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A microwave brain imaging system model is envisaged to detect and visualize tumor inside the human brain. A compact and efficient microstrip patch antenna is used in the imaging technique to transmit equivalent signal and receive backscattering signal from the stratified human head model. Electromagnetic band gap (EBG) structure is incorporated on the antenna ground plane to enhance the performance. Rectangular and circular EBG structures are proposed to investigate the antenna performance. Incorporation of circular EBG on the antenna ground plane provides an improvement of 22.77% in return loss, 5.84% in impedance bandwidth, and 16.53% in antenna gain with respect to the patch antenna with rectangular EBG. The simulation results obtained from CST are compared to those obtained from HFSS to validate the design. Specific absorption rate (SAR) of the modeled head tissue for the proposed antenna is determined. Different SAR values are compared with the established standard SAR limit to provide a safety regulation of the imaging system. A monostatic radar-based confocal microwave imaging algorithm is applied to generate the image of tumor inside a six-layer human head phantom model. S-parameter signals obtained from circular EBG loaded patch antenna in different scanning modes are utilized in the imaging algorithm to effectively produce a high-resolution image which reliably indicates the presence of tumor inside human brain.

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Abstract-In this paper, three different types of graphene based tapered slot antennas are designed for ultra-wideband (UWB) applications. The taper profiles for three antenna types are linear, exponential, and constant width. A single layer graphene sheet of 35 µm thickness is used to model the radiating element and feeding structure of the designed antennas. To feed the antennas, microstrip to slotline transition technique is adopted. An approximate analytical theory based on conical transmission line model is considered to authenticate the design of graphene based tapered slot antennas. Better impedance matching over 2-20 GHz is obtained by designing a balun in the form of a radial stub. Return loss, bandwidth, radiation pattern, and directive gain are the considered antenna performance parameters. Time domain solver of CST MWS software is used to evaluate the performances of linearly tapered slot antenna (LTSA), exponentially tapered slot antenna (Vivaldi), and constant width slot antenna (CWSA). The results obtained from CST are compared with that from HFSS to further validate the design. Simulation results with extensive parametric study confirm that the novel 2-D material graphene can be considered as a promising one to model UWB tapered slot antennas. Furthermore, the effectiveness of designed graphene based tapered slot antennas is revealed by comparing their performances with other existing UWB antennas. Moreover, as a UWB application, Vivaldi antenna shows promising results in microwave brain tumor detection.