Date of Award

Spring 1-1-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical, Computer & Energy Engineering

First Advisor

Dejan S. Filipovic

Second Advisor

W. Neil Kefauver

Third Advisor

Zoya Popovic

Fourth Advisor

Edward Kuester

Fifth Advisor

Scott Palo

Abstract

This thesis researches several novel high power wideband antennas with omnidirectional, horizon- and broadside-directional, and bi-directional coverage for various electronic warfare (EW) systems. The developed antennas are designed and analyzed with the considerations in frequency domain (FD), time domain (TD), and power domain (PD) using full-wave electromagnetic simulations, transient analysis, multiphysics simulations, field analysis, equivalent circuit modeling, spherical mode decomposition, etc., as needed. The theoretical models of all antenna configuration are carefully validated with measurements.

Equivalent circuit models of monopole-like antennas are derived based on the physical structure and field distribution around a monopole. These models are used to ease physical understanding, analyze antenna impedance, and design derivatives with improved performance. A novel wideband omnidirectional antenna with consistent monopole-like patterns is proposed for millimeter-wave integrated towed decoy receiving subsystems by combining annular slot mode with a monopole into a single structure. The bandwidth of the combined antenna is improved to cover the wide range of radar signals from 18 GHz to 45 GHz, and its operating principle is analyzed using the proposed equivalent circuit model. In addition, compact paraboloid reflector fed by the combined antenna is designed for the same platform but with enabled horizon-directional coverage. The path toward using the proposed combined antenna for transient high power electromagnetics (HPEM) applications with good TD and PD performances is described.

Reconfigurability between steerable horizon-directional and omnidirectional modes for transient HPEM pulses is demonstrated by a monocone fed reflector antenna system. To do so, a conventional monocone is modified to a conical monopole first. The spherical mode expansion (SME) analysis shows that this structure has consistent monopole-like patterns and can be used as a feeder of a wideband reflector antenna system. Owing to the small diameter and consistent patterns of the modified monocone feeder, a paraboloid reflector is engineered and stable impedance and far-field performances from 1.66 GHz to 20 GHz are demonstrated. Analysis in TD and PD proves the suitability of the proposed antenna concept for transient HPEM applications. The electrical size of the monocone is also reduced by loading shorted semi-helical wires. The circuit model analysis demonstrates that typical miniaturization techniques require large monocone diameter though height can be greatly reduced. The proposed loading does not contribute to additional antenna volume, while lowering its electrical size by 34%, and the prototype monocone achieves good impedance match and gain from 1.23 GHz to 11 GHz.

Planar bi-directional and flush-mountable broadside unidirectional log-periodic (LP) antennas for long range communication, radar, or jammer systems with over a decade wideband performance are also introduced. To maintain inherent bi-directionality of a planar LP antenna, microstrip feed is preferred over a typical coax-based exciter. However, this leads to deteriorated impedance match and pattern distortion when the boom angle is not wide enough. To resolve this issue, a novel wide-boom geometry of the LP antenna is proposed. Since the wide-boom provides wide ground plane for the feeding microstrip line, good impedance match and gain performances can be achieved without sacrificing the antenna size. Moreover, electro-thermal multiphysics analysis of the antenna shows that the wide-boom also improves the temperature response, and thus, the average power handling capability is increased. The multiphysics simulation results are validated using a non-contact infrared (IR) camera. To achieve broadside unidirectional coverage, a slot-loaded cavity backing design is engineered. Instead of filling the cavity with carbon loaded absorber, the proposed slot-cavity backed LP antenna is loaded with the slot terminated by a coax cable that can be easily used for energy recycling. Fabricated prototype maintains high gain and efficiency with good impedance match over a wide bandwidth from 0.59 GHz to 5 GHz.

All ideas and concepts proposed in this thesis are thoroughly validated with circuit and full-wave simulations as well as experiments on representative prototypes.

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