Hierarchical sinuous-antenna phased array for millimeter wavelengths

TL;DR

This paper introduces a hierarchical sinuous-antenna phased array for millimeter wavelengths that achieves wideband, dual-polarization sensitivity with approximately frequency-independent beam widths, enhancing telescope coupling and broad-band sensitivity.

Contribution

The paper presents a novel hierarchical phased array design with three levels of triangular arrays, enabling constant beam width across a 3:1 bandwidth, and discusses its fabrication, measurement, and potential applications.

Findings

Prototype device achieves near frequency-independent beam widths.

Array design improves coupling to telescope optics.

Broadband hybrid simplifies multichroic focal plane design.

Abstract

We present the design, fabrication and measured performance of a hierarchical sinuous-antenna phased array coupled to superconducting transition-edge-sensor (TES) bolometers for millimeter wavelengths. The architecture allows for dual-polarization wideband sensitivity with a beam width that is approximately frequency-independent. We report on measurements of a prototype device, which uses three levels of triangular phased arrays to synthesize beams that are approximately constant in width across three frequency bands covering a 3:1 bandwidth. The array element is a lens-coupled sinuous antenna. The device consists of an array of hemispherical lenses coupled to a lithographed wafer, which integrates TESs, planar sinuous antennas and microwave circuitry including band-defining filters. The approximately frequency-independent beam widths improve coupling to telescope optics and keep the the sensitivity of an experiment close to optimal across a broad frequency range. The design can be straightforwardly modified for use with non-TES lithographed cryogenic detectors such as kinetic inductance detectors (KIDs). Additionally, we report on the design and measurements of a broadband 180-degree hybrid that can simplify the design of future multichroic focal planes including but not limited to hierarchical phased arrays.