Abstract: A multichannel phase noise measuring system is disclosed which is capable of measuring the phase noise of two signal source operating between 100 MH.sub.z and 24 GH.sub.z. This system has two input channels and a mixer which produces a difference frequency between the signals received in the input channels. The difference frequency containing the phase noise is frequency multiplied and amplified to raise the phase noise level 12 dB. The multiplied and amplified difference signal is phase locked to a commercially available frequency synthesizer with inferior noise characteristics to the units being tested. By amplifying the phase noise of the original signals above the phase noise levels of the commercially available frequency synthesizer, they become measurable.

Abstract: This invention is directed to a narrow band filter for eliminating out-of-band noise in the oscillator signal of a doppler radar system. It provides a very high Q filter derived from a Bulk Acoustic Resonator's (BAR) high Q, L-Band response and uses thermal feedback to lock the BAR's response band onto the input frequency. The BAR is a very narrow band filter with a Q near 40,000 and a comblike frequency response having passbands occurring every 5 MHz, approximately. The comblike response of the BAR shifts down 60 KHz for every 1.degree. C. rise in temperature. In this invention a frequency sensitive heater is used to move the response comb of the BAR up or down in accordance with changes in the frequency of the incoming signal. The input frequency can be allowed to drift and the heat source will produce more heat or less heat, keeping the response right at the input frequency.

Abstract: A system for comparing the frequency of a voltage controlled oscillator to a stable reference oscillator to generate control signals which maintain the voltage controlled oscillator in phase lock with the reference oscillator. The circuit utilizes a digital frequency comparator to determine whether the output frequency of the voltage controlled oscillator is above or below the reference frequency. When the frequency of the oscillator is either above or below the desired value, pulses are generated which are integrated to produce a DC signal which changes the frequency of the oscillator to achieve the desired value. Additionally, a continuous electrical signal is generated when the output of the voltage controlled oscillator is in phase with the reference signal. When phase lock is achieved the output of the frequency determining circuit goes to zero and phase lock is maintained by the continuous electrical signal.