US3764939A

US3764939A - Rf matching system for high frequency relays

Info

Publication number: US3764939A
Application number: US00261581A
Authority: US
Inventors: R Stokes
Original assignee: General Electric Co
Current assignee: Genicom Corp
Priority date: 1972-06-12
Filing date: 1972-06-12
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09

Abstract

A radio frequency relay circuit having movable and/or fixed contacts positioned above a conductive housing member, the contacts having adjustable tabs extending generally parallel to the housing member which enable the relay circuit to be tuned to the characteristic impedance of a transmission line to which the radio frequency relay is connected.

Description

United States Patent [1-91 Stokes RF MATCHING SYSTEM FOR HIGH FREQUENCY RELAYS [75] Inventor: Roy E. Stokes, Staunton, Va.

[73] Assignee: General Electric Company,

Waynesboro, Va.

22 Filed: June 12, 1972 21 Appl.No.: 26l,58l

s21 U.s.c i. 333/7, 333/97 s, 333/33 511 Int.Cl. H0lp 1/10 [58] Field of Search"... 333/97 S, 7, 97 R- [56] I References Cited UNITED STATES PATENTS 2,784,379 3/1957 Schunemann 333/97 S [451 Oct. 9, 1973 Primary Examiner-Rudolph V. Rolinec Assistant Examiner--Wm. H. Punter Attorney-Michael Masnik et al.

57 ABSTRACT A radio frequency relay circuit having movable and/or fixed contacts positioned above a conductive housing member, the contacts having adjustable tabs extending generally parallel to the housing memberiwhich enable the relay circuit to be tuned to the characteristic impedance of a transmission line to which the radio frequency relay is connected.

8 Claims, 4 Drawing Figures.

PATENTEUBBT 91m 3.764.939

sum 1% 2 v Z OUTPUT 2 h Z OUTPUT I "III II 1 Y RF'MATCIIING SYSTEM FOR HIGH FREQUENCY RELAYS BACKGROUND 05 THE INVENTION High frequencyrelays are used as switches to selectively connect together various sections of transmission line. For example, a high frequency relay may be used to selectively switch a transmission line section connected to an antenna alternatively between lines connected to a receiver and a transmitter or separate receivers or separate transmitters.

' Any mismatch between the impedance of the relay and the transmission media to which it is connected results in radio frequency power being reflected from the mismatch and lost. A mismatch in the first example given above would result in loss of signal strength from the antenna delivered to the receiver and loss of signal strength transmitted to the antenna by the-transmitter.

Hence, the degree of mismatch or voltage standing wave ratio (VSWR) is a critical factor in determining the efficiency of any radio frequency relay circuit. The

, best results are obtained when a match exists between the characteristic impedance of the transmission media and the effect impedance of the relay circuit.

The problem of reducing mismatches in radio frequency relay circuits is complicated by the fact that radio frequency relay circuits are most often produced in large quantities. Therefore, to be economical any design changes to improve matching must: require a minimumof added material, involve a minimum of additional labor, and produce an operable relay without demandingindividual testing and adjustment. Furthermore, it is mostdesirable to maintain the overall size of therelay circuit as small as possible consistent with power handling requirements.

The prior art has recognized the general fact that stray distributive capacitance exists between electrical conductors which carry radio frequency signals. The present invention utilizes this basic principle in connection with uniquely structured relay contacts to provide an economic radiofrequency relay circuit which is readily adjustable or tuned to be matched to a transmission media connected to the relay. Also, in relaysmade according to the present invention, matching to a particular transmission line may be effected during mass production without the need for any individual testing or adjustment.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide in a radio frequency relay circuit means for matching the circuit with the transmission media to which the circuit is connected.

Further objects and advantages of the invention will be apparent to those skilled in the art from the following description of the invention taken in conjunction with the attached drawings.

In one preferred form, the present invention comprises a radio or high frequency relay mounted on a conductive housing member. The relay includes a movable arm electrically insulated from and positioned ad.- jacent the housing member. The arm is movable between first and second positions, and means are pro- I housing member. The first fixed contact is positioned to be in electrical connection with the arm in the first position and out of electrical connetion with the'arm in the second position. Means are also provided to make the fixed contact readily accessible electrically for external connection to a portion of transmission line.

