Planar Array of UWB Active Slot Antennas for Microwave Imaging of the Breast

A shielded planar array of active slot antennas is proposed for applications in the microwave imaging of the breast. The frequency band is from 3 to 8 GHz, where reflection loss better than 10 dB and interelement mutual coupling less than -20 dB are achieved. The center-to-center element spacing is 12 x 12 mm. A low-noise amplifier (LNA) is integrated with each antenna element for use in a receiving configuration. A ground plane within the multilayer design separates the antenna array from the electronics array while providing shielding from the back and improving the power coupling into the tissue. The proposed structure resolves an outstanding problem in the design of large shielded antenna arrays for tissue imaging, namely, the interconnects between the array elements and the electronic circuits, which are separated by multiple dielectric layers and a grounded plane. The critical development is the new low-reflection triple-wire vertical transition that carries the signal from the antenna layer to the electronics layer while traversing through multiple layers of different permittivities and through openings in the ground plane. The design is verified by simulations and measurements. The passive and active designs are compared, illustrating the full utilization of the LNA gain. The performance of the proposed active array is also examined in imaging experiments with a compressed-breast phantom.