Systems and methods relating to improving transmit (TX) port to receive (RX) port isolation of a duplexer or multiplexer are disclosed. In some embodiments, a system includes a duplexer or multiplexer having a transmit port, a receive port, and an antenna port. The system further includes a leakage cancellation subsystem adapted to cancel a leakage signal from the TX port of the duplexer or multiplexer to the RX port of the duplexer or multiplexer across a desired cancellation bandwidth. The leakage cancellation subsystem compensates for variation of the leakage signal across the desired cancellation bandwidth, thereby improving TX port to RX port isolation over conventional systems.