Method and apparatus for RF communication system signal to noise ratio improvement

• US 8,010,055 B2
• Filed: 02/13/2008
• Issued: 08/30/2011
• Est. Priority Date: 02/13/2008
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: Buer, Kenneth V.
• Primary Examiner(s): Milord; Marceau
• Application Number:
  US12/030,300
• Publication Number:
  US 20090203328A1
• Time in Patent Office: 1,294 Days
• Field of Search: 455/78, 455/82, 455/114.2, 455/118, 455/63.1, 455/207, 455/314, 375/150, 375/152, 375/143, 330/133, 333/207
• US Class Current: 455/78
• CPC Class Codes: H04B 1/50 using different frequencies for the two directions of communication

Abstract

The signal to noise ratio performance of a RF communication system can be improved by providing resistance to transmitter self-jamming and eliminating or reducing the need for a transmit rejection filter or other measures such as limiters or blanking switches. An anti-jam low noise amplifier provides enough rejection and jamming immunity to reduce or eliminate the need for the transmit reject filter. Thus, the system noise performance is improved by eliminating the filter and the associated losses which cause signal to noise ratio performance degradation.

Claims

1. An apparatus for a radio frequency (RF) signal communication system with improved noise performance, said apparatus comprising:

a RF combiner/splitter unit;

an anti jam low noise amplifier (LNA) in communication with said RF combiner/splitter unit;

absent a transmit reject filter;

wherein said apparatus is configured to not inhibit wrap-around leakage of a RF transmit signal from passing through said anti jam LNA; and

wherein a RF receive signal travels through said RF combiner/splitter unit and then directly to and through said anti jam LNA.

2. The apparatus of claim 1, further comprising at least one of a transmitter, a receiver, a power amplifier, and an antenna feed system.

3. The apparatus of claim 1, wherein said RF signal combiner/splitter unit is an orthomode transducer.

4. The apparatus of claim 1, wherein said RF signal combiner/splitter unit is a diplexer.

5. The apparatus of claim 1, wherein the RF receive signal travels through said RF combiner/splitter unit and then through said anti jam LNA, said anti jam LNA is configured to control a RF signal communication noise component;

and

whereby said RF signal communication noise component comprises wrap-around leakage from the RF transmit signal.

6. The apparatus of claim 5, wherein said anti jam LNA controls said RF signal communication noise component by at least one of reducing the gain of said anti jam LNA, band-limiting said anti jam LNA, and adjusting the linearity of said anti-jam LNA.

7. The apparatus of claim 1, where the gain of said anti-jam LNA is designed to compensate for the absence of said transmit reject filter.

8. An apparatus for radio frequency (RF) signal communication noise control, said apparatus comprising:

a RF combiner/splitter unit;

a transmit reject filter with only 20-50 dB rejection connected to said RF combiner/splitter unit;

an anti jam low noise amplifier coupled to said transmit reject filter; and

wherein a RF receive signal is communicated through said RF combiner/splitter unit to said transmit reject filter and then through said anti jam low noise amplifier.

9. The apparatus of claim 8, said transmit reject filter comprises a number of poles in the range of 1 to 4.

10. The apparatus of claim 8, wherein said transmit reject filter has a signal loss in the range of 0.2-0.5 dB.

11. The apparatus of claim 8, wherein there is no more than 50 dB of reject filtering between said RF combiner/splitter unit and said anti jam low noise amplifier.

12. The apparatus of claim 8, wherein said RF signal combiner/splitter unit is an orthomode transducer.

13. The apparatus of claim 8, wherein said RF signal combiner/splitter unit is a diplexer.

14. A method of isolating a radio frequency (RF) receive signal from a RF transmit signal, said method comprising:

generating the RF transmit signal;

amplifying the RF transmit signal with a power amplifier;

communicating the RF transmit signal from said power amplifier to a RF combiner/splitter unit;

communicating the RF transmit signal over a common channel to an antenna feed;

receiving the RF receive signal into said antenna feed;

communicating the RF receive signal from said antenna feed to said RF combiner/splitter unit over said common channel;

communicating the RF receive signal from said RF combiner/splitter unit into an anti-jam low noise amplifier (anti-jam LNA);

amplifying the RF receive signal through said anti jam LNA;

controlling leakage of the RF transmit signal into said anti jam LNA absent a transmit reject filter; and

relaying the RF receive signal from said anti jam LNA to a receiver.

15. The method of claim 14, wherein said controlling leakage comprises at least one of reducing the gain of said anti jam LNA, band-limiting said anti-jam LNA, and configuring the linearity of said anti jam LNA.

16. A method of optimizing a signal to noise ratio of a RF communication system, said method comprising:

adding a degree of design freedom by designing a transmit reject filter and a low noise amplifier in combination;

utilizing a multivariable optimization simulation of said transmit reject filter and said low noise amplifier in combination; and

wherein designing said transmit reject filter and said low noise amplifier in combination is based upon selecting the transmit filter rejection, the LNA linearity, the LNA band limiting and the reduced LNA gain.