Dual-polarity low-noise block downconverter systems and methods

• US 6,424,817 B1
• Filed: 09/04/1998
• Issued: 07/23/2002
• Est. Priority Date: 02/04/1998
• Status: Expired due to Term

• Current Assignee: CalAmp Corporation
• Original Assignee: California Amplifier Inc.
• Inventors: Hadden, Ian, Buchan, Bruce J.
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): Mehrpour, Naghmeh
• Application Number:
  US09/148,913
• Time in Patent Office: 1,418 Days
• Field of Search: 455/3.02, 455/12.1, 455/313, 455/323, 455/295, 455/296, 455/302, 455/310, 455/317, 455/20, 725/68, 725/69
• US Class Current: 455/3.02
• CPC Class Codes: H04B 7/18517 Transmission equipment in earth stations
• CPC Class Codes: H04H 40/90 specially adapted for satellite broadcast receiving

Abstract

Methods and systems are provided for spectrally separating first and second satellite signals that occupy a common frequency band with different first and second electromagnetic polarizations. These systems and methods facilitate the use of inexpensive single-cable distribution networks to simultaneously deliver all transmitted channels of a satellite communication system to a plurality of subscriber locations. In particular, a frequency-converter system is provided that includes first and second low-noise block downconverters whose outputs are coupled into an output diplexer. The low-noise block downconverters each have a downconverter mixer and a local oscillator that couples a local oscillator signal to the mixer but the local oscillator signals are sufficiently spaced apart to convert the first and second satellite signals to spectrally spaced first and second intermediate-frequency (IF) bands. The IF bands are isolated because they are spectrally separated. Accordingly, they can be combined in the diplexer and distributed to subscribers over an economical single-cable distribution network.

Claims

1. A downconverter system which reduces spurious signals as it downconverts first and second polarized satellite signals that occupy a common frequency band to thereby form combined communication signals, the system comprising:

first and second probes arranged to respectively detect said first and second polarized signals and process them to first and second detected signals;

first and second local oscillators that respectively provide a first local oscillator (LO) signal and a second LO signal that is spectrally spaced from said first LO signal;

a first low-noise block downconverter that has a first mixer which responds to said first LO signal and downconverts said first detected signals to first downconverted signals in a first frequency band that is at least two octaves below said first and second LO signals;

a second low-noise block downconverter that has a second mixer which responds to said second LO signal and downconverts said second detected signals to second downconverted signals in a second frequency band that is spectrally spaced from said first frequency bald and is at least two octaves below said first and second LO signals;

a diplexer that combines said first and second downconverted signals to form said combined communication signals;

a first intermediate-frequency (IF) filter coupled between said first mixer and said diplexer and configured to pass said first downconverted signals in said first frequency band and attenuate said second dow converted signals in said second frequency band;

a second IF filter coupled between said second mixer and said diplexer and configured to pass said second downconverted signals in said second frequency band and attenuate said first downconverted signals in said first frequency band;

a first LO isolation filter set to the frequency of said second LO signal and coupled between said first mixer and said diplexer to inhibit passage of said second LO signal to said first mixer;

and

a second LO isolation filter set to the frequency of said first LO signal and coupled between said second mixer and said diplexer to inhibit passage of said first LO signal to said second mixer;

said first and second LO isolation filters thus inhibiting crosstalk between said first and second mixers to thereby reduce spurious signals in said combined communication signals.

2. The downconverter system of claim 1, wherein said first and second probes are orthogonally arranged.

3. The downconverter system of claim 2, further including an antenna that is configured to receive said first and second polarized signals and deliver them to said first and second probes.

4. The downconverter system of claim 1, wherein said common frequency band is substantially 12.2-12.7 GHz, said first LO signal has a frequency of substantially 11.25 GHz, said second LO signal has a frequency of substantially 10.675 GHz, said second LO isolation filter is a trap filter set to substantially 11.25 GHz and said first LO isolation filter is a trap filter set to substantially 16.675 GHz.

