An altimeter system is provided. The altimeter system includes a receiver mixer including an antenna-input and a local-oscillator-input; a transceiver circulator communicatively coupled to an antenna via a transmission line having a selected length and communicatively coupled to the antenna-input of the receiver mixer; and a transmitter configured to output a transmitter signal to the antenna via the transceiver circulator. The transmitter signal is frequency modulated with a linear ramp. The transmitter is communicatively coupled to the receiver mixer to input a local oscillator signal at the local-oscillator-input of the receiver mixer. The receiver mixer is communicatively coupled to input a target-reflected signal from the antenna at the antenna-input of the receiver mixer. The selected length of the transmission line is set so that a composite-leakage signal at the antenna-input of the receiver mixer has a linear phase across a sweep bandwidth.