Scalar network analyzer

• US 5,072,189 A
• Filed: 03/29/1990
• Issued: 12/10/1991
• Est. Priority Date: 03/29/1990
• Status: Expired due to Fees

• Current Assignee: Direct Conversion Technique Incorporated
• Original Assignee: Direct Conversion Technique Incorporated
• Inventors: Openlander, Wayne R.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/502,129
• Time in Patent Office: 621 Days
• Field of Search: 324/638, 324/639, 324/641, 324/642, 324/645, 324/646, 324/637, 324/629, 324/615, 455/315
• US Class Current: 324/638
• 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 low cost and portable scalar network analyzer for the simultaneous measurement of forward and reflected scalar scattering parameters of devices under test. Plural UHF oscillators of similar construction are mixed to produce a wideband test instrument having good stability characteristics. A dual-diode biased RF detector with feedback, including an in-loop adjustable gain buffer stage, provides enhanced linearity, over a wide dynamic range, and at low cost. The forward transfer parameter measurement arrangement further includes a selectable attenuation/gain PIN-diode switched stage to accommodate the widely varying gain/attenuation characteristics of devices under test.

Claims

1. Portable self-contained apparatus for measuring the magnitude of the reflection or forward transmission coefficients of a device under test at one or more frequencies over a predetermined wide range of test frequencies including first and second connections for operatively interconnecting the apparatus to the device under test;

a low power frequency generator, said frequency generator having means for selectively setting the frequency thereof within said wide frequency range;

a directional coupler operatively connected to the frequency generator and to said first test device connection, the directional coupler having a reflected power port, the power at the reflected power port being proportional to the reflection coefficient of the device under test;

detector means operatively connected to the directional coupler reflected power port for producing a DC voltage representative of the reflected power at the first connection, the detector means including linearizing means whereby the magnitude of the detected DC voltage is generally proportional to the reflection coefficient, the linearizer means further including means for selecting the reflection coefficient sensitivity range;

forward transmission coefficient measuring means including gain means operatively connected to the second test device connection and to a detector means for selectively attenuating, amplifying, and passing the signal from the test device at the second connection whereby the signal level at the forward detector may be maintained within a predetermined range;

the forward detector means including linearizing means whereby the magnitude of the DC voltage from the detector is generally proportional to the forward transmission coefficient;

the low power frequency generator includes first and second continuous=wave oscillators and mixer means operatively connected to the oscillators for obtaining the difference product therebetween, said difference product defining a continuous-wave test frequency within said wide frequency range;

the first and second oscillators being of substantially similar design and construction and being retained within the self-contained apparatus whereby both oscillators are subjected to substantially similar environmental conditions thereby causing each oscillator to experience similar environmentally induced frequency instability characteristics, such instabilities being canceled in the difference product of the mixer means thereby improving the stability of the test frequency.

2. The portable self-contained forward transfer and reflection coefficient measuring apparatus of claim 1 including means for decoupling the first and second oscillators thereby minimizing test frequency instability caused by oscillator frequency locking.

3. Portable self-contained apparatus for measuring the magnitude of the reflection or forward transmission coefficients of a device under test at one or more frequencies over a predetermined wide range of test frequencies including first and second connections for operatively interconnecting the apparatus to the device under test;

a low power frequency generator, said frequency generator having means for selectively setting the frequency thereof within said wide frequency range;

a directional coupler operatively connected to the frequency generator and to said first test device connection, the directional coupler having a reflected power port, the power at the reflected power port being proportional to the reflection coefficient of the device under test;

detector means operatively connected to the directional coupler reflected power port for producing a DC voltage representative of the reflected power at the first connection, the detector means including linearizing means whereby the magnitude of the detected DC voltage is generally proportional to the reflection coefficient, the linearizer means further including means for selecting the reflection coefficient sensitivity range;

forward transmission coefficient measuring means including gain means operatively connected to the second test device connection and to a detector means for selectively attenuating, amplifying, and passing the signal from the test device at the second connection whereby the signal level at the forward detector may be maintained within a predetermined range;

the forward detector means including linearizing means whereby the magnitude of the DC voltage from the detector is generally proportional to the forward transmission coefficient;

the detector and linearizing means operatively connected to the reflected power port includes a dual biased diode feedback detector, said detector having at least one gain switchable stage within the feedback loop whereby the DC level of the detector and linearizer output may be range switched as required to increase detection sensitivity and to accurately perform measurement over a wide range of reflection coefficients.

