System and method for split isolation in radio frequency electronics

1. A method for designing a full duplex communications transceiver to enable a reduction in isolation between a transmit signal and a receive signal at a diplexer, comprising:

providing a receiver, a transmitter, and a radio frequency electronics (RFE) front-end comprising a diplexer receive filter located before a low noise amplifier, an RFE receive filter located after the low noise amplifier and coupled to the receiver, a diplexer transmit filter located after a power amplifier, an RFE transmit filter located before the power amplifier and coupled to the transmitter;

determining an RFE transmit filter attenuation level sufficient to attenuate a noise power of the transmitter below a thermal noise floor of the power amplifier;

determining a minimum diplexer transmit filter attenuation level to attenuate noise power output from the power amplifier in a receive band to a level below a noise floor of the receiver

configuring the RFE transmit filter to provide at least the RFE transmit filter attenuation level; and

configuring the diplexer transmit filter to provide at least the minimum diplexer transmit filter attenuation level.

2. A method as in claim 1 , further comprising:

determining a minimum diplexer receive filter attenuation level to attenuate a transmit signal output from the power amplifier to a level below a 1 dB compression point of the low noise amplifier; and

configuring the diplexer receive filter to provide at least the minimum diplexer receive filter attenuation level.

3. A method as in claim 2 , further comprising calculating an RFE receive filter attenuation level such that the diplexer receive filter and the RFE receive filter together provide sufficient filtering to attenuate the transmit signal below a thermal noise power of the receive band.

4. A method as in claim 3 , wherein determining the minimum diplexer receive filter attenuation level further comprises determining the minimum diplexer receive filter attenuation level according to the equation:

I DRx =P−OP 1dB +G Rx +M

where I DRx is the attenuation level of the diplexer receive filter in dB, P is a power level of the transmitter, OP 1dB is the 1 dB compression point of the low noise amplifier, G Rx is a gain of the low noise amplifier, and M is a margin having a predetermined value.

5. A method as in claim 4 , wherein the predetermined value for the margin M is selected to provide a substantially linear output from the low noise amplifier.

6. A method as in claim 4 , further comprising calculating the RFE receive filter attenuation level according to the equation

I FRx =I Rx −I DRx

where I FRx is the attenuation level of the RFE receive filter in dB and I Rx is a transmit band isolation in dB.

7. A method as in claim 6 , wherein calculating the transmit band isolation I Rx further comprises calculating the transmit band isolation according to the equation:

I Rx =P− 10 log(290κ( F Rx −1) B )+ M−I IF

where P is a transmit power from the power amplifier in decibels referenced to a watt (dBW), κ is Boltzmann's constant, F Rx is a receiver noise factor, B is a receiver RF bandwidth in Hz, M is a margin in dB, and I IF is additional isolation provided by filters after the RFE in dB.

8. A method as in claim 1 , wherein determining the RFE transmit filter attenuation level further comprises calculating the RFE transmit filter attenuation level according to the equation:

I FTx =N Tx −10 log(290κ F Tx B )+ M

where I FTx is the RFE transmit filter attenuation level in dB, N Tx is a total noise power in a receive bandwidth from the transmitter, 10 log(290kF Tx B ) is a noise floor of the power amplifier where k is Boltzman's constant, FTx is a power amplifier noise factor, B is a receive bandwidth in Hz, and M is a margin having a predetermined value.

9. A method as in claim 8 , wherein M is selected such that a degradation of a signal to noise ratio of the receive band is less than a predetermined amount.

10. A method as in claim 1 , wherein determining the minimum diplexer transmit filter attenuation level further comprises determining the minimum diplexer transmit filter attenuation level according to the equation:

I DTx =NF Tx +G Tx +M

where I DTx is the minimum diplexer transmit filter attenuation level in dB, NF Tx is a power amplifier noise figure, G Tx is a gain of the power amplifier, and M is a margin having a predetermined value.

