Phase accuracy and stability of quadrature IF demodulators

A technique developed in order to realize extremely low (less than 0.5 deg) differential phase error demodulators over a 40-dB dynamic range is described. The requirement for such low phase errors is to control the sidelobe level in a digital beamformer for a bistatic radar system. The IF demodulator used is 70 MHz. It is shown that to achieve good matching and repeatability, reliance is placed on careful design and the use of 1 percent tolerance resistors. The oscillator gating technique, used to measure the stability of the demodulators, is also reported, realizing a resolution of less than one second of phase, with a realistic accuracy of less than one min.