An effective procedure for accounting for the mutual coupling between rectangular apertures in the design of nonuniform array antennas is discussed. The central element of the procedure is a two-dimensional interpolation scheme allowing the evaluation of the coupling admittance between arbitrarily located rectangular apertures based on 9 pre-computed values. The manner in which the interpolation strategy can serve a purpose in optimisation schemes for reaching certain radiation pattern or active reÁection coefÀcient design requirements is focused upon. The method's effectiveness is illustrated by examining the case of some medium-large nonuniform placements with demonstrated superior performance. The inclusion of the mutual coupling is shown to affect pronouncedly the performance predicted by means of the array factor, only. Indications on the computational costs of including the computational strategy in iterative optimisation schemes are also given.

A complete tool for analyzing the mutual coupling in nonuniform (interleaved) array antennas consisting of rectangular aperture radiators is discussed. It relies on deriving the coupling admittances between arbitrarily located apertures via a two-dimensional interpolation scheme. Realistic radiators are accounted for through their scattering matrix evaluated by means of full-wave analyses. The method yields accurate results while greatly reducing the computation time. Its validity is demonstrated against measurements done on a medium-sized, interleaved, nonuniform array of cavity-backed apertures.

This contribution discusses a near-field antenna setup capable of delivering multiple input signals with controllable (i.e., user defined) amplitude and phase relations to an antenna under test, operating in the X-band. The setup is based on a Cartesian modulation (phase and quadrature signals) of phase coherent signals, achieved employing broadband passive IQ-mixers controlled via high-resolution digital-to-analogue converters (DACs). A dedicated calibration procedure allows achieving independent phase and amplitude control on the different signal paths to compensate for loss and delay mismatches among the different channels. The capability to align the relative phases of the various paths with respect to one enables the direct testing of phased antenna arrays. The system calibration is elaborately described. The proposed Cartesian modulation is demonstrated by studying a complex antenna array, with a subset of its elements being controlled independently and phase delayed for actively controlling the far-field radiation pattern.

An experimental method to perform near-field measurement of system-embedded antennas is presented. The proposed approach employs two probe antennas, one fixed and one scanning, enabling to retrieve both amplitude and phase of the near-field. This allows to employ conventional nearfield to far-field transformations, without the need to resort to phase retrieval approaches. The technique is first demonstrated on a standalone 60GHz patch, showing the good agreement between the proposed method and a conventional (one probe) near-field characterization. Then, the method is applied to the characterization of embedded antennas operating in the 60GHz and 94GHz bands, and it is benchmarked with simulations and conventional far-field characterization techniques.