5. The downconverter system of claim 1, wherein said common frequency band is substantially 12.2-12.7 GHz, said first LO signal has a frequency of substantially 11.25 GHz and said second LO signal has a frequency of substantially 10.675 GHz and wherein said first IF filter passes signals in the range of 950-1450 MHz and attenuates signals in the range of 1525-2025 MHz and said second IF filter passes signals in the range of 1525-2025 MHz and attenuates signals in the range of 950-1450 MHz.

6. The downconverter system of claim 1, wherein:

said first low-noise block downconverter further includes;

a) a low-noise amplifier that amplifies said first detected signals;

b) a bandpass filter that passes said first detected signals; and

c) an amplifier that amplifies said first downconverted signals;

and said second low-noise block downconverter further includes;

a) a low-noise amplifier that amplifies said second detected signals;

b) a bandpass filter that passes said second detected signals; and

c) an amplifier that amplifies said second downconverted signals.

7. The downconverter system of claim 1, wherein said first LO isolation filter is a trap filter set to the frequency of said second LO signal and said second LO isolation filter is a trap filter set to the frequency of said first LO signal.

8. The downconverter system of claim 1, wherein said first and second isolation filters, are included in said diplexer.

9. A method for reducing spurious signals as polarized satellite communication signals that occupy a common frequency band are downconverted to form combined communication signals, comprising the steps of:

detecting said polarized signals with first and second probes to generate first and second detected signals;

in a first mixer, mixing said first detected signals with a first local oscillator (LO) signal to generate first downconverted signals;

in a second mixer, mixing said second detected signals with a second LO signal that is spectrally spaced from said first LO signal to generate second downconverted signals that are spectrally spaced from said first downconverted signals wherein said first and second downconverted signals are at least two octaves below said first and second LO signals;

in a first, signal path following said first mixer, passing said first downconverted signals and attenuating said second downconverted signals with a first intemediate-frequency (IF) filter;

in a second signal path following said second mixer, passing said second downconverted signals and attenuating said first downconverted signals with a second IF filter;

in said first signal path, providing a first LO isolation filter set to the frequency of said second LO signal to inhibit passage of said second LO signal;

in said second signal path, providing a second LO isolation filter set to the frequency of said first LO signal to inhibit passage of said second LO signal; and

at terminations of said first and second signal paths, combining said first and second downconverted signals to form said combined communication signals;

crosstalk between said first and second mixers thus inhibited by said second and first LO isolation filters to thereby reduce spurious signals in said combined communication signals.

10. The method of claim 9, further including the step of distributing said combined communication signals over a single-cable distribution network.

11. The method of claim 9, wherein:

said common frequency band is substantially 12.2-12.7 GHz;

said first and second LO signals have frequencies respectively of substantially 11.25 GHz and 10.675 GHz; and

said first and second LO isolation filters are first and second trap filters respectively set to substantially 10.675 and 11.25 GHz.

12. The method of claim 9, wherein said first LO isolation filter is a trap filter set to the frequency of said second LO signal and said second LO isolation filter is a trap filter set to the frequency of said first LO signal.

13. A communication system which reduces spurious signals as it downconverts and distributes polarized satellite signals to a plurality of system subscribers wherein said polarized satellite signals occupy a common frequency band, comprising:

a dual-polarity antenna that receives first and second polarized signals;

a downconverter that includes;

a) first and second probes arranged to respectively detect said first and second polarized signals and process them to first and second detected signals;

b) first and second local oscillators that respectively provide a first local oscillator (LO) signal and a second LO signal that is spectrally spaced from said first LO signal;

c) a first low-noise block downconverter that has a first mixer which responds to said first LO signal and downconverts said first detected signals to first downconverted signals in a first frequency band that is at least two octaves below said first and second LO signals;

d) a second low-noise block downconverter that has a second mixer which responds to said second LO signal and downconverts said second detected signals to second downconverted signals in a second frequency band that is spectrally spaced from said first frequency band and is at least two octaves below said first and second LO signals;

e) a diplexer that combines said first and second downconverted signals to form said combined communication signals;

f) a first intemediate-frequency (IF) filter coupled between said first mixer and said diplexer and configured to pass said first downconverted signals in said first frequency band and attenuate said second downconverted signals in said second frequency band; and

g) a second IF filter coupled between said second mixer and said diplexer and configured to pass said second downconverted signals in said second frequency band and attenuate said first downconverted signals in said first frequency band;

