A very low-profile sub-THz high-gain frequency beam steering antenna, enabled by silicon micromachining, is reported for the first time in this paper. The operation bandwidth of the antenna spans from 220 GHz to 300 GHz providing a simulated field of view of 56 •. The design is based on a dielectric filled parallel-plate waveguide (PPW) leaky-wave antenna fed by a pillbox. The pillbox, a two-level PPW structure, has an integrated parabolic reflector to generate a planar wave front. The device is enabled by two extreme aspect ratio, 16 mm x 16 mm large perforated membranes, which are only 30 µm thick, that provide the coupling between the two PPWs and form the LWA. The micromachined low-loss PPW structure results in a measured average radiation efficiency of −1 dB and a maximum gain of 28.5 dBi with an input reflection coefficient below −10 dB. The overall frequency beam steering frontend is extremely compact (24 mm x 24 mm x 0.9 mm) and can be directly mounted on a standard WM-864 waveguide flange. The design and fabrication challenges of such high performance antenna in the sub-THz frequency range are described and the measurement results of two fabricated prototypes are reported and discussed.

Abstract-An equivalent-network model is here proposed to characterize two-dimensional planar periodic arrays of arbitrary scatterers/apertures embedded in a layered environment. The model is an extension of the approach previously developed by some of the authors, which only considered simple rectangular scatterers. A key underlying assumption in the present approach is that the current/field distribution in the scatterer can be factorized so that the spatial profile is independent of the frequency in the considered range of interest. This approximation is proven to work properly for a great variety of useful planar scatterer/aperture patterns, even at frequencies within the diffraction regime. The spatial current/field profile is determined from a full-wave simulation at a single and low frequency value. Our numerical results are validated through comparison to commercial simulators for very wide frequency ranges as well as with previously proposed circuit-model approaches.

An original mechanism is here proposed to achieve polarization conversion from linear to circular with the use of full-metal polarizing screens. Such screens are self-supported and conceived from the periodic arrangement of 3-D unit cells. They are built from sections of rectangular waveguides operating below the cutoff frequency and loaded with slotted discontinuities. The polarizer operates in transmission mode; the discontinuities are responsible for both its high return losses and the conversion of the impinging linear polarization to circular. Two types of 3-D cells are presented, and both of them are analyzed and designed through equivalent circuit models (CMs). These models have been thoroughly built in order to capture all the phenomena underlying the discontinuities' behavior. The characterization of the first cell is fully done analytically, whereas the second cell needs reduced help from a full-wave solver. Furthermore, the CMs allow simple design guidelines to be identified for this type of polarizer. Two designs are performed operating in Kaband, proving that an extension of the operation bandwidth (axial ratio and S 11 ) to 11% is possible by employing the second cell. Index Terms-Analytical circuit modeling, circular polarization (CP), metallic polarizer in transmission, 3-D unit cells. I. INTRODUCTION T HE conception of directive radiating systems for modern satellite communications is facing several bottlenecks, one of them related to the generation of circular polarization (CP) [1]-[7]. The most extensive solution consists in the integration of waveguide polarizers within the beamforming network (BFN) and before the radiating elements (the recent examples can be found in [2], [6], and [8]). Typical polarizing components are implemented in dual-polarized waveguides (supporting two degenerate modes) which are loaded with discontinuities or perturbations, such as stepped septums, ridges, irises, or corrugated grooves [1]-[3], [9]-[11]. The design strategy consists in obtaining the required 90 • phase shift between the two signals and high return loss (RL) for both polarizations. In this paper, compactness and sim-