Apparatus and method for measuring the phase and magnitude of microwave signals

A measurement system comprising:

• source means for providing respective signals at a respective discrete frequency in a prescribed microwave frequency range;
• first local oscillator means for providing first oscillator signals in a first oscillator frequency range;
• harmonics means for receiving the first oscillator signals, and for providing harmonics of the first oscillator signals;
• first mixing means for receiving respective signals at the respective discrete frequency and for receiving the respective harmonics of the first oscillator signals and for providing first intermediate signals in a first intermediate frequency range;
• second local oscillator means for providing second oscillator signals in a second oscillator frequency range;
• second mixing means for receiving the respective first intermediate signals and for receiving the second oscillator signals and for providing second intermediate signals in a second intermediate frequency range;
• third local oscillator means for providing third oscillator signals in a third oscillator frequency range;
• third mixing means for receiving the respective second intermediate signals and for receiving the respective third oscillator signals and for providing third intermediate signals in a third intermediate frequency range;
• bandpass filter means for filtering signals in the third intermediate frequency range;
• synchronous detector means for receiving the third intermediate signals and for providing in-phase and quadrature versions of the third intermediate signals;
• and
• variable bandwidth filter means for filtering the in-phase and quadrature versions of the third intermediate signals.

A system for measuring microwave frequency signals incident upon a device under test (DUT), comprising:

• source means for producing a microwave frequency stimulus signal at any of a plurality of discrete frequencies, said source means including means which substantially locks the stimulus signal at a respective one of said discrete frequencies in response to at least one correction signal;
• splitting means for splitting the stimulus signal so as to provide at least one reference stimulus signal and at least one test stimulus signal;
• coupling means for providing the at least one test stimulus signal to the DUT and for receiving from the DUT the at least one test stimulus signal that has been incident upon the DUT;
• first downconverting means including,
• at least one first local oscillator means for producing first local oscillator signals in at least one first local oscillator frequency range,
• harmonics generator means for receiving the first local oscillator signals and for producing sampling pulses, and
• sampling means responsive to the sampling pulses for sampling the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon he DUT so as to downconvert the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT to a first intermediate frequency range;
• second downconverting means for simultaneously linearly downconverting the at least one reference stimulus signal in said first intermediate frequency range and the at least one test stimulus signal that has been incident upon the DUT in said first intermediate frequency range to a second intermediate frequency range;
• and
• reference oscillator means for producing a first signal at a first frequency;
• phase comparison means for comparing the phase of the linearly downconverted version of the at least one reference stimulus signal in the second intermediate frequency range with the phase of the first signal at the first frequency and producing the at least one correction signal.

A system for measuring microwave frequency signals incident upon a device under test (DUT), comprising:

• source means for producing a microwave frequency stimulus signal at any of a plurality of discrete frequencies, said source means including means which substantially locks the stimulus signal at a respective one of said discrete frequencies in response to at least one correction signal;
• splitting means for splitting the stimulus signal so as to provide at least one reference stimulus signal and at last one test stimulus signal;
• coupling means for providing the at least one test stimulus signal to the DUT and for receiving from the DUT at least one test stimulus signal that has been incident upon the DUT;
• at least one first local oscillator means for producing first local oscillator signals in at least one first oscillator frequency range;
• harmonics generator means for receiving the first local oscillator signals and for producing sampling pulses;
• sampling means responsive to the sampling pulses for sampling the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT so as to downconvert the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT to a first intermediate frequency range;
• at least one second local oscillator means for producing second local oscillator mixing signals in at least one second oscillator frequency range;
• mixer means for mixing the second local oscillator mixing signals with the at least one reference stimulus signal downconverted to the first intermediate frequency range and the at least one test stimulus signal that has been incident upon the DUT and that has been downconverted to the first intermediate frequency range so as to further downconvert the at least one reference stimulus signal and the at least one test stimulus signal to a second intermediate frequency range;
• reference oscillator means for producing a first signal at a first frequency;
• phase comparison means for comparing a phase of the version of the at least one reference stimulus signal downconverted to the second intermediate frequency range with the phase of the first signal at the first frequency and producing the at least one correction signal;
• at least one third local oscillator means for producing third local oscillator mixing signals in at least one third oscillator frequency range;
• mixer means for mixing the third local oscillator mixing signals with the version of the at least one reference stimulus signal downconverted to the second intermediate frequency and for mixing the third mixing signals with the version of the at least one test stimulus signal that has been incident upon the DUT and that has been downconverted to the second intermediate frequency so as to further downconvert the at least one reference stimulus signal and the at least one test stimulus that has been incident upon the DUT to a third intermediate frequency;
• means responsive to said third intermediate frequency for producing DC Real and DC Imaginary versions of the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT;
• and
• means responsive to said DC Real and DC Imaginary version producing means for calculating a phase shift in the at least one test stimulus signal that has been incident upon the DUT relative to the at least one reference stimulus signal.

