US3611402A

US3611402A - Antenna impedance matching device

Info

Publication number: US3611402A
Application number: US620A
Authority: US
Inventors: Ronald W Thomas; Stanley W Gorajczyk
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1970-01-05
Filing date: 1970-01-05
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05

Abstract

An antenna impedance matching device is formed of a pair of spaced-apart disclike conductive members which have struckout portions to form annular spirallike conductive paths beginning at the center and terminating at a point at or near the periphery thereof. Confronting surfaces of the conductive members are spaced apart by a dielectric member and form a capacitive component of the impedance matching device. At least one of the conductive members forms an inductance component as well as the capacitive component in conjunction with the other of the conductive members. The impedance matching device is circular in configuration and of a size to fit within a cavity formed in the base of an antenna structure.

Description

United States Patent Primary Examiner-Eli Lieberman Attorney-Mueller and Aichele ABSTRACT: An antenna impedance matching device is formed of a pair of spaced-apart disclike conductive members which have struckout portions to form annular spirallike conductive paths beginning at the center and terminating at a point at or near the periphery thereof. Confronting surfaces of the conductive members are spaced apart by a dielectric member and form a capacitive component of the impedance matching device. At least one of the conductive members forms an inductance component as well as the capacitive component in conjunction with the other of the conductive members. The impedance matching device is circular in configuration and of a size to fit within a cavity formed in the base of an antenna structure.

PATENTED [JCT 5I97l 3,611,402

Inventors RONALD W. THOMAS STANLEY W GORAJCZYK ANTENNA IMPEDANCE MATCHING DEVICE BACKGROUND OF THE INVENTION This invention relates generally to impedance matching devices for matching of the terminating impedance of a transmission line with that of an RF energy-receiving load connected thereto, and more particularly to an adjustable impedance matching device which can be readily positioned within a cavity formed in the base of an antenna structure.

Impedance matching devices of the type used for matching the impedance of a terminating end of a transmission line with that of the impedance of an RF receiving load, such as an antenna, are well known in the art. The nature of such impedance matching device require that the device be located at or very near the load to which the transmission line is connected. Generally, this offers no great problem when matching the input impedance of a transmission line to an output circuit of a transmitter, or the like, because the necessary circuit components can be mounted within the common cabinet of the transmitter or, if desired, mounted within an auxiliary cabinet positioned adjacent the transmitter. However, the problem becomes unmanageable when it is necessary to match the impedance of a transmission line with that of an antenna because of the requirement of having the electrical components, such as capacitors and inductors, mounted at the antenna. One form of impedance matching device of the prior art is that provided by a large coil located between the mounting base of the antenna and the radiating element thereof and which also may serve as a spring mounting to allow the antenna to bend and flex at or near the mounting end. However, helical springs which form inductive elements have limited use as an impedance matching device because of the frequency involved and are not readily adjustable for use with different frequencies.

SUMMARY OF THE INVENTION It is an object of this invention to provide an impedance matching device which is small in size and which can be mounted within the base of an antenna structure.

Another object of this invention is to provide an impedance matching device which can be adjusted over a given range of frequencies to provide the proper impedance match.

Briefly, the impedance matching device of this invention includes a pair of spaced-apart disclike metal members having struckout portions thereby forming radially and arcuately extending conductive paths beginning preferably at the center thereof and terminating at a point on the periphery of each disclike member. The confronting surface portions of the disclike members are spaced apart by a dielectric member and together therewith form a capacitive component of the impedance matching device. Preferably, the dielectric material is selected to be capable of operating at high RF power levels with little or no RF losses. Also the dielectric material should be stable over a wide range of temperatures. One such dielectric material used to advantage in the impedance matching device of this invention is 25 percent glass filled PTFE free sintered Teflon.

At least one of the disclike members of conductive material has a plurality of apertures formed therein preferably arcuately spaced apart at a common radius spaced from the center of the disclike member selectively to receive a fastening and adjusting screw. This adjusting screw passes through a selective one of the apertures and through an aperture formed in the dielectric material to engage with a threaded aperture formed in the other of the disclike conductive members. The screw preferably is made of conductive material and forms a conductive path between the disclike members. However, the length of the conductive path beginning at the center of the disclike member having the plurality of apertures formed therein is determined and adjusted by inserting the conductive screw into the appropriate aperture. That is, by changing the position of the screw to various apertures within the disclike conductive member the length of the conductive path forming the inductance element of the impedance matching device is selectively adjusted which, in turn, adjusts the impedance matching device over a given range of frequencies.

