Design, Development, And Deployment of Airborne and Ground-Based High-Power, UHF Radars With Multichannel, Polarimetric Antenna Arrays for Radioglaciology

This work describes the building and deployment of airborne and ground-based high-power, UHF radars from a systems engineering perspective. Its primary focus is on the design and development of compact, low-profile, polarimetric antenna arrays for these radars using a rapid prototyping methodology. The overarching goal of this effort is to aid the Center for Oldest Ice Exploration (COLDEX), a multi-institution collaboration to explore Antarctica using airborne and ground radars for the identification of a drill site to retrieve the oldest possible continuous ice record.  A multichannel  600 – 900 MHz, pulsed frequency modulated (FM) radar with up to 1.6 kW of peak output power per channel is designed and implemented. The ground-based frontend is a 16-element antenna array power-combined into a single channel per polarization in a sled platform. The airborne frontend has a 64-element fuselage-mounted antenna array power-combined into 16 independent channels and two 12-element wing arrays power-combined into 6 channels for operation on a Basler aircraft.

Three major design revisions of the antenna element design are presented. The first two design revisions of the dual-polarized, microstrip dipole antenna have the typical vertically integrated aperture-coupled microstrip baluns. The third and newly proposed design is a near-planar, integrated feed which combines a 2-sided microstrip balun board (one balun for each polarization) and a custom 6-layer balanced-to-balanced feed board. A microstrip matching network 2-layer board with two order-4 LC-filters is directly connected using micro-coaxial (MCX) connectors. The total antenna height of the proposed design is reduced by nearly one-third relative to the first two design revisions while improving electrical performance.

A novel methodology for efficient wideband tuning of the active impedance of the elements of an antenna array using lumped components is demonstrated. The goal of the method is to achieve >10 dB active return loss with a single order-4 LC-circuit for all four  power-combined channels of the 16-element antenna array with minimal iteration loops. It combines the simulation and measurement spaces at different stages to account for platform scattering, mutual coupling, and non-ideal behavior of the lumped components and circuit board parasitic effects in the UHF range.

Each antenna array design is fed using 1:2 and 1:4 microstrip, Wilkinson high-power dividers. Two major design revisions of the high-power divider are presented. The first design has three implementations: ground-based, airborne fuselage-mounted, and airborne wing-mounted. It uses a 100-ohm flange resistor under the requirements of fire safety in the case of all transmitted power reflected from the antenna port. Two drawbacks of the flange design feature are high parasitic capacitance (which results in sub-optimal performance) and large profile. The second and newly proposed design uses chemical vapor deposition (CVD) diamond resistors on a custom copper flange. The resistors are wire-bonded between the resistor’s gold contacts and soft gold pads on the circuit board using 25 µm gold wire. Results for an ideal prototype and the first implemented version on a ground-based array are presented. System engineering aspects such as thermal cycling, high-power RF tests, and bond integrity are explored.

The effectiveness of the circuits developed in the context of this work is demonstrated in real field environments. This includes the operation of the airborne version of the UHF multichannel radar for surveys near Dome A in Antarctica during the 2022 – 2023 and 2023 – 2024 Austral summer seasons, the five-fold deployment of the ground-based versions of the UHF multielement radar  for surveys in Greenland and Antarctica from 2022 to 2024, and the operation of the newly proposed version to Taylor Dome in Antarctica during the 2025 Austral summer season, currently underway.