A novel feeding method for a dielectric resonator (DRA) array antenna is introduced. Unlike in a corporate feed network, power dividers or quarter-wave transformers are not needed in the new feeding scheme as the design is based on the standing-wave concept. Consequently, the feed network is greatly simplified and undesired spurious radiation in the feeding network is minimized. The simulated and measured results are in good agreement. A 3D printer is utilized where the entire array structure is fabricated as a single piece with a dielectric material of Polylactic Acid (PLA). The 3D printer provides a cost-efficient, simple and rapid manufacturing process.

In order to meet the requirements of the new generation of radio telescopes, we have developed a new topology called DYQSA, which stands for DYson Quad-Spiral Array. The design exhibits dual circular polarization in contrast to dual linear polarization of state-of-the-art feeds. It covers the required ultra-wideband (UWB) from 2 GHz to 14 GHz with an almost constant and real input impedance which facilitates the design of the feeding structure and the Low Noise Amplifiers (LNAs). Different versions are investigated for enhancing feed performance, ensuring higher aperture efficiencies and mechanical stability. Simulation results of the reflector loaded by the proposed feed show an aperture efficiency of 65 ± 5% can be achieved with a noise antenna temperature around 14 K and a System Equivalent Flux Density (SEFD) of about 1300 Jy, both averaged over the required bandwidth at zenith. Measurements of the single-element and the four-element feeds are presented. Comparisons with other state-of-the-art feeds are shown in terms of total aperture efficiencies, design adaptability to different reflectors, calibration signal injection, the required number of LNAs per feed, cost, and physical volume.

In this paper, a detailed description of the optical coupling into a Whispering Gallery Mode (WGM) resonator through a prism via frustrated total internal reflection (FTIR) is presented. The problem is modeled as three media with planar interfaces and closed expressions for FTIR are given. Then, the curvature of the resonator is taken into account and the mode overlap is theoretically studied. A new analytical expression giving the optimal geometry of a disc-shaped or ring-shaped resonator for maximizing the intra-cavity circulating power is presented. Such expression takes into consideration the spatial distribution of the WGM at the surface of the resonator, thus being more accurate than the currently used expressions. It also takes into account the geometry of the prism. It is shown an improvement in the geometry values used with the current expressions of about 30%. The reason why the pump laser signal can be seen in experiments under critical coupling is explained on this basis. Then, the conditions required for exciting the highest possible optical power inside the resonator are obtained. The aim is to achieve a highly-efficient up-conversion of a THz signal into the optical domain via the second-order nonlinearity of the resonator material.

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