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 GHz to 8 GHz, where reflection loss better than 10 dB and inter-element mutual coupling less than –20 dB are achieved. The center-to-center element spacing is 12× 12 mm. A low-noise amplifier (LNA) is integrated with each antenna element for use in a receiving configuration. A ground plane within the multi-layer 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.

A transmitting (Tx) array comprising 16×16 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 GHz to 8 GHz. The element area is only 12×12 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: (i) for simultaneous transmission from all array elements (power-splitting feed network) and (ii) 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.

We present the design and the performance evaluation of a new interconnect for large-scale densely packed electronically scanned antenna arrays that utilize a high-speed digital board-to-board vertical connector. The application targets microwave tissue, imaging in the frequency range from 3 GHz to 8 GHz. The tissue-imaging arrays consist of hundreds of active antenna elements, which require low-reflection, low-loss, and low-crosstalk connections to their respective receiving and transmitting circuits. The small antenna size and the high array density preclude the use of coaxial connectors, which are also expensive and mechanically unreliable. Modern board-to-board high-speed connectors promise bandwidths as high as 12 GHz, along with high pin density, mechanical robustness, and low cost. However, their compatibility with the various transmission lines leading to/from the miniature printed antenna elements and microwave circuitry is not well studied. Here, we focus on the design of the transitions from coplanar waveguide transmission lines to/from a high-speed vertical connector. The performance of the interconnect is examined through electromagnetic simulations and measurements. Comparison is carried out with the expensive sub-miniature push-on sub-micro coaxial connectors commonly used in miniature radio-frequency electronics. The results demonstrate that high-speed vertical connectors can provide comparable performance in the UWB frequency range.

When I received Francesca’s invitation to contribute to the “Women in Engineering” column in IEEE Antennas and Propagation Magazine , my first thought was that I was not cut out for nontechnical writing. Inspiration and excitement come easy when you report “to the world” that you found a solution to an important problem. But talking about my professional experience…well, that, I am afraid, could be somewhat boring.

A broadband wide-angle absorbing structure for the non-reflective termination of tissue is proposed for enclosures needed in microwave tissue imaging. A prototype consisting of 10 × 10 unit cells is fabricated and experimentally tested using breast-tissue phantoms. Through simulations and measurements, it is demonstrated that the proposed absorbing structure achieves a reflection coefficient better than −20 dB for TE polarization and better than −12 dB for TM polarization for incidence angles from 0° to 80° and within the frequency band from 3 GHz to 8 GHz. The design principles are delineated, enabling the development of other absorbing structures suitable for any tissue of interest. A calibration method and procedure are also developed and employed with the reported measurements, which allow for de-embedding the effect of the lossy tissue medium and extracting the intrinsic reflection coefficient of the absorber. The proposed structure demonstrates superior absorption compared to prior designs and provides a much-needed solution for the construction of non-reflective enclosures for microwave biomedical imaging applications.