This dissertation deals with novel ways to reconfigure the bandwidth of tightly-coupled arrays (TCAs). TCAs constitute a class of phased antenna arrays that demonstrate ultra-wide bandwidth, high gain, wide scanning, compact size and low fabrication cost. These attributes render them attractive for a wide range of applications, including multiple-input multiple-output (MIMO) systems, synthetic aperture radar (SAR) and software defined radio (SDR).
However, TCAs, like all wideband systems, suffer from signal-to-interference-plus-noise ratio (SINR) degradation, reducing channel capacity and quality of communication. Existing spatial and digital filtering techniques fail to provide a comprehensive solution suppressing both noise and interference simultaneously. Therefore, bandwidth reconfiguration techniques, implemented in analog and at the RF frequency, are highly attractive.
In this work, a low loss reconfiguration approach, using variable capacitors within a TCAs balun feed structure, is proposed. Specifically, a rejection notch, tunable both in center frequency and bandwidth, is created, rejecting noise and interference within the entire TCA scanning volume. The proposed reconfigurable array exhibits strong advantages over the use of stand-alone band rejection antennas or the alternative use of tunable band rejection filters, placed after the antenna.
The proposed scheme is validated experimentally via fabrication and testing of reconfigurable balun prototypes, both in isolation and within an array environment. Digital MEMS capacitors were utilized for the practical implementation of the tunable band rejection. Measurement results demonstrate tunability with >2:1 frequency tuning range and rejection magnitude in excess of 30dB. The scheme can be expanded to multiple rejection notches, providing complete control over the bandwidth.
An alternative way of reconfiguring the bandwidth of a TCA is also examined. This method incorporates a reconfigurable frequency selective surface (FSS), which operates as a tunable bandpass filter. The FSS can be placed on top of a wideband radiating aperture, creating a narrow passband that can be tuned within the original apertures bandwidth. The concept is verified via full wave simulations and presents several advantages, such as modularity and biasing ease.
Finally, the dissertation touches other hot topics on wideband array design, such as bandwidth and polarization. In particular, a dual polarized TCA achieving a 13:1 bandwidth is presented. Fabricated prototypes and respective measurements are available here as well, verifying the TCA operation, while offering an insightful result analysis.
Keywords: tightly-coupled array, phased antenna array, wideband, ultra-wideband, reconfigurable, bandwidth reconfiguration, tunable capacitor, variable capacitor, band rejection, rejection notch, bandstop, frequency selective surface, FSS