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

• US 5,524,281 A
• Filed: 03/07/1995
• Issued: 06/04/1996
• Est. Priority Date: 03/31/1988
• Status: Expired due to Term

• Current Assignee: Anritsu Co (Anritsu Corporation)
• Original Assignee: Wiltron Company
• Inventors: Finch, David P., Thornton, Douglas R., Bradley, Donald A., Grace, Martin I.
• Primary Examiner(s): Urban, Edward F.
• Application Number:
  US08/400,458
• Time in Patent Office: 455 Days
• Field of Search: 455/67.1, 455/67.4, 455/67.5, 455/67.6, 455/314, 455/315, 455/316, 455/317, 455/165.1, 455/166.1, 455/183.1, 455/184.1, 455/185.1, 455/186.1, 455/207 , 455/208, 455/209, 455/226.1, 324/73.1, 324/601, 324/606, 331/2, 331/18, 331/22
• US Class Current: 455/67.15
• CPC Class Codes: G01R 27/28 Measuring attenuation, gain, phase shift or derived characteristics of electric four pole networks, i.e. two-port networks; Measuring transient response in line transmission systems H04B3/46

Abstract

A measurement system is provided which comprises: source circuit for receiving feedback signals and for providing respective signals at respective discrete frequencies in a prescribed microwave frequency range, wherein the respective provided signals at respective discrete frequencies are substantially phase locked to at least one downconverted signal in response to the feedback signals; downconverting circuit for linearly downconverting the respective provided signals and for providing the at least one respective downconverted signal; and phase detector circuit for receiving the at least one respective downconverted signal and for providing the feedback signals.

Claims

1. 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 respective signals in the second oscillator signals and for providing second intermediate signals in a second intermediate frequency range;

third local oscillator means for providing third local 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 the third intermediate signals; and

oscillator frequency selection means for selecting, for the respective discrete frequency, first and second oscillator frequencies which result in a provision, by said first and second mixing means, of provide no spurious signals in the passband of said bandpass filter means.

8. The system of claim 1 wherein said mixer means includes at least one double balanced mixer means.

2. 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.

3. 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.

4. The system of claim 3 further including:

third downconverting means for simultaneously linearly downconverting, to DC levels, the 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.

5. The system of claim 3 and further including:

means for calculating a phase shift n the at least one test stimulus signal that has been incident upon the DUT, the phase shift being calculated relative to the at least one reference stimulus signal.

6. The system of claim 5 further including means for calculating an amplitude change in the at least one test stimulus signal that has been incident upon the DUT.

7. The system of claim 3 wherein said second downconverting means includes:

at least one second local oscillator means for providing second local oscillator mixing signals in at least one second oscillator frequency range; and

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 for mixing the second mixing signals with 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 downconvert the at least one reference and the at least one test stimulus signals from the first intermediate frequency range to the second intermediate frequency.

9. The system of claim 3 and further including:

synchronous detector means 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.

10. The system of claim 9 further comprising:

variable bandwidth filter means for filtering out noise in the respective 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.

11. The system of claim 3 and further including:

third downconverting means for simultaneously linearly downconverting, to DC levels the 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;

wherein said third downconverting means includes synchronous detector means 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.

12. The system of claim 3 wherein the second intermediate frequency is a microwave frequency signal.

13. The system of claim 3 and further including:

third downconverting means for simultaneously linearly downconverting the at least one reference stimulus signal and the t least one test stimulus signal that has been incident upon the DUT so as to downconvert to a third intermediate frequency range the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT.

14. The system of claim 13 wherein said third downconverting means includes at least one image reject mixer means.

15. The system of claim 3 and further including:

local oscillator means for producing mixing signals; and

mixer means for mixing the mixing signals with the version of the at least one reference stimulus signal downconverted to the second intermediate frequency range and for mixing the mixing signals with the version of the at least one test stimulus signal that has been downconverted to the second intermediate frequency range and that has been incident upon the DUT so as downconvert the at least one reference and the at least one test stimulus signals to a third intermediate frequency range.

16. The system of claim 3 wherein the 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 are microwave frequency signals.

