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The essential dielectric properties, the basic alignment techniques, and the common measurement methods of the nematic liquid crystal (LC) at RF are briefly reviewed. A new device for the broadband measurement of the dielectric constants and loss tangents of nematic LCs at microwave and millimeter-wave frequencies is presented. This device whose specification and fabrication are outlined is essentially a two dielectric layer microstrip structure with coplanar-waveguide terminals, which is easy to fabricate. Compared to previous structures, the proposed device is extremely broadband with 15-65-GHz bandwidth, benefits from a solid exposed ground plane for easy temperature test, and operates under bias voltage. The technique for the extraction of the dielectric parameters of the nematic LC analyzed by this device is explained and the sources imposing the frequency limits on the device performance are identified. Two different nematic LCs, MDA-00-3506 and GT3-23001, are characterized and the results are shown to compare well with those available in the literature. In the comparisons, the maximum difference found for the dielectric constants for MDA-00-3506 is 5% and for GT3-23001 is 5.3%.

A novel hybrid high impedance surface is presented and a beam steerable four feed square loop antenna is built on this structure. At a test frequency of 4.7 GHz, the proposed hybrid high impedance surface based square loop antenna is 4.69 mm high and has an impedance bandwidth of 650 MHz and directivity of 8.7 dBi. Compared with the earlier reported steerable square loop antenna the new antenna's performance equates to a thickness reduction of 61%, bandwidth enhancement of 150%, a directivity improvement of 2 dBi, a co-polar sidelobe reduction of 11 dB, and a cross-polarisation sidelobe reduction of 5 dB.Introduction: For beam steering applications the single element beam steerable antennas [1][2][3] have demonstrated advantages over array antennas by reducing antenna size and eliminating the use of phase shifters, multiple antenna arrays and complex signal processing. In [3], for the first time experimental investigations were presented for a steerable square loop antenna, and with the aid of its current distribution an explanation for the formation of a tilted beam pattern was given. By using the antenna's four feeds, the tilted beam can be steered in four different quadrants. However, this antenna had the following three major limitations that restricted its implementation for modern practical applications: (i) it was a quarter wavelength thick (12 mm), (ii) it had a limited bandwidth (260 MHz) and (iii) it had radiation pattern with strong sidelobes. These limitations are overcome by deploying a novel form of high impedance surface (HIS), which is referred to as a hybrid high impedance surface (HHIS).The problems of thick substrate and limited bandwidth were alleviated by implementing one of the well-known existing HIS structures [4 -6]. However, the direct use of HIS designs (with numerous periodic vias between the HIS metal patches and the ground plane) caused radiation pattern distortion. This was due to the existence of strong coupling between the HIS vias and the square loop radiating element [7]. The via-less approach suggested in [8] is an effective solution for avoiding the via-antenna interactions, but it increases the periodicity of the HIS patch arrays which is not always desirable for portable antenna solutions. These obstacles were overcome by using the proposed hybrid HIS, which is similar to the HIS designed in [4-6] but has vias only under the outermost patches. Keeping the vias at the outer patches ensures low interaction between the antenna radiating element and the vias, which affects the purity of radiation patterns. At the same time, the vias at the edges prevent sidelobe generating surface waves from leaking out at the sides of the antenna. Thus, the hybrid HIS (via-less lattice beneath the loop and vias only at the edge) enabled the achievement of a low profile steerable square loop antenna with large bandwidth and with its radiation pattern having low sidelobes. The antenna is designed for a resonant frequency of 5 GHz with 210 dB bandwidth from 4.57 -5.22 GHz. The antenna test frequen...

For the first time, integration of a commercial single-pole four-throw RF switch with beam steerable square loop antenna is presented. By controlling the switch bias the high gain tilted beam of the antenna can be steered electronically in all the four space quadrants. A model of the complete integrated switch with the antenna has been developed and simulated. Further, for achieving distortion-free patterns and errorfree simulation comments are made on the placement of the RF switch and associated meshing considerations. For the test band (4.3 -5.0 GHz) the antenna generates a steerable tilted beam with a directivity of 8.0 dBi + 0.4 dB.

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A patch antenna array with beam steering capability in one dimension for 60 GHz applications is presented. In this array the phase shifters are liquid crystal based meander lines, each providing a maximum differential phase shift of 38°. The array elements (the patch antennas) are coupled to the microstrip feed line through coupling gaps. These gaps are adjusted in order to uniformly excite the antenna patches. The final design comprises of a 4 × 1 patch array, which is able to scan up to 9° in the E-plane as the bias on the liquid crystal changes from zero to saturation voltage.Index Terms -Liquid crystal (LC), phased arrays, millimeter-wave phase shifters.