Claims
- 1. A filter apparatus wherein a predetermined frequency band is located in an attenuation band of said filter apparatus, comprising:
- an input terminal,
- a non-reversible circuit element, a first terminal of which is connected to said input terminal,
- a band-pass filter which has a resonator, said band-pass filter being connected to a second terminal of said non-reversible circuit element, wherein said second terminal operates as an output with respect to signals received at said first terminal, and wherein a pass band of said band-pass filter is located in said attenuation band,
- an output terminal which is connected to a third terminal of said non-reversible circuit element, wherein said third terminal operates as an output with respect to signals received at said second terminal, and
- an active circuit which is coupled to said resonator of said band-pass filter, and becomes a negative resistance in an operation band of said band-pass filter;
- wherein said band-pass filter further includes a plurality of additional resonators, said resonator with said active circuit coupled thereto being a last-stage resonator of said band-pass filter.
- 2. A filter apparatus in accordance with claim 1, wherein an output end of said band-pass filter is in no-load state.
- 3. A filter apparatus in accordance with claim 2, which comprises a plurality of additional said band-pass filters.
- 4. A filter apparatus in accordance with claim 1, which comprises a plurality of additional said band-pass filters.
- 5. A filter apparatus in accordance with claim 1, which further comprises a case, wherein said input terminal is fixed to one side wall of said case;
- said non-reversible circuit element is formed in said case;
- said band-pass filter is formed in said case; and
- said output terminal is fixed to said one side wall of said case.
- 6. A filter apparatus in accordance with claim 5, which comprises a plurality of additional said band-pass filters.
- 7. A filter apparatus in accordance with claim 5, wherein an output end of said band-pass filter is in no-load state.
- 8. A filter apparatus in accordance with claim 7, which comprises a plurality of additional band-pass filters.
- 9. A filter for filtering an undesired frequency band from an input signal, comprising:
- a main input terminal;
- a non-reversible circuit element having at least first, second and third terminals, wherein the second terminal outputs a signal received at said first terminal, and the third terminal outputs a signal received at the second terminal;
- input means for receiving said input signal from said main input terminal of said filter and supplying said input signal to said first terminal;
- a band-pass filter connected to said second terminal, said band-pass filter having a passband corresponding to said undesired frequency band, thereby absorbing signals in said undesired frequency band and reflecting signals in other frequency bands;
- said band-pass filter comprising a resonator and an active circuit coupled to said resonator which provides a negative resistance at said passband frequency; and
- output means for supplying an output signal from said third terminal to further circuitry.
- 10. A filter as in claim 9, wherein said input means further comprises an additional band-pass filter which interconnects said main input terminal of said filter and said first terminal, wherein said additional band-pass filter passes signals in a desired frequency band.
- 11. A filter as in claim 9, wherein said resonator is a quarter-wave dielectric resonator.
- 12. A filter as in claim 9, wherein said resonator is a half-wave dielectric resonator.
- 13. A filter as in claim 9, further comprising a plurality of additional resonators.
- 14. A filter as in claim 13, wherein said resonators are tuned to a plurality of respective frequency bands.
- 15. A filter as in claim 13, wherein said resonators are tuned to the same frequency band.
- 16. A filter as in claim 13, further comprising an active circuit providing a negative resistance at said passband frequency coupled to each said additional resonator.
- 17. A filter as in claim 13, wherein said resonator and said additional resonators are coupled to one another in series and the filter has only one said active circuit which is coupled to a last one of said resonators.
- 18. A filter as in claim 13, wherein said resonator and said additional resonators are capacitively coupled in series to one another.
- 19. A filter as in claim 9, wherein said band-pass filter has an unloaded output.
- 20. A filter as in claim 9, further comprising a plurality of additional band-pass filters connected to said second terminal, each said additional band-pass filter having a passband corresponding to said undesired frequency band, thereby absorbing signals in said undesired frequency band and reflecting signals in other frequency bands, wherein each said band-pass filter has an unloaded output.
Priority Claims (2)
Number |
Date |
Country |
Kind |
1-150998 |
Jun 1989 |
JPX |
|
1-219882 |
Aug 1989 |
JPX |
|
Parent Case Info
This is a division of application Ser. No. 07/536,175, filed Jun. 11, 1990, allowed U.S. Pat. No. 5,132,651.
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
4538123 |
Mariani et al. |
Aug 1985 |
|
4816788 |
Ishikawa et al. |
Mar 1989 |
|
5132651 |
Ishikawa et al. |
Jul 1992 |
|
Foreign Referenced Citations (1)
Number |
Date |
Country |
0142701 |
Jun 1988 |
JPX |
Divisions (1)
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Number |
Date |
Country |
Parent |
536175 |
Jun 1990 |
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