17. The system of claim 3 wherein said splitting means splits the stimulus signal so as to provide the at least one reference stimulus signal and the at least one test stimulus signal at substantially equal amplitudes.

18. The system of claim 3 wherein said coupling means includes:

at least one first coupler means for providing the at least one test stimulus signal to the DUT in a forward direction; and

at least one second coupler means for providing the at least one test stimulus signal to the DUT in a reverse direction.

19. The system of claim 3 wherein said phase comparison means includes:

noise reduction means for reducing noise in the 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.

20. The system of claim 19 wherein said noise reduction means includes at least one integrator circuit.

21. The system of claim 20 wherein said noise reduction means includes at least two integrator circuits.

22. The system of claim 21 wherein said phase comparison means includes:

mixer means for mixing the at least one linearly downconverted version of the reference stimulus signal with the signal at the prescribed frequency.

23. The system of claim 22 wherein said mixer means includes at least one double balanced mixer means.

24. The system of claim 23 wherein said mixer means includes at least two double balance mixer means.

25. The system of claim 3 wherein said source means produces an unsynthesized signal.

26. The system of claim 3 further including processor means for calculating a phase shift in the at least one test stimulus signal that has been incident upon the DUT, the phase shift being calculated relative to the at least one reference stimulus signal.

27. The system of claim 3 further comprising processor means for:

(i) calculating a phase shift in the at least one test stimulus signal that has been incident upon the DUT, the phase shift being calculated relative to the at least one reference stimulus signal, and

(ii) calculating an amplitude change in the at least one test stimulus signal that has been incident upon the DUT.

28. 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.

29. The system of claim 28 wherein said sampling means includes mode switching means for switching said sampling means between,

(i) a sampling mode in which sampling pulses sample the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT, and

(ii) a direct mode in which the at least one reference stimulus signal and the at least one test stimulus signal that has been incident upon the DUT pass said sampling means substantially without frequency downconversion.

30. The system of claim 29 wherein:

said mode switching means switches said sampling means into the sampling mode when said source means produces the stimulus signal in a prescribed higher frequency range; and

said mode switching means switches said sampling means into the direct mode when said source means produces the stimulus signal in a prescribed lower frequency range.

31. The system of claim 30 further comprising:

filter means for respectively filtering 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 pass only signals in a first passband.

32. The system of claim 31 further comprising:

filter switching means for coupling said filter means to said sampling means and for decoupling said filter means from said sampling means;

wherein said filter switching means couples said filter means to said sampling means when said sampling means is in the sampling mode and said filter switching means decouples said filter means from said sampling means when said sampling means is in the direct mode.

33. The system of claim 32 wherein said mixer means for providing signals in said second intermediate frequency range includes at least one double balanced mixer means.

34. The system of claim 28 further comprising:

processor means for controlling the frequency of operation of said at least one first local oscillator means and said at least one second local oscillator means.

35. The system of claim 34 wherein:

said processor means causes said at least one first local oscillator means to produce the first local oscillator signals at a respective first unique frequency in at least one other prescribed frequency range for each respective discrete stimulus signal frequency; and

said processor means causes said at least one second local oscillator means to provide second local oscillator mixing signals at a respective second unique frequency in at least one prescribed frequency range for each respective discrete stimulus signal frequency.

36. 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.

37. The system of claim 36 wherein said mode switching means switches said sampling means into:

(i) the harmonic mode when said source means produces the stimulus signal in a prescribed higher frequency range; and

(ii) the direct mode when said source means produces the stimulus signal in a prescribed lower frequency range.

38. The system of claim 36 further comprising:

at least one second local oscillator means for providing second local oscillator mixing signals in at least one second oscillator frequency range; and

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 for mixing the second mixing signals with 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 downconvert the at least one reference and the at least one test stimulus signals from the first intermediate frequency range to a second intermediate frequency range.

39. The system of claim 38 further comprising:

at least one third local oscillator means for producing third local oscillator mixing signals in a third oscillator frequency range;

mixer means for mixing the third local oscillator mixing signals with the at least one reference stimulus signal downconverted to the second intermediate frequency and for mixing the third mixing signals with the at least one test stimulus signal that has been downconverted to the second intermediate frequency and that has been incident upon the DUT so as to downconvert the at least one test reference stimulus signals to a third intermediate frequency; and

synchronous detector means 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.

