Publication Date

Fall 2011

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical Engineering

Advisor

Sotoudeh Hamedi-Hagh

Keywords

EVM, phased array, phase shifter, X-band, YIG

Subject Areas

Electrical engineering

Abstract

A novel technique for effecting phase shift of X-band signals has been developed and analyzed for use with quadrature amplitude modulation (QAM) of signals in a phased array application, and the impact of this phase shifter on error vector magnitude (EVM) has been quantified. A commercially available filter consisting of yttrium iron garnet (YIG) spheres was characterized by means of a network analyzer. The gain and phase response was measured across a 25 MHz frequency band centered at 10 GHz, while the filter was tuned in frequency steps such that a 360° range of phase shifts was achieved. The S-parameters from these measurements were integrated with Matlab representations of QAM-16 modulation, demodulation, and phased array antennas to model a complete radio system. The EVM caused by non-ideal gain and phase response of the YIG filter was determined for various beam angles and data patterns.

It was found that a YIG filter does provide stable phase shift suitable for phased array applications, with acceptable attenuation so long as the frequency being transmitted remains within the filter's pass band. The particular filter analyzed did not contain sufficient stages to maintain 3 dB flatness across the required 360° tuning range, but performed satisfactorily for a limited range of beam orientation. The capability to provide continuously variable phase shift offered by the YIG filter was found to not offer significant advantage over the discrete steps produced by switched delay lines.

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