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A system, apparatus and method for performing differential return loss measurements and other measurements as a function of frequency uses a digital storage oscilloscope (DSO) having spectral analysis functions. A waveform generator generates a differential test signal in the form of a series of pul

A system, apparatus and method for performing differential return loss measurements and other measurements as a function of frequency uses a digital storage oscilloscope (DSO) having spectral analysis functions. A waveform generator generates a differential test signal in the form of a series of pulses where each pulse includes spectral components associated with each of a plurality of frequencies of interest. A test fixture presents the differential test waveform to a load including at least one of a device under test (DUT), a short circuit, an open circuit and a balanced load. A signal acquisition device differentially measures the test waveform during each of the load conditions. The signal acquisition device computes an error correction parameter using measurements made during the short circuit, open circuit and balanced load conditions. The correction parameter tends to offset signal acquisition errors within measurements made during the DUT load condition.

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What is claimed is: 1. A method of determining a characteristic parameter of a device under test (DUT), comprising: determining, using a test signal having spectral components associated with each of a plurality of frequencies of interest, and for each of a short circuit, open circuit and balanced

What is claimed is: 1. A method of determining a characteristic parameter of a device under test (DUT), comprising: determining, using a test signal having spectral components associated with each of a plurality of frequencies of interest, and for each of a short circuit, open circuit and balanced load condition, a reflection coefficient magnitude and phase of a testing system output port; calculating error correction terms adapted to substantially compensate for the determined reflection coefficient magnitude and phase of the testing system output port under the load conditions; causing the application of said test signal to a device under test (DUT) operatively coupled to said output port; measuring a response of said DUT to said test signal; and correcting said measured response of said DUT using said calculated error correction terms to produce a corrected measurement result that represents said characteristic parameter of said DUT in the form of a return loss parameter calculated using an equation of the following form: 2. The method of claim 1, wherein said test signal is generated by summing a plurality of sine waves having amplitude and phase parameters selected to provide energy at each of said frequencies of interest. 3. The method of claim 1, wherein: said phase parameters of said sine waves are adjusted to cause a relatively even distribution of signal energy over said frequencies of interest. 4. The method of claim 1, wherein said test signal is generated by summing a plurality of sine waves having phase parameters selected to provide energy at each of said frequencies of interest. 5. The method of claim 1, wherein said characteristic parameter of said DUT comprises in addition to the return loss parameter at least one of a transmission coefficient, a return angle parameter, a transmission angle parameter and an impedance parameter. 6. The method of claim 1, wherein said error correction terms comprise coefficients a, b and c calculated using equations of the following form: description="In-line Formulae" end="lead"Γm1=a.ΓA1+b-c.ΓA1. Γm1;description="In-line Formulae" end="tail" description="In-line Formulae" end="lead"Γm2=a.ΓA2+b-c.ΓA2. Γm2; anddescription="In-line Formulae" end="tail" description="In-line Formulae" end="lead"Γm3=a.ΓA3+b-c.ΓA3. Γm1description="In-line Formulae" end="tail" where Γm1 is a measurement value for the short circuit load condition with ΓA1 being one, Γm2 is a measurement value for the open circuit load condition with ΓA2 being negative one, and Γm3 is a measurement value for the balanced load condition with ΓA3 being zero. 7. A system for determining a characteristic parameter of a device under test (DUT), comprising: a waveform generator for generating a test signal comprising spectral components associated with each of a plurality of a frequencies of interest; a test fixture have a series reference impedance adapted to present said test signal to a load comprising at least one of said device under test (DUT), a short circuit, an open circuit and a balanced load; and a signal acquisition device coupled to the test fixture adapted to differentially measure across the series reference impedance said test signal during each of said load conditions; wherein said signal acquisition device computes an error correction parameter using measurements made during said short circuit, open circuit and balanced load conditions, said error correction parameter being used to compensate for signal acquisition errors within measurements made during said DUT load condition, the characteristic parameter being in the form of a return loss parameter calculated using an equation of the following form: where Γm are the measurements made during said DUT load condition and a, b and c are the error correction parameter. 