A COMB LINEAR AMPLIFIER COMBINER (CLAC)

Abstract: The present invention is a Comb linear amplifier combiner (CLAC) apparatus that allows one or more transmitters to transmit through one transmit antenna. The CLAC apparatus passes low powered transmit signals through a bank of bandpass filters. The transmit signals then pass through Class A amplifiers which amplify the transmit signals to the full transmit power. The full transmit power signals then pass through a second bank of bandpass filters. The transmission signals are then transmitted through a single transmission antenna.

Description: A COMB LINEAR AMPLIFIER COMBINER (CLAC) STATEMENT OF GOVERNMENT INTEREST: The invention described herein may be manufactured and used by or for the Government of the United States of Americas for governmental purposes without the payment of any royalties thereon or therefor. RELATIONSHIP TO OTHER APPLICATIONS: The present disclosure is a continuation-in-part application related to the United States Patent Application entitled "Comb Limiter Combiner (CLIC)," Serial No. 08/868,473 , filed on June 3, 1997. This patent incorporates United States patent application No. 08/868,473 by reference in its entirety. FIELD OF THE INVENTION This invention relates generally to connecting one or more transmitters to a single transmit antenna. More particularly, the present invention is used to mitigate intermodulation effects in transmitters for wideband transmission. BACKGROUND OF THE INVENTION Military communications need to be secure. One method to achieve secure communications is to use wideband (spread spectrum) communications systems. Wideband communications are effective against anti-jam communications and have a low probability of being intercepted. In the commercial industry, wideband communications allow multiple users to communicate over the same communication line at the same time. However, wideband communications comes with some problems as well. When two or more radios are using wideband radio transmission or a single radio is multiplexing multiple radio signals, mutual interference is a frequently encountered. Mutual interference is primarily a non-linear effect caused by saturation and intermodulation in the radios. Mutual interference results in a reduced communication range for any given signal strength that would not otherwise occur absent the mutual interference. Presently, there are two methods to reduce mutual interference, antenna separation and bandpass filtering. Antenna separation is an easy and effective solution to solve mutual interference problems. However, antenna separation requires space, which may not always be available. For instance military ships have barely enough space for one antenna. Additional space for other antennas with proper antenna separation is virtually impossible. Considering that most ships also require more than one secure radio the problem is magnified. Therefore there is a need to provide a means for secure communication from multiple radios where proper antenna separation is not feasible. SUMMARY OF THE INVENTION It is therefore an object of the present invention to connect one or more transmitters to a single transmitting antenna. A further object of the present invention is to restrict intermodulation products to the passband of a single passband filter. A further obj ect of the present invention is to operate without knowledge of the frequency excursions of the transmitted signal. A further object of the present invention is to operate without switching and control circuitry. The present invention is a Comb Linear Amplifier Combiner (CLAC) apparatus that allows one or more transmitters to transmit through one transmit antenna. The CLAC apparatus passes low- powered transmit signals through a bank of bandpass filters. The transmit signals then pass through CLAC amplifiers which amplify the transmit signals to the full transmit power. The full transmit power signals then pass through a second bank of bandpass filters. The transmission signals are then transmitted through a single transmission antenna. The CLAC apparatus reduces the intermodulation effects in two ways. First, the CLAC amplifiers are linear Class A amplifiers which reduce the power levels of the intermodulation products. Secondly, the CLAC apparatus reduces the number of intermodulation products by employing frequency selective power amplification. Therefore, at any given time, only a small fraction of the transmitters' signals are in the passband of a given amplifier. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of the Comb Limiter Amplifier Combiner. DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1, a diagram of a Comb Linear Amplifier Combiner (CLAC) is shown. The CLAC is used for transmitting wideband radio communications. Low powered wideband radio transmission signals come from a combiner which is coupled to a radio (not shown). In the preferred embodiment, the radio is a digital communication radio. As shown, the low powered transmission signals enter input (first) filter bank 102. Input filter bank 102 contains multiple bandpass filters with each filter spanning a portion of a wideband or ultra- wideband communications signal. The center frequency and passband of each input filter in input filter bank 102 is selected to balance the channel separation of the communications signal and the typical frequency separation of strong interfering signals. Each input bandpass filter preferably has a bandwidth small enough so that the possibility of two or more signals occurring in the same passband is sufficiently low. Furthermore, each input bandpass filter has sufficient rolloff to avoid the generation of significant intermodulation products in adjacent passbands. To cover the entire communications signal bandwidth, the passbands of input bandpass filters 102 generally overlap at the 3 dB points. The transmission signals then enter a bank of linear power amplifiers 104. In the preferred embodiment, power amplifiers 104 are Class A amplifiers. Power amplifiers 104 amplify the filtered transmission signals to the full transmission power. The Class A amplifiers are used because the amplifiers reduce the number of intermodulation products. Since Class A amplifiers operate entirely in the biased or active region, the resulting amplified transmission signals are typically more linear than other types of amplified signals. In addition, power amplifiers 104 reduce the number of intermodulation products by employing frequency selective power amplification. Since only a small fraction of the transmission signal is in each passband only a frequency limited signal is being amplified which reduces the number of intermodulation products as well. The amplified transmission signals then pass through output (second) filter bank 106. In the preferred embodiment, output filter bank 106 is identical to input filter bank 102. In an alternate embodiment, output filter bank 106 can be eliminated. Again, the filter bank filters the desired transmission signals and rejects noise and other extraneous signals. After the transmission signals are filtered, the fully amplified transmission signals are transmitted through transmission antenna 108. The Comb Linear Amplifier Combiner of the present invention may be designed for virtually any frequency band according to well known techniques of filter design. Different types of bandpass filters may also be used, including but not limited to cavity, stripline, surface acoustic waves, and LC (inductor and capacitor) filters. Although this invention has been described using banks of filters and multiple power amplifiers, alternate embodiments can be implemented using one input filter, one power amplifier, and one output filter. However, by reducing the number of components, the overall system will be less effective in reducing intermodulation interferences. A Comb Linear Amplifier Combiner for transmitting at least one radio through one transmit antenna has been described in detail for the purpose of illustration. It is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention as disclosed.

Claims: We Claim: L A comb linear amplifier combiner comprising a first bandpass filter and a power amplifier coupled to the bandpass filter. 2. The comb linear amplifier combiner as in claim 1 , wherein the first bandpass filter is selected from the group consisting of cavity, stripline, surface acoustic wave, and LC filters. 3. The comb linear amplifier combiner as in claim 1 , wherein the power amplifier is a linear power amplifier. 4. The comb linear amplifier combiner as in claim 3, wherein the linear power amplifier is a Class A amplifier. 5. The comb linear amplifier combiner as in claim 1 , further comprising a combiner coupled to the bandpass filter. 6. The comb linear amplifier combiner as in claim 5, further comprising at least one radio coupled to the combiner. 7. The comb linear amplifier combiner as in claim 6, wherein the at least one radio is a digital radio. 8. The comb linear amplifier combiner as in claim 1, further comprising a transmission antenna coupled to the power amplifier. 9. The comb linear amplifier combiner as in claim 1 , further comprising a second bandpass filter coupled to the power amplifier. 10. The comb linear amplifier combiner as in claim 9, wherein the second bandpass filter is selected from the group consisting of cavity, stripline, surface acoustic wave, and LC filters. 11. The comb linear amplifier combiner as in claim 9, further comprising a transmission antenna coupled to the second bandpass filter. 12. A comb linear amplifier combiner comprising at least one first passband filter and at least one power amplifier coupled to the at least one bandpass filter. 13. The comb linear amplifier combiner as in claim 12, wherein the at least one first bandpass filter is selected from the group consisting of cavity, stripline, surface acoustic wave, and LC filters. 14. The comb linear amplifier combiner as in claim 12, wherein the at least one power amplifier is a linear power amplifier. 15. The comb linear amplifier combiner as in claim 14, wherein the linear power amplifier is a Class A amplifier. 16. The comb linear amplifier combiner as in claim 12, further comprising a combiner coupled to the at least one first bandpass filter. 