In one preferred form of the present-invention, the fixed contact further includes an impedance matching stub having a substantially planar surface. The stub is dimensioned with respect to the conductive housing member to adjust the impedance of the relay circuit to match the characteristic impedance of the transmission line. Further embodiments of the present invention include the disclosure of anadditional fixed contact with a corresponding impedance matching stub connected thereto, the employment of an impedance matching stub in connection with the movable arm and the employment of at least one matching stub having two substantially planar surfaces at'an angle to each other.

BRIEF DESCRIPTION OF TI-IE DRAWINGS.

For a further understanding of the invention, reference is made to the detailed description below taken in conjunction with the drawings, wherein:

FIG. 1 is a top view of one embodiment of the present invention;

FIG. 2 is a side view of the embodiment of the present invention disclosed in FIG. 1 taken along line FIG. 3 is a top view of another embodiment of the present invention; and

FIG. 4 is a side view of the embodiment-of the present invention disclosed in FIG. 3 taken along line A-l3 DETAILED DESCRIPTION OF THE INVENTION FIGS. 1'and'2 illustrate one embodiment of the present invention. For a relay designed for DC or low frequency AC power levels, little consideration is given to matching the reactive impedance characteristics-of. the input and output circuits to that of the relay. The single pole, double throw relay shown in FIG. 1 with the movable contact and its associated ground plane 10 (which may constitute part of an enclosing conductive housing) is connected to an input circuitlabeled Z input. The two

fixed contacts

20a and 20b, which are designed to contact with movable contact 14, and the associated ground plane 10 are connected to respective output circuits labeled Z output 1 and Z output 2. At high radio frequencies, the relay contacts develop an undesirable reactive impedance producing a mismatch with the input and/or output circuits. This mismatch produces undesirable standing waves at the high radio frequency which reduces the amount of available power which is conducted to the load circuit through the relay. The standing waves generate excessive currents which result in undesirable heat losses. To conduct the maximum power at the radio frequency, applicant proposes to modify the structure of the contacts of the relay such that the impedance mismatch is reduced. This is accomplished by extending and enlarging the contacts in a desirable direction with respect to the ground plane such that the added distributed capacitance modifies the inherent characteristic impedance of the contacts to where the resulting characteristic impedance of the contacts to where the resulting characteristic impedance matches more closely the im- 3 pedance of the associated input and/or output circuits. In one embodiment of the invention, a relay was required to operate with circuits over a frequency band of 25 to 1,000 megacycles per second. At these frequencies, the contacts exhibited a distributed inductance which modified the relay impedance. The contacts were extended in a direction opposite to that of their working ends and dimensioned to exhibit a lumped capacitive effect to offset this inductance and permit a matching of relay and circuit impedances. The extension or stub providing the capacitance was located opposite the direction where the contact making or breaking was to take place. By providing stubs to all contacts, movable and fixed, the relay impedance would match the impedances of the input and output circuits or transmission lines even if the connections of thesecircuits to the movable and fixed contacts were interchanged.

Referring to FIG. 1, there is shown a conductive housing member or header 10 having extending from it a plurality. of conductive terminal pins 12. A conductive movable arm 14 is electrically insulated from and supportedabove a conductive header 10 by the combination of insulating sleeve 16 and pin 18. Insulating sleeve 16 is fixedly positioned in header l and may comprise a good radio frequency insulator such as a plastic, rubber or glass composition. Pin 18 extends through insulating sleeve 16 to provide at its lower end a means for externally connecting movable arm 14 to an external circuit such as a transmission line section (shown in FIG. 4).

Fixed

contacts

200 and 20b are also electrically insulated from header by respective insulating sleeves 22d and 22b. Insulating sleeves 22a and 22b may be comprised of the same material used to form insulating sleeve 16.

Conductive pins

24a and 24b extend through respective insulation sleeves 22a and 22b to fixedly support contacts a and 20b above conductive header 10in a manner to facilitate connecting transmission line sections (shown in FIG. 4) to the respective

fixed contacts

20a and 20b.

Fixed

contacts

20a and 20b include conductive

rodlike members

26a and 26b which extend generally parallel to header 10. The rod-

like members

26a and 26b areshown to have a-ge'nerally circular cross-sectional area, but may be structured in any geometric configuration which ideally acts to minimize the capacitive coupling between the rod-

like members

26a and 26b and the movable arm 14.

