This paper introduces simple analytical formulas for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied. I. INTRODUCTIONIn this paper we consider planar periodic arrays of infinitely long metal strips and periodic arrays of square patches, as well as artificial high-impedance surfaces based on such grids. [17]. Capacitive strips and square patches have been studied extensively in the literature (e.g., [18]-[20]). However, to the best of the authors' knowledge, there is no known easily applicable analytical model capable of predicting the plane-wave response of these artificial surfaces for large angles of incidence with good accuracy.Models of planar arrays of metal elements excited by plane waves can be roughly split into two categories: computational and analytical methods. Computational methods as a rule are based on the Floquet expansion of the scattered field (see, e.g., [2], [3], [21], [22]). These methods are electromagnetically strict and general (i.e., not restricted to a particular design geometry). Periodicity of the total field in tangential directions allows one to consider the incidence of a plane wave on a planar grid or on a high-impedance surface as a single unit cell problem. The field in the unit cell of the structure can be solved using,

The Russian Academy of Sciences and Federal Space Agency, together with the participation of many international organizations, worked toward the launch of the RadioAstron orbiting space observatory with its onboard 10-m reflector radio telescope from the Baikonur cosmodrome on July 18, 2011. Together with some of the largest ground-based radio telescopes and a set of stations for tracking, collecting, and reducing the data obtained, this space radio telescope forms a multi-antenna groundspace radio interferometer with extremely long baselines, making it possible for the first time to study various objects in the Universe with angular resolutions a million times better than is possible with the human eye. The project is targeted at systematic studies of compact radio-emitting sources and their dynamics. Objects to be studied include supermassive black holes, accretion disks, and relativistic jets in active galactic nuclei, stellar-mass black holes, neutron stars and hypothetical quark stars, regions of formation of stars and planetary systems in our and other galaxies, interplanetary and interstellar plasma, and the gravitational field of the Earth. The results of ground-based and inflight tests of the space radio telescope carried out in both autonomous and ground-space interferometric regimes are reported. The derived characteristics are in agreement with the main requirements of the project. The astrophysical science program has begun.

The authors propose to use microelectromechanical systems (MEMS) to produce novel phase shifters based on an electronically reconfigurable high-impedance surface (HIS). Typically, HIS is a textured metal surface with reactive impedance varying from an initial value to a very high value. Such phase shifters can be developed with introducing a surface with variable impedance in, e.g., a rectangular metal or dielectric rod waveguide. Placed along narrow walls of the rectangular metal waveguide or adjacent to the dielectric waveguide, the HIS affects the propagation constant, which results in changing the phase of the propagating wave. The authors manufactured a prototype of the microelectromechanical systems-based HIS consisting of a dielectric layer placed on a ground plane, and two arrays of metal patches. The gap between the upper and lower arrays of patches was fixed and filled with SiO 2 . The measured phase of the wave reflected from the prototype HIS varies in the range of 50°, and its insertion loss is below 0.5 dB (out of resonance).

Abstract-The conventional integrated lens antennas (ILAs) for beam steering suffer from internal reflections that deteriorate the scanning properties. The internal reflections are known to affect side lobes, cross-polarisation level, input impedance of the feed, and mutual coupling. In this paper, ILAs are designed to exhibit very low reflection loss, i.e., to minimize the internal reflections. Wide ranges of realistic relative permittivities of the lens and of the feed element directivities are considered. It is shown that with any permittivity and with any feed directivity it is possible to design the lens shape in such a way that the reflection loss is low, for moderate beam-steering angles, without resorting to a complicated matching layer. The gain, directivity, beam-width, and the resulting distance between the feed elements are compared for all the designed lenses.

Holograms-diffractive elements-are designed and fabricated for shaping millimetre-wave radio fields. Methods for the synthesis of hologram elements are discussed and several beam shapes are tested: plane waves, radio-wave vortices and Bessel beams. Here we present an overview of the methods applied and results obtained with quasi-optical hologram techniques using both amplitude and phase holograms.