Improved Efficiency Lens-Loaded Cavity-Backed Transmit Sinuous Antenna

A dual-circular polarized dielectric lens-loaded cavity-backed four-arm sinuous antenna operating in the frequency range from 600 MHz to 2.5 GHz is proposed. The antenna is built without lossy absorber with several design aspects discussed, including substrate/lens loadings, effects of backing, and impedance match to 50 Ω. Fabricated prototype is integrated with a dual-CP beamformer network. The complete configuration is unidirectional, flush-mountable, has input , isolation > 7 dB, boresight realized gain > 3.9 dBic, boresight axial ratio 2.3 dB, and Wobble of Wave (WoW) at the 3-dB elevation cut 2 dB. Through a high power test, the antenna is shown to be capable of transmitting 200 W of CW power with a maximum temperature rise of 60 ^°C without any external cooling in the operating frequency range. Average overall efficiency of 70% is demonstrated. Two other high-power capable ferrite-tile-backed sinuous antennas are also fabricated to fully showcase unique benefits of the proposed antenna. Presented results should pave the way for the use of sinuous as a transmit antenna in many nontraditional applications requiring higher radiated powers and efficient high-quality dual-polarized patterns over wide frequency ranges.