Microwave resonant switched-slot probe with perpendicular coaxial feed

Development of efficient microwave real-time imaging systems is of great interest for many applications. A cost-effective design of such systems utilizes a switched transmit-receive array composed of efficient antenna elements. The utilized imaging arrays are typically planner and consist of large number of closely-spaced elements. The performance of these systems depends largely on the efficiency of the array element and its feeding structure, isolation between the elements as well as the transmit-receive isolation. Implementing the required efficient feeding and high-isolation switching, in-plane with the elements of a compact array is rather challenging at high microwave frequencies, e.g., 24 GHz. In this paper, a resonant switched slot with an out-of-plane coaxial feed is introduced as an efficient element for microwave imaging arrays. The slot is loaded with a PIN Diode and hence it is switched directly. The proposed array element design involves coupling the transmitted/received signals into/from the slot using a coaxial feed perpendicular to the plane of the slot. Two design variations of this out-of-plane feeding structure are considered here, namely; electrical and magnetic coupling. Simulation and measurement results show that high radiation and switching isolation can be obtained with these feed designs.