Design of a Six-band, 2.4-Octave (80--420 GHz) Hierarchically Summed Phased-Array Slot-Dipole Antenna Array for NEW-MUSIC

TL;DR

To enable six-band polarimetry in the trans-millimeter regime, the paper presents a broadband, hierarchically summed phased-array of slot-dipole antennas with integrated lumped-element low-pass and band-pass filter banks for NEW-MUSIC. The approach uses a three-scale hierarchy (level-0 16×16 fundamental, level-1 and level-2 aggregations) to coherently sum signals and define six bands, implemented with Nb microstrip routing, $\alpha$-Si:H dielectric, and KID readout. Through detailed LPF and BPF design and careful layout to minimize parasitic coupling, the authors achieve an overall transmittance greater than $80\%$ across all bands. They outline a path toward a four-pixel test device and a $4\times4$ array for deployment on NEW-MUSIC (planned for 2027), enabling multi-band, time-domain studies and Sunyaev-Zeldovich–effect observations of hot plasmas and dusty galaxies.

Abstract

The Next-generation Extended Wavelength Multi-band Sub/millimeter Inductance Camera (NEW-MUSIC), located on the Leighton Chajnantor Telescope (LCT), will be the first six-band trans-millimeter wave polarimeter. This paper proposes a broadband, hierarchical phased-array antenna with integrated band-defining filters necessary to realize NEW-MUSIC. It covers a spectral bandwidth of 2.4 octaves from 80~GHz to 420~GHz, a frequency range ideal for studying trans-millimeter emission from a range of time-domain sources, using the Sunyaev-Zeldovich effects to study hot plasmas in galaxy clusters and galaxies, and to observe dusty sources, from star-forming regions in our galaxy to high-redshift dusty, star-forming galaxies. To achieve these goals, three groups of superconducting lumped-element on-chip low-pass/band-pass filter-banks were designed to hierarchically sum the superconducting, broadband, non-resonant, slot-dipole antenna arrays and band-pass filter the trans-mm light before outputting it on microstripline to detectors (KIDs in the case of NEW-MUSIC).

Figures (8)

• Figure 1: (a) A level 0 (fundamental) element of our hierarchical antenna, composed of 16 slots each with 16 feeds. (b) The radiation efficiency of the our hierarchical antenna overlaid with the typical atmospheric transmission on the Chajnantor Plateau for 1 mm precipitable water vapor (PWV) from the ATM model*. The efficiency is for an infinite array of slot antennas without bandpass filters but accounts for the backshort and anti-reflection treatment. (c) The real and imaginary parts of the antenna's impedance ($Z_{out}$) as a function of frequency.
• Figure 2: The schematic of the three-scale hierarchical antenna pixel design with 6 bands. Each square unit represents a 16 × 16 fundamental element (level-0)l and each "FbX" represents a filter-bank. Of the four elements of a level 1 group, the left ones match the schematic in Fig. 1(a) while the right ones have been mirrored through a vertical line so the summing tree exits to the right, not the left. (There is no mirroring through a horizontal line because that would cause a $180^\circ$ phase shift of the feed excitation.) Fb1 consists of LPF1234 (316 GHz), BPF5 (335-360 GHz) and BPF6 (390-411 GHz). Fb2 consists of LPF12 (175 GHz), BPF3 (201-246 GHz) and BPF4 (270-310 GHz). Fb3 consists of BPF1 (77.5-106 GHz) and BPF2 (133.5-172.5 GHz). The transmission lines of the filter-banks extend to the edge of the hierarchical antenna.
• Figure 3: The LP filter designs. (a) Lumped-element schematic. (b) L12 layout showing meandered inductors and shunt capacitor top plates. The inductors sit in holes cut out of the ground plane, while the shunt capacitors' other plate is the ground plane. (c) L1234 layout. (d) Power transmittance ($|S_{21}|^2$) calculated for lumped-element circuits and from Sonnet for the physical layouts, after adjusting the shunt capacitor values as described in the text.
• Figure 4: Transmittance calculated in Sonnet for optimized 3rd-order and 5th-order bandpass filter designs for B5 and B6. The narrow atmospheric windows necessitate sharper cutoffs than for B1--B4, which use 3rd-order filters.
• Figure 5: Steps for 5th-order BPF design, based on IEEEtas2009. (a) 5th-order (5 element) Chebyshev LPF prototype. (b) Transformation of LPF into BPF by replacing series inductors and shunt capacitances with, respectively, series and parallel LC networks. (c) Replacement of shunt inductors with impedance inverters for fabrication simplification. (d) Absorption of inverter capacitors into series capacitances. (e) Replacement of single series capacitances by dual series capacitances for fabrication simplification.