Performance Analysis of Frequency Reconfigurable Antenna Using RF MEMS

Abstract

In the present age, the development of reconfigurable multiband antennas (RMA) have great prospective for wireless communication systems and circuits to accomplish the requirement with a single compact element operating better on multiple frequencies and/or generating same/different radiation patterns. Working this way, in future a single RMA shall be able to avoid the need of multiple antennas as used in earlier and also, the present communication devices. Due to the advantage of thin profile, adaption in any shape, low constructional cost, and mass and readily available for bulk integrated circuit (IC) fabrication, microstrip antenna (MA) is suitable contenders for RMA. There are numerous switching elements options are available in market such as PIN diode, FET, varicap/varactor diode, CMOS and MEMS, which can be used to reconfigure the antenna. The prime objective towards the right choice of switching element for the antenna is that it not only has excellent electromagnetic performance but at the same time has also the advantages of micro-size as well as consumption of less power is desired. From all the available options of RF switches, micro-meter MEMS RF switch is the best in this class. Multi-functional RF MEMS is one of the key MEMS application areas that generates communication devices that have the unlimited potential to increase the performance of RF systems and circuits in addition to permitting the understanding of small size automated switches embedded in microelectronic devices. In addition, RF MEMS has the feature of fabrication through standard IC microelectronics technology which allows it’s compatibility with other RF and digital signal processing (DSP) devices. In the procedure of realizing low actuated MEMS RF switches, spring constant (k) of movable beam essentially be reduced. Design, optimization and analysis of four different proposed MEMS RF switches (includes capacitive, DC shunt, metal-contact, and cantilever film bulk acoustic resonator) are presented to achieve low pull in voltage, current and power consumption as well insertion loss and high isolation. Aforementioned optimized switches are than integrated on three different MAs (includes swastika-shaped, hexagonal fractal and spiral-shaped) for converting into RMA and their electromagnetic post processing characteristics are analyses in next preceding section of thesis. Testing and simulated results of RMAs are also compared and displaying comparatively good agreement with respect to each other. For complete designing of the RMA structures, the whole methodology is divided into three steps. In first step, to design and study the proposed MEMS switches characteristics, a commercial multi-physics solver, Coventorware (ver. 2010) is used. In second step, the electromagnetic properties and optimization of MEMS switches is done with the help of EM solver Ansoft HFSS. Optimization algorithms preferred in this work are artificial neural network (ANN), pattern search (PS) and quasi-newton (QN). All these optimization techniques are compatible with HFSS simulator. The parametric analysis of some proposed switches is also performed in EM solver and later on for optimization purpose; its S-parameter results used as an input values of presented ANN model. The advanced ANN algorithm scheme permits the optimization explanations of the MEMS switches to be supported by exchanging repetitive simulations and also be responsible for reduced processing times whilst still keep in mind a unlimited accuracy as related to traditional mathematical formulation. Further, the actual equivalent circuit of proposed MEMS structures is produced by means of HSPICE model file. The HSPICE file from HFSS is exported in advance design system (ADS) RF simulation tool to generate lumped RLC components, validate the results through equivalent circuit and layout approach. In third step, multiband MA is analysed for EM characteristics for RMA. Antenna is fabricated by photo-lithography technology and RF switches are integrated on it for proof of concept. Finally, RMA is tested using vector network analyzer (VNA) in ideal aneochic chamber condition. The proposed MEMS switches and RMA results presented in this work are broadly and well-studied in the frequency range of 1.0 to 10.0 GHz. Talking about the presented MEMS switches in aforementioned frequency range, lowest pull-in voltage recorded is 0.70 V for serpentine beam. The lowest insertion loss is measured as 0.1 dB again for serpentine beam and highest isolation is 79.8 dB for fixed beam. All switches display negligible power consumption. The results of all three RMAs realizing fairly normalized omni-directional radiation patterns and also presenting well-behaved linearly polarized performance in all possible switching states. The proposed spiral-shaped RMA showing wide bandwidth ranging from 200 MHz to 1.65 GHz at different multiband indicates device contribution in enhancing the mobile TV and internet application speed. Different MEMS switches have been proposed in this dissertation are mainly divided into four categories and useful for reconfigurable microstrip device applications. The proposed RMAs are designed to cover all the current as well as upcoming wireless and portable communication bands as frequencies lying between 1.5 to 7.5 GHz.