Low Cross-Polarization Vivaldi Arrays

Abstract

ACKNOWLEDGMENTSI would like to begin by extending my gratitude for having the opportunity and privilege to study under the guidance of my advisor, Prof. Marinos Vouvakis, over the course of five years for my Master's and PhD research. His energy, drive, and motivation to not only teach but also to stimulate critical thinking, to invoke a practical mindset, and to create with meaning have left me with invaluable principles. I am indebted to him for challenging me and his endless patience and support throughout this research.I'd like to also thank Prof. Do-Hoon Kwon and Prof. Gopal Narayanan for serving on my dissertation committee and providing many insightful comments and support.I would like to additionally extend my gratitude to Prof. Robert Jackson, Prof.Paul Siqueira, and Prof. Joseph Bardin for serving on my research qualifying exam committee. Also, although I never had the pleasure of having him as a professor at UMass, I'd like to thank Prof. Dan Schaubert for taking the time to inadvertently introduce Vivaldi arrays to a curious kid at a phased array conference nearly six years ago; likewise thanks to Prof. Jorge Salazar for seeing some potential in that kid to encourage him to apply for graduate study at UMass. I appreciate it greatly. 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 widescan 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 viii 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

Wide band wide scan low cross‐polarised grooved tapered slot antenna array

“…2 shows the simulated Γ < − 10 dB for TSA (without grooves) shown as a dotted line over FBW∼0.59 (1.1-2.0 GHz). The fact that the x-pol level in TSAs is higher and even more severe while scanning is illustrated in the vast literature [3,[13][14][15][16][17][18][19][20][21]. The present study provides a solution to suppress the x-pol level by the virtue of TSA's geometry modification.…”

“…Nalumakkal et al [20] showed the measured low x-pol <−20 dB at the broad side, which increased to higher values of the order of −5 to −10 dB at scan angles farther than 20° from the broad side. Logan et al [21] have shown x-pol <−25 dB over a larger scan volume than 45°. The present work complements the existing approaches for the design and realisation of wide scan and wide band TSA element/TSA arrays with low levels of x-pol at the broad side and also during scanning in non-principal planes as well.…”

“…Researchers have reported various wideband wide scan TSA structures exhibiting low x-pol levels [11,[13][14][15][16][17][18][19][20][21]. They have proposed different approaches for resolving the high levels of x-pol by either providing modifications in TSA geometry or corrections in the measurement software.…”

“…However, these are restricted to narrow band and limited scan angles. The geometry-based solutions [11,14,[17][18][19][20][21], however, has provided valid broadband solutions for wider scanning volumes.…”

Dual‐polarised wideband tightly coupled dipole array for airborne applications

“…Among UWB arrays, the tapered slot or Vivaldi arrays are known for their broad >10:1 impedance bandwidths, but are typically large in size with poor polarisation purity [2]. To address the polarisation purity, recent Vivaldi variants, known as the sliced notch antenna array, compensate for the imbalanced current potentials on the Vivaldi fin edges [3].…”