Investigations on frequency agile behavior of narrowband and wideband microstrip patch antennas by employing variable height ground planes

Title from first page of PDF file (viewed September 9, 2010)Includes bibliographical references (p. 80-82)Microstrip patch antennas have been studied and designed extensively over the years which find many applications in wireless communications, satellite communications and radar applications. These antennas have features such as simple, robust, low profile, cheaper and versatile for various modes of operations. However, the patch antennas are inherently narrow band, hence require wide-bandwidth and/or frequency agile property in order to meet the need of modern wireless communications applications. This thesis presents investigation results on the effect of employing variable height ground plane and copper ribbon switches on the frequency agile behavior of wideband microstrip patch antenna. The effect of ground plane height variation not only alters operating frequency, but also, Gain and impedance bandwidth. First a narrow band patch antenna and its array configuration will be studied for its frequency agility and far-field performance by varying the ground plane, followed by the proposed wideband patch antenna, which is basically a U-slot loaded modified E-shape microstrip patch antenna (USLMES). The narrowband patch antenna achieves 33% frequency agility which increases to 43% for the array configuration. The proposed USLMES antenna is excited using the notch feed mechanism by a 50 [upper case omega] coaxial probe outside the patch surface so that coaxial probe does not contribute significantly to the peak-cross-polarization levels. The parametric study results are presented for the wideband patch antenna design and important parameters have been noted. The proposed wideband patch antenna offers impedance (S11 = -10 dB) and 3dB gain bandwidths of at least 35% (3.09GHz to 4.42GHz) and approaches 38% (3.09GHz to 4.59GHz) based on experimental measured data with stable radiation patterns and acceptable cross-polarization levels. Frequency agility is also achieved from 3.02GHz to 4.95 GHz by turning different combination of copper ribbon switches ON/OFF in the later part of the thesis. The prototype antennas were fabricated and experimentally verified for both frequency agility and wideband patch performance verifications. The simulated performance is in reasonable agreement with the measured results. The proposed wideband microstrip patch antenna can be used as the radiating elements in base station applications