izvorni znanstveni rad
Recent progress on cellular systems, personal communication systems and wireless local loop systems, has increased the need for new antenna designs. High-performance radiation and impedance characteristics are required in wider operating frequency bands than in earlier designs. Therefore both uplink and downlink antennas undergo a lot of innovations, modifications and performance improvement.
This paper reports some new designs and results for wireless antennas, which have been done at the University of Zagreb in cooperation with the Chalmers University of Technology in Gothenborg and Dr. Tuli Herscovici. In all designs the numerical analysis is utilized in which G1DMULT algorithm was used to calculate the Green's functions of planar and cylindrical multilayer structures in spectral domain.
Firstly, we present a broadband planar probe-fed stacked patch structure for circular polarization. Typically, microstrip antennas for circular polarization lack on small bandwidth. This is due to inherently small axial ratio-bandwidth of a single patch element. The procedure of adding a parasitic element over the driven patch in order to enhance the bandwidth, usual in linearly polarized wideband patches, is investigated in the case of the circular polarization. The results show that this approach may be applied for circularly polarized structures as well. For achieving good performances, the optimization of the antenna parameters was performed using the hybrid optimization technique, consisting of real coded, steady state genetic algorithm and modified Newton method routine. The antenna is modeled using the Method of Moments in Spectral domain. In the following section the description of the antenna design, cost function and optimization procedure is given.
In addition, two conformal cylindrical structures are analyzed. The first one is wrapped-around stacked patch antenna. This is a modification of the single patch version with increased operating frequency band. The second one is a microstrip patch array on cylindrical multilayer structure.
antenna; stacked patch antenna; wrapped-around patch antenna; antenna array; circular polarization
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