Active Matching Circuits for Enhanced Antennas
Michaël Blaakman (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Klaas de Kroon (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Daniele Cavallo – Mentor (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Filipe Arroyo Cardoso – Graduation committee member (TU Delft - Electrical Engineering, Mathematics and Computer Science)
José Luis Rueda Torres – Graduation committee member (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
Wide-band phased-array antennas are an essential technology for modern communication, radar, and radio astronomy systems because they enable operation across broad frequency ranges while maintaining performance over large scan angles. Connected array antennas provide inherent wide-band behavior, but the introduction of a backing reflector to ensure unidirectional radiation creates frequency-dependent reactive effects that limit the operational bandwidth. This project investigates the use of active matching circuits that create a negative inductance to compensate for the inductive behavior introduced by the reflector, thereby improving antenna impedance matching over a broad frequency range. A connected slot array antenna was modeled and analyzed using electromagnetic simulations. Equivalent circuit models were developed to represent the antenna and reflector system, after which three active matching topologies were studied, based on operational amplifiers, transistors, and tunneling diodes. The circuit parameters were optimized to minimize reflections and improve matching performance across the operating band and for different scanning angles. The results demonstrate that negative inductance compensation can significantly enhance the impedance bandwidth of reflector-backed connected arrays compared to the unmatched configuration. The transistor and tunneling diode circuits delivered satisfactory matching performance under broadside operation, with the tunneling diode showing slightly better behavior at higher scan angles. The operational amplifier delivered poor results, showing that its high frequency performance is restricted by its limited gain-bandwidth product. The study concludes that active non-Foster matching is a promising technique for extending the bandwidth of connected array antennas, although practical challenges related to stability, power consumption and biasing active components must be addressed before implementation in real-world wide band antenna systems.