US2407847A - Radio frequency switch - Google Patents

Description

. sept. 17, 1946. 11m/PETERSON 2,407,847

R. F. SWITCH Filed May l, 1945 Patented Sept. 17, 1946 RADIO FREQUENCY SWITCH Donald W. Peterson, Princeton, N. J., assignor` to Radio Corporation of America, a corporation of Delaware Application May 1, 1943, Serial No. 485,388

This invention relates to radio-frequency switches, such as are used for making and breaking electively connections between radio frequency sources and loads, reversing or changing the phases of the currents flowing in various parts of radio frequency circuits, and the like.

Such switching and phasing functions are required for example in the operation of directive antenna systems when a plurality of directive patterns are to be provided selectively. It is com-mon practice to employ various combinations of variable capacitors and transmission line sections for these purposes. `For example, if two points in a radio frequency circuit are to be alternately connected together and disconnected, a capacitor capable of being varied between two values Cmin and Cmax is coupled to the two points through a transmission line. The line is of such length that the reactance o1 the capacitor atone of its settings, for example, Cinex is transformed to a short circuit at the end of the line. The reactance presented at the end of the line by Cmin is tuned to parallel resonance by a stub line or a similar reactive element, so as to produce an open circuit. Thus, by changing the capacitance from Cmax to Cmin or vice versa, a short circuit or open circuit may be provided. Similar arrangements are used for phase shifting or phase reversal in radio frequency networks.

' Although radio frequency switching systems of the above described type can be made highly effective by careful design, the variabl-e capacitors are relatively bulky and expensive. Also, the transmission line networks necessary to achieve the desired operations may be somewhat compleX. Accordingly, it is the principal object of the present invention to provide an improved method of and means for controlling the ilow of radio frequency currents.

Another object of the invention is to provide an improved radio frequency switch structure comprising a minimum of moving parts and requiring no close mechanical tolerances.

A further object is to provide an improved radio frequency switch structure which is readily adaptable to remote control. These and other objects will become apparent to those skilled in the art upon consideration of the following description with reference to the accompanying drawing, in which Figs. l and 2 are sectional schematic diagrams of switches constructed in accordance with the invention and Fig. 3 is a schematic diagram of a typical network including the switch of Fig. 2.

Referring t0v Fig. 1, a concentric transmission 6 Claims. (Cl. 178-44) line l is to be selectively short circuited and open circuited between the inner conductor 3 at a point 5 and the outer conductor l'. A tubular conductive member 9 is connected to the outer conductor l' of the line I and extends substantially at right angles thereto. A second tubular conductive member II is supported concentrically within the conductor 9 and connected to the point 5 on the inner conductor 3 of the line I. The space between the walls of the tubular members 9 and I I may be filled With insulating material it, such as hard rubber, polystyrene, or the like. The insulator I3 extends beyond the end of the member I I and is provided `with a cylindrical bore concentric with and substantially of the same diameter as that of the member II. The length of the member I! is onequarter electrical wavelength at the frequency at which the system is to operate.

An iron rod I5, insulated by a coating I1 of polystyrene or the like, is provided within the bore of the member I3 and is adapted to move longitudinally therein between the positions shown in Fig. 1 and Fig. 2. A winding I9 is provided on the outside of the member 9 at the end adjacent to line l. The winding i9V is connected through a switch 2l lto an electrical source'23 such as a generator. The rod I5 is substantially one-half wavelength long so that when itis in the position shown in Fig. 2 it extends substam tially one-quarter electrical wavelength beyond the end of thetubulai` member iI. The operation of the above described structure is as follows: I

When the parts are in the position illustrated in Fig. 1 the tubular members 9 and I I cooperate to function as a quarter wave line open-circuited at one end and connected across the line I at the other end. Owing to the well known impedance inversion characteristics of quarterwave lines the open circuit at the far end of this line is reflected as a short circuit between the point 5 and the outer conductor l. When switch 2| is closed the solenoid winding i8 is energized,

drawing the iron rod I5 into the position shown l in dot and dash lines. Since the rod I5 and the tubular member II overlap for substantially a quarter wavelength they present the electrical characteristics of a single conductor one-half wavelength long. Thus, the members 9, I I and I5 together constitute a half wavelength line open-circuited at its far end and present an open circuit between the point 5 and the outer conductor 1 To retract the member `I5 from the member II a second solenoid mayI be provided Afrequency line.

at the outer end of the member 9 or the device may be mounted in such a position that gravity will effect a withdrawal when the switch 2| is opened. If desired, the rod I may be magnetically polarized, and the coil I9 energized from a D.-C. source through a reversing switch.