FIG. 2 illustrates that rod-

like members

26a and 26b define two spaced apart parallel planes. An end section 28 of movable arm 14 is positioned between the two planes and arm 14 may be biased so as to come into electrical contact with either rod-

like member

26a or 26b. In FIG. 2, arm 14 is designed so that it is normally in a first position contacting rod-like member 26a and can be moved down to contact 26b when a magnetic force is developed by a relay coil to be described. In addition, the end section 28 of movable arm 14 which comes in electrical contact with rod-

like members

26a and 26b is bifurcated to increase the ability of arm 14 to enter good electrical connection along a goodly portion of its planar surface with the two rod-

like members

26a and 26b.

Fixed contacts

20a and 20b include

impedance matching stubs

30a and 30b respectively. Each matchingstub 30a and-30b comprises a generally planar conductive surface electrically and physically conected to respective rod-like members 26a and

26b.Matching stubs

30a and 30b may comprise unitary extensions of respective rod-

like members

26a and 26b or, in the al ternative, comprise separate conductive entities electrically and physically attached to the respective rodlike members.

Movable arm 14 also includes a substantially planar section extending beyond pin 18 to form a matching stub 32.

In operation, pins l2'are utilized to electrically connect the base member or header 10 to an appropriate ground plane in a selected transmission media. Pin 18 is used to connect a first conductive portion of the transmission media to movable arm 14 while pin 24a is used to connect a second conductive portion of the transmission media to fixed contact 20a. If desired, fixed contact 20b may be connected by pin 24b to a third conductive portion of the transmission media.

Any appropriate means, known to those skilled in the art, is employed to selectively movearm 14 from the first position in electrical contact with rod-like member 26a to a second position in electrical contact with rodlike member 26a, thereby selectively connecting the first conductive portion of the transmission media to the second and third conductive portions respectively. A description of one such arrangement comprising a relay coil is described subsequently.

Impedance matching stubs

30a, 30b and 32 are selectively employed to adjust the impedance of the relay circuit to match the characteristic impedance of the transmission media. The impedance matching is dependent upon the shape of the impedance matching stubs employed and the dimensioning of the stubs with respect to a conductive housing shown in FIGS. 1 and 2 as header 10. It is to be understood that the conductive housing may also include a conductive cover enclosing the relay circuit.

When employing the embodiment of the present invention disclosed in FIGS. '1 and 2 in connection with a transmission line having a characteristic impedance of 50 ohms and transmitting a band of frequencies and when the relay circuit is used in an air dielectric, the following dimensions may besatisfactorily employed:

stubs

30a and 30b having a planar surface area of approximately .02 square inch and positioned at a heigm' of approximately 0.072 inch above the surface of header 10; and arm 14 having a planar surface area between bend X and pin 18 of approximately 0.019 square inch, stub 32 having a planar surface area of approximately .021 square inch and arm 14 from bend X to the end of stub 32 positioned at a height of approximately 0.030 inch above header 10. These dimensions are given merely as one example of an operable embodiment of the present invention built under mass production conditions. The present invention is not intended to be limiting solely to the transmission line impedance characteristics described or the dimensions given.

A modification of the embodiment of the present invention disclosed in FIGS. 1 and 2 is shown in FIGS. 3 and 4. The components of the embodiment shown in FIGS. 3 and 4 which are substantially the same as those shown in FIGS. land 2 are identically numbered.

In FIGS. 3 and 4, a substantially planar surface of conductive material 42 is shown electrically connected to and extending at an angle from impedance matching stub'32. A substantially planar conductive surface 44 is also shown electrically connected to and extending at an angle from impedance matching stub 30a of contact a. The

planar surfaces

42 and 44 aredimen sioned with respect to a conductive cover 46, to provide an additional means for adjusting the impedance of the relay circuit to match the characteristic impedance of a transmission line to which the relay will be connected. It is to be understood that an additional planar surface 48qmay also be connected to impedance matching stub b shown in FIG. 1 and that the additional planar surfaces are not to be limited to the precise geometric configurations illustratively show-n in FIGS. 3 and 4. I I

