Patent ID: 9297885
Filing Date: 2016-03-29
CPC Classification: G01S

Claim Text:
1. A method to reduce self-interference in a single antenna frequency modulated continuous wave (FMCW) altimeter system, the method comprising: setting a length of a transmission line to a selected length to ensure a compositeleakage signal at the antenna-input of a receiver mixer has a linear phase across an operating bandwidth of the altimeter system and to ensure composite-leakage-amplitude nulls are outside the operating bandwidth, wherein the composite-leakage signal is a coherent superposition of an antenna-reflection-leakage signal and a circulator-leakage signal at an antenna input of the receiver mixer, wherein the transmission line communicatively couples an antenna to the antenna-input of the receiver mixer; tuning an input impedance of the antenna 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 a 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 adjusting a phase of a local oscillator signal input to a local-oscillator-input of the receiver mixer 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 an antenna-input of the receiver mixer across the operating bandwidth of the altimeter system.