4. Portable self-contained apparatus for measuring the magnitude of the reflection or forward transmission coefficients of a device under test at one or more frequencies over a predetermined wide range of test frequencies including first and second connections for operatively interconnecting the apparatus to the device under test;

a low power frequency generator, said frequency generator having means for selectively setting the frequency thereof within said wide frequency range;

a directional coupler operatively connected to the frequency generator and to said first test device connection, the directional coupler having a reflected power port, the power at the reflected power port being proportional to the reflection coefficient of the device under test;

detector means operatively connected to the directional coupler reflected power port for producing a DC voltage representative of the reflected power at the first connection, the detector means including linearizing means whereby the magnitude of the detected DC voltage is generally proportional to the reflection coefficient, the linearizer means further including means for selecting the reflection coefficient sensitivity range;

forward transmission coefficient measuring means including gain means operatively connected to the second test device connection and to a detector means for selectively attenuating, amplifying, and passing the signal from the test device at the second connection whereby the signal level at the forward detector may be maintained within a predetermined range;

the forward detector means including linearizing means whereby the magnitude of the DC voltage from the detector is generally proportional to the forward transmission coefficient;

the forward transfer coefficient gain means includes at least one stage having two or more independently selectable signal paths, switch means operatively connected to the stage for selectively enabling at least one of said paths;

each path defining a predetermined gain, attenuation, or pass characteristic whereby the overall gain or attenuation of the gain means may be selectively adjusted to maintain the signal to the forward transfer coefficient detector means within a predetermined range.

5. Portable self-contained apparatus for measuring the magnitude of the reflection or forward transmission coefficients of a device under test at one or more frequencies over a predetermined wide range of test frequencies including first and second connections for operatively interconnecting the apparatus to the device under test;

a low power frequency generator, said frequency generator having means for selectively setting the frequency thereof within said wide frequency range;

a directional coupler operatively connected to the frequency generator and to said first test device connection, the directional coupler having a reflected power port, the power at the reflected power port being proportional to the reflection coefficient of the device under test;

detector means operatively connected to the directional coupler reflected power port for producing a DC voltage representative of the reflected power at the first connection, the detector means including linearizing means whereby the magnitude of the detected DC voltage is generally proportional to the reflection coefficient, the linearizer means further including means for selecting the reflection coefficient sensitivity range;

forward transmission coefficient measuring means including gain means operatively connected to the second test device connection and to a detector means for selectively attenuating, amplifying, and passing the signal from the test device at the second connection whereby the signal level at the forward detector may be maintained within a predetermined range;

the forward detector means including linearizing means whereby the magnitude of the DC voltage from the detector is generally proportional to the forward transmission coefficient;

the forward transfer coefficient gain means includes at least one stage having two or more independently selectable signal paths, switch means operatively connected to the stage for selectively enabling at least one of said paths;

each path defining a predetermined gain, attenuation, or pass characteristic whereby the overall gain or attenuation of the gain means may be selectively adjusted to maintain the signal to the forward transfer coefficient detector means within a predetermined range;

the switch means includes a plurality of diodes;

first DC biasing means for maintaining the diodes in an open signal blocking condition; and

second DC biasing means for maintaining the diodes in a closed signal passing condition;

the biasing level of the second biasing means being greater than, and overriding, the level of the first biasing means whereby the diodes are switched by selectively enabling the second biasing means without disabling the first biasing means.

6. Portable self-contained apparatus for measuring the magnitude of the reflection or forward transmission coefficients of a device under test at one or more frequencies over a predetermined wide range of test frequencies including first and second connections for operatively interconnecting the apparatus to the device under test;

a low power frequency generator, said frequency generator having means for selectively setting the frequency thereof within said wide frequency range;

a directional coupler operatively connected to the frequency generator and to said first test device connection, the directional coupler having a reflected power port, the power at the reflected power port being proportional to the reflection coefficient of the device under test;

detector means operatively connected to the directional coupler reflected power port for producing a DC voltage representative of the reflected power at the first connection, the detector means including linearizing means whereby the magnitude of the detected DC voltage is generally proportional to the reflection coefficient, the linearizer means further including means for selecting the reflection coefficient sensitivity range;

forward transmission coefficient measuring means including gain means operatively connected to the second test device connection and to a detector means for selectively attenuating, amplifying, and passing the signal from the test device at the second connection whereby the signal level at the forward detector may be maintained within a predetermined range;

the forward detector means including linearizing means whereby the magnitude of the DC voltage from the detector is generally proportional to the forward transmission coefficient;

the forward transfer coefficient gain means includes at least one stage having two or more independently selectable signal paths, switch means operatively connected to the stage for selectively enabling at least one of said paths;

each path defining a predetermined gain, attenuation, or pass characteristic whereby the overall gain or attenuation of the gain means may be selectively adjusted to maintain the signal to the forward transfer coefficient detector means within a predetermined range;

the switch means includes a plurality of diodes and selectable biasing means for maintaining the diodes in one of a first open signal blocking condition or in a second closed signal passing condition;

said biasing means including non-inductive means for limiting the current and for RF decoupling and isolating the switch means whereby proper operation and decoupling of the switch means may be maintained over the entire predetermined wide frequency range.