Date of Award

12-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Electrical Engineering

Advisor

Pearson, L W

Committee Member

Xu , Xiao-Bang

Committee Member

Harrell , William R

Committee Member

Rafert , James B

Abstract

Coupled oscillator arrays (COAs) have excellent synchronization properties that can be utilized to develop a low cost alternative to phased array systems for beam steering applications. The primary concerns in implementing the COA architecture are the sensitivity to cell-to-cell component variation and poor phase noise performance. Wide injection locking range oscillators reduce the sensitivity to component variation but degrade the array phase noise performance. The objective of this dissertation is to alleviate the concerns hindering the application of COAs by employing techniques to realize COAs with wide mutual injection locking ranges (MILR), improved phase noise characteristics and beam steering capabilities. In the first manuscript , a dually resonant oscillator configuration, which offers the flexibility of mutual coupling at different locations, is optimized for low Q and used to fabricate two three-element COAs - one in which oscillators are mutually coupled at the drain terminal and another in which oscillators are mutually coupled at the gate terminal. In both arrays, the oscillator elements are coupled with coupling phases of 23 and 4radians at 3.75 GHz. For both arrays the coupling phase that resulted in broadside operation yielded the largest MILRs, whereas the coupling phase that caused the array to lock with a limited range resulted in out of phase synchronization of the oscillator elements. In the second paper, the behavior of COAs in the strongly coupled regime is analyzed. For large coupling strengths, the resonant nature of the coupling network increases resulting in the breakdown of the broadband condition. A five-element COA operating at 3.75 GHz was fabricated and the MILR, phase noise and oscillator amplitude and phase variation were measured for coupling strengths varying from 0.5 to 2.5. A two-fold improvement in the MILR and 25 dB improvement in the array free-running phase noise is achieved. The beam steering capability of strongly coupled arrays is also presented. Strong coupling causes the amplitudes of the oscillator elements to grow toward the extremes of the array. When strongly coupled arrays are employed in a phased array system the side lobe level will be undesirably large. Tapering of the array amplitude distribution is utilized to achieve reduction in the side lobe level. The beam steering capability of strongly coupled arrays is also presented. In the third paper, the multiport injection technique is shown as a means to enhance the beam steering and phase noise performance of the array. For a nine element COA operating at 10 GHz, the maximum beam steering (15.6○) is obtained when oscillators #4 and #6 are simultaneously injection locked with a 174○ phase difference. Two, three and four port injection locking of the array is performed and the measured phase noise performance is compared with theory. Regardless of the number of oscillators simultaneously injection locked, the best phase noise performance is observed when the oscillators nearest to the center element are chosen for injection locking. By injection locking the oscillators nearest to the center element the same phase noise performance is obtained with fewer injection- locked oscillators.

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