When the impedance matching of this invention is used within the base of an antenna structure, a flatspring plate and a mating flat contact plate may be used to provide electrical coupling between the terminating end of a transmission line which is connected to the base of the antenna and the impedance matching device positioned within the base. The spring plate and contact plate may also provide additional capacitance in circuit with the impedance matching device at the particular frequencies involved and, under certain circumstances, can be considered part of the impedance matching device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary respective, exploded view of an antenna structure wherein the impedance matching device of this invention is mounted in the base thereof;

FIG. 2 is an enlarged sectional view of a portion of the mounting base of FIG. 1 wherein all the components are as sembled therein to illustrate the details of the impedance matching device coupled between the antenna and a transmission line connected thereto; and

FIG. 3 is an enlarged perspective, exploded view of the im pedance matching device of this invention further illustrating means for adjusting the relative impedance thereof over a given range of frequencies.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2 there is seen an antenna structure designated generally by reference numeral 10 wherein an adjustable impedance matching device II, which is constructed in accordance with this invention, is positioned within a base 12 of the antenna. Preferably, the base 12 is of molded dielectric material and has an antenna radiating element 14 extending therefrom.

The impedance matching device 11 is illustrated herein as forming means to match the impedance between the monopole antenna 14 and a transmission line conductor l6, but it will be understood that the impedance matching device 1 1 can be used to match the impedance between the terminating end of a transmission line in any suitable RF energy receiving load. The impedance matching device 11 is most advantageously fashioned to fit within a cavity I8 formed within the mounting base 12 through a cavity opening 18a. A coupling portion 14a of the radiating element 14 extends into i the cavity 18 and is exposed to come in contact with one portion of the impedance matching device 11. A disclike flat spring 20 is provided adjacent the impedance matching device 11 and positioned to have the inner substantially flat portion 20a thereof in contact with another portion of the impedance matching device and the arcuately shaped longitudinally displaced fingerlike portions 20b extending toward and in contact with a contact disc 22. A terminating contact 24 is connected to the end of a center conductor 26 of the transmission line 16 to engage with the contact disc 22 thus electrically coupling the transmission line 16 to the antenna-radiating element 14 through the impedance matching device 11. A retainer ring 28, preferably of dielectric material, is inserted into the cavity I8 to hold the impedance matching components firmly therein, and the retainer ring 28 is flexible to allow removal thereof, which, in turn, allows removal of the impedance matching device 11 so that it can be quickly and easily adjusted if desired.

A threaded locking nut 30, preferably having threads at both the inner and outer diameters, is embedded into the mounting base 12 to provide secure mechanical connection with a connector 32 formed at the terminating end of the transmission line 16. The threaded locking nut 30 and the connector 32 also fonn means for securing the antenna structure to any suitable antenna receiving surface 34 which is provided with an aperture 34a. If the antenna-receiving surface 34 is, for example, the rooftop of an automobile, it is desired to remove a portion of the paint about the aperture 34a as indicated by the area 34b. This assures a firm grounding connection for the antenna system. An O-ring 36 may be provided within an annular recess 38 formed within the threaded locking nut 30 to provide a weathertight seal about the aperture 34a.

Referring now to FIG. 3 there is seen an exploded perspective view showing the details of the impedance matching device 1 l. The impedance matching device 11 includes a pair of spaced-apart

members

40 and 42 of conductive material, with a dielectric member 44 interposed between the confronting surface portions of the

members

40 and 42. Preferably, each of the

members

40 and 42 is plated with a suitable conductive material to prevent corrosion of these components. Also, the dielectric member 44 preferably is formed of 25 percent glass filled PTFE free sintered Teflon, but it will be understood that any dielectric material having low RF losses may be used.

The conductive member 40 includes an annular inner portion 40a'which also has formed thereat a domelike portion 40b. The annular inner portion 400 extends to a radial portion 40: which, in turn, is integrally formed with an annular outer portion 40d. The annular outer portion 40d circumscribes the periphery of the member 40 and terminates short of the radial portion 400 to form a gap 40c. Therefore, the conductive path of the member 40 begins at the inner portion 40b and extends radially and arcuately therefrom to terminate at the periphery thereof at or near the gap 40e. The member 40 can be formed by a stamping operation which cuts the circular shape thereof and strikes out an annular inner portion as well as a peripheral portion to form the various contiguous components of the member 40. I

Most advantageously, a plurality of spaced-apart screwreceiving holes 46 are formed in the disclike member 40 selectively to receive an assembly and adjusting screw 48 formed of conductive material. The adjusting screw 48 also extends through an aperture 50 formed within the dielectric member 44 and is received by a threaded aperture 52 formed within the bottom disclike member 42. The effective conductive length of the member 40 is then determined by the location of the conductive screw 48 within the selected hole 46.

