A S/K/Ka Triple-Band Shared-Aperture Antenna Hybridizing Monopole Array and Transmitarray

This paper presents a triple-band shared-aperture antenna operating in the S-, K-, and Ka-bands. The antenna is based on a modified transmitarray antenna (TA) where a 2×2 monopole array (MA) is integrated into its transmitting surface (TS). In the S-band, the proposed antenna functions as the MA, while in the K-and Ka-bands, it operates as a dual-band TA. To tightly integrate the two kinds of antennas, the reflector of the MA is redesigned as a high-pass frequency selective surface (FSS), which behaves like a conventional metal sheet in the S-band and allows K-and Ka-band waves to pass through and illuminate the TS. For dual-band operation of the TA, the TS employs a multi-layered unit cell (UC), where two rectangular slots of different lengths are arranged in an interlaced form. By adjusting the slot lengths, independent phase shifts covering 360∘ can be achieved for both bands. The proposed antenna features a compact size and high gain across all three bands. In the K-and Ka-bands, it eliminates the need for a feeding network due to the spatial feeding architecture of the TA, resulting in very low feeding loss. As a proof of the concept, a prototype is fabricated and measured. The experimental results show peak gain of 11.5 dBi, 17.9 dBi, and 21.3 dBi in the S-, K-, and Ka-bands, respectively. Beam scanning ranges of ±27∘ and ±25∘ are achieved in the K-and Ka-bands, respectively. The proposed antenna could be a promising candidate for multi-band communications.