Swept signal analysis instrument and method

• US 5,420,514 A
• Filed: 02/07/1994
• Issued: 05/30/1995
• Est. Priority Date: 03/13/1990
• Status: Expired due to Term

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Potter, Ronald W., Gibbs, John A., Wardle, Jay M.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US08/192,927
• Time in Patent Office: 477 Days
• Field of Search: 364/724.06, 364/724.11, 364/724.16, 364/571.01, 324/76.27, 324/615, 324/619, 324/618
• US Class Current: 324/615
• CPC Class Codes: G01R 23/14 by heterodyning; by beat-frequency comparison
• CPC Class Codes: G01R 23/173 Wobbulating devices similar to swept panoramic receivers
• CPC Class Codes: G01R 27/30 with provision for recording characteristics, e.g. by plotting Nyquist diagram

Abstract

The sweep rate limitations that heretofore have constrained the maximum sweep rates of swept analysis instruments are obviated by optimizing filter circuitry and post-processing the IF signal using various techniques to compensate for errors caused by fast sweeping. Some selective windowing is also used to compensate for distortions due to fast sweep rates.

Claims

1. In a network analyzer comprising:

first means for exciting a network under test with a sine wave stimulus swept at a first rate to yield an output signal;

second means for sweeping a variable frequency oscillator at said first rate to mix said output signal to an intermediate frequency signal; and

third means for;

filtering the intermediate frequency signal;

detecting the amplitude and phase of the filtered intermediate frequency signal; and

determining a transfer characteristic of the network under test as a function of frequency;

an improvement including;

means for windowing the transfer characteristic of the network under test with a windowing function dependent on said first sweep rate; and

means for providing a variety of windowing functions and for selecting therebetween.

2. In a network analyzer comprising:

first means for exciting a network under test with a sine wave stimulus swept at a first rate to yield an output signal;

second means for sweeping a variable frequency oscillator at said first rate to mix said output signal to an intermediate frequency signal; and

third means for;

filtering the intermediate frequency signal;

detecting the amplitude and phase of the filtered intermediate frequency signal; and

determining a transfer characteristic of the network under test as a function of frequency;

an improvement including;

means for windowing the transfer characteristic of the network under test with a windowing function dependent on said first sweep rate; and

means for windowing the transfer function of the network under test with a single-sided exponential frequency response window function.

3. In a network analyzer comprising:

first means for exciting a network under test with a sine wave stimulus swept at a first rate to yield an output signal;

second means for sweeping a variable frequency oscillator at said first rate to mix said output signal to an intermediate frequency signal; and

third means for;

filtering the intermediate frequency signal;

detecting the amplitude and phase of the filtered intermediate frequency signal; and

determining a transfer characteristic of the network under test as a function of frequency;

an improvement comprising;

means for windowing the transfer characteristic of the network under test with a windowing function dependent on said first sweep rate; and

the third means includes an analog Nyquist zero symbol interference filter.

4. The network analyzer of claim 3 which further comprises digital means for implementing a desired window shape and for compensating sweep-rate dependent phase errors in the determined transfer characteristic.