Transmitting Array for an Electronically Switched Microwave Breast Imager

A transmitting (Tx) array comprising $16\times 16$ shielded slot-antenna elements realized on printed circuit board (PCB) technology is proposed. The array is designed for an electronically switched microwave compressed-breast imager operating in the frequency range from 3 to 8 GHz. The element area is only $12\times 12$ mm2 with the mutual coupling being below −20 dB and the element return loss being better than 10 dB. The seamless interconnect between the high-density array and the radio frequency (RF) feed network becomes possible due to the innovative use of low-cost high-speed vertical board-to-board connectors (common in computer technology) instead of coaxial connectors. The array can be easily reconfigured to operate in switched or simultaneous transmission regimes by pairing it with the respective RF feed network PCBs inserted in the vertical connectors. Here, we present two such networks: 1) for simultaneous transmission from all array elements (power-splitting feed network) and 2) for transmission from one antenna at a time (RF-switched feed network). The performance of the array and the RF feed networks is verified through simulations and measurements. The benefits of a tissue-matched buffer layer between the array and the compressed breast are demonstrated to render the antenna impedance match insensitive to the dielectric properties of the breast tissue and to enhance the uniformity of the incident-field magnitude distribution. We also investigate the specific absorption rate (SAR) distribution in the breast tissue under conditions of simultaneous or single-element illumination and provide means to compute the input power levels that ensure compliance with safety regulations.