Noise figure measurement using narrowband compensation
View Patent ↗A method of determining a noise figure (NF) response of a device under test (DUT) comprises determining a frequency response of a noise receiver over a first frequency range, measuring a gain of the DUT over a second frequency range encompassing the first frequency range, measuring output-noise power of the DUT over the second frequency range, determining an estimated gain of the DUT based on the frequency response of the noise receiver and the gain of the DUT over the first frequency range, and determining the NF response of the DUT over the second frequency range based on the estimated gain and the output-noise power.
1. A method, executed by a network analyzer comprising a noise receiver, of determining a noise figure (NF) response of a device under test (DUT), the method comprising:
determining a frequency response of the noise receiver over a first frequency range;
measuring, with the noise receiver, a gain of the DUT over a second frequency range broader than and encompassing the first frequency range;
measuring, with the noise receiver, output-noise power of the DUT over the second frequency range;
determining an estimated gain of the DUT based on the frequency response of the noise receiver and the gain of the DUT over the first frequency range; and
determining the NF response of the DUT over the second frequency range based on the estimated gain and the output-noise power.
2. The method of claim 1 , wherein determining the estimated gain of the DUT comprises multiplying the frequency response of the noise receiver by the determined gain of the DUT over the first frequency range and normalizing the product of the multiplication.
3. The method of claim 1 , wherein determining the frequency response of the noise receiver over the first frequency range comprises:
with a cable connected directly between first and second test ports of the network analyzer, measuring a noise floor of the noise receiver and measuring power of the noise receiver and a reference receiver while sweeping a test signal over the first frequency range; and
determining the frequency response of the noise receiver over the first frequency range based on the measured noise floor, the measured power of the noise receiver, and the measured power of the reference receiver.
4. The method of claim 1 , wherein determining the gain of the DUT over the second frequency range comprises, with the DUT connected between first and second test ports of the network analyzer, sweeping a test signal across the second frequency range and measuring S-parameters of the DUT based on the swept test signal.
5. The method of claim 4 , further comprising measuring the output-noise power of the DUT over the second frequency range.
6. The method of claim 5 , further comprising:
determining a gain-bandwidth product of the noise receiver over the second frequency range; and
determining S-parameter vector-error correction terms of the noise receiver over the second frequency range.
7. The method of claim 6 , wherein determining the estimated gain of the DUT comprises:
in the frequency domain, for a specified frequency in the second frequency range, multiplying the frequency response of the noise receiver by the gain of the DUT over the first frequency range to produce a first result, multiplying the first result by the gain-bandwidth product to produce a second result, and integrating the second result to produce the estimated gain for the specified frequency.
8. The method of claim 1 , wherein the NF response is determined according to an equation NF=10 log(N o /(G′kT o B)), wherein G′ denotes the estimated gain of the DUT, N o denotes the output-noise power of the DUT, T o denotes a reference temperature, k denotes Boltzmann's constant, and B denotes a noise bandwidth of the noise receiver.
9. The method of claim 1 , wherein the DUT comprises at least one bandpass filter.
10. The method of claim 1 , wherein the first frequency range corresponds to a noise bandwidth of the DUT.
11. The method of claim 1 , wherein determining the frequency response of the noise receiver over the first frequency range comprises accessing a file including a stored representation of the frequency response.
12. A method, executed by a network analyzer comprising a noise receiver, of determining a noise figure (NF) response of a device under test (DUT), the method comprising:
determining a frequency response of the noise receiver over a first frequency range;
measuring, with the noise receiver, a gain of the DUT over a second frequency range broader than and encompassing the first frequency range;
for a specified frequency point, multiplying the gain of the DUT over the first frequency range with the frequency response of the noise receiver over the first frequency range to produce a first result, integrating the first result to produce a normalization factor, and dividing the first result by the normalization factor to produce an effective gain value of the DUT at the specified frequency point; and
determining an NF value for the specified frequency point based on the effective gain value of the DUT and an output-noise power of the DUT.
13. The method of claim 12 , further comprising:
with a cable connected directly between first and second test ports of the network analyzer, measuring a noise floor of the noise receiver and measuring power of the noise receiver and a reference receiver while sweeping a test signal over the first frequency range; and
determining the frequency response of the noise receiver over the first frequency range based on the measured noise floor, the measured power of the noise receiver, and the measured power of the reference receiver.
14. The method of claim 12 , wherein the network analyzer determines the frequency response of the noise receiver across the first frequency range by reading it from a file and determines the gain of the DUT by performing S-parameter measurements with the DUT connected between first and second test ports.
15. The method of claim 12 , wherein the NF value is determined according to an equation NF=10 log(N o /(G′kT o B)), wherein G′ denotes the effective gain value, N o denotes the output-noise power of the DUT, T o denotes a reference temperature, k denotes Boltzmann's constant, and B denotes a noise bandwidth of the noise receiver.
16. The method of claim 12 , wherein the first frequency range corresponds to a noise bandwidth of the DUT.
17. The method of claim 12 , wherein the DUT comprises at least one bandpass filter.
18. A system configured to determine a noise figure (NF) response of a device under test (DUT), the system comprising:
a network analyzer comprising a noise receiver;
a first module configured to determine a frequency response of the noise receiver over a first frequency range;
a second module configured to measure a gain of the DUT over a second frequency range broader than and encompassing the first frequency range;
a third module configured to measure output-noise power of the DUT over the second frequency range;
a fourth module configured to determine an estimated gain of the DUT based on the frequency response of the noise receiver and the gain of the DUT over the first frequency range; and
a fifth module configured to determine the NF response of the DUT over the second frequency range based on the estimated gain and the output-noise power.
19. The system of claim 18 , wherein the first through fifth modules are disposed in the network analyzer.
20. The system of claim 18 , wherein the fourth module determines the estimated gain of the DUT by multiplying the frequency response of the noise receiver by the determined gain of the DUT over the first frequency range and normalizing a product of the multiplication.