We present the antenna design for a radio interferometer , the Arcminute Microkelvin Imager , together with its beam pattern measurement .
Our aim was to develop a low-cost system with high aperture efficiency and low ground-spill across the frequency range 12–18Â GHz .
We use a modified cassegrain system consisting of a commercially-available paraboloidal primary mirror with a diameter of 3.7Â m , and a shaped secondary mirror .
The secondary mirror is oversized with respect to a ray-optics design and has a surface that is bent towards the primary near its outer edge using a square term for the shaping .
The antennas are simple to manufacture and therefore their cost is low .
The design increased the antenna gain by approximately 10 per cent compared to a normal Cassegrain system while still maintaining low contamination from ground-spill and using a simple design for the horn .