Date of Award

6-2013

Degree Name

MS in Electrical Engineering

Department

Electrical Engineering

Advisor

Dennis Derickson

Abstract

Phased arrays are electromagnetic antenna systems comprised of many radiating elements and processing electronics. Radiating elements are typically positioned in an orderly grid within the antenna aperture. In the receive mode of operation, radiating elements capture some of the signal energy from incoming radiation and guide these signals to processing electronics. Signals are filtered and amplified to maintain the desired sensitivity and complexly weighted using circuits with reconfigurable amplification gain and phase delay. Finally, all signals are combined. The summation of these complexly weighted spatial samples forms a spatial filter in the same way complexly weighted temporal samples establish a temporal filter in a finite impulse response discrete-time filter. Therefore, a phased array behaves like a spatial filter that strongly favors signals arriving from a specific direction. This favored direction represents the look angle of its beam, and the shape of the beam directly relates to the complex weights applied to the signals in the array. Analogous to the flexibility offered by digital filters, phased arrays enable agile beam steering, sidelobe control, and multiple independent beams. These capabilities have revolutionized radar, radioastronomy, and communication systems.

Phased arrays have increasingly employed printed circuit board (PCB) fabrication techniques and processes to maximize array channel density, achieve lower profile, and minimize component integration cost. A few applications which leverage these qualities include low-cost radar, mobile satellite communication (SATCOM), and intelligence, surveillance, and reconnaissance (ISR). Further, PCB-based arrays readily accommodate advancements in highly integrated beamforming radio frequency integrated circuits (RFICs), multi-chip modules, and RF micro-electro-mechanical system (MEMS) device technologies.

On a prior effort, an integrated unit cell design was developed for a PCB-based SATCOM array application. However, the design failed to meet the requirements. The primary objective of this work is to demonstrate an improved design using systematic microwave design techniques and modern analysis tools to meet the requirements for the same application. The proposed design must improve gain, bandwidth, size, and manufacturability over the prior design. Additionally, the design must be generally extensible to phased array implementations across the SHF band (3-30 GHz).

This work discusses the advantages of phased arrays over continuous apertures (e.g. reflectors), reviews phased array theory, and proposes an improved unit cell design. The proposed design is 35% smaller than a dime and consists of an orthogonally-fed, slot-coupled stacked patch antenna and dual-stage branchline coupler implemented in a multilayer PCB. Within the operating band from 10.7 to 14.5 GHz, the design achieves an average return loss of 15 dB, a uniform radiation pattern with peak realized gain of 4.8 to 7.0 dBic, cross-polarization level below -17 dB, and stable performance in a closely-spaced array. When configured in an array, the design supports X/Ku-band SATCOM in full-duplex operation, electronically rotatable polarization, and a 47.5˚ grating lobe free conical scan range. Further, a Monte Carlo analysis proves the design accommodates tolerances of material properties and manufacturing processes, overcoming a major challenge in PCB-based high frequency antenna design.