h) a first LO isolation filter set to the frequency of said second LO signal and coupled between said first mixer and said diplexer to inhibit passage of said second LO signal to said first mixer; and

i) a second LO isolation filter set to the frequency of said first LO signal and coupled between said second mixer and said diplexer to inhibit passage of said first LO signal to said second mixer;

a single able distribution network that distributes said combined communication signals to said subscribers;

and

an impedance matching network configured to provide an impedance match between said diplexer and said distribution network;

said first and second LO isolation filters thus inhibiting crosstalk between said first and second mixers to thereby reduce spurious signals in said combined communication signals.

14. The system of claim 13, wherein:

said first low-noise block downconverter further includes;

a) a low-noise amplifier that amplifies said first detected signals;

b) a bandpass filter that passes said first detected signals; and

c) an amplifier that amplifies said first downconverted signals;

and said second low-noise block downconverter further includes;

a) a low-noise amplifier that amplifies said second detected signals;

b) a bandpass filter that passes said second detected signals; and

c) an amplifier that amplifies said second downconverted signals.

15. The system of claim 13, wherein said common frequency band is substantially 12.2-12.7 GHz, said first LO signal has a frequency of substantially 11.25 GHz, said second LO signal has a frequency of substantially 10.675 GHz, said second LO isolation filter is a trap filter set to substantially 11.25 GHz and said first LO isolation filter is a trap filter set to substantially 10.675 GHz.

16. The system of claim 13, wherein said common frequency band is substantially 12.2-12.7 GHz, said first LO signal has a frequency of substantially 11.25 GHz and said second LO signal has a frequency of substantially 10.675 GHz and wherein said first IF filter passes signals in the range of 950-1450 MHz and attenuates signals in the range of 1525-2025 MHz and said second IF filter passes signals in the range of 1525-2025 MHz and attenuates signal In the range of 950-1450 MHz.

17. The system of claim 13, further including a plurality of interface modules that terminate said single-cable distribution network and provide said combined communication signals to said subscribers.

18. The system of claim 13, wherein said first LO isolation filter is a trap filter set to the frequency of said second LO signal and said second/LO isolation filter is a trap filter set to the frequency of said first LO signal.

19. The Communication system of claim 13, wherein said first and second isolation filters are included in said diplexer.

20. A downconverter for reduction of spurious signals in the downconversion of orthogonally-polarized satellite signals that occupy a common frequency band, comprising:

orthogonally-arranged first and second probes for respective detection of said, first and second orthogonally-polarized satellite signals;

a diplexer that has an output port for delivery of downconverted satellite signals;

a first mixer that is coupled between said first probe and said diplexer;

a first local oscillator that drives said first mixer to downconvert satellite signals to a first intermediate-frequency (IF) band that is spaced at least two octaves below the frequency of said first local oscillator;

a second mixer that is coupled between said second probe and said diplexer;

a second local oscillator that drives said second mixer to downconvert satellite signals to a second IF band that is different from said first IF band and that is spaced at least two octaves below the frequency of said second local oscillator;

a first IF filter that is coupled between said first mixer and said output port to pass signals in said first IF band and attenuate signals in said second IF band;

a second IF filter that is coupled between said second mixer and said output port to pass signals in said second IF band and attenuate signals in said first IF band;

a first isolation filter that is coupled between said first mixer and said diplexer and is set to the frequency of said second local oscillator to thereby inhibit signal transmission from said second local oscillator to said first mixer; and

a second isolation filter that is coupled between said second mixer and said diplexer and is set to the frequency of said first local oscillator to thereby inhibit signal transmission from said first local oscillator to said second mixer;

said first and second isolation filters inhibiting crosstalk between said first and second local oscillators and thereby reducing spurious signals at said output port.

21. The downconverter of claim 20, wherein said first and second isolation filters are first and second trap filters.

22. The downconverter of claim 20, wherein said common frequency band is substantially 12.2-12.7 GHz, said frequency of said first local oscillator is substantially 11.25 GHz and said frequency of said second local oscillator is substantially 10.675 GHz.

23. The downconverter of claim 20, wherein said first and second isolation filters are included in said diplexer.