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In the recent years, there has been iterative advancements in the field of mobile handheld devices that can flexibly support various multi-functionalities. The decreasing handset size and restriction in space due to various other integrated components in a mobile device, increases the demand for small antennas with multi-band capability. This makes quarter–wavelength internal antennas preferable candidates in hand-held devices. Several techniques are proposed in literature to obtain reduced patch size by quarter wave length operation, such as use of a shorting pin [1-3], shorting wall or partially shorting wall [4-6]. A classic shorted patch antenna is a microstrip patch antenna having a short connecting the ground plane and top radiating patch. The short can be a pin at a suitable location or a plate that fully or partially covers the plane, where the electric field of the resonant mode is zero. This decreases the resonant length by half compared to a regular patch, thus reducing the area by a factor of four for the same aspect ratio. The structure of PIFA is similar to a shorted rectangular microstrip patch antenna with air as dielectric [7-9]. Both these are thus λ/4 resonant structures that are small, conformal, and low profile compared to the conventional microstrip patch antenna leading to a smaller patch size for fixed operating frequency. However the suitability and performance of these antennas may vary due to structural differences. The paper attempts to experimentally study the feasibility of implementing these antennas in modern cellular devices.
For this, initially, a triple –band, Planar Inverted-F Antenna (PIFA) and shorted patch antenna (SPA) that work in the same communication bands were designed and optimized, and then the various structural and performance parameters of these antennas like compactness, return loss, radiation pattern, gain and Specific Absorption Rate are analysed to understand the difference. To model and simulate the antennas, CST microwave studio is used. The final configuration of these antennas were developed after several simulations and optimization processes. CST Microwave Studio is a specialized tool for 3DEM simulation of high frequency components. It enables fast and accurate analysis of high frequency (HF) devices such as antennas . For biological simulations and SAR calculations, Specific Anthropomorphic Mannequin (SAM) phantom head model provided by CST MWS is used. The SAM phantom head model is composed of two layers namely an outer shell and a homogenous fluid inside it, which is capable of simulating the characteristics of the biological tissues. Prototype of these antennas were also fabricated and its performance parameters were measured except SAR Practical SAR measurement require sophisticated analytical instruments and facilities, which makes the measurement difficult. Hence SAR values for the proposed antennas, in the presence of SAM phantom head model with the handset in speaking position averaged over l0 g and 1g of tissue were computed using CST Microwave Studio. Since the experimental analysis of other parameters exhibit similar results in simulation and experiment, it is assumed that the SAR values will also yield similar results. Finally the results were analysed to understand the practical feasibility of these antennas in modern handsets.
How to Cite
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