Using spectral estimation methods for external problems of microwave measurements

Antenna pattern (AP) and reflection coefficient (RC) determination is one of the most widely occurring external problems of microwave measurements. It is very important to develop the means of antenna measurements in the presence of echo signals. For narrow band antennas in the presence of frequency dispersion, especially in the millimeter wave range, the time-domain pulse method has restrictions. It is more perspective to transform multifrequency data to time domain by spectral estimation methods such as the discrete Fourier transform (DFT), Prony method (PM), generalized pencil-of-function (GPOF) method, least square method (LSM). A multifrequency method of RC measurement in free space using transformation from frequency to time domain has been elaborated previously. This approach permitted us to measure RC approximately equal to -28 dB. But many absorbant materials have frequency dispersion, thus only single frequency measurement can be used. For both problems the aforementioned methods of spectral estimation are the key problems and some results of LSM are presented.