A low-cost leaky-wave antenna using cylindrical surface waves propagating on a grounded dielectric slab is proposed. The excited surface waves are then perturbed into a leaky-wave regime, by the addition of annular microstrip-based ("bull-eye") gratings. Various surface-wave modes may be considered, however, we desire to achieve radiation from the fundamental TM0 mode due to its zero cutoff frequency and possibility for efficient excitation. A comprehensive design strategy is detailed in the paper. It is based on both an accurate knowledge of the modal spectrum, obtained with the method of moments, and an analysis of the resonant modes supported by the constituent microstrip rings. To further support our methodology, numerical calculations, full-wave simulations, and antenna measurements are reported for the basic structure. Also, additional designs for enhanced gain at broadside, reduced cross-polarization levels, and improved wide-angle frequency beam scanning are presented

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The step-frequency radar is proposed as a means of detecting targets imbedded in high loss media. The radar derives information on target distance by exploiting the phase and amplitude characteristics of the returned signal. With a given frequency change, the phase angle change from a faroff target is larger, and therefore its phasor rotates faster, than that from a closeby target. Distance information is conveniently derived by applying the Fast Fourier Transform algorithm. The radar is able to offset an arbitrary distance and zoom to the targets, thereby obtaining fine resolution. With Wiener filtering, the resolution of the radar is high enough to identify the type, as well as the orientation, of the buried targets. A subtraction feature has also been incorporated which allows scattering from unwanted targets to be cancelled out from that of the wanted targets. The radar was successfully demonstrated for the detection and identification of various targets buried in sand, moist clay soils, underwater, as well as for the mapping of thin ice.

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Alow-cost planar leaky-wave antenna (LWA) offering directive antenna beam patterns as well as linear beam scanning through broadside is proposed. The design is based on a one-sided annular slot grating placed on a dual-layer grounded dielectric slab with an integrated TM0 antenna feed system in the bottom ground plane. By appropriate selection of the width and the period of the top radiating annular slots, as well as the substrates, the structure is optimized to excite and perturb the dominant TM mode for the generation of directive beam patterns that can scan with frequency in the far field. In particular, the antenna parameters are chosen to obtain a narrow open stopband frequency range at broadside as well as control the dispersive scanning behavior. A method-ofmoments dispersion analysis has also been developed to assist in the design and fully characterize the proposed antenna. These results are complemented by full-wave simulations and measurements of a LWA prototype offering realized gain values in excess of 14 dBi with scanning through broadside at 23.5 GH

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