Viktor Mattsson and Sebastian Ekman, Electrical Engineering

Abstract:
The satellite communications industry is evolving rapidly and has seen a lot of re-newed interest as of late, especially with the advent of the Starlink, OneWeb and Telesat constellations. There is thus a considerable need for well designed ground-based terminals to utilize the opportunity provided by the satellites. Many of these satellites are situated in low Earth orbit (LEO) and thus require that terminal antennas have the possibility to track the constantly moving satellites. This can be done fully electrically through beam scanning or fully mechanically through rotors and gears in conjunction with a fixed beam antenna. 

This work covers a compromise between these two options by presenting the design of a feed network for a 1D beam scanning array antenna. The electrical scanning in 1D can be complemented by a rotating mechanical system to cover the other dimension (though this is not covered in this report). The advantages include a quadratic reduction in beamformer chips as well as offering a compact design with fewer bulky mechanical components. The feed network is built using ridge gap waveguide technology, with the exception of a small microstrip line section to connect beamformer chips, to obtain low losses at Ka-band. The feed network utilizes a combination of the corporate feed and series feed to obtain a spatially efficient solution. To create this network, a vertical microstrip to ridge gap waveguide power divider and a vertical ridge gap waveguide power divider has been created, as well as a center fed series slot array antenna. The antenna columns are adequately spaced to avoid grating lobes for the 8 element case in order to have some margin while also allowing the design of a 40 x 8 element prototype suitable for manufacturing. 

The results show that a compact 40 x 32 element linearly polarized antenna with the possibility of 1D beam scanning can be created with low loss using primarily gap waveguide technology. Future improvements include extensions to dual band operation, the addition of circularly polarized antenna element as well as the manufacturing of a prototype for verification.