Method of system compensation to reduce the effects of self interference in frequency modulated continuous wave altimeter systems

An altimeter system, comprising:

• 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;
• a transmitter configured to output a transmitter signal to the antenna via the transceiver circulator, wherein the transmitter signal is frequency modulated with a linear ramp;
• and
• a local oscillator delay line configured to input the transmitter signal from the transmitter and to output a local oscillator signal derived from the transmitter signal to the local-oscillator-input of the receiver mixer,
• wherein the transmitter is communicatively coupled to the receiver mixer to input the local oscillator signal at the local-oscillator-input of the receiver mixer,
• wherein the receiver mixer is communicatively coupled to input a target-reflected signal from the antenna at the antenna-input of the receiver mixer,
• wherein the target-reflected signal is reflected from a target to the antenna, and
• wherein 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 frequency range and composite-leakage-amplitude nulls are outside an operating bandwidth of the altimeter system, wherein the composite-leakage signal is a coherent superposition of an antenna-reflection-leakage signal and a circulator-leakage signal at the antenna input of receiver mixer,
• wherein an input impedance of the antenna is tuned so:
• an amplitude response of an antenna-return signal reflected from the antenna is relatively flat a phase response of the composite leakage signal input at the antenna-input of the receiver mixer is linear across the sweep-frequency range of the altimeter system;
• and an output voltage of a receiver mixer is a direct current (DC) voltage with reduced alternating current (AC) voltage across the operating bandwidth;
• and
• wherein a phase of the local oscillator signal input to the local-oscillator-input of the receiver mixer is adjusted by adjusting a phase length of a local oscillator (LO) delay line to maintain a quadrature relationship to a phase of the composite-leakage signal input to the antenna-input of the receiver mixer across the operating bandwidth.