Adjustable electronic filter and method of tuning same

• US 4,800,348 A
• Filed: 08/03/1987
• Issued: 01/24/1989
• Est. Priority Date: 08/03/1987
• Status: Expired due to Term

• Current Assignee: CTS Corporation
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Rosar, George C., Clifford, David G. Jr.
• Primary Examiner(s): Nussbaum, Marvin L.
• Application Number:
  US07/081,264
• Time in Patent Office: 540 Days
• Field of Search: 333/202, 333/203, 333/206, 333/207, 333/223, 333/235, 333/219, 333/222
• US Class Current: 333/202
• CPC Class Codes: H01P 1/2056 Comb filters or interdigital filters with metallised resonator holes in a dielectric block

Abstract

An adjustable electronic filter apparatus is disclosed comprising a dielectric block having one or more through-holes and having a conformal conductive coating substantially over all outside surfaces as well as each through-hole therein. Each through-hole so plated forms a resonator from a transmission line which includes an open portion, for providing capacitive reactance at a first end, and a short-circuited end as a base, for providing an associated distributed inductance at a second end thereof. A unique method of tuning the adjustable electronic filter, whether a single resonator, a plurality of resonators, or a plurality of intercoupled multi-resonator filters, is disclosed that permits bi-directional tuning for at least one resonator in each of the above exemplary embodiments. By selectively adjusting an inductive portion of the plating at the base of each resonator so tuned, a resonator is quickly and accurately adjusted to a desired frequency. The selective adjusting may be accomplished by subtractive processes, such as abrasion or laser trimming, or by an additive process, such as by adding conductive paint for partially filling in a removed or absent portion of the plating at the base of a resonator.

Claims

1. A method for tuning a resonator, formed from a transmission line having a short-circuited end as a base within a dielectric block and including at least one through-hole therein, the dielectric block and the through-hole having a conformal conductive coating that covers essentially the entire surfaces thereof, the method comprising the step of:

removing a portion of the conductive coating near the base of the resonator so as to effect a change in inductance of said resonator.

2. A method for tuning a resonator, formed from a transmission line having a short-circuited end as a base within a dielectric block and including at least one through-hole therein, the dielectric block and the through-hole having a conformal conductive coating that covers essentially the entire surfaces thereof, and the base of the resonator including an area having an initial absence of conductive coating, the method comprising the step of:

adding conductive material to a portion of said area at the base of the resonator, so as to effect a change in inductance for the resonator therein.

3. A method for tuning an electronic filter having at least two resonators, each formed from a transmission line having a short-circuited end as a base within a dielectric block and including at least two through-holes spatially disposed at a predetermined distance from one another, the dielectric block and the through-holes having a conformal conductive coating that covers essentially the entire surfaces thereof, the method comprising the steps of:

(a) removing a portion of said conductive coating near the base of at least one of said resonators in a preestablished tuning sequence, in order to tune said at least one resonator to modify a value of inductance associated with said resonator; and

(b) adding to said conformal coating near the base of at least one resonator to modify a value of inductance associated with said resonator;

said steps (a) and (b) providing a change in resonant frequency for attaining the predetermined phase target of each such resonator, thereby providing bidirectional tuning for at least one resonator in the filter.

4. A method for tuning an electronic filter having at least two resonators, each formed from a transmission line having a short-circuited end as a base within a dielectric block and including at least two through-holes spatially disposed at a predetermined distance from one another, the dielectric block and the through-holes having a conformal conductive coating that covers essentially the entire surface thereof, except for an open area around each through-hole at an end opposite that of said base, the method comprising the steps of:

(a) removing a portion of said conductive coating near said open area, for at least one of said resonators in a preestablished tuning sequence, in order to capacitively tune each resonator to a respective predetermined phase target; and

(b) removing a portion of the conductive coating near the base of at least one of said resonators.

5. The method according to claim 4, wherein said desired phase accuracy is measured as within 10 degrees of the predetermined phase target for each resonator therein.

6. The method according to claim 4, wherein said step (a) of removing includes removing incremental portions of the conductive coating so as to effect a resultant incremental increase in the resonant frequency of the resonator therein.

7. The method according to claim 4, wherein said step (b) of removing includes removing incremental portions of the conductive coating so as to effect a resultant incremental decrease in the resonant frequency of the resonator therein.

8. The method according to claim 4, further comprising the step of:

(c) repeating either of the above steps a number of times sufficient to incrementally tune at least one of the resonators to a desired accuracy, so as to effect bidirectional tuning for said at least one resonator of the filter.

9. An electronic filter apparatus comprising in combination:

dielectric means for housing an electronic filter having at least two through-holes spatially disposed at a predetermined distance from one another;

conductive coating means, applied conformally to said dielectric means over substantially all outside surfaces as well as each through-hole therein, for forming at least two resonators, each formed from a transmission line which includes a short-circuited end as a base and an open area around each through-hole at an end opposite that of said base, said open area constituting a first end having capacitive reactance thereat, and said base constituting a second end having an associated distributed inductance,

said base of at least one of said resonators having a portion of conductive coating near said base in which said conductive coating has been removed to cause the inductance of said at least one resonator to increase relative to the inductance of said at least one resonator prior to said portion being removed.

10. The apparatus according to claim 9, wherein said dielectric means comprises a solid dielectric block having an essentially parallelpiped shape.

11. The apparatus according to claim 9, wherein said conductive coating means comprises a plated metallic material.

12. The apparatus according to claim 9, wherein said conductive coating means comprises silver.

13. The apparatus according to claim 9, wherein said conductive coating means is initially configured to provide a plurality of resonators in an interdigital arrangement.

14. The apparatus according to claim 9, wherein said conductive coating means is initially configured to provide a plurality of resonators in a comb-line arrangement.

15. The apparatus according to claim 9, wherein said conductive coating comprises copper.

16. In a two-way radio, improved electronic filter apparatus comprising in combination:

dielectric means for housing an electronic filter having at least two through-holes spatially disposed at a predetermined distance from one another;

conductive coating means, applied conformally to said dielectric means over substantially all outside surfaces as well as each through-hole therein, for forming at least two resonators, each formed from a transmission line which includes a short-circuited end as a base and an open area around each through-hole at an end opposite that of said base, said open area constituting a first end having capacitive reactance thereat, and said base constituting a second end having an associated distributed inductance,

said base of at least one of said resonators having a portion of conductive coating near said base in which said conductive coating has been removed to cause the inductance of said at least one resonator to increase relative to the inductance of said at least one resonator prior to said portion being removed.

17. The apparatus according to claim 19, wherein said conductive coating means includes conductive plating having portions removed from near said first end, as well as portions removed from near said second end of said at least one resonator therein.

18. The apparatus according to claim 16, wherein said dielectric means includes at least two electronic filters intercoupled to provide a plurality of passband responses.

19. The apparatus according to claim 18, wherein said dielectric means includes two electronic filters intercoupled as a duplexer to provide a combined transmit frequency passband and a receive frequency passband response to a common antenna port.