A chemically etched corrugated feedhorn array for D-band CMB observations

TL;DR

This paper introduces a scalable, low-cost manufacturing process for a 37-element corrugated feedhorn array designed for CMB observations in the D-band, demonstrating high electromagnetic performance suitable for advanced cosmological experiments.

Contribution

The study presents a chemically etched aluminum plate process for fabricating high-performance corrugated feedhorn arrays, offering a fast, scalable alternative to traditional methods for CMB instrumentation.

Findings

High repeatability in electromagnetic measurements

Excellent polarization purity with -20 dB cross polarization

Low return loss and sidelobe levels

Abstract

We present the design, manufacturing, and testing of a 37-element array of corrugated feedhorns for Cosmic Microwave Background (CMB) measurements between $140$ and $170$ GHz. The array was designed to be coupled to Kinetic Inductance Detector arrays, either directly (for total power measurements) or through an orthomode transducer (for polarization measurements). We manufactured the array in platelets by chemically etching aluminum plates of $0.3$ mm and $0.4$ mm thickness. The process is fast, low-cost, scalable, and yields high-performance antennas compared to other techniques in the same frequency range. Room temperature electromagnetic measurements show excellent repeatability with an average cross polarization level about $-20$ dB, return loss about $-25$ dB, first sidelobes below $-25$ dB and far sidelobes below $-35$ dB. Our results qualify this process as a valid candidate for state-of-the-art CMB experiments, where large detector arrays with high sensitivity and polarization purity are of paramount importance in the quest for the discovery of CMB polarization $B$-modes.