Band pass filter with tunable phase cancellation circuit

• US 20090121937A1
• Filed: 11/14/2008
• Published: 05/14/2009
• Est. Priority Date: 11/14/2007
• Status: Active Grant

• Current Assignee: Comprod Communications Corporation
• Original Assignee: Comprod Communications Corporation
• Inventors: Kaegebein, Daniel P.
• Granted Patent: US 8,154,363 B2
• Time in Patent Office: Days
• US Class Current: 342/381
• CPC Class Codes: H01P 1/208 Cascaded cavities; Cascaded resonators inside a hollow waveguide structure H01P1/205 takes precedence

Abstract

A phase cancellation circuit for a cavity filter including a sampler loop assembly arranged to receive an input signal, a variable loop assembly connected to the sampler loop assembly by a cable, wherein the variable loop assembly is arranged to transmit an output signal from cavity filter, wherein the sampler loop assembly samples a cancellation signal at an isolation frequency from the input signal and transmits the cancellation signal to the variable loop assembly via the cable, and, wherein the cable has a length equal to a multiple of a half-wavelength at the desired isolation frequency, wherein the cancellation signal undergoes a 180° phase shift by traveling through the cable, wherein the variable loop assembly combines the cancellation signal with the input signal to cancel the input signal at the isolation frequency due to the 180° phase shift for creating the output signal with a notch at the isolation frequency.

Claims

1. A phase cancellation circuit for a cavity filter comprising:

a sampler loop assembly operatively arranged to receive an input signal to said cavity filter;

a variable signal insertion loop assembly connected to said sampler loop assembly by a cable, wherein said variable signal insertion loop assembly is operatively arranged to transmit an output signal from said cavity filter;

wherein said sampler loop assembly samples a cancellation signal at a desired isolation frequency from said input signal and transmits said cancellation signal to said variable signal insertion loop assembly via said cable; and

,

wherein said cable has a length, and said length is equal to a multiple of a half-wavelength at said desired isolation frequency, wherein said cancellation signal undergoes a 180°

phase shift by traveling through said cable, wherein said variable signal insertion loop assembly combines said cancellation signal with said input signal, wherein said 180°

phase shift cancels said input signal at said isolation frequency for creating said output signal, and wherein said output signal substantially resembles said input signal but with a notch at said desired isolation frequency.

2. The phase cancellation circuit recited in claim 1 wherein said cavity filter is a bandpass cavity filter.

3. The phase cancellation circuit recited in claim 1 wherein said sampler loop assembly comprises:

a bulkhead connector for receiving said input signal;

a connector block secured to said bulkhead connector, wherein said connector block is hollow and includes an aperture for enabling insertion of said cable into said connector block;

a loop ring secured to said connector block opposite from said bulkhead connector; and

,

a loop extending out of said connector block, wherein a first end of said loop is affixed to a center pin of said bulkhead connector and a second end of said loop is grounded to said loop ring.

4. The phase cancellation circuit recited in claim 3 wherein a first end of said cable is stripped to a center conductor wire of said cable, and said center conductor wire is affixed to said center pin of said bulkhead connector and to said loop.

5. The phase cancellation circuit recited in claim 4 wherein a rigid sleeve is affixed to said cable proximate to said first end of said cable, and wherein said rigid sleeve is positioned in said aperture and clamped to said connector block by a set screw.

6. The phase cancellation circuit recited in claim 1 wherein said variable signal insertion loop assembly comprises:

a bulkhead connector for transmitting an output signal;

a connector block secured to said bulkhead connector, wherein said connector block is hollow and includes an aperture for enabling insertion of said cable into said connector block;

a loop ring secured to said connector block opposite from said bulkhead connector;

a coupling tube housed within said connector block, wherein said coupling tube includes a hole for partial insertion of a central pin of said bulkhead connector into said coupling tube, wherein said couple tube rests on a non-conductive spacer that separates said bulkhead connector from contacting said coupling tube;

a dielectric ring concentrically arranged within said coupling tube; and

,

a loop extending out of said connector block, wherein a first end of said loop is affixed to a said coupling tube and a second end of said loop is grounded to said loop ring.

7. The phase cancellation circuit recited in claim 6 wherein a second end of said cable is stripped down to a center conductor wire of said cable, wherein said center conductor wire is fitted with a voltage probe, and wherein said voltage probe is inserted through said aperture in said block connector and concentrically positioned within said dielectric tube for creating a field coupling between said coupling tube and said voltage probe.

8. The phase cancellation circuit recited in claim 7 wherein a rigid sleeve is affixed to said cable proximate to said second end of said cable, and wherein said rigid sleeve is positioned in said aperture and clamped in place by a shaft lock arranged about said aperture.

9. A method of creating a notch in a signal at a desired isolation frequency transmitted through a cavity filter comprising the steps of:

(a) receiving an input signal with a cavity filter;

(b) sampling a cancellation signal from said input signal at said desired isolation frequency;

(c) shifting said cancellation signal 180°

by transmitting said cancellation signal through a cable having a length equal to a multiple of a half-wavelength at said desired isolation frequency;

(d) combining said cancellation signal with said input signal for cancelling said input signal at said desired isolation frequency, thereby creating an output signal that substantially resembles said input signal, but with a notch at said desired isolation frequency; and

,

(e) transmitting said output signal from said cavity filter.

10. The method of claim 9 wherein a sampler loop assembly of said cavity filter receives said signal in step (a), and said sampler loop assembly samples said cancellation signal in step (b), a variable signal insertion loop assembly combines said cancellation signal with said signal in step (d), and said sampler loop assembly, said variable signal insertion loop assembly and said cable comprise a phase cancellation circuit.

11. The method of claim 10 further comprising the step of:

(f) tuning said phase cancellation circuit by altering a position of a voltage probe with respect to a coupling tube housed within a connector block of said variable signal insertion loop assembly, wherein said voltage probe is affixed to one end of said cable.

12. The method of claim 11 wherein step (f) occurs before step (a).

13. A cavity filter comprising:

a phase cancellation circuit for a cavity filter including;

a sampler loop assembly operatively arranged to receive an input signal to said cavity filter;

a variable signal insertion loop assembly connected to said sampler loop assembly by a cable, wherein said variable signal insertion loop assembly is operatively arranged to transmit an output signal from cavity filter;

wherein said sampler loop assembly samples a cancellation signal at a desired isolation frequency from said input signal and transmits said cancellation signal to said variable signal insertion loop assembly via said cable; and

,

wherein said cable has a length, and said length is equal to a multiple of a half-wavelength at said desired isolation frequency, wherein said cancellation signal undergoes a 180°

phase shift by traveling over said length of said cable, wherein said variable signal insertion loop assembly combines said cancellation signal with said input signal to cancel said input signal at said isolation frequency due to said 180°

phase shift for creating said output signal, and wherein said output signal substantially resembles said input signal but with a notch at said desired isolation frequency.

14. The cavity filter recited in claim 13 wherein said cavity filter is a bandpass filter.