| Abstract: |
The principal contributions of this study include the design, fabrication, and analysis of a new compact wideband overlapped patches microstrip antenna. In this design the bandwidth of a single layer microstrip patch antenna is enhanced by using multi-resonance technique without significantly enlarging the size of the proposed antenna. In this work the validity of the design concept is demonstrated by two examples with 51.4% and 56.8% bandwidths.In The first example multiple resonances are achieved by overlapping three square patches of different dimensions along their diagonals to form a non-regular single patch, but in the second example a slot is incorporated into this patch to expand its bandwidth, the second antenna has been designed, fabricated, and measured. Good agreements have been found between the calculated results and the experiments.These two antennas provide stable far field radiation characteristics in the entire operating band, with relatively high gain. The effects of the substrate thickness and the dielectric constant of the substrate on the bandwidth havebeen studied in this work.It has been found that, in order to obtain a wideband microstrip patch antenna with good efficiency, a thick substrate with a very low dielectric constant should be used.The feeding technique utilized in this design is the coaxial probe-feed. The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the patch in order to match with its input impedance. This feed method is easy to fabricate and has low spurious radiation. Such antenna configurations are very useful in the wireless communications industry.To simulate these antennas The FIDELITY simulator which is FDTD based has been used. The obtained results from FIDELITY have been compared to other results produced using IE3D a commercial simulator based on the method of moments and good agreements have been found.It has been found that, when properly implemented, FDTD analysis of different shapes of antennas produces results for near-fields, far-fields, return loss, and input impedance that agree very well with published experimental data. FDTD method has a powerful ability to provide, in straight forward manner, results of antenna structures performance over a wideband of frequency. This robustness allows the use of the FDTD method to confidently test proposed novel antenna designs on the computer before they are built.In this thesis the FDTD method has been used to characterize several forms of wideband microstrip patch antennas such as rectangular, circular, and annular ring patch antennas. The time domain response, the return loss, the input impedance and the radiation patterns of these patch antennas are obtained.Another major contribution is the design and analysis of a new circularly polarized wideband probe-fed microstrip patch antenna with capacitive feed mechanism. this antenna consists of two small probe-fed rectangular patches, which are capacitively coupled to the radiating element. The proposed antenna is designed to achieve three targets; wide bandwidth up to 27 %, perfect matching at the input (Zin ? 50 ohms), and circular polarization at resonance. This antenna is designed to operate at 1.8 GHz so it is applicable to Personal Communication System (PCS) which uses the frequency range from 1850-1990 MHz. One can claim that this is the first time to achieve and realize a microstrip antenna to satisfy the mentioned three targets together.It has been found that, the FDTD method has a major disadvantage which is that it simulates structures in the time-domain. This requires a large memory storage and large run-times. However, this problem can be reduced by using modern powerful computers.It has been found that, the type of feeding and the position of the feeder affect greatly the value of the resonance frequency. For nonsymmetrical shapes of patch fed with coaxial probe, different values of resonance frequency can be obtained through different positions of probe which may be useful to design a smart antenna by varying the feed point using an appropriately designed feed network
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