17. The comb linear amplifier combiner as in claim 16, further comprising at least one radio coupled to the combiner. 18. The comb linear amplifier combiner as in claim 17, wherein the at least one radio is a digital radio. 19. The comb linear amplifier combiner as in claim 12, further comprising a transmission antenna coupled to the at least one power amplifier. 20. The comb linear amplifier combiner as in claim 12, further comprising at least one second bandpass filter coupled to the at least one power amplifier. 21. The comb linear amplifier combiner as in claim 20, wherein the at least one second bandpass filter is selected from the group consisting of cavity, stripline, surface acoustic wave, and LC filters. 22. The comb linear amplifier combiner as in claim 20, further comprising a transmission antenna coupled to the at least one second bandpass filter. 23. A comb linear amplifier combiner comprising: a first bank of bandpass filters; and a bank of power amplifiers coupled to the first bank of bandpass filters. 24. The comb linear amplifier combiner as in claim 23, wherein the first bank of bandpass filters are selected from the group of consisting of cavity, stripline, surface acoustic wave, and LC filters. 25. The comb linear amplifier combiner as in claim 23, wherein each bandpass filter in the first bank of bandpass filters has substantially equal bandwidths and frequency rolloff and wherein each bandpass filter has a different center frequency. 26. The comb linear amplifier combiner as in claim 23, wherein the bank of power amplifiers are linear power amplifiers. 27. The comb linear amplifier combiner as in claim 26, wherein the linear power amplifiers are Class A amplifiers. 28. The comb linear amplifier combiner as in claim 23, further comprising a combiner coupled to the first bank of bandpass filters. 29. The comb linear amplifier combiner as in claim 28, further comprising at least one radio coupled to the combiner. 30. The comb linear amplifier combiner as in claim 29, wherein the at least one radio is a digital radio. 31. The comb linear amplifier combiner as in claim 23, further comprising a transmission antenna coupled to the bank of power amplifiers. 32. The comb linear amplifier combiner as in claim 23, further comprising a second bank of bandpass filters coupled to the bank of power amplifiers. 33. The comb linear amplifier combiner as in claim 32, wherein the second bank of bandpass filters are selected from the group consisting of cavity, stripline, surface acoustic wave, and LC filters. 34. The comb linear amplifier combiner as in claim 32, wherein the second bank of bandpass filters have substantially equal bandwidths and frequency rolloff and each bandpass filter has a different center frequency. 35. The comb linear amplifier combiner as in claim 32, further comprising a transmission antenna coupled to the second bank of bandpass filters. 36. A comb linear amplifier combiner comprising: a first filter bank adapted to receive at least one signal; at least one power amplifier coupled to the first filter bank; a second bandpass filter bank coupled to the at least one power amplifier; and an antenna coupled to the second filter bank. 37. The comb linear amplifier combiner as in claim 36, where the first filter bank further comprises a plurality of bandpass filters. 38. The comb linear amplifier combiner as in claim 36, where the first filter bank is selected from the group consisting of cavity, stripline, surface acoustic wave and LC filters. 39. The comb linear amplifier combiner as in claim 36, where the first filter bank have substantially equal bandwidth and frequency rolloff and wherein each bandpass filter has a different center frequency. 40. The comb linear amplifier combiner as in claim 36, where the number of power amplifiers equals the number of filters in the first filter bank. 41. The comb linear amplifier combiner as in claim 40, where power amplifiers are linear power amplifiers. 42. The comb linear amplifier combiner as in claim 41, where the linear power amplifiers are Class A amplifiers. 43. The comb linear amplifier combiner as in claim 36, where the second bank of filters comprises a plurality of bandpass filters. 44. The comb linear amplifier combiner as in claim 43, where the second filter bank is selected from the group consisting of cavity, stripline, surface acoustic wave, and LC filters. 45. The comb linear amplifier combiner as in claim 43, where the first filter bank have substantially equal bandwidths and frequency rolloff and each bandpass filter has a different center frequency. 46. The comb linear amplifier combiner as in claim 43, where the number of filters in the second filter bank equals the number of power amplifiers.

Inventors: LI SHING T, MAIUZZO MICHAEL A, ROCKWAY JOHN W, SCHUKANT JAMES H, TAM DANIEL W, LI, SHING, T., MAIUZZO, MICHAEL, A., ROCKWAY, JOHN, W., SCHUKANT, JAMES, H., TAM, DANIEL, W.
Applicants: LI SHING T, MAIUZZO MICHAEL A, ROCKWAY JOHN W, SCHUKANT JAMES H, SENTEL CORP, TAM DANIEL W, LI, SHING, T., MAIUZZO, MICHAEL, A., ROCKWAY, JOHN, W., SCHUKANT, JAMES, H., SENTEL CORPORATION, TAM, DANIEL, W.
Application year: 1999
Main classification: H03F3
IPC codes: H03F3