The four spaced-apart holes 46 provide means for adjusting the impedance value of the impedance matching device 11 to one of several relatively narrow, but contiguous, frequency ranges over an entire frequency band in which the impedance device 11 is to be used. For example, if the antenna structure is to be used within a frequency range of 450 to 455 MHz. the first hole, which extends toward the viewer of FIG. 3, is used to receive the assembly screw 48. On the other hand, if the frequency range is to be between 455 to 460 MHz. the second hole will receive the assembly screw 48. If the impedance matching device 11 is to be used within a frequency range of 460 to 465 MHz. the third hole will receive the assembly screw 48, and if the frequency range is to be between 465 and 470 MHz. the fourth hole, which extends away from the viewer of FIG. 3, is used to receive the assembly screw 48. To provide a certain amount of overlap, of each of the frequency ranges mentioned hereinabove the impedance matching device 11 is tuned to the center of each frequency range, this being 452.5, 457.5, 462.5 and 467.5 MHz., respectively. As all of the screw-receiving holes 46 are located along a common radius of the disclike member 40, mechanical alignment of the

members

40 and 42 and the dielectric member 44 is maintained in all four positions of adjustment. Also, adjusting the desired frequency range within the given band of frequencies is a relatively simple matter requiring nothing more than a small screwdriver.

The bottom member 42 is substantially of the same configuration as the top member 40 except that a single-screw-receiving hole 52 is provided therein. However, it will be noted that the member 42 of the illustrated embodiment has the arcuate portion thereof turning in the opposite direction than the arcuate portion of the member 40. Also, the conductive path from the center portion 42a to the periphery thereof is determined only by the radial portion 42b in the embodiment disclosed herein. However, it will be understood that the threaded aperture 52 can be located anywhere along the peripheral portion 420 to provide additional inductance for the impedance matching device 11. Also, the impedance matching device 11 may take any desired form other than circular.

Accordingly, the impedance matching device 1] has the necessary inductance formed by the conductive path beginning at the center portion 40b and extending therefrom through the radial portion 40c and the arcuate portion 40d to terminate at the location of the aperture 46 which receives the conductive assembly screw 48. The current path then extends through the assembly screw 48 into the periphery of the member 42 and therefrom to center portion 42a thereof. Also, the confronting surface portions of the

members

40 and 42 spaced apart by the dielectric member 44 form all or a portion of the necessary capacitance of the impedance matching device for the frequency range in which it is used. The impedance matching device 11 can be used if desired, to match the impedance between the terminating end of a transmission line and any suitable RF energy-receiving load other than an antenna.

We claim:

1. An impedance matching device to be positioned between the terminating end of a transmission line and an RF energy load for coupling signals thereto having frequencies greater than 400 MHz., comprising, a first member of flat conductive material having a struckout portion to form a continuous conductive path beginning at a contact point within the periphery of said first member and terminating at some point at the periphery thereof to form an inductance characteristic of the impedance matching device, said contact point being arranged for connection with the RF energy load, a second member of flat conductive material in alignment with and parallel to said first member, whereby said first and second members have confronting surface portions, a nonconductive member interposed between said first and second members and forming therewith the capacitance characteristic of the impedance matching device, said second member having a contact point arranged for connection to the transmission line, and conductive means interconnecting said first and second members along the periphery thereof to provide a conductive path therebetween.

2. The impedance matching device of claim 1, wherein said conductive means includes means to adjust the length of the conductive path of said first member to effect adjustment of the frequency response of the impedance matching device.

3. The impedance matching device of claim 1 wherein said dielectric member is formed of 25 percent glass filled PTFE free sintered Teflon.

4. The impedance matching device of claim 1 wherein said second member of flat conductive material has a struckout portion to form a continuous conductive path beginning at the contact point within the periphery of said second member and terminating at the point along the periphery of said second member.

5. The impedance matching device of claim 4 wherein the struckout portions of said first and second members of conductive material form conductive paths beginning at the center of each member and extending radially and arcuately therefrom to terminate at a point at the periphery thereof, and a raised portion extending perpendicular to the plane of each member of flat conductive material formed at the center thereof to form contact means between the terminating end of the transmission line and the input of the RF energy-receiving load.

6. The impedance matching device of claim 1 wherein said first and second members of flat conductive material and said member of dielectric material are circular in the configuration, the struckout portion of said first member forming a conductive path beginning at the center thereof and extending to a first portion radially outwardly of the center and therefrom into a circumferential portion about the periphery thereof which terminates short of the radially extended portion, and said second member of flat conductive material has a struckout portion forming a conductive path beginning at the center thereof and extending radially outwardly to an arcuate peripheral portion, said first and second members of flat conductive material and said dielectric member having apertures formed therein and arranged in alignment to receive a fastener of conductive material therethrough.

