Investigations on Ultra-Wideband Dielectric Resonator Antennas for Detection of Breast Cancer

Abstract

Microwave Imaging (MWI) is a field that uses the dielectric contrast between the healthy and malignant cells to distinguish between them using microwaves transmitted by antennas. Antennas that operate at the ISM band or UWB are basically utilized to scan the cancer affected body part and collect S parameters which are used to reconstruct the 2D/3D image of the scanned body part. Since the ultra-wideband (UWB) technology has accomplished much consideration in the recent years because of its innate advantages of large bandwidth, low power consumption and high speed, data transmissions over short distances, it is the preferred band of antenna operation for the proposed doctoral research work. Compact antennas that work on UWB technology are therefore in demand to scan the cancer affected human breast and then the collected data can be used to plot a 2D image of the scanned breast area. Therefore, this doctoral research wok presents the design and development of UWB antennas; mainly microstrip patch antennas and dielectric resonator antennas that can be used as sensors to detect the breast cancer at an early stage using Monostatic Radar based Microwave Imaging technique (MRMIT). A MRMIT technique uses a single antenna structure to transmit and receive the backscattered signals from the scanned breast area. Based upon the difference between the received reflected signals from the normal and malignant breast tissues, tumors can be identified. The S parameter data that is collected after the scan of the cancerous tissues is used to plot a dielectric profile of the scanned area. Thus this thesis presents the design and development of a stacked aperture coupled MPA and four DRAs with ultra wideband and miniaturization characteristics. Since the Dielectric resonator antennas (DRA) have advantages over microstrip patch antenna (MPA) in terms of lesser conduction losses, easy construction strategies, and flexibility in the structure to meet the required UWB behavior, they are preferred candidates for the proposed doctoral research work. The designed antennas are rotated around the heterogeneous breast phantom that is fabricated with ingredients like gelatin, petroleum jelly and wheat-flour for the different layers of skin, fat and tumor respectively at an optimized distance. The back-scattered S parameter signals from the phantom are recorded at every rotation of antenna around the phantom in both elevation and azimuthal plane. Because of larger water content in tumors, more reflections are observed in the S parameters. The recorded S parameter data is processed in microwave imaging (MWI) beam forming algorithms i.e. delay and sum (DAS), delay multiply and sum (DMAS), improved delay and sum (IDAS) etc. to reconstruct 2D images/ dielectric profile in MATLAB that identifies the position and size of the breast tumor iv inside the phantom. A summary of coverage of objectives of the research work is presented as follows: Objective 1, is covered by designing a stacked aperture coupled MPA to achieve an UWB operation 4.9- 10.9GHz (bandwidth of 6GHz) and peak gain of 6dB at a frequency of9.1GHz. The placement of the antenna around the phantom is defined using the non-linear time domain inverse algorithm. The antenna is allowed to transmit UWB pulses to the breast phantom and receive backscattered signals from it. A variation in the S-parameters results with both cases with and without the presence of tumor inside the breast phantom helps to detect the malignancy inside the breast tissues. Objective 2, is covered by proposing a compact cubical DRA with impedance bandwidth of 8.3GHz (4.3-12.6GHz) and a peak gain of 5.97dB at 12GHz of frequency for MWI of breast cancer. In simulation set up, the designed breast phantom (with and without tumor) is placed parallel to the DRA which transmits UWB pulses to the breast phantom and receives backscattered signals from it. A noticeable variation in the S-parameter results is observed for the cases of with and without presence of breast tumor that helps in detection of the breast cancer. Objective 3 has been achieved by proposing three elliptically polarized (EP) UWB DRA designs; C-shaped DRA, stair-cased DRA and rectangular DRA with Sierpinski fractal based DGS. The first antenna design consists of C-shaped DRA that achieved the UWB characteristics i.e. 3.4-10.7GHz with EP characteristics for the bands 2.9- 7.1GHz and 8.05- 10.7GHz. The second antenna design is a stair-case shaped DRA that operates from 5.1- 15GHz and also offers EP characteristics from 5.12-8.2GHz and 11.02-13.8GHz. The 3rd antenna design is rectangular DRA with Sierpinski fractal DGS that operates from 5.6- 14.2GHz frequency band with Elliptically polarized behavior at 5.6-6.38, 7.8-8.57, 9.29- 10.67 and 11.43- 12.76GHz and a peak gain of 5.8dB at 11.4GHz. The breast phantom is placed parallel to the DRAs and they are allowed to transmit and receive UWB pulses towards and from the phantom respectively .These backscattered signals are recorded by rotating the DRA around the breast phantom. A variation in the S parameter value helps in detection of tumor in the breast phantom. Objective 4, is covered by performing the image reconstruction of the scanned breast area using all the antennas proposed for the current research work. This is done by recording the variation in the S-parameter (with and without the tumor inside the phantom) and using the recorded data in different spatial beam forming algorithms to plot a 2D image of the scanned breast area. In the 1st objective, DAS algorithm is used to perform the reconstruction process v of the cancerous affected area from the measured backscattered signals that collected at different time intervals. 2D images are reconstructed from collected S-parameters and diagnose the presence of 4mm and 5mm sized maligned tumor inside breast phantom. In 2nd objective, two different beam forming algorithms: DAS and DMAS beam-forming algorithms are used to reconstruct the 2D image of ≤ 5mm breast tumor. In 3rdobjective, for the C shaped DRA antenna, recorded back scattered signals are processed with three different algorithms i.e. DAS, IDAS and DMAS for reconstruction of image for the cancerous affected area with tumor of radius 4mm. For stair-case DRA antenna design, recorded signals are processed with DAS and DMAS algorithms to reconstruct the 2D image of breast tumor of radius 4mm. Similarly, for rectangular DRA with Sierpinski fractal ground plane, DAS with coherent factor (CF) and DMAS with coherent factor (CF) algorithm have been used to reconstruct the 2D image of 5mm breast tumor. The thesis work has been organized into chapters and each chapter covers the work done under a respective objective presented in detail.