Uwb microstrip antenna design for microwave imaging systems

In this thesis, an UWB microstrip antenna is designed which can be used for microwave imaging applications such as breast cancer detection. Detection of cancerous tissues can be possible because of the difference between electrical properties of normal tissues and cancerous tissues. A high gain UWB antenna can be used for this application. Microwave imaging, which is the application of microstrip antenna utilizing ultra-wide band frequency range, is low cost and effective compared to others, which makes it more popular amongst other techniques that involve heavy machinery, which cost a lot, such as MRI. Microwave imaging is sensitive in detecting most of the affected tissues. Ultra-wide band devices, as explained by Federal Communication Commission (FCC) in 2002, are devices that have fractional bandwidth of at least 25% or operating frequency range of 1.5 GHz or more. In the beginning, we described the basics of patches and their types with detail in terms of technical information. There are several types of antennas such as dipole, array, and reflector antennas, but we focused on the special type of antennas known as microstrip patch antennas. Important parameters of antennas such as return loss, voltage standing wave ratio, and gain help to understand the radiation characteristics of antenna. Return loss is the power loss in the signal, which is reflected back because of the lack of coherence in the transmission line, while voltage standing wave ratio is the coefficient of return loss. Comparatively microstrip antennas have many advantages over other antennas in terms of efficiency, size and cost. Microstrip antennas consist of a radiating patch mounted on one side of the dielectric substrate and grounded on the other side. Radiating patch is fed with different techniques such as microstrip feeding line, coaxial probe, aperture coupling and proximity coupling. These techniques are categorized either contacting or non-contacting. Microstrip feed line is commonly used because of easy fabrication while impedance matching can be improved by size and position of feed line. Proposed antenna consists of a radiating patch on one side of substrate while ground on the other side. Substrate used in proposed antenna is FR4 with the thickness of 1.6 mm having relative permittivity, ε_r of 4.4 and loss tangent, δ equals to 0.02. Frequency range is in between 2.01 GHz to 7.64 GHz having a Fractional Bandwidth (FBW) of 116%. Antenna is using low cost low profile substrate with length of 38 mm and width of 40 mm. In short, a very compact design is created for ultra-wide band applications. Reducing the size of antenna affect the performance of antenna such as; varying thickness affect the bandwidth of antenna. Radiating patch consist of rectangular shape patch having length and width of 23.5 × 12 mm2. Stub is introduced to enhance the radiation efficiency and electric field distribution in the patch. Microstrip feed line is used to provide 50Ω impedance. Antenna can provide better gain of 9.40 dB, which is considerably a good result for microwave imaging purpose. High frequency structural simulator (HFSS) is used to design and analyze the structure of antenna.