The Rotman lens is a beam former which is attractive due to its wide bandwidth, wide angular cove rage, planar nature and simple fabrication. Its angular resolution is limited because only a discrete number of steering angles (equal to the number of input ports) can be achieved. This limitation is overcome using a new type of RetroDlrective Array {RDAJ based on the a Rotman lens, and a Rotman lens used in conjunction with liquid crystal (LC) phase shifters to provide reconfigurable radiation patterns. Parametric studies into the geometry of the lens were first carried out to develop design guidelines. A new type of RDA based on the Rotman lens was designed which requires additional features not normally considered in conventional operation of the lens. A prototype Rotman lens based RDA was fabricated and experimental measurements of the monostatic and bistatic radar cross-section patterns were used to demonstrate continuous angular coverage of ±40° in azimuth over an 8 -12 GHz f requency range. A new low loss GT3-24002 liquid Crystal (l C) developed by Merck was used to fabricate inverted microstrip line based LC phase shifters, with figures of merit of up to 110• phase shift per dB of loss were measured over a 6 -10 GHz frequency band. These devices were integrated into the array feed circuitry of a Rotman lens to implement a reconfigurable beamforming network which exhibits significantly higher angular resolution than conventional Rotman architectures. Beams centred at 0•, ±l5• and ±30°, were switched between monopulse sum and difference pattern operation over 6 - 10 GHz by applying suitable voltages to the LC lines to provide phase shifts of O• and 180•, and in addition, the dynamic phase responses at the outputs of the LC lines were varied to continuously scan the radiation patterns over an angular range of ±39°.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:601108 |
| Date | January 2013 |
| Creators | Christie, Steven James |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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