8. The system of claim 7, wherein said test signal comprises a differential test signal. 9. The system of claim 7, wherein said test fixture comprises: a resistive power splitter adapted to split said test signal into a plurality of reduced power test signals; and a plurality of substantially resistive bridges, each of said resistive bridges adapted to present a respective reduced power test signal to a respective portion of a device under test (DUT); each of said resistive bridges presenting an output impedance adapted to an input impedance of said respective portion of said DUT; each of said resistive bridge bridges including reference impedance points adapted to enable signal measurement. 10. The system of claim 7, wherein: said test signal is generated by summing a plurality of sine waves having amplitude and phase parameters selected to provide energy at each of said frequencies of interest. 11. The system of claim 10, wherein: said phase parameters of said sine waves are adjusted to evenly distribute energy over said frequencies of interest. 12. The system of claim 10, further comprising: an arbitrary waveform generator (AWG) for generating said test signal. 13. The system of claim 7, wherein said characteristic parameter of said DUT comprises in addition to the return loss parameter at least one of a transmission coefficient, a return angle parameter, a transmission angle parameter and an impedance parameter. 14. The system of claim 7, wherein said error correction parameter comprises coefficients a, b and c calculated using equations of the following form: description="In-line Formulae" end="lead"Γm1=a.ΓA1+b-c.ΓA1. Γm1;description="In-line Formulae" end="tail" description="In-line Formulae" end="lead"Γm2=a.ΓA2+b-c.ΓA2. Γm2; anddescription="In-line Formulae" end="tail" description="In-line Formulae" end="lead"Γm3=a.ΓA3+b-c.ΓA3. Γm1description="In-line Formulae" end="tail" wherein ΓA1, ΓA2 and ΓA3 are reflection coefficients for, respectively, the open circuit, short circuit and balanced load conditions. 15. A compensation method adapted for use within a test and measurement device for determining a characteristic parameter of a device under test (DUT), said compensation method performing the steps of: determining, using a test signal comprising spectral components associated with each of a plurality of frequencies of interest, and for each of a short circuit, open circuit and balanced load condition, a reflection coefficient magnitude and phase of a testing system output port; calculating error correction terms adapted to substantially compensate for the determined reflection coefficient magnitude and phase of the testing system output port under the load conditions; causing the application of said test signal to a device under test (DUT) operatively coupled to said output port; measuring a response of said DUT to said test signal; and correcting said measured response of said DUT using said calculated error correction terms to produce a corrected measurement result that represents said characteristic parameter of said DUT. 16. The compensation method of claim 15 wherein the steps are performed in accordance with computer readable instructions stored within a memory of said test and measurement device which are executed by a processor within said test and measurement device. 17. A test system for performing measurements on a device under test (DUT) as a function of frequency including differential return loss measurements comprising: a waveform generator for providing a test signal of an arbitrary waveform having signal energy at each of a plurality of frequencies; a test fixture having an input to receive the test signal and an output to couple the test signal to a load via a reference impedance, the load being one of a short circuit, an open circuit, a balanced load and the DUT; a signal acquisition device coupled to the test fixture for receiving return signals from the test fixture across the reference impedance indicative of a response of the load to the test signal, for determining an error correction function from the return signals for the short circuit, open circuit and balanced load, and for determining from the return signals for the DUT actual measurements after application of the error correction function. 18. The test system as recited in claim 17 wherein the signal acquisition device comprises a digital storage oscilloscope for determining return loss measurements for the DUT, the digital storage oscilloscope coupling across the reference impedance via probes. 19. The test system as recited in claim 17 wherein the test fixture comprises a power splitter to split the test signal into a plurality of lower power test signals for application to the DUT having a plurality of inputs with the digital storage oscilloscope having a corresponding plurality of inputs for receiving the return signals from the test fixture.