Precise Incident Power Density Pattern Measurement through Antenna Pattern Deconvolution

Abstract

Future cellular and fixed wireless loops (FWL) systems employing highly directive base stations antennas (5 to 8 degrees beamwidth) and moderately directive subscribers' antennas (15 to 25 degrees beamwidth) offer very large capacity due to reduced interference. An important property of the environment of such systems is the interference caused by scattering of the signal from a subscriber transmitter into directions other than the direct line of sight between the subscriber and the base station. In particular, for multibeam base station applications scattering could arrive at the base station in the direction being used by a different beam, resulting in interference that is difficult to reduce by normal nulling techniques. Thus interference can be highly dependent on the incident power density pattern (IPDP) caused by scattering of the signal radiated from the subscriber. We discuss herein the use of a uniformly illuminated array accompanied by electric field deconvolution to measure the crucial IPDP with the same performance as a low sidelobe array of the same size. The mathematical correction technique uses deconvolution of the measured complex electric field pattern with that of the antenna in free space by means of the Fourier Series and limiting the range of Fourier coefficients to those that are not negligible in the free space pattern. Application of the technique to an experimental uniform array with a 2.5 degree azimuthal beamwidth shows the practicality of the deconvolution with real antennas in real environments. The improved resolution and accuracy provided by Taylor weighting versus unweighted deconvolution when trying to measure weak scattered components in the presence of a nearby strong specular component is demonstrated. The IPDP was measured from many sites surrounding a suburban base station. A plot of the cumulative distribution of the ratio of the widely scattered power to that within a prescribed beamwidth summarizes the result of using the deconvolution technique on this experimental data.