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Abstract A novel approach to linear array antennas with adaptive inter-element spacing is presented for the first time. The main idea is based upon electronically displacing the phase center location of the antenna elements, which determine their relative coordinates in the array configuration. This is realized by employing dual-mode microstrip patch antennas as a constitutive element, whose phase center location can be displaced from its physical center by simultaneously exciting two modes. The direction and the amount of displacement is controlled by the amplitude and phase of the modes at the element level. This in turn facilitates reconfiguring the inter-element spacing at the array level. For instance, a uniformly-spaced array could be electronically transformed into a non-uniform one without any mechanical means. The proposed idea is demonstrated in two- and three-element linear antenna arrays. The technique has the potential to control the radiation characteristics such as sidelobe levels, position of the nulls, and the beamwidths in small arrays, which are useful for adaptively controlling the array performance in emerging wireless communication systems and radars. 

Abstract|The experimental validation of reduced grating lobes in a seven-element, hexagonal, scanning phased array antenna with the one-wavelength element spacing is presented. The base element of the array is a single-layer, dual-mode antenna with self-scanning and nulling properties. For the selected scan angle of ¡30±, the required microstrip transmission line based feeding network, consisting of ring hybrids, power splitters, and branchline couplers, are designed and developed. A prototype of the complete array and feeding network was fabricated and successfully tested to show the e®ectiveness of the grating lobe reduction method using the dual-mode antenna elements in scanning phased array antennas with the one-wavelength element spacing. 

A wideband microstrip patch antenna, exciting the fundamental transverse electric (TE) mode, is investigated. The excitation of the TE mode is facilitated through replacing both of the patch and ground plane of a conventional microstrip antenna with artificial magnetic conductors (AMC), consisting of unipolar compact photonic bandgap (UC-PBG) unit cells. The AMC patch and the ground plane of this antenna behave as magnetic conductors within the bandgap region of the unit cells. Similar to conventional patch antennas, it is shown that by cutting a U-shaped slot in the AMC patch, wideband characteristics are realized. The antenna shows a 40% impedance bandwidth and operates at the TE10 mode. Moreover, the width of the patch is 1.75 times smaller than its length, reducing the overall size of the antenna by about 60%, compared with the conventional U-slot PEC antenna supporting the transverse magnetic (TM) mode.