Large-Frequency-Ratio Dual-Band Shared-Aperture Conformal Transmit-Reflect-Array Antenna with Independent Beam Control for UAV-Based Space-Air-Ground Emergency Communication Networks

This paper proposes a large-frequency-ratio (140 GHz: 35 GHz) dual-band shared-aperture conformal transmit-reflect-array antenna (CTRA) for unmanned aerial vehicle (UAV)-based emergency communication applications. A 3×3 cascaded multilayer frequency selective surface (FSS) is designed as the low-frequency (35 GHz) ground plane while also enabling transmission of high-frequency waves (140 GHz). Subsequently, a radius-limited double-split ring is placed underneath the cascaded FSS layers to form the transmissive element (TE, defined as Unit-1). In addition, a miniaturized multilayer FSS unit is proposed as another TE (defined as Unit-2) at 140-GHz band and arranged around Unit-1 to form a full ground plane for the split ring, constituting a complete reflective element at 35-GHz band. Independent modulation of the reflection/transmission coefficients can be achieved by rotating the split ring and tuning the TE dimensions, respectively. Moreover, the joint operation of the two TEs can effectively suppress the elevated sidelobe levels caused by the larger frequency ratio. To validate the design, a prototype of the whole CTRA architecture was fabricated and measured. Experimental results have indicated the proposed CTRA exhibits a peak transmitted gain of 34.3 dBi at the 140-GHz band and a peak reflected gain of 22.8 dBi at the 35-GHz band, which demonstrates its significant potential for UAV-based space-air-ground emergency communication networks.