High-selectivity low-loss duplexer

An electronic duplexer comprising:

• a first port coupled to a transmit port by a primary winding of a first transformer;
• a second port coupled to the transmit port by a primary winding of a second transformer;
• a receive port bridging a secondary winding of the first transformer connected to a secondary winding of the second transformer;
• a phase shifter configured to phase shift an input signal at the first port to generate a phase-shifted signal at the second port, the phase shifter shifting the input signal by 180 degrees at a receive frequency and by zero degrees at a transmit frequency;
• a third port coupled to an inverted transmit port by a primary winding of a third transformer;
• a fourth port coupled to the inverted transmit port by a primary winding of a fourth transformer;
• the receive port bridging a secondary winding of the third transformer connected to a secondary winding of the fourth transformer;
• and
• the phase shifter further configured to phase shift an inverted input signal at the third port to generate an inverted phase-shifted signal at the fourth port, the phase shifter shifting the inverted input signal by 180 degrees at a receive frequency and by zero degrees at a transmit frequency.

A high-selectivity low-loss duplexing system comprising:

• a first duplexer having a first port, a second port, a transmit port and a receive port;
• a second duplexer having a third port, a fourth port, an inverted transmit port and the receive port, the first port and the third port connected to an antenna by a balun, the transmit port and the inverted transmit port connected to at least one power amplifier, and the receive port connected to a low noise amplifier;
• and
• a phase shifter comprising a lattice filter configured to short the second port to the third port and the fourth port to the first port at a receive frequency, and short the second port to the first port and the fourth port to the third port at a transmit frequency.