11. A method as in claim 10 , wherein M is selected such that a degradation of a signal to noise ratio of the receive band is less than a predetermined amount.

12. A method as in claim 2 , wherein determining the minimum diplexer receive filter attenuation level and the minimum diplexer transmit filter attenuation level enables a split isolation RFE having a reduced size and weight relative to a standard RFE.

13. A method as in claim 2 , wherein determining the minimum diplexer receive filter attenuation level and the minimum diplexer transmit filter attenuation level enables a split isolation RFE having an improved link margin relative to a standard RFE.

14. A system for reducing isolation between a transmit signal and a receive signal at a diplexer, comprising:

a receiver;

a transmitter;

a radio frequency electronics (RFE) front-end comprising a diplexer receive filter located before a low noise amplifier, an RFE receive filter located after the low noise amplifier and coupled to the receiver, a diplexer transmit filter located after a power amplifier, an RFE transmit filter located before the power amplifier and coupled to the transmitter;

wherein the diplexer transmit filter provides sufficient filtering to attenuate noise power output from the power amplifier in a receive band to a level below a noise floor of the receiver; and

wherein the RFE transmit filter provides sufficient filtering to attenuate a noise power of the transmitter below a thermal noise floor of the power amplifier.

15. A system as in claim 14 , wherein the diplexer receive filter provides sufficient filtering to attenuate a transmit signal output from the power amplifier to a level below a 1 dB compression point of the low noise amplifier.

16. A system as in claim 15 , wherein the diplexer receive filter and the RFE receive filter together provide sufficient filtering to attenuate the transmit signal below a thermal noise power in a receiver band.

17. A system as in claim 14 , wherein the diplexer receive filter and the diplexer transmit filter are cavity filters.

18. A system as in claim 14 , wherein a reduced filtering level in the diplexer receive filter and the diplexer transmit filter enables a split isolation RFE having a reduced size and weight relative to a standard RFE.

19. A system as in claim 18 , wherein the split isolation RFE is a full duplex command data link capable split isolation RFE assembly weighing less than 2 pounds.

20. A system as in claim 18 , wherein the split isolation RFE has a volume of less than 25 cubic inches.

21. A system as in claim 18 , wherein the split isolation RFE is located on a single circuit card.

22. A system as in claim 14 , wherein a reduced filtering level in the diplexer receive filter and the diplexer transmit filter enables a split isolation RFE having an improved link margin relative to a standard RFE.

23. A system as in claim 14 , further comprising a transfer switch located external to and coupled with the radio frequency electronics front-end to flop the transmit band and the receive band.

24. A method for designing a full duplex communications transceiver to enable a reduction in isolation between a transmit signal and a receive signal at a diplexer, comprising:

providing a receiver, a transmitter, and a radio frequency electronics (RFE) front-end comprising a diplexer receive filter located before a low noise amplifier, an RFE receive filter located after the low noise amplifier and coupled to the receiver, a diplexer transmit filter located after a power amplifier, an RFE transmit filter located before the power amplifier and coupled to the transmitter;

determining a minimum diplexer receive filter attenuation level to attenuate a transmit signal output from the power amplifier to a level below a 1 dB compression point of the low noise amplifier;

configuring the diplexer receive filter to provide at least the minimum diplexer receive filter attenuation level;

calculating an RFE receive filter attenuation level such that the diplexer receive filter and the RFE receive filter together provide sufficient filtering to attenuate the transmit signal below a thermal noise power of a receive band;

configuring the RFE receive filter to provide at least the RFE receive filter attenuation level;

determining an RFE transmit filter attenuation level sufficient to attenuate a noise power of the transmitter below a thermal noise floor of the power amplifier;

configuring the RFE transmit filter to provide at least the RFE transmit filter attenuation level;

determining a minimum diplexer transmit filter attenuation level to attenuate noise power output from the power amplifier in the receive band to a level below a noise floor of the receiver;

configuring the diplexer transmit filter to provide at least the minimum diplexer transmit filter attenuation level.