An HF balun (balanced-to-unbalanced) and a matching filter for a SuperDARN TTFD antenna

Background:
The Super Dual Auroral Radar Network (SuperDARN) radar is part of an international network of 35 radars distributed over the northern and southern polar regions. SuperDARN is a High Frequency (HF) Skywave radar used to study the ionosphere and other space weather related phenomena. SuperDARN is used and operated by the South African National Space Agency (SANSA).
SANSA’s SuperDARN radar comprises of a fully reconfigurable, digit platform consisting of 20 transceiver boxes each with full transmit and receive functionality and controlled by a custom FPGA board (Tiger-3). The radar uses a 16-element Twin Terminated Folded Dipole (TTFD) phased array and a 4-element secondary array to transmit and receive 300us/100us pulses at up to 2.4 kW per antenna over a frequency range between 8 MHz and 20 MHz. Each antenna gets its own transceiver box and the timing is controlled via a dedicated timing node, which distributes a common clock signal to all 20 transceivers via fast Ethernet cables.

This project:
A balun is a device that converts between a balanced signal (two signals working against each other where ground is irrelevant) and an unbalanced signal (a single signal working against ground or pseudo-ground). The balun and filter response should be optimal over a frequency extent centred at 12.5±2.5 MHz and be able to handle the full transmit power of the radar, 2.4 kW.