Patent ID: 7124043

Claim:
A spectrum analyzer comprising: (a) A frequency converter that includes: a first conversion stage formed of a first mixer, a first band pass filter and a first local oscillator; a second conversion stage formed of a second mixer, a second band pass filter and a second local oscillator; a third conversion stage formed of a third mixer; (b) A control unit that regulates the sequence and parameters of operations during the spectrum measurements; and (c) A phase noise compensation unit that has two signal inputs connected to the outputs of the first and the second local oscillators, a control input connected to the output of the control unit, and an output connected to the input of the third mixer wherein the phase noise compensation unit comprises: (a) A first auxiliary frequency converter for producing a signal with a phase noise that equals the difference between the phase noise of the first local oscillator and the phase noise of the second local oscillator, said first auxiliary frequency converter having two inputs that are used as the signal inputs of the phase noise compensation unit, and an output; (b) A reference oscillator for generating a reference signal, said reference oscillator having a control input that is used as the control input of the phase noise compensation unit, and an output; (c) A second auxiliary frequency converter for producing the third local signal, said second auxiliary frequency converter having two inputs connected to the outputs of the first auxiliary frequency converter and the reference oscillator, and an output that is used as the output of the phase noise compensation unit.