7. The impedance matching device of claim 6 wherein the arcuate peripheral portion of said first member of conductive material has a plurality of apertures formed therein at arcuately spaced-apart locations thereon, the impedance of the impedance matching device being adjusted within a given range of impedances for a corresponding range of frequencies by selecting the desired aperture to receive the fastener of conductive material.

8. An antenna having a base, a radiating element extending from the base, an open cavity formed in the base, signalcoupling means having one end connected to the radiating element and the other end thereof exposed in the cavity, transmission line connecting means formed at the opening of said cavity to receive the terminating connector end of a transmission line, the improvement comprising: an impedance matching device positioned in said cavity, said impedance matching device including a first member of flat conductive material, said first member having a struckout portion forming a continuous conductive path beginning at the point within the periphery of said first member and terminating at a portion on the periphery thereof to form inductance and capacitance characteristics of the impedance matching device, said first member having a portion in contact with said signal-coupling means, a second member of flat conductive material spaced from, in alignment with, and parallel to said first member to have a confronting surface portion thereof forming a capacitor with said first member, said second member having a portion in contact with said transmission line connecting means, and a nonconductive member interposed between said first and second members of conductive material to form the dielectric of the capacitor formed by said first and second members of conductive material.

9. The antenna of claim 8 wherein a fastener of conductive material extends through said first member and said dielectric member into said second member to form a short circuit termination of the conductive path of said first member, the distance of said conductive path beginning in the center of said first member ad terminating at the conductive fastener fastening extending therethrough determining the inductance value exhibited by said first member of conductive material.

l0. The antenna of claim 8 including means to adjust the effective length of the conductive path of said first member to effect adjustment of the impedance matching device.

11. The antenna of claim 8 wherein said first and second members of flat conductive material and said member of dielectric material are circular in the configuration, the struckout portion of said first member forming a conductive path beginning at the center thereof and extending to a first portion radially outwardly of the center and therefrom into a circumferential portion about the periphery thereof which terminates short of the radially extended portion and said second member of flat conductive material has a struckout portion forming a conductive path beginning at the center thereof and extending radially outwardly to an arcuate peripheral portion, said first and second members of fiat conductive material and said dielectric member having apertures formed therein and arranged in alignment to receive a fastener of conductive material therethrough.

12. The antenna of claim 11 wherein the arcuate peripheral portion of said first member of conductive material has a plurality of apertures formed therein at arcuately spaced-apartlocations thereon, the impedance of the impedance matching device being adjusted within a given range of impedances for a corresponding range of frequencies by selecting the desired aperture to receive the fastener of conductive material.

Claims

8. An antenna having a base, a radiating element extending from the base, an open cavity formed in the base, signal-coupling means having one end connected to the radiating element and the other end thereof exposed in the cavity, transmission line connecting means formed at the opening of said cavity to receive the terminating connector end of a transmission line, the improvement comprising: an impedance matching device positioned in said cavity, said impedance matching device including a first member of flat conductive material, said first member having a struckout portion forming a continuous conductive path beginning at the point within the periphery of said first member and terminating at a portion on the periphery thereof to form inductance and capacitance characteristics of the impedance matching device, said first member having a portion in contact with said signal-coupling means, a second member of flat conductive material spaced from, in alignment with, and parallel to said first member to have a confronting surface portion thereof forming a capacitor with said firsT member, said second member having a portion in contact with said transmission line connecting means, and a nonconductive member interposed between said first and second members of conductive material to form the dielectric of the capacitor formed by said first and second members of conductive material.

10. The antenna of claim 8 including means to adjust the effective length of the conductive path of said first member to effect adjustment of the impedance matching device.

11. The antenna of claim 8 wherein said first and second members of flat conductive material and said member of dielectric material are circular in the configuration, the struckout portion of said first member forming a conductive path beginning at the center thereof and extending to a first portion radially outwardly of the center and therefrom into a circumferential portion about the periphery thereof which terminates short of the radially extended portion and said second member of flat conductive material has a struckout portion forming a conductive path beginning at the center thereof and extending radially outwardly to an arcuate peripheral portion, said first and second members of flat conductive material and said dielectric member having apertures formed therein and arranged in alignment to receive a fastener of conductive material therethrough.

12. The antenna of claim 11 wherein the arcuate peripheral portion of said first member of conductive material has a plurality of apertures formed therein at arcuately spaced-apart locations thereon, the impedance of the impedance matching device being adjusted within a given range of impedances for a corresponding range of frequencies by selecting the desired aperture to receive the fastener of conductive material.