Duplexer filter having harmonic rejection to control flyback

• US 5,023,866 A
• Filed: 05/22/1989
• Issued: 06/11/1991
• Est. Priority Date: 02/27/1987
• Status: Expired due to Term

• Current Assignee: Quarterhill Inc. (f/k/a Wi-LAN Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: De Muro, David M.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): PASCAL, LESLIE C
• Application Number:
  US07/355,844
• Time in Patent Office: 750 Days
• Field of Search: 370/24, 370/30, 370/32, 379/59, 455/33 D, 333/202, 333/200, 333/205, 333/206, 333/208, 333/211, 333/212, 333/219, 333/227, 333/231, 333/236, 333/245, 333/242, 333/134-137, 334/42, 343/850, 343/905
• US Class Current: 370/278
• CPC Class Codes: H01P 1/2056 Comb filters or interdigital filters with metallised resonator holes in a dielectric block
• CPC Class Codes: H01P 1/2136 using comb or interdigital filters; using cascaded coaxial cavities H01P1/2131, H01P1/2135 take precedence

Abstract

A radio frequency duplexer filter for a duplex transceiver is disclosed. To prevent spurious signals conducted by flyback responses of the transmit bandpass filter 103 from reaching the antenna (105), a band reject circuit consisting of third harmonic quarter-wave transmission line stubs (601 and 603) are advantegeously coupled to an output transmission line (107). Likewise, to prevent spurious signals conducted by flyback responses of the receive bandpass filter (113) from reaching the receiver (109), a band reject circuit consisting of third harmonic quarter-wave transmission line stubs (605 and 607) are advantageously coupled to an input transmission line (111).

Claims

1. A duplexer filter for a duplex radio communications transceiver comprising:

first periodically resonant means tuned to pass a band of frequencies utilized by the radio transmitter;

second periodically resonant means tuned to pass a band of frequencies utilized by the radio receiver;

a first transmission line coupling said first periodically resonant means to an antenna port, having a length determined by a phase shift necessary to produce an essentially open circuit at said antenna port at said band of frequencies utilized by the radio receiver, and having at least one open-circuited stub with a length substantially equal to one-fourth the electrical wavelength of the third harmonic of a frequency within said band of frequencies utilized by the transmitter; and

a second transmission line coupling said second periodically resonant means to said antenna port, having a length determined by a phase shift necessary to produce an essentially open circuit at said antenna port at said band of frequencies utilized by the radio transmitter, and having at least one open-circuited stub with a length substantially equal to one-fourth the electrical wavelength of the third harmonic of a frequency within said band of frequencies utilized by the receiver.

2. A duplexer filter in accordance with claim 1 wherein said first and second transmission lines further comprise microstrip transmission lines realized as copper conductors over a ground plane of a printed circuit board.

3. A duplexer filter in accordance with claim 1 wherein said first and second transmission lines further comprise stripline transmission lines realized as copper conductors between ground planes of a printed circuit board.

4. A radio frequency duplexer for a cellular telephone transceiver selectively coupling a transmitter to an antenna and selectively coupling the antenna to a receiver, comprising:

a first bandpass filter of a plurality of periodically resonant structures tuned to a first band of frequencies and coupled to the transmitter whereby signals within said first band of frequencies may be passed by said first bandpass filter;

a first transmission line having an input end and an output end and a first length and coupling said first bandpass filter at said input end to a duplex point at said output end to which the antenna may be coupled, said first length determined by a phase shift necessary to produce an open circuit at a second band of frequencies at said duplex point;

a first open-circuited transmission line stub having a first characteristic impedance and a first stub length and coupled to said first transmission line at a place being a first distance from said first transmission line input end;

a second open-circuited transmission line stub having a second characteristic impedance and a second stub length and coupled to said first transmission line a second distance from said place said first stub is coupled to said first transmission line;

a second bandpass filter of a plurality of periodically resonant structure tuned to said second band of frequencies and coupled to the receiver whereby signals within said second band of frequencies may be passed by said second bandpass filter;

a second transmission line having an input end, an output end, and a second length and coupling said second bandpass filter at said output end to said duplex point at said input end, said second length determined by a phase shift necessary to produce an open circuit at said first band of frequencies at said duplex point;

a third open-circuited transmission line stub having a third characteristic impedance and a third stub length and coupled to said second transmission line at a place being a third distance from said second transmission line output end; and

a fourth open-circuited transmission line stub having a fourth characteristic impedance and a fourth stub length and coupled to said second transmission line a fourth distance from said place said third stub is coupled to said second transmission line.

