A Miniaturized Wideband Sinuous Antenna for Microwave Brain Imaging Systems

In this article, a broadband, miniaturized cavity-backed sinuous antenna is presented to be utilized as an array element for microwave brain imaging (MBI) systems. The proposed antenna consists of a sinusoidal radiating patch printed on an FR4 substrate, three-strip rings on the back side, and a balun built on a Rogers 4003 substrate. The radiating section of the antenna is immersed inside a medium with a relative permittivity of epsilon(r) = 40 and a conductivity of 0.55 S/m to improve the matching between the antenna and the brain tissues. The broadband characteristic of the antenna is achieved by connecting the radiating patch to the backside strip rings with three pairs of shorting vias. The first pair of via holes creates additional frequency resonances at 2.55 and 3.45 GHz; by plugging the second one of via holes, the lower and higher bands of frequency response in the antenna are improved at 1.95 and 3.7 GHz, respectively. Finally, by combining the previous pair of via holes and the third one of via holes, additional frequency resonances at 1.88, 2.39, 2.8, and 3.41 GHz extend the operational bandwidth of the antenna from 1.75 to 4 GHz. The radiating section of the antenna has a compact diameter of 0.16 lambda where lambda is the minimum frequency of the operating band range of the antenna. Furthermore, the radiation characteristics of the proposed antenna were analyzed and studied near the Hugo head model, ensuring that it meets the necessary criteria for microwave imaging (MWI) systems. The suitable and well-matched simulated and measured antenna characteristics results show that the proposed antenna can be a good candidate for brain imaging applications.