Swept microwave power measurement system and method

• US 4,958,294 A
• Filed: 04/01/1988
• Issued: 09/18/1990
• Est. Priority Date: 04/01/1988
• Status: Expired due to Fees

• Current Assignee: Giga-tronics, Inc.
• Original Assignee: Wavetek Microwave Incorporated
• Inventors: Herscher, Bret A., Munro, Paul R.
• Primary Examiner(s): Teska, Kevin J.
• Application Number:
  US07/176,729
• Time in Patent Office: 900 Days
• Field of Search: 364/571.01-571.07, 364/483, 364/484, 364/487, 364/570, 364/572, 375/10, 375/60, 375/94, 324/77 A, 324/77 B, 324/77 F, 324/57 R, 324/57 PS, 324/57 SS, 324/99 D, 324/58 R, 324/58.5 R
• US Class Current: 324/142
• CPC Class Codes: G01R 23/16 Spectrum analysis; Fourier analysis
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

A swept microwave power measurement system and method capable of performing accurate high performance absolute power measurements on the fly for integration with a scalar analyzer. The system interpolates a calibration factor of the detector at a given frequency point in the sweep between previously established calibration factors at various predetermined frequencies which are stored in memory and then determines an "apparent" power level of the input signal at a standard frequency. The interpolated calibration factor is applied to the "apparent" power level to determine the "absolute" power level at the given frequency point in the sweep.

Claims

1. A method for determining a swept absolute power level (P_abs) of an input signal within a scalar analyzer comprising the steps of:

providing a detector calibrated at a plurality of predetermined frequencies (n) over a range of F_min to F_max ;

storing a predetermined calibration factor (K(F_n)) for said detector at each of said predetermined frequencies n;

determining a frequency (F_in) of said input signal;

interpolating a calibration factor K(F_in) of said input signal wherein said calibration factor K(F_in) is one of said predetermined calibration factors (K(F_n));

establishing an apparent power level (P_app) of said input signal with respect to said calibration factor of a predetermined frequency standard; and

correcting said apparent power level P_app to said swept absolute power level P_abs by application of K(F_in).

2. The method of claim 1 wherein said step of providing is carried out by calibrating said detector with respect to NBS Standards.

3. The method of claim 1 wherein said step of interpolating is carried out by means of a linear interpolation between calibration factors immediately preceding and succeeding said frequency F_in.

4. The method of claim 1 wherein said step of storing is carried out by means of an EEPROM associated with said detector.

5. The method of claim 4 additionally comprising the step of reading said calibration factors K(F_in) from said EEPROM into an EEPROM interface.

6. The method of claim 1 wherein said predetermined frequency standard is 50 MHz.

7. The method of claim 6 wherein said step of measuring is carried out by means of an A to D convertor.

8. The method of claim 1 wherein said step of determining is carried out by measuring an analog sweep signal.

9. The method of claim 8 wherein said step of measuring is carried out by means of an A to D convertor.

10. The method of claim 8 wherein said step of determining is further carried out by means of a plurality of digital control signals coupling a source of said input signal with a microcomputer.

11. The method of claim 1 wherein said input signal is a swept signal.

12. The method of claim 11 further comprising the step of displaying a visual representation of swept absolute power.

13. The method of claim 12 wherein said step of displaying is carried out by means of a CRT.

14. The method of claim 12 wherein said step of displaying is sufficiently rapid to allow real time tuning of a component.

15. A system within a scalar analyzer for determining a swept absolute power level (P_abs) of an input signal from a source comprising:

means coupled to said source for detecting said input signal calibrated at a plurality of predetermined frequencies (n) over a range of F_min to F_max ;

means coupled to said detecting means for storing a predetermined calibration factor (K(F_n)) at each of said predetermined n frequencies;

means coupled to a sweep voltage line of said source for determining a frequency (F_in) of said input signal;

means coupled to said determining means for interpolating a calibration factor K(F_in) of said input signal;

means coupled to said interpolating means for establishing an apparent power level (P_app) of said input signal with respect to a frequency standard; and

,

means coupled to said establishing means for correcting said apparent power level P_app to said swept absolute power level P_abs by application of said calibration factor K(F_in).

16. The system of claim 15 wherein said means for detecting comprises a microwave sensor calibrated to NBS standards.

17. The system of claim 15 wherein said means for interpolating comprises a microcomputer having as inputs said calibration factors (K(F_n) and a digital signal representative of said frequency F_in.

18. The system of claim 15 wherein said means for correcting comprises a microcomputer having as input said apparent power level and said calibration factor K(F_in).

19. The system of claim 15 wherein said means for storing comprises an EEPROM.

20. The system of claim 19 further comprising an EEPROM interface serially coupled to said EEPROM.

21. The system of claim 15 wherein said means for determining comprises an A to D convertor coupled to a sweep voltage line.

22. The system of claim 21 further comprising a digital control signal bus coupled between said system and a source of said input signal.

23. The system of claim 15 wherein said means for establishing comprises an A to D convertor having as an input a signal V_det from said detecting means.

24. The system of claim 23 wherein said means for establishing further comprises a microcomputer coupled to said A to D convertor.

25. The system of claim 24 wherein said frequency standard is 50 MHz.

26. The system of claim 15 wherein said input signal is a swept signal.

27. The system of claim 26 further comprising means for displaying a visual representation of swept absolute power.

28. The system of claim 27 wherein said displaying means comprises a CRT.

29. The system of claim 27 additionally comprising a component under test coupled between said swept signal and said means for detecting wherein said displaying means is sufficiently rapid to allow real time tuning of the component.