A triangular, common-path interferometric rf spectrum analyzer arrangement has been demonstrated which has the property of high immunity to ambient vibration. Calculations show the TCPI arrangement, with two counter-propagating laser beams, is highly angle compensated and alignment stable when components are disturbed in position or orientation. Proper light polarization and Bragg cell geometry allows one Bragg cell to diffract primarily the clockwise beam and the other Bragg cell the counterclockwise beam. A birefringent quartz wedge shifts the heterodyne signal to a nonzero IF carrier frequency. Measured ambient phase noise is less than two degrees and calculated values indicate that further improvement may be possible.
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