5. A radio frequency duplexer in accordance With claim 4 wherein said first transmission line predetermined length further comprises the sum of said first distance, said second distance, and a fifth distance.

6. A radio frequency duplexer in accordance with claim 5 wherein the sum of said first distance and said fifth distance is a constant.

7. A radio frequency duplexer in accordance with claim 5 wherein said first transmission line further comprises a transmission line having a fifth characteristic impedance over said first distance and said fifth distance and having a sixth characteristic impedance over said second distance.

8. A radio frequency duplexer in accordance with claim 4 wherein said second transmission line predetermined length further comprises the sum of said third distance, said fourth distance, and a sixth distance.

9. A radio frequency duplexer in accordance with claim 8 wherein the sum of said third distance and said sixth distance is a constant.

10. A radio frequency duplexer in accordance with claim 8 wherein said second transmission line further comprises a transmission line having a seventh characteristic impedance over said third distance and said sixth distance and having an eighth characteristic impedance over said fourth distance.

11. A radio frequency duplexer in accordance with claim 4 wherein said first stub length is substantially equal to one-fourth the electrical wavelength of the third harmonic of a frequency above said first band of frequencies.

12. A radio frequency duplexer in accordance with claim 4 wherein said second stub length is substantially equal to one-fourth the electrical wavelength of the third harmonic of a frequency below said second band of frequencies.

13. A radio frequency duplexer in accordance with claim 4 wherein said third stub length is substantially equal to one-fourth the electrical wavelength of the third harmonic of a frequency above said second band of frequencies.

14. A radio frequency duplexer in accordance with claim 4 wherein said fourth stub length is substantially equal to one-fourth the electrical wavelength of the third harmonic of a frequency below said second band of frequencies.

15. A radio frequency duplexer in accordance with claim 4 wherein said first and second transmission lines further comprise microstrip transmission lines realized as copper conductors over a ground plane of a printed circuit board.

16. A radio frequency duplexer in accordance with claim 4 wherein said first and second transmission lines further comprise stripline transmission lines realized as copper conductors between ground planes of a printed circuit board.

17. A duplexer filter for a duplex radio communications transceiver comprising:

first periodically resonant means tuned to pass a band of frequencies utilized by the radio transmitter;

second periodically resonant means tuned to pass a band of frequencies utilized by the radio receiver;

a first transmission line coupling said first periodically resonant means to an antenna port, having a length determined by a phase shift necessary to produce an essentially open circuit at said antenna port at said band of frequencies utilized by the radio receiver, and having at least one open-circuited stub with a length substantially equal to one-fourth the electrical wavelength of the third harmonic of a frequency within said band of frequencies utilized by the radio transmitter; and

a second transmission line coupling said second periodically resonant means to said antenna port and having a length determined by a phase shift necessary to produce an essentially open circuit at said antenna port at said band of frequencies utilized by the radio transmitter.

18. A duplexer filter in accordance with claim 17 wherein said first and second transmission lines further comprise microstrip transmission lines realized as copper conductors over a ground plane of a printed circuit board.

19. A duplexer filter in accordance with claim 17 wherein said first and second transmission lines further comprise stripline transmission lines realized as copper conductors between ground planes of a printed circuit board.

20. A duplexer filter for a duplex radio communications transceiver comprising:

first periodically resonant means tuned to pass a band of frequencies utilized by the radio transmitter;

second periodically resonant means tuned to pass a band of frequencies utilized by the radio receiver;

a first transmission line coupling said first periodically resonant means to an antenna port and having a length determined by a phase shift necessary to produce an essentially open circuit at said antenna port at said band of frequencies utilized by the radio receiver; and

a second transmission line coupling said second periodically resonant means to said antenna port, having a length determined by a phase shift necessary to produce an essentially open circuit at said antenna port at said band of frequencies utilized by the radio transmitter, and having at least one open-circuited stub with a length substantially equal to one-fourth the electrical wavelength of the third harmonic of a frequency within said band of frequencies utilized by the radio receiver.

21. A duplexer filter in accordance with claim 20 wherein said first and second transmission lines further comprise microstrip transmission lines realized as copper conductors over a ground plane of a printed circuit board.

22. A duplexer filter in accordance with claim 20 wherein said first and second transmission lines further comprise stripline transmission lines realized as copper conductors between ground planes of a printed circuit board.