40. The system of claim 39 further comprising:

processor means for calculating a phase shift in the at least one test stimulus signal that has been incident upon the DUT, the phase shift being calculated relative to the at least one reference stimulus signal.

41. The system of claim 39 further comprising processor means for:

(i) calculating a phase shift in the at least one test stimulus signal that has been incident upon the DUT, the phase shift being calculated relative to the at least one reference stimulus signal, and

(ii) calculating an amplitude change in the at least one test stimulus signal that has been incident upon the DUT.

42. 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.

43. The method of claim 42 wherein said step of locking comprises the step of varying the respective discrete frequency so as to cause a limiting of a phase difference between the linearly downconverted version of the at least one reference stimulus signal and the first signal at the first frequency.

44. The method of claim 43 wherein said step of locking comprises the step of substantially removing the phase drift in a frequency of the respective discrete stimulus signal.

45. The method of claim 43 further comprising the step of:

calculating a phase shift in the at least one test stimulus signal that has been incident upon the DUT, the phase shift being calculated relative to the at least one reference stimulus signal.

46. The method of claim 43 further comprising the steps of:

calculating a phase shift in the at least one test stimulus signal that has been incident upon the DUT, the phase shift being calculated relative to the at least one reference stimulus signal; and

calculating an amplitude change in the at least one test stimulus signal that has been incident upon the DUT.

47. The method of claim 43 wherein the first frequency is a microwave frequency.

48. The method of claim 47 further comprising the steps of:

downconverting the 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; and

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.

49. 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_ST ;

(ii) generating initial first and a second local oscillator signal having the frequencies F_LO1 and F_LO2 ;

(iii) providing first and second intermediate frequency signals having the frequencies IF₁ and IF₂, respectively as determined by the following equations

space="preserve" listing-type="equation">IF.sub.1 =M * F.sub.LO1 -F.sub.ST, where M is an initial harmonic

number; and

space="preserve" listing-type="equation">IF.sub.2 =F.sub.L02 -IF.sub.1 ;

(iv) generating in response to said second intermediate frequency signal having the frequency IF₂ and a third local oscillator signal having the frequency F_LO3, a third intermediate frequency signal having the frequency IF₃ ;

(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

space="preserve" listing-type="equation">|M * F.sub.LO1 -N * F.sub.LO2 |<

IF.sub.3 -PB.sub.3 /2 and (1)

space="preserve" listing-type="equation">|M * F.sub.LO1 -N * F.sub.LO2 |>

IF.sub.3 +PB.sub.3 /2 where PB.sub.3

space="preserve" listing-type="equation">is the bandwidth of a filter for filtering IF.sub.3 (

     2)

and

(vi) repeating steps (ii) through (v) with new values of F_LO1 and F_LO2 for each combination of M and N until neither the first or the second condition is met.

50. 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_LO1 and F_LO2, respectively, as determined by the following algorithm,

F=F_ST * 20

H=1+Integer(F+1788)/10730

Z=5365/(3+H/1250)

F_LO1 =1+Integer /20

F_LO2 =H * F_LO1 -F/20+2.25 for producing first and second intermediate frequencies IF₁ and IF₂, respectively;

(iii) generating a third local oscillator signal having a frequency F_LO3 which, when mixed with F₂, produces a predetermined third intermediate frequency F₃ ;

(iv) testing for harmonics of F_LO1 and F_LO2 which will produce a spurious F₃ if the following first and second conditions of inequalities are met,

space="preserve" listing-type="equation">|M * F.sub.LO1 -N * F.sub.LO2 |<

IF.sub.3 -PB.sub.3 /2 (1)

space="preserve" listing-type="equation">|M * F.sub.LO1 -N * F.sub.LO2 |>

IF.sub.3 -PB.sub.3 /2 (2)

where M and N are harmonic numbers and PB₃ is the bandwidth of a filter for filtering IF₃ ; and

(v) changing the values of M, N, F_LO1 and F_LO2 while maintaining the relationship F_ST =H * F_LO1 -F_LO2 +IF₂ and avoiding the conditions of inequalities (1) and (2) above.