Low profile fully planar folded dipole antenna on a high impedance surface Abstract-A fully planar antenna design incorporating a high impedance surface (HIS) is presented. The HIS is composed by a periodic array of subwavelength dogbone-shaped conductors printed on top of a thin dielectric substrate and backed by a metallic ground plane. First, the characteristics of a dipole over PEC or PMC layers, a dielectric slab, and the HIS are compared and studied in detail, highlighting the advantages provided by the use of the HIS. Then, the design of a low profile folded dipole antenna working at 5.5 GHz on top of the HIS is described. The surface provides close to 6% antenna impedance bandwidth and increased gain up to 7 dBi, while shielding the lower half space from radiation. The antenna structure comprises three metal layers without any vias between them, and its overall thickness is . The dipole is fed by a balanced twin lead line through a balun transformer integrated in the same antenna layer. A prototype has been built and measurements confirming simulation results are provided.Index Terms-AMC ground plane, artificial magnetic conductor, artificial magnetism, artificial substrate, impedance surface, low profile antenna, metamaterials, reflection phase.
Ferroelectric materials (FEM's) are very attractive because their dielectric constant can be modulated under the effect of an externally applied electric field perpendicular to the direction of propagation of a microwave signal. FEM may be particularly useful for the development of a new family of planar phase shifters which operate up to X X X-band. The use of FEM in the microwave frequency range has been limited in the past due to the high losses of these materials tan = 0:3 at 3 GHz is typical for commercial BaTiO 3 (BTO) and due to the high electric field necessary to bias the structure in order to obtain substantial dielectric constant change. In this paper, how a significant reduction in material losses is possible is demonstrated. This is achieved by using a new sol-gel technique [1] to produce barium modified strontium titanium oxide [Ba10xSrxTiO3 (BST)], which has ferroelectric properties at room temperature. Also demonstrated is how the use of thin ceramics reduces the required bias voltage below 250 V, with almost no power consumption required to induce a change in the dielectric constant. A phase shift of 165 was obtained at 2.4 GHz, with an insertion loss below 3 dB by using a bias voltage of 250 V. Due to the planar geometry and light weight of the device, it can be fully integrated in planar microwave structures.
In this paper, we present a theoretical analysis on the gains offered by a reconfigurable Multiple-Input MultipleOutput (MIMO) system using Orthogonal Space-Time Block Codes (OSTBCs) and reconfigurable antennas at the receiver only. The proposed system using reconfigurable antennas selects the optimal radiation state of the receive antennas in which the receive Signal-to-Noise Ratio (SNR) is maximized. The theoretical findings show that under certain channel propagation conditions and using an appropriate codification and power allocation of the transmitted signal, the diversity order of the proposed reconfigurable MIMO system is given by the product of transmit and receive antennas as well as the number of reconfigurable radiation states of the receive antennas. The impact of correlated radiation states and imperfect channel estimation are also considered. The geometrical and physical constrains of reconfigurable antennas are also taken into account through the concept of antenna group. Assuming an ideally scattered NonLine-of-Sight (NLOS) flat Rayleigh channel, the antenna design criteria is given. Finally, we evaluate the theoretical findings through simulations on the array gain, bit error rate and ergodic capacity, where the detrimental impact of channel estimation is observed.
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