Characterising radio frequency signal processing paths
A method for determining amplitude and phase correction coefficients for one or more signal processing paths across a frequency band of interest is provided. The method comprises transforming an input test signal from the time domain to the frequency domain to obtain an input magnitude spectrum and an input phase spectrum for the/each signal processing path. It further comprises transforming an/each respective output test signal from the time domain to the frequency domain to obtain an output magnitude spectrum and an output phase spectrum for the/each signal processing path. It also comprises comparing the/each input magnitude spectrum with its respective output magnitude spectrum to determine an amplitude correction coefficient for the/each signal processing path and/or comparing the/each input phase spectrum with its respective output phase spectrum, to determine a phase correction coefficient for the or each signal processing path.
1. A method of determining relative amplitude and phase correction coefficients for a plurality of parallel signal processing paths across a frequency band of interest, each of the plurality of parallel signal processing paths having an input and an output, the method comprising:
transforming an output test signal, resulting from an input test signal provided to the respective inputs of the each of the plurality of parallel signal processing paths being processed along the respective signal processing path, from the time domain to the frequency domain to obtain an output magnitude spectrum and an output phase spectrum for the each of the plurality of parallel signal processing paths;
comparing the output magnitude spectrum of a first of the plurality of parallel signal processing paths with the output magnitude spectrum of another of the plurality of parallel signal processing paths to determine, at one or more frequencies of the frequency band of interest, a relative amplitude correction coefficient for the another of the plurality of parallel signal processing paths; and/or
comparing the output phase spectrum of the first of the plurality of parallel signal processing paths with the output phase spectrum of the another of the plurality of parallel signal processing paths to determine, at one or more frequencies of the frequency band of interest, a relative phase correction coefficient for the another of the plurality of parallel signal processing paths.
2. The method of claim 1 , wherein the input test signal provided to each signal processing path is time shifted with respect to the input test signal provided to each other signal processing path; and/or is provided to each signal processing path simultaneously.
3. The method of claim 1 , wherein the input test signal provided to each signal processing path comprises a zero amplitude portion and an oscillatory non-zero amplitude portion.
4. The method of claim 3 , wherein the non-zero portion of each input test signal is the same;
and/or the non-zero portion of the input test signal provided to each signal processing path is temporally separated from the non-zero portion of the input test signal provided to each other signal processing path by a guard time interval.
5. The method of claim 1 , the method further comprising:
applying, at the one or more frequencies of the frequency band of interest, the relative amplitude correction coefficients for the another of the plurality of parallel signal processing paths to the magnitude components of the data signal magnitude spectrum of the data signal intended to be provided to the input of the another of the plurality of parallel signal processing paths; and/or
applying, at the one or more frequencies of the frequency band of interest, the relative phase correction coefficients for the another of the plurality of parallel signal processing paths to the phase components of the data signal phase spectrum of the data signal intended to be provided to the input of the another of the plurality of parallel signal processing paths.
6. The method of claim 1 , further comprising temporally aligning each input test signal with its respective output signal; and, optionally or preferably, wherein temporally aligning each input test signal with its respective output signal comprises performing a cross-correlation operation between each input test signal and its respective output signal.
7. The method of claim 1 , further comprising:
providing an input test signal to the input of the or each signal processing path; and
detecting each respective output test signal at the respective output of each signal processing path.
8. The method of claim 1 , wherein the input test signal provided to the input of each signal processing path comprises a predetermined frequency bandwidth; and, optionally of preferably, wherein the predetermined frequency bandwidth of the input test signal is up to 20 MHz, 60 MHz, 100 MHz or 200 MHz.
9. The method of claim 1 , wherein the input test signal provided to the input of each signal processing path comprises a signal whose magnitude spectrum exhibits a substantially uniform amplitude profile in the frequency band of interest, and/or whose phase spectrum exhibits a substantially linear phase profile in the frequency band of interest.
10. The method of claim 1 , wherein the input test signal provided to the input of each signal processing path comprises a truncated sinc function; and, optionally or preferably, wherein the truncated sinc function is or comprises a sinc function multiplied by a window function; and, optionally or preferably, wherein the window function is or comprises any of: a Hamming window, a Blackman window, a Hanning window, a Hann window, or a Nuttall window.
11. The method of claim 1 , wherein the input test signal provided to each signal processing path is or comprises a chirp signal.
12. The method of claim 1 , wherein comparing the output magnitude spectrum of the first of the plurality of parallel signal processing paths with the output magnitude spectrum of the another of the plurality of parallel signal processing paths comprises:
dividing the output magnitude spectrum of the first of the plurality of parallel signal processing paths by the output magnitude spectrum of the another of the plurality of parallel signal processing paths, or dividing the output magnitude spectrum of the another of the plurality of parallel signal processing paths by the output magnitude spectrum of the first of the plurality of parallel signal processing paths.
13. The method of claim 1 , wherein comparing the output phase spectrum of the first of the plurality of parallel signal processing paths with the output phase spectrum of the another of the plurality of parallel signal processing paths comprises:
subtracting the output phase spectrum of the first of the plurality of parallel signal processing paths from the output phase spectrum of the another of the plurality of parallel signal processing paths, or subtracting the output phase spectrum of the another of the plurality of parallel signal processing paths from the output phase spectrum of the first of the plurality of parallel signal processing paths.