FIG. 4 discloses connection of three terminal pins 12 of header 10 to an external circuit such as the ground plane 52 of a microstrip transmission line. This line usually has individual conductor strips separated from a surface ground plane for propagating signals. The pins in a particular embodiment were of standard length to either connect with

conductors

52, 54 or 56. Pins 12 are shown connected by soldering toconductor 52. Pins 12 are shown passing through the insulating medium 61 and through openings in

strip lines

54 or 56 without touching 54 or 56. In this manner, during a dip soldering operation solder may be drawn to surface 54 by pins I2 by capillary action. A first section of transmission line 54 is shown electrically connected to pin 18 which passes through an opening in 52 while a second section of transmission line 56 is shown electrically connected by soldering to pin 240 which also passes through an opening in 52. An insulative bead or ball 58 is shown mounted on member or armature 60. Energizing relay coil 50 attracts end 60a of the armature 60 moving bead 58 down to overcome spring action of movable arm 14 and driving contact end 28 away from 26a and into contact with 26b. Actuator means 50 may, for example, comprise an electromagnet or other suitable-electromechanical mechanism which when energized to produce a magnetic field, attracts extension 60a of armature 60 to the left causing the bead 58 to move downward. While the external circuit has been described as a strip line, it is obv-iuos that other circuits are possible. For example, the connection to pin 18 and ground may be by coaxial connector with the inner coaxial conductor connected to pin 18 and the outer coaxial conductor connected to ground as, for example, to the case 10.

As is apparent from the above description, the embodiment of the present invention shown in FIGS. 3 and 4 operates in substantially the same manner as the embodiment shown in FIGS.,1 and 2.

Having described two embodiments of a high frequency relay with adjustable stubs for matching the im-, pedance of the relay to the characteristic impedance of a transmission line, it will be understood that various changes may be made in detail within the scope of the claims without departing from the spirit of the invention. It is, therefore, to be understood that the invention is not to be limited to the specific details as shown and described.

I claim:

1. In combination, a switching device comprising a first contact in the form of a rod-like member, a second contact movable to cause one end thereof to come into electrical connection with one end of said rod-like member, one of said contacts forming a first circuit with said housing and the other contact forming a second circuit with said housing, means forcoupling a radio frequency transmission line having a given characteristic impedance. to at least one of said circuits, means for matching the characteristic impedance of said coupled circuit to said transmission line comprising an impedance matching stub extending from the other end of said contact associated with said one of said circuits and being physically spaced from at least one side of said housing, said stub having a substantially planar surface dimensioned with respect to'one of said sides of said housing to provide a capacitive coupling to said housing. I

2. In combination, a switching device comprising a first fixed contact, a second movable contact, means for moving one end of said second contact to contact one end of said first contact, said first contact end being sloped to minimize capacitive coupling to said second contact, one of said contacts forming a first circuit with said housing and the other contact forming a second circuit with said housing, means for coupling a radio frequency transmission line having a given characteristic impedance to at least one of said circuits, means for matching the characteristic impedance of said coupled circuit to said transmission line compris ing an impedance matching stub extending from the other end of said contact associated with said one of said circuits and being physically spaced from at least one side of said housing, said stub having a substantially planar surface dimensioned with respect to one of said sides of said housing to adjust the impedance of the switching device to match the characteristic impedance of the transmission line. I

3. An arrangement according to claim 2 wherein:

said second contact has a bifurcated planar surface at said one end to improve contact closure reliability with minimum capacitive coupling to said first contact and the other end of said second contact is shaped to increase capacitive coupling to said housing.

4. An arrangement according to claim 2 wherein:

the stub .is formed to have two substantially planar surfaces at an angle to each other.

5. A high frequency relay for switching sections of transmission line comprising:

a housing member having at least one conductive surface;

a movable arm electrically insulated from and positioned adjacent said housing member, said arm being movable between first and second positions;

a first contact electrically insulated from and positioned adjacent said housing member, said contact positoned to be in electrical connection with said arm in said first position and out of electrical connection with said arm in said second position;

means for electrically connecting said movable arm and said first contact to respective sections of transmission line having a given characteristic impedance; and

