Absorptive tunable bandstop filter with wide tuning range and electrically tunable all-pass filter useful therein

• US 20120212304A1
• Filed: 02/18/2011
• Published: 08/23/2012
• Est. Priority Date: 02/18/2011
• Status: Active Grant

• Current Assignee: Hittite Microwave, LLC (Analog Devices, Inc.)
• Original Assignee: Hittite Microwave, LLC (Analog Devices, Inc.)
• Inventors: Zhang, Cemin, Koechlin, Michael
• Granted Patent: US 8,981,873 B2
• Time in Patent Office: Days
• US Class Current: 333/174
• CPC Class Codes: H03H 2007/013 Notch or bandstop filters
• CPC Class Codes: H03H 7/0153 Electrical filters; Controlling thereof
• CPC Class Codes: H03H 7/12 Bandpass or bandstop filters with adjustable bandwidth and fixed centre frequency H03H7/09 takes precedence; automatic control of bandwidth in amplifiers H03G5/16
• CPC Class Codes: H03H 7/20 Two-port phase shifters providing an adjustable phase shift

Abstract

This invention features an absorptive tunable bandstop filter with wide tuning range including first and second branches of all-pass filter networks, an input power divider for splitting the input signal and passing approximately half of the input signal power through each said branch of said all-pass filter networks, and an output power divider for recombining the signal power from each said branch of said all-pass filter networks, at least one of said branches of said all-pass filter networks being electrically tunable to provide an approximately 180° phase difference with similar amplitudes of the split said signal power to be recombined at said output power divider for rejecting but substantially absorbing selected frequencies.

Claims

1. An absorptive tunable bandstop filter with wide tuning range comprising:

first and second branches of all-pass filter networks;

an input power divider for splitting the input signal and passing approximately half of the input signal power through each said branch of said all-pass filter networks; and

an output power divider for recombining the signal power from each said branch of said all-pass filter networks;

at least one of said branches of said all-pass filter networks being electrically tunable to provide an approximately 180°

phase difference with similar amplitudes of the split said signal power to be recombined at said output power divider for rejecting but substantially absorbing selected frequencies.

2. The absorptive tunable bandstop filter of claim 1 in which said first branch includes at least first and second all-pass filters and said second branch includes at least a third all-pass filter.

3. The absorptive tunable bandstop filter of claim 1 in which one of said first and second all-pass filters has a relatively lower center frequency and the other a higher center frequency and said third all-pass filter has a center frequency corresponding to said higher center frequency.

4. The absorptive tunable bandstop filter of claim 1 in which each of said branches of all-pass filter networks includes a plurality of all-pass filters.

5. The absorptive tunable bandstop filter of claim 1 in which said electrically tunable all-pass filter networks are voltage tunable.

6. The absorptive tunable bandstop filter of claim 1 in which said power divider includes a 3 dB coupling device.

7. The absorptive tunable bandstop filter of claim 1 in which said 3 dB coupling device includes a Wilkinson divider.

8. The absorptive tunable bandstop filter of claim 1 in which said 3 dB coupling device includes a quadrature hybrid.

9. The absorptive tunable bandstop filter of claim 1 in which said 3 dB coupling device includes a 180°

hybrid.

10. The absorptive tunable bandstop filter of claim 1 in which said 3 dB coupling device includes a Lange coupler.

11. The absorptive tunable bandstop filter of claim 1 in which said 3 dB coupling device includes a directional coupler.

12. The absorptive tunable bandstop filter of claim 2 in which said all-pass filter includes first and second series connected inductors connected in parallel with first and second series connected electrically tunable variable capacitors;

a shunt electrically tunable variable capacitor connected to the junction of said first and second inductors, and a shunt bias network connected to the junction of said first and second variable capacitors.

13. The absorptive tunable bandstop filter of claim 12 further including an input bias network which connects an electrical tuning voltage to said variable capacitors.

14. The absorptive tunable bandstop filter of claim 12 in which said shunt bias network and input bias network are similar.

15. The absorptive tunable bandstop filter of claim 14 in which said shunt bias network and input bias network each include a series connected bias resistance and bias inductor.

16. The absorptive tunable bandstop filter of claim 12 in which said shunt bias network and said shunt variable capacitor are connected to ground.

17. The absorptive tunable bandstop filter of claim 12 in which each of said electrically tunable variable capacitors includes a varactor.

18. The absorptive tunable bandstop filter of claim 17 in which each of said varactors includes a diode.

19. The absorptive tunable bandstop filter of claim 17 in which at least one of said varactors includes two diodes with like electrodes coupled together.

20. The absorptive tunable bandstop filter of claim 17 in which each of said varactors includes a pn junction.

21. The absorptive tunable bandstop filter of claim 17 in which each of said varactors includes a field effect transistor.

22. The absorptive tunable bandstop filter of claim 17 in which said electrically tunable variable capacitor includes a ferroelectric capacitor.

23. The absorptive tunable bandstop filter of claim 17 in which said electrically tunable variable capacitor includes a MEMS based capacitor.

24. The absorptive tunable bandstop filter of claim 1 in which said all-pass filter networks are implemented on a planar monolithic substrate.

25. The absorptive tunable bandstop filter of claim 24 in which said planar monolithic substrate is selected from the group of GaAs and SiGe.

26. The absorptive tunable bandstop filter of claim 24 in which said planar monolithic substrate is mounted on a surface-mount package.