Fig. 2 showga modification of the switch of Fig. 1 arranged to short circuit and open circuit selectively two transmission lines I and I. The outer conductor 9 is connected between the outer conductors I and I. The inner tubular conductor I I is duplicated with a conductor II connected to the inner conductor of the line I. A solenoid I9' surrounds the outer conductor 9 at the end adjacent the line I. The windings I9 and I9 are connected through a double throw switch 2| to the source 23. A single rod member I5 is provided as in the structure of Fig. 1. When the switch 2| is thrown to -the left, the rod I5 is drawn into the tubular member |I, short circuiting the line I at the point 5. When the switch 2|' is thrown to the right, ythe rod I5 is drawn into the tubular member Il', short circuiting the line I at the point 5 and presenting an open circuit across the line I.

Fig. 3 Vshows the above described switch arranged to reverse the phase on a balanced radio Conductors 25 and 2'! constitute a parallel open-wire transmission line, balanced with respect to ground. Juxtaposed points 29 and 3| on the lines 25 -and 2'! respectively are interconnected by a concentric line S5 one-half electrical wavelength long. A point 3l one-quarter wavelength to the left of point 29 is connected to the point 39 one-quarter wavelength to the right of the point 3| by a half-wave line 4|. The point 43 one-quarter wavelength to the left of the point 3| is similarly connected to the point 45 one-quarter wavelength to the right of the line 29 by a half wave line 41. The mid points 5| and 53 of the lines 4| and 4'! respectively are connected together by a half-wave line 49. A switch 55A is connected between the points 29 and 5I. The switch 55 may comprise a structure similar to that of Fig. 2 arranged to provide a short circuit at one end at the same time as an open circuit is presented at the other end. The operation of the system of Fig. 3 is as follows:

VAssume that the switch 55 is actuated so that the point 29 is short-circuited while the point 5i is open-circuited. The short circuit at the point 29 is reected as an open circuit at the points 31 and The open circuit at the point 5I has no effect upon the performance of the line 4I. Thus, the short circuit presented at the point 29 reflects a short circuit at the point 3| through the half wave line 35. The short circuit at the point 3| is reiiected at the points 39 and 43 as open circuits. Energy applied to the line 25 flows from the point 31 through the line 4I to the point 39 and energy applied to the line 2 lflows through the line 4l to the point 45. Thus the polarities of the points 39 and 45 are reverse with respect to the corresponding points 43 and. 31. When the switch 55 is actuated so as to provide a short circuit at the point 5Il and an open circuit at the point 29, open circuits are presented at the points 31 and 39 by the line 4| and at points 43 and 45 by the line 4'I. Energy applied through the lines 25 and 21 to the points 45 and 39 directly through points 29 and 3| and the polarity of the point 45 with respect to that of point 39 is the same as the polarity of the point 3'I with respect to that of `point 43.

Although only one application of the invention has been specifically described it will be apparent that its utility is not limited thereto. For example, it will be clear without further illustration that switches of the described type may be employed to insert or remove line sections of undesired length in a transmision line circuit for providing different phase shifts between predetermined points. It should also be noted that although the illustrated embodiment is arranged to be operated electro-magnetically, the outer conductor 9 may be slotted to provide for mechanical operation by means of a pin or the like' extending radially from the member I5. In the case of a single ended structure such as that of Fig. 'l the member I5 may be provided with an extension rod of insulating material for mechanical operation through the outer end of the switch structure.

The invention covered herein may be manufactured and used by or for the Government of the United States for governmental, military, naval and national defense purposes without payment to me or assigns of any royalty thereon.

I claim as my invention:

l. A system for selectively presenting an open circuit and a short circuit between two predetermined points in a radio frequency transmission system, comprising a tubular member of conductive material connected to one of said points, a second tubular conductive member connected to the other of said points and positioned. within and coaxial with said first tubular member, and an insulated rod of conductive material adapted to move longitudinally within said second tubular member.

2. A system for selectively presenting an open circuit and a short circuit between two predetermined points in a radio frequency transmission system, comprising a tubular member of conductive material connected to one of said points, a second tubular conductive member connected to the other of said points and positioned within and coaxial with said first tubular member, an insulated rod of conductive magnetic material adapted to move longitudinally within said second tubular member, and solenoid means supported on the outer surface of said first tubular member.

cluding a body of insulated material positioned between the inner wall of said first tubular member and the outer wall of said second tubular member,

4. The invention as set forth in claim 1 wherein said second tubular member is substantially 1A, electrical wave length long and said rod member is substantially 1/2 electrical wave length long.

5. A radio frequency distributioncircuit, including an open wire, transmission line comprising two conductors, a concentric line 1/2 wave length long connected between juxtaposed points on said conductors, second and third concentric lines each 1/2 wave length long cross-connected between points on said first and second conductors 1/4 wave length to each side of said juxtaposed points, a fourth concentric line 1/2 wave length long connected between the midpoints of said second and third lines, means for alternately providing a short circuit and an open circuit at one of said midpoints, and means for simultaneously providing respectively an ope-n circuit and a short circuit at one of saidjuxtaposed points, said last named means comprising Y 6. The invention as set forth in claim 5 Wherein said rod member is made of magnetic material and said outer tubular member is surrounded by electro magnet means comprising at least 5 one solenoid Winding.

DONALD W. PETERSON.

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