Details of Grant 

EPSRC Reference:	GR/H15110/01
Title:	CONVOLUTED ARRAY ELEMENTS AND CURVED FREQUENCY SELECTIVE SURFACES
Principal Investigator:	Parker, Professor EA
Other Investigators:	Langley, Professor RJ
Researcher Co-Investigators:
Project Partners:
Department:	Sch of Engineering & Digital Arts
Organisation:	University of Kent
Scheme:	Standard Research (Pre-FEC)
Starts:	01 April 1992	Ends:	30 September 1995	Value (£):	108,661
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Summary on Grant Application Form
To quantify effects of array distortion produced by curvature of frequency selective surfaces.To develop analysis and design software for convoluted array elements.To identify further members of this class of elements.Progress:Seven papers have been published or submitted to journals, 5 presented or accepted for presentation at conferences, and at least 2 journal papers are in preparation. Three papers deal with passive convoluted array elements while a fourth has followed on to consider an approach to producing a frequency selective surface with a bandpass transmission response which can be dynamically controlled.A computer program has been written for evaluating and plotting the distortion in FSS array elements when projected from a planar mask on to a curved surface. Elongation produced by projection produces an approximately proportional decrease in the resonant frequency fr, adding to the (smaller) decrease that already occurs when undistorted elements are illuminated obliquely. In addition to a change in resonance frequency, curvature alters the profile of an array's transmission response. Two methods have been devised for modelling highly curved dichroic surfaces. The first is an element-by-element approach which involves expressing the scattered pattern of each element in the form of an integral equation for the current induced in the element by the external field. At present this is confined to the case of dipole patch elements where this problem can be formulated in terms of Pocklington's equation and solved by the method of moments. It is capable of being put into a form suitable for the investigation of radome/antenna interaction. This program has been used to study the transmission response of sharply curved arrays, and to compute near field distributions. The predicted results have been verified by limited measurements. An alternative technique uses the ray-tracing approach to trace ray paths through a curved FSS array embedded in curved dielectric. The predicted plane wave transmission performance has been compared with measured values for a cylindrically curved parabolic array of circular ring slot elements embedded in a half-wavelength thick dielectric substrate, a configuration which provides a bandpass response. The results again agree well with predicted values till the onset of grating responses. Measurements of the far field radiation pattern of a pyramidal horn enclosed by this curved FSS also agree well with the predicted patterns over the main beam region. The deterioration in on axis gain of the horn and the general increase in sidelobe levels are both correctly predicted, but it is clear that feed/radome interactions need to be included for accurate prediction, even more so when the antenna is closer to the radome apex, or when antenna input impendances are required. This technique has not yet been applied to the receiving case.
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Organisation Website:	http://www.kent.ac.uk