Patent ID: 7016438

Claim:
A cross polarization interference canceller comprising: (a) first and second signal receivers which receive signals having been transmitted through first and second polarizations which are orthogonal; (b) first and second local oscillators each of which converts one of said signals into an IF signal; (c) first and second demodulators each of which demodulates said IF signal for producing a base-band signal and a cross polarization interference cancel reference signal; (d) a phase-difference detector which detects a phase-difference between local signals transmitted from said first and second local oscillators, and transmits a phase-difference signal indicative of the thus detected phase-difference; and (e) first and second phase controllers associated with said first and second demodulators, respectively, and each equalizing phases of said base-band signal and said cross polarization interference cancel reference signal to each other in accordance with said phase-difference signal; wherein said phase-difference detector includes: (d1) a multiplier which multiplies signals transmitted from said first and second local oscillators, by each other to thereby transmit a frequency-difference signal; (d2) an analog-digital converter which converts said frequency-difference signal to a digital signal; (d3) a numerical controlled oscillator which transmits a local phase-difference signal; (d4) a phase comparator compares said local phase-difference signal and said frequency-difference signal to each other, and transmits a difference signal indicative of a difference between said local phase-difference signal and said frequency-difference signal; and (d5) a filter which controls a frequency of said local phase-difference signal in accordance with said difference signal.