Beam Steering Performance of an X-Band Offset Parabolic Cylindrical Reflector Fed by Triple-Mode Horn Integrated With Risley Prism and Phase Correcting Dielectric Lens

In this article, a broadband 1-D high-gain beam steering solution to steer sum and difference patterns for tracking the optimum common scatter volume of troposcatter links at ${X}$ -band is presented. The novel steering arrangement consists of a $D = 70$ cm offset parabolic cylindrical (OPC) reflector fed by a triple-mode circular waveguide (TM-CW) horn antenna integrated with a two-element dielectric wedge-based Risley prism and a parabolic phase correcting dielectric lens (PCDL). The proposed hybrid beam steering reflector-feed obviates the need for complex 3-axes based gimbals to mechanically steer the conventional reflector-feed assembly. In the proposed hybrid reflector-feed arrangement, steering is achieved using a simple axial rotation of smaller Risley prism components at the feed. The broadband high-gain attribute required for an efficient troposcatter link is achieved by the proposed hybrid reflector-feed with much smaller and compact moving parts compared to traditional axial rotation-based mechanical steering arrangements. The simulated gain of the proposed antenna operating in TE11 mode at broadside is 25.7 dBi. A prototype of the proposed beam steering solution is built and tested in an anechoic chamber. The OPC reflector prototype is made of lightweight composite carbon fiber/fiber glass material thus reducing the overall antenna assembly weight. Experimental results show close agreement with the simulated ones. All three modes of TM-CW horn are steered by ±19° with TE11 mode patterns showing scan losses lower than 1 dB. The measured null depths for TM01 and TE21 modes are lower than −23 dB at 10 GHz. The peak of the sum and the nulls of the difference patterns are separated by a minimum difference of 25 dB at 10 GHz.