A system for measuring microwave frequency signals incident upon a device under test (DUT) comprising:

• reference oscillator means for producing a signal at a prescribed frequency;
• source means for producing a microwave frequency stimulus signal at any of a plurality of respective discrete frequencies;
• splitting means for splitting the stimulus signal so as to provide at least one reference stimulus signal and at least one test stimulus signal;
• coupling means for providing the at least one test stimulus signal to the DUT and for receiving from the DUT at least one test stimulus signal that has been incident upon the DUT;
• and
• means responsive to the frequency of said stimulus signal having a harmonic mode of operation and means for downconverting said at least one reference stimulus signal and said at least one test stimulus signal to a first intermediate frequency range when said frequency of said stimulus signal is within a first predetermined range of frequencies and a direct mode of operation and means for providing said at least one reference stimulus signal and said at least one test stimulus signal without their being downconverted when said frequency of said stimulus signal is within a second predetermined range of frequencies, said downconverting means including at least one first local oscillator means for producing first local oscillator signals in a first oscillator frequency range, harmonic generator means for receiving the first local oscillator signals and for producing sampling pulses, and sampling means responsive to the sampling pulses for sampling and downconverting the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT to a first intermediate frequency range.

A method for measuring microwave frequency signals incident upon a device under test (DUT) comprising the steps of:

• producing a first signal at a first frequency;
• producing a microwave frequency stimulus signal at any of a plurality of respective discrete frequencies;
• locking the stimulus signal at a respective discrete frequency in response to at least one correction signal;
• splitting the stimulus signal so as to provide at least one reference stimulus signal and at least one test stimulus signal;
• providing the at least one test stimulus signal to the DUT;
• receiving from the DUT at least one test stimulus signal that has been incident upon the DUT;
• simultaneously linearly downconverting the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT so as to produce linearly downconverted versions of the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT;
• comparing a phase of the linearly downconverted version of the at least one reference stimulus signal with a phase of the first signal at the first frequency;
• and
• producing the at least one correction signal in response to the phase comparison.

A method of operating a network analyzer so as to avoid the generation of spurious intermediate frequency signals when measuring microwave frequency signals incident upon a device under test (DUT) comprising the steps of:

• (i) generating a reference and test stimulus signal having a frequency F.sub.ST ;
• (ii) generating initial first and a second local oscillator signal having the frequencies F.sub.LO1 and F.sub.LO2 ;
• (iii) providing first and second intermediate frequency signals having the frequencies IF.sub.1 and IF.sub.2, respectively as determined by the following equations
• IF.sub.1 =M * F.sub.LO1 -F.sub.ST, where M is an initial harmonic
• number;
• and
• IF.sub.2 =F.sub.L02 -IF.sub.1 ;
• (iv) generating in response to said second intermediate frequency signal having the frequency IF.sub.2 and a third local oscillator signal having the frequency F.sub.LO3, a third intermediate frequency signal having the frequency IF.sub.3 ;
• (v) generating a signal for different combinations of M and N, where M and N are harmonic numbers, when the following first and second conditions are met
• .vertline.M * F.sub.LO1 -N * F.sub.LO2 .vertline.<IF.sub.3 -PB.sub.3 /2 and (1)
• .vertline.M * F.sub.LO1 -N * F.sub.LO2 .vertline.>IF.sub.3 +PB.sub.3 /2 where PB.sub.3
• is the bandwidth of a filter for filtering IF.sub.3 ( 2)
• and
• (vi) repeating steps (ii) through (v) with new values of F.sub.LO1 and F.sub.LO2 for each combination of M and N until neither the first or the second condition is met.

A method of operating a network analyzer as to avoid the generation of spurious intermediate frequency signals when measuring microwave frequency signals incident upon a device under test (DUT) comprising the steps of:

• (i) generating a stimulus signal having the frequency FST;
• (ii) generating first and second local oscillator signals having the frequencies F.sub.LO1 and F.sub.LO2, respectively, as determined by the following algorithm,
• F=F.sub.ST * 20
• H=1+Integer(F+1788)/10730
• Z=5365/(3+H/1250)
• F.sub.LO1 =1+Integer /20
• F.sub.LO2 =H * F.sub.LO1 -F/20+2.25 for producing first and second intermediate frequencies IF.sub.1 and IF.sub.2, respectively;
• (iii) generating a third local oscillator signal having a frequency F.sub.LO3 which, when mixed with F.sub.2, produces a predetermined third intermediate frequency F.sub.3 ;
• (iv) testing for harmonics of F.sub.LO1 and F.sub.LO2 which will produce a spurious F.sub.3 if the following first and second conditions of inequalities are met,
• .vertline.M * F.sub.LO1 -N * F.sub.LO2 .vertline.<IF.sub.3 -PB.sub.3 /2 (1)
• .vertline.M * F.sub.LO1 -N * F.sub.LO2 .vertline.>IF.sub.3 -PB.sub.3 /2 (2)
• where M and N are harmonic numbers and PB.sub.3 is the bandwidth of a filter for filtering IF.sub.3 ;
• and
• (v) changing the values of M, N, F.sub.LO1 and F.sub.LO2 while maintaining the relationship F.sub.ST =H * F.sub.LO1 -F.sub.LO2 +IF.sub.2 and avoiding the conditions of inequalities (1) and (2) above.