A method for ensuring polarization agility in conjunction with beam steering in planar array antennas is proposed. It relies on interleaving two subarrays with orthogonal, linear polarizations that, together, can generate arbitrary polarization states: adjustable linear, elliptical, and left- or right-handed circular. The complexity of the resulting system is comparable with that of standard, fully populated array antennas consisting of identical, linearly polarized elements. By dynamically controlling the amplitude and the phase of the signals fed to the subarrays, a stable polarization state can be maintained during beam steering. The concept is validated by numerically investigating an architecture obtained by interleaving nonuniform subarrays designed by means of a deterministic placement strategy. The effects of the mutual coupling between the different radiating elements are modeled and discussed.@en

Application such as polarization diversity communications, frequency re-use and syntheti aperture radar (SAR) may benefit from the use of polarization-agile antennas, i.e. antennas whose polarization state can be dynamically changed over time (see [1] fir a comprehensive survey on this topic). Most polarization-agile antennas described [1] make use of doubly-polarized elementrary radiators in conjunction with active devices, such as PIN diodes, for varying the polarization properties of the radiated waves 9see[2] for a typical implemention of this conept). The present contribution advocates and alternative approach to obtaining polarization-agility. The strategy relies on interleaving (complementary) sparse sub-arrays each of which radiates waves with linear, orthogonal polarizations. In this manner, any polarization state: adjustable linear, right- and left-handed circular or elleptical can be synthesized at array level. The advantage of the proposed appraoach is that it makes use of simple elementary antennas radiating linearly-polarized waves, thus avoiding the complicated doubly-polarized elements abd the need fir PIN diodes for controlling the obtained polarization. The validity of this approach is demonstrated by analyzing two examples of inter-leaved array antennas that allow obtaining an arbitrarily rotated, linear polarization.@en

The reconfigurability is widely regarded as a viable option for meeting the changing requirements of modern radio links. Telecommunciaton satellites may benefit from antenna reconfirgurability, in particular the coverage areas of broadcasting satellites may be reconfigured by making use of reflector-type antennas using multiple feeds [1]. Moreover, antenna reconfigurability can be used for switching between different transmission modes in terms of the received/ transmitted power, allowing the antenna gain to be dynamically adjusted to the changing channel requirements. For example, [2] describes a strategy for dynamically tuning the antenna gain for counteracting the extra attenuation occurrin gin case of cloud coverage or rain precipation over the illuminated areas. In the present contribution we propse a strategy for reconfiguring non-uniform array-antennas. The proposed approach is based on the thinning of a uniform array achieved by switching on and off the transmit/ receive modules (TRMs) feeding the individual radiators. By strating from a fully populated, uniform configuration, different thinned arrays can be obtained by electronically switching off some of the individual TRMs. By changing the thinning ratewe are able to compensate for the gain-loss due to the steering of the antenna beam while keeping the peak sidelobes level (PSLL) under control. In order to assess the scanning performance of the thinned arrays a non-uniform array-antenna designed by means of a Genetic Algorithm (GA) approach [3] is compared with an array obtained by thinning down a uniform, lambda/2 spaced configuration (with lambda denoting the wavelength at the maximum operational frequency). The number of elements in the two arrays is 30 and 36, respectively, and their total length is approximately the same. The thinned array turns out to perform better than the GA array as the main beam is steered away from the boresight direction, providing, at the same time, a certain degree of reconfigurability.@en

A post-processing procedure that yields accurate array-antenna radiation-pattern estimaions is described. By resorting to this strategy, measurements of large array antennas inside small anechoic chambers become feasible. The method employs an adequate phase-correction derived from an optical ray approach, under the assumption that teh elementary radiators themselves are electrically small and van be measured under far-field conditions inside the relevant anechoic chamber. The effectiveness of the proposed thecnique is demonstrated by examing the case of nonuniform linear array antenna.@en

A new family of structures launching the fundamental mode in rectangular waveguides is proposed. Individual or stacked cavity-backed patch antennas radiate into a rectangular waveguide, providing a good matching with a coaxial input over a wide frequency range. The configuration results in a very compact, colinear transition from a standard coaxial connector to a rectangular waveguide. The components have applications as general-purpose coaxial-to-rectangular waveguide transitions and are well suited for low-profile, phased-array antennas. Experimental results confirm the computional estiumations of the proposed components' performance.@en

The mutual couplings between patch antennas printed on a common dielectric board is evaluated experimentally. two variants of this type of radiators are taken into account: with and without a cavity enclosure of the patches. Experiments are conducted on patch antennas manufactured in a standard printed circuit board (PCB) technology. The presences of cavities, fabricated by means of equally-spaced. metal-plated through-holes surrounding the antennas, reduces the amount of energy flowing from one radiator to another.@en

A grid-search type placement method for the assembling of large, non-uniform, linear arrays is presented. The required data is generated by means of an efficient computational engine that provides the locations of the elementary radiators for user-specified beam-widths and peak side-lobe levels. The scanning properties of the designed arrays are also investigated. An effective method for reducing the side-lobe level at large scanning angles is contrived.@en

The design of large antenna arrays that are amenable to a cost-effective fabrication in a lithographic technology is demonstrated. For reducing the inter-element coupling, cavities consisting of metal-plated through-holes are employe. The required bandwidth is achieved by resorting to U-slot patch antennas. The genetic algorithm is used for assembling a 30 elements non-uniform, linear array antenna. Experimental results confirm the predicted behaviour of the antenna.@en

A novel structure for launching the fundamental mode in rectangular waveguides is proposed. The geometry consists of a cavity-backed circular patch radiating into a rectangular waveguide. The matching properties of the proposed components are comparable with the ones of the classicallu used L-shaped loop end-launcher. The structure results in a very compact, colinear transition form a standard coaxial connector to a retangular waveguide. The component has applications as general purpose coaxial-to-waveguide transition and is well suited for low-profile phased-array antennas.@en

A novel approach to designing antenna systems, based on the preeminence of the fabrication technology, is discussed. In view of creating the basis for developing ubiquitous radio-channel applications, the use of a tecnologies that are adequate to mass-production, namely lithographic ones, is advocated. For demonstrating the concept, a helix antenna, implemented in a stratified, printed technology, is presented.@en

Keywords mode matching ¿ modal coupling coefficients ¿ waveguide junctions Abstract The explicit expressions of modal coupling coefficients at planar waveguide junctions are discussed. The coupling coefficients are expressed in terms of projections of the modes on the modal spectrum of a fictitious rectangular waveguide located at the junction plane. The proposed formulation results in an efficient implementation of the modal based analysis of waveguide junctions. Copyright © 2005 John Wiley & Sons, Ltd@en

An overview on the model-order reduction techniques for linear electriomagnetic problems is presented. The different methods are classified in Krylov and non-Krylov subspace methods. A number of domains where these techniques may play an instrumental role is ctalogued.@en

An automatic procedure for direct-dimension definition of stepped-impedance low-pass filters is presented. The procedure does not require any kind of iterative optimization, thus resulting in a very fast desing. Two examples of rectangular waveguide low-passfilters are presented. The results are validated through mode matching and finite-element method analyses, showing excellent agreement.@en