Details of the design of circumferentially corrugated conical horns are presented. Radiation pattern and phase-center characteristics for both "wide-band" and "narrow-band" horns are considered, and a comparison is made between the relative sizes of the two types of horns. The effects of horn aperture size, slot width-to-pitch ratio and frequency on the cross-polarization of the radiation pattern are included. The range of slot parameters which can be used and the design of the slots near the throat of the horn to achieve a low VSWR for bandwidths of 1.5 to 1 are also considered. The results of measurements on horns with both narrow and wide included angles are given.

Design of corrugated conical horns

The fundamental mechanisms of microwave backscattering from mechanically generated short gravity waves with 25-cm wavelength have been investigated in the laboratory using a CW coherent dual-polarized focused radar operating at 9.23 GHz and a laser scanning slope gauge which provides an almost instantaneous profile of the water surface while scattering is taking place. The surface was also monitored independently for specular reflection using an optical sensor. It is found that microwave backscattering occurs in discrete bursts which are highly correlated with "gentle" breaking of the waves. These backscattering bursts are either completely nonspecular or are partially specular in nature. The specular contribution is found to be more important than generally expected, even at moderate to high incidence angles, and its source seems to be the specular facets in the turbulent wake and the capillary waves generated during breaking. Completely nonspecular backscattering bursts are analyzed by using the Method of Moments to compute numerically the backscattering complex amplitudes from the measured profiles and then comparing the computed results with the measured results. Using numerical modeling, it can be shown that for a wave in the process of breaking, its small-radius crest is the predominant scattering source in a manner akin to wedge diffraction as described by the Geometric Theory of Diffraction (GTD). The parasitic capillary waves generated during wave breaking also scatter. Their contribution is in general smaller than that of the crest and can be understood in terms of small-perturbation theory. The relationship between GTD and small-perturbation theory in the description of wedge diffraction is established. Implications of these results for microwave backscattering from the ocean surface are examined.

A deterministic, coherent, and dual-polarized laboratory study of microwave backscattering from water waves, Part I: Short gravity waves without wind

A step horn structure is presented that yields about 90% aperture efficiency with low cross-polar radiation. It is found that for obtaining high aperture efficiency, the horn aperture should consist of only the TE/sub z/ type of modes in appropriate amplitudes and phases. The desired TE/sub z/ modes are produced using multiple steps in the horn walls. The distances between the steps are critical to suppress the undesired TM/sub z/ modes. Radiation characteristics of high efficiency circular and square horns are presented and potential applications of such high efficiency horns are discussed.

A novel horn radiator with high aperture efficiency and low cross-polarization and applications in arrays and multibeam reflector antennas

Topology optimization based on nonlinear programming techniques and design sensitivity analysis are used to maximize directional emission from a waveguide termination in a two-dimensional square lattice rods-in-air photonic crystal Maximizing directional emission from a photonic crystal waveguide termination is desirable since a horn antenna style termination of comparable functionality is very large, while small simple terminations show strong angular spread The optimized waveguide termination designed here is compact and exhibits a fivefold increase in power incident upon the target area over the simple termination This improvement is achieved by creating surface modes that interfere to produce highly directional emission

Topology optimization of a photonic crystal waveguide termination to maximize directional emission

Summary We have presented a complete analysis of the Cornell mm-wave spectrometer using quasioptical formalism with sufficient flexibility to predict the performance of a novel reflection spectrometer with variable input coupling and transmit-receive duplexing based on polarization coding and we present a practical realization of these design concepts in Earle et al. (1996b). At every stage we have chosen parameters that correspond to practical performance values and measured response. The treatment given here is self-contained, but the references contain many useful extensions of our results and alternative treatments may deepen the reader’s understanding. We have tried, where possible, to take advantage of EPR spectroscopists’ knowledge of microwave circuits and analysis. As high-field ESR becomes more common, we predict that analogies from other fields will continue to be a useful method for extending the generality and utility of the method. Implementing the advanced techniques discussed in Sections IX-XI will give significant inprovements in signal-to-noise ratio as we have demonstrated elsewhere (Earle et al., 1996b).

Allan Walter Love

Papers

Electromagnetic Horn Antennas