3D-Printed Reflect-Transmit-Array Antenna With Modified Transmitarray Mode for RCS Reduction

In this paper, a 3D-printed dual-band reflect-transmit-array (RTA) antenna has been presented, which operates as a reflectarray (RA) in the 28 GHz band and as a transmitarray (TA) in the 41.5 GHz band along with modified TA mode operation for radar cross-section (RCS) reduction. It consists of a metallic and a dielectric 3D-printed layers placed in close proximity to each other. The RTA comprises 316 unit cells placed across a circular aperture, where each unit cell simultaneously obtains a desired transmission and reflection phase characteristics in order to compensate for the spatial phase delay in RA as well as the TA mode of operations. A uniform transmission and reflection amplitude distribution has been assumed for design simplicity. The metallic layer consists of periodic cross-slots, whereas the dielectric layer comprises of periodic square dielectric posts. The combination of the metallic layer and dielectric layer provides reflection characteristics at 28 GHz and passband transmission characteristics at 41.5 GHz. A Ka-band pyramidal horn antenna, designed to maintain similar radiation characteristics in both the orthogonal planes, has been utilized as a feed antenna. Measured peak gain, peak aperture efficiency, 1-dB gain bandwidth (BW), and 3-dB gain BW for the RTA in the RA (TA) mode of operations are 26.6 (19.1) dBi, 40 (6) %, 32.3 (8.7) % and 51.8 (16.4) %, respectively. Further, the dielectric layer has been altered for RCS reduction in the TA mode operation while the RA mode of operation remains unaffected. An RCS reduction of up to 22.6 dB at 41.5 GHz along with a 10 dB RCS reduction BW of 6 % is accomplished. The antenna system can be highly useful for bi-directional communication, defense, radar, and low-detectable applications.