A: The literature on horn antennas dedicated to radio astronomy and satellite communications applications is very extensive and at times disjointed, relevant contributions being distributed as far back as from the 60's until the present today. This work combines a compact but complete review of the different theories, methodologies and techniques used to describe corrugations and metamaterials in their application to feedhorns used in radio astronomy and satellite communications along with some new work to help explain the theory in a more practical way. Starting with the hybrid-mode condition firstly corrugated horns are explained describing soft and hard boundaries and also the theory from a plasmonic optics point of view. Following this the use of metamaterials in order to design horn antennas with quasi-null cross-polarization and low E-Plane sidelobes level over an ultra-wideband is described. The objective of this work is to help to ease the learning curve of the post graduate students and young professionals dedicated to these tasks, and try to inspire the work of the senior professionals toward a new direction and approach.

The electromagnetic metamaterials at microwaves frequencies are well established in industrial applications nowadays. Recent research has shown that a specific kind of metallic metamaterial can contribute to improve the performance of the microwave feedhorns used in radioastronomy and satellite telecommunications. In this article, we theoretically justify this argument finding a new type of meta-ring with a record bandwidth in terms of cross-polarization, and we explore the manufacturability of these particular metamaterials, successfully fabricating a meta-ring and applying it to a novel and very compact prototype microwave antenna which covers a 2:1 bandwidth.1 The usable frequency is the centre frequency of the transmission/reception band.2 Surprisingly finding a notable electromagnetic benefit, explained in section 2.

In this article we present the Dark-photons&Axion-Like particles Interferometer (DALI), a novel experiment designed for the detection of photon-mixing cold dark matter in the microwave band between 6 and 60 GHz. DALI is a haloscope for the simultaneous search for axions, axion-like particles and dark photons, with a number of novelties that make it unique. First, it is a dark matter telescope, with a capacity for pointing, tracking and rastering objects and areas in the sky. This potentially allows one to detect relativistic dark matter particles, substructures and flows, without compromising the simultaneous scanning for dark matter relic particles present in the laboratory. Second, it has been designed using commercial technology. This will allow feasible manufacture at a reasonable cost, thereby mitigating the need for R&D and facilitating maintenance. Finally, it benefits from a high sensitivity over a broad band of frequencies with only minimal reconfiguration.