Noise performance of a phased-array feed composed of thick Vivaldi elements with embedded low-noise amplifiers

Phased-array feeds (PAFs) can provide multi-beam capability for reflector antennas at microwave bands. For radio astronomy applications it is critical that the effective noise temperature of the PAF system be as low as practicable to be competitive with more conventional optimised single-beam systems. We describe our efforts to reduce the noise of a Vivaldi-element array by three means. The first is increase the thickness of the element to 5 mm, thereby increasing the surface area of the element, reducing surface current densities, resulting in lower resistive loss. The second is to eliminate dielectric materials wherever possible, enabled by the self-supporting nature of this design. Lastly, having thick elements permits low-noise amplifiers to be embedded within the antenna element, eliminating the lossy transmission line link between the LNA and the element feed point. To demonstrate these improvements a 41-element array has been constructed with an analogue beamformer to combine the central 9 elements. Y-factor measurements using free-space hot and cold loads show a minimum array noise temperature less than 35K.