said first contact including a substantially planar stub physically spaced from at least one of said conducting surfaces to adjust the impedance of said relay to match the characteristic impedance of the transmission line. 6. The high frequency relay as claimed 7 8 said movable arm includes a fixedly positioned subsaid second contact including a substantially planar stantially planar second stub physically spaced third stub physically spaced from at least one of f at least one of Sald Ponductmg Surfaces to said conducting surfaces to adjust the impedance Just l f P of Sam relay to 'j f h char of said relay to match the characteristic impedance acteris tic impedance of the transmiss on line. I of the transmission lines 7. The high frequency relay as claimed in claim 6 m- 8 Th h f I l d l eluding: e ig requency re ay c aime in c mm 7 ma second contact electrically insulated from and posieluding:

tioned adjacent Said housing member Said Contact at least one substantially planar conductive member positioned to be out of electrical contact with said 10 elecmcally and P y y attached at an angle to arm in said first position and in electrical contact at least one Of Said first, Second and third Stubs. with said arm in said second position; and

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 764 ,939 Dated October 9 1973 lnventofls) Roy E. Stokes It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 lines 33 & 34 cancel A-=-l3 A andv insert Column 5, line '26 cancel "54" and insert 52' cancel obviuos and insert Column 5, line 43 obvious Signed and sealed this 16th day of April 197A.

(SEAL) Attest:

EDWARD M.FLET HER,JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM'DC 60376-P69 U.5. GOVERNMENT PRINTING OFFICE I969 0-3693. 0

RM PO-1050 (10-69)

Claims

1. In combination, a switching device comprising a first contact in the form of a rod-like member, a second contact movable to cause one end thereof to come into electrical connection with one end of said rod-like member, one of said contacts forming a first circuit with said housing and the other contact forming a second circuit with said housing, means for coupling a radio frequency transmission line having a given characteristic impedance to at least one of said circuits, means for matching the characteristic impedance of said coupled circuit to said transmission line comprising an impedance matching stub extending from the other end of said contact associated with said one of said circuits and being physically spaced from at least one side of said housing, said stub having a substantially planar surface dimensioned with respect to one of said sides of said housing to provide a capacitive coupling to said housing.

2. In combination, a switching device comprising a first fixed contact, a second movable contact, means for moving one end of said second contact to contact one end of said first contact, said first contact end being sloped to minimize capacitive coupling to said second contact, one of said contacts forming a first circuit with said housing and the other contact forming a second circuit with said housing, means for coupling a radio frequency transmission line having a given characteristic impedance to at least one of said circuits, means for matching the characteristic impedance of said coupled circuit to said transmission line comprising an impedance matching stub extending from the other end of said contact associated with said one of said circuits and being physically spaced from at least one side of said housing, said stub having a substantially planar surface dimensioned with respect to one of said sides of said housing to adjust the impedance of the switching device to match the characteristic impedance of the transmission line.

3. An arrangement according to claim 2 wherein: said second contact has a bifurcated planar surface at said one end to improve contact closure reliability with minimum capacitive coupling to said first contact and the other end of said second contact is shaped to increase capacitive coupling to said housing.

4. An arrangement according to claim 2 wherein: the stub is formed to have Two substantially planar surfaces at an angle to each other.

5. A high frequency relay for switching sections of transmission line comprising: a housing member having at least one conductive surface; a movable arm electrically insulated from and positioned adjacent said housing member, said arm being movable between first and second positions; a first contact electrically insulated from and positioned adjacent said housing member, said contact positoned to be in electrical connection with said arm in said first position and out of electrical connection with said arm in said second position; means for electrically connecting said movable arm and said first contact to respective sections of transmission line having a given characteristic impedance; and said first contact including a substantially planar stub physically spaced from at least one of said conducting surfaces to adjust the impedance of said relay to match the characteristic impedance of the transmission line.

6. The high frequency relay as claimed in claim 5 wherein: said movable arm includes a fixedly positioned substantially planar second stub physically spaced from at least one of said conducting surfaces to adjust the impedance of said relay to match the characteristic impedance of the transmission line.

7. The high frequency relay as claimed in claim 6 including: a second contact electrically insulated from and positioned adjacent said housing member, said contact positioned to be out of electrical contact with said arm in said first position and in electrical contact with said arm in said second position; and said second contact including a substantially planar third stub physically spaced from at least one of said conducting surfaces to adjust the impedance of said relay to match the characteristic impedance of the transmission lines.

8. The high frequency relay claimed in claim 7 including: at least one substantially planar conductive member electrically and physically attached at an angle to at least one of said first, second and third stubs.