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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Electrical and Computer Engineering

Year Degree Awarded

2016

Month Degree Awarded

September

First Advisor

Marinos Vouvakis

Second Advisor

Do-Hoon Kwon

Third Advisor

Gopal Narayanan

Subject Categories

Electrical and Computer Engineering | Electrical and Electronics | Other Electrical and Computer Engineering

Abstract

Ultra-wideband (UWB) electronically scanned arrays (ESA) with high efficiency, excellent polarization agility, and wide-scan matching remain essential for servicing multifunctional RF front-ends and other communications, sensing, and jamming or countermeasure systems. To this day, the most popular antenna array element in modern UWB-ESA systems is the Vivaldi, or flared notch, due to its superior wide-scan wide impedance bandwidth, well-known design guidelines, and practical embodiment versatility. Despite their popularity, these arrays tend to radiate unacceptably high cross-polarization levels, thus encouraging a great research opportunity.

This dissertation presents the theory and design of a new class of UWB-ESAs, termed Sliced Notch Antenna (SNA) arrays, that remedy the high cross-polarization problems in Vivaldi arrays while maintaining their desirable impedance performance. The critical enabling insight of this work lays in revealing the nature of polarization purity or cross-polarization ratio (CPR) degradation in Vivaldi arrays to arise from a highly imbalanced ratio of longitudinal and transverse currents within the element. This work introduces a novel design strategy that intrinsically balances these currents over a UWB operating band, achieving decade-order (10:1) bandwidths and low cross-polarization. Moreover, the design approach is simple, intuitive, and can be implemented in a manner that does not inflate cost expenditures. In fact, the proposed topology can facilitate significantly reduced costs and manufacturing times in Vivaldi arrays by permitting electrically disconnected elements over a large portion of the original Vivaldi fin. Following the presentation of the theoretical and operational principles, a few infinite SNA array design implementations are proposed that achieve decade-order bandwidths and low cross-polarization (e.g. active VSWR

A single-polarized 19×19 SNA array and its Vivaldi counterpart are designed, fabricated, assembled, and measured to comparatively demonstrate similar wideband impedance behavior over a 1.2-12 GHz (10:1) operating range that covers near the entirety of four popular RF bands (L, S, C, and X); center embedded element impedance measurements show good agreement with finite array simulations out to θ=60° scans. The SNA array embedded element pattern offers better than 15 dB cross-polarization level improvements over the Vivaldi array out to wide angles in the D-plane. Active finite array scan simulations suggest both arrays closely track the directivity in the principal planes (e.g. less than 0.5 dB co-polarized gain drop at broadside), while the SNA array offers up to 25 dB improvements in co-polarized gain for non-principal plane scans in and around the D-plane with approximately 15 dB improvement on average over the Vivaldi array in the mid-band and high-band.

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