Ultra-wideband dielectric resonator antennas for communication and microwave imaging applications

Since the Federal Communication Commission (FCC) allowed the 3.1-10.6GHz unlicensed band for UWB communication, Ultra-wideband (UWB) systems have attracted great attention in the wireless worldwide because of their advantages, including high speed data rate, extremely low spectral density, high precision, low cost, and low complexity.;As in the case in conventional wireless communication systems, antennas play a very crucial role in UWB systems. However, there are more challenges in designing a UWB antenna than a narrow band one. UWB antennas should have sufficient impedance bandwidth, and in some cases it is required to have band-notch characteristics to avoid interference with other bands for the communication system. For radar and sensor applications it is required to have constant group delay to achieve better pulse shape for the microwave signal.;Here we show several promising UWB antennas to overcome several difficulties. The interference problem of the wireless communication systems is resolved by adding strip(s) to a UWB antenna, which can control not only the rejection frequency as well as the width of the band-notch. The efficiency problem of UWB antennas is resolved by using a Dielectric Resonator as a radiating element, because DRAs provide higher than 98% radiation efficiency. The radiation pattern problem of the monopole UWB antennas is also solved by the characteristics of the DRA, because there are no edge currents as in the printed antennas. Also, the volume characteristic of DRAs provide small size at the expense of the thickness compared with the printed antennas, because the maximum path length in a certain direction can be reduced to the other introduced direction. To solve the radiation pattern problem of the UWB DRA with broadside pattern, we introduce a gap between the DR and the ground plane edge to make balanced the electric field between both sides, and eliminate some disordered field at two spots that affect the radiation patterns. Therefore, we removed the dielectric materials from these spots to shift the resonant frequency of these modes far away from our frequency band of interest and to leave a well structured higher order field distribution.;Due to very good characteristics of the UWB DRA with broadside pattern such as the high antenna efficiency, nearly constant gain, consistent radiation pattern, compact size, and very low variation of the group delay, we apply this sensor to the breast tumor detection for proving the performance in a radar sensor application. Our sensor provides very wide half power beamwidth, so that it can scan whole breast even if the location of the sensor is close to or in contact with the breast skin. Also, the compact size of our proposed sensor allows a large number of sensors to be placed around the breast. In addition, the small variation of the point source makes a very compact image of the breast tumor.