Amplifiers – With plural amplifier channels – Amplifying different frequencies in different channels
Reexamination Certificate
1998-03-12
2001-04-03
Shingleton, Michael B (Department: 2817)
Amplifiers
With plural amplifier channels
Amplifying different frequencies in different channels
C330S295000, C330S12400D, C330S300000, C330S306000
Reexamination Certificate
active
06211732
ABSTRACT:
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 object 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.
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Li Shing T.
Maiuzzo Michael A.
Rockway John W.
Schukantz James H.
Tam Daniel W.
Roberts Abokhair & Mardula LLC
Sentel Corporation
Shingleton Michael B
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