.

The present invention relates to an impedance switching device for controlling the flow of radio frequence energy.

At high frequenoies it has been suggested that switching be accomplished by using the impedance inversion characteristics of quarter wavelength transmission lines, i. e., transmission lines having an electrical length at the frequency to be controlled equal to an odd number of quarter wavelengths. However, due to the inherent reactance of the switch contacts and end effects of the quarter wavelength transmission line, it is difficult to provide the necessary 90 electrical degree phase relationship so that no reactioh is presented in the radio frequency circuit to be controlled.

The object of my invention is to provide an improved impedance switching arrangement :or preventing reaction in the circuit to be controlled due to the reactance of the switch contacts and leads.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with :further objects and advantages thereof, 'may best be understood by reference to the following description taken in' connection with the accompanying drawing in which Fig. 1 is a diagram illustrating the application of my impedance switching device 'to a radio frequency circuit; Fig. 2 is a sectional view of an impedance switchln'g device for obtaining a 180 degree phase Shift in 'the controlled radio frequency circuit; and Fig. 3 is a diagram showing the application of the Fig. 2 device.

Referring to the drawing, there is shown a transmission line I carrying radio frequency energy to be controlled. This line is connected to' terminals 2 at one end of a transmission line 3 having an electrical length at the frequency to be controlled different from an odd number of quarter wavelengths. The other end of the transmission line 3 is provided with terminals 4 which may be short circuited by a switch 5. If the transmission line 3 had an electrical length exactly equal to a quarter wavelength (or odd multiple thereof), shorting of the terminals i by the switch 5 would produce the effect of an open circuit at the terminals 2 and accordingly no reaction would be produced in the transmission line I to the flow of radio frequency energy. Opening the switch 5 under the same ;conditions would produce a short circuit at the terminals 2 which lengths. Since the the impedance switching would prevent the flow of radio irequency energy along the transmission line l.

Due to the inherent reactance associated with the contacts 4 and switch 5, it is difficult to obtain the exact quarter wavelength reiation necessary for the above described operation. In the present Construction the desired relation is obtained by tuning reactances 8 and 1, indicated as condensers, respectively shunted across terminals 2 and 4.

The tuning reactance 6 has a value such that when the switch 5 is closed against the contacts 4 the electrical length of the transmission line 3 is tuned to an odd number of quarter wavelengths and, as explained above, causes an open circuit to appear at the terminals 2. The tuning reactance 1 has no eflect since it is shorted by the switch 5.

The tuning reactance 'I has a value such that when the switch 5 is open the transmission line 3 is tuned to an odd number of quarter waveterminals 4 are open circuited, a high impedance appears at these terminals, while a low impedance (short circuit) appears at the terminals 2, shorting the reactance 6.

The reactance 6 tunes for the condition in which a high impedance appears at the terminals 2 and the react'ance 1 tunes the transmission line 3 for the condition in which a short appears at the terminal 2. When one of the reactances is eective for tuning, the other reactance is shorted. The reactances 5 and 1 accordir ly are independently adiustable.

In Figs. 2 and 3 is shown an application of arrangement of Fig. 1

to a clrcuit in which a degree phase shiit .may be produced in the controlled radio tre-- ueney energy. The radio frequency energy to be controlled fiow through a transmission line 8 (equivalent to transmission line l in Fig. 1) connected in series with input terminals 9 and output terminals lb of an impedance switching device comprising four quarter wavelength transmission lines il, 12, !3, and M (transmission lines having an electrical length equal to an odd multiple of a quarter wavelength at the frequency to be controlled) connected in a bridge circuit between the terminals 9 and o. The transmission lines H and i! form a series circuit from the input terminals 9 through intermediate terminals I5 to output terminals o. The transmission lines I3 and ll form another series circuit between the input terminals 9 through intermediate termlnals !6 to output terminals III.

the transmlssion line trolled by quarter wavelength transmission lines respectively connected to the intermediate terminals !5 and !S of the bridge. As shown in Figs. 2 and 3, the transmission lines comprise conductors I& and !9 extending through openings in side walls of a metal casing 2| and leads !sa and lsa connecting-the conductors |8 and 19 to the terminals [5 and !8. The conductors 18 and i 9 are supported by conical insulators 22 having bases 23 abutting opposite sides of the casing side walls. The outer ends of the conductors [8 and [9 are provided with threaded terminals 24 and 25 for connection with the conductors I aa and isa. At the inner ends of the conductors !8 and IS are threaded metal bushings 26 and 21 in the outer ends of which are threaded ccntacts 28 and 29 which cooperate with switch blades 30 and 3! carried on a rock shalt 32 journaled in a partition 33 in the casing 2| and controlled by solenoids 34 and 35 arrang'ed between the partition 33 and the end wall 36 of the casing. Upon energizing the solenoid 34, the switch blade 30 is moved into engagement with the contacts 28 and the switch blade 3| is moved away from the contacts 29. Upon energizing the solencid 35 the switch blade 3| is moved into engagement with the c'ontacts 29 and the switch blade 30 is moved away from the contacts 28.

The transmission lines I 8, isa, and s, !sa serve the same function as the transmission line 3 in the Fig. l Construction, i. e., are transmission lines having an electrical length different from an odd multiple of a quarter wavelength at the controlled frequency. The contacts 28 and 29 correspond to the terminals 4, the terminals 15 and !0 correspond to the terminals 2, and the switch blades 30 and 3! correspond to the switch 5.'

The function of the tuning reactance 1 is obtained by condenser plates 31 and 38 carried by adjusting screws 39 and 40 respectively threaded into the metal sleeves 26 and 21. The function of the tuning reactance 6 is obtained by transmission line stubs 4! and 12 projecting respectively beyond the terminals !5 and iS. The condenser plates 31 and 38 are so adjusted that when the switches 30 and 3! are open the electrical length of the transmission lines !8, Isa and s, lsa is tuned exactly to an Odd multiple of a quarter wavelength of the radio frequency to be controlled. The transmission line stubs ,H and 42- are of such length that when the switches 30 and 3! are closed the electrical length of the transmission lines !8, isa and i9, isa is tuned exactly to an odd multiple of a quarter wavelength.

, The solenoids 34 and 35 are arranged so that one or the other is alternatively energized so as to close one or the other of the switches 30 and 31.' In the position shown in Fig. 2 the switch 30 is closed and the switch 31 is open. Since the inner end of the transmission line !8, i8a is shc'ted, a low impedance appears at the inner end anda high impedance appears at the terminals !5. At the terminals' l5 no resistance is offered to the flow of radio frequency energy through the transmission lines I! and |2 and no reaction appears in the transmission line a.

. sion lines, causes the switches 30, 3| are Under this condition the switch 3| is open, causing a high impedance to appear at the inner end of the transmission line s, lsa and a short circuit to appear at the terminals !6. Shorting ot the terminals IS, due to the impedance inversion characterlstlcs of quarter wavelength transmisa high impedance to appear at the terminals 8 and l0 to the flow of radio frequency energy through the transmission lines |3 and H. In the Flg. 2 position, radio frequency energy accordingly flows through the transmission lines ll and |2.

In the position shown is energized, ciosing the quency energy through the transmission lines II and !2. In the Fig.` 3 position, radio frequency energy therefore fiows wholly through the transmission lines !3 and H, and, due to the transposition H; has a degree phase displacement. Since the transmission lines II and |2 are of the same length as the transmission lines l3 and the impedance between the terminals 8 and Io is constant and is' independent of which path the radio frequency energy flows. The 180 degree phase displacement is accordingly obtained without producing any reaction in the transmis` sion line 8.

In the Construction of Figs. 2 and 3 the transmission line stubs ll and 42 and the condensers 31 and 38 which respectively perform the functions of the tuning reactances e and 1 of the Fig. 1 construction are not wholly independent due to the fact that the condensers 31 and 38 are not connected directly at the contact surfaces of the contacts 28 and 29. When the switches 30 and 3l are closed, the condensers 31 and 38 are not completely shorted, although shorting is suflicient for practical purposes. This means that when closed. the transmission lines Is, |8a and Is, lsa are tuned to a very minor extent by the condensers 31 and 38. When the switches 30, 3! are open, tuning of the transmission lines is wholly by the condensers 31 and 38.

What I claim as new and desire to Letters Patent of the United States Es:

1. An impedance switching device for controlling the flow of radio frequency energy, comprising a transmission line having an electricai length different from an odd number oi' quarter wavelengths of the frequency to be controlled, terminals at one end of the line for connection to the source of radio frequency energy, terminals at the other end of the line shunted by a galvanic switch means, a reactance shunting said first terminals of a value such that the electricai length c'i' the iine when the switch means is closed is tuned to an odd number, of quarter wavelengths, and an adjustable reactance shunting the switch means of a value such that the eiectrical length of the line when the switch is open is tuned to an odd number of quarter wavelengths.

2. An impedance switching device for controlling the now of radio frequency energy, comprising a pair of series connected quarter wavelength transmission lines for connection in series with the source of radio frequency energy to be consecure by aseaevo oi' lines to cause respectively a to the flow of radio line having terminals at one switch means is open is line having an eectrical be controlled diflerent quarter wavelengths, a

10 appear at said Junction.

certificate of correction MICHAEL E. IIEHLE It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, second column, line 6, claim 2, for "resistance" read reactance; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case Patent No. 2395370. March 5, 1946.

^ in the Patent Ofl'ce.

Signed and sealed this 15th day of October,

LESLIE FBAZEB,

Fire: Am'tat Oomm'as'omr of Patenta.

reactance shunting said first terminals of a' value such that the eiectrical length of said third line when the switch means is closed is tuned to an odd number of quartcr wavelengths, causing a, high impedance to appear at said Junction, and an adjustable resistance shunting said switch terminals of a. value such that said third line when the tuned to an odd number of quarter wavelengths causing a. low impedance to MICHAEL HIEHLE.

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