Design and performance analysis of the miniaturised water-filled double-ridged horn antenna for active microwave imaging applications

The design and analysis of a miniaturised double-ridged horn antenna for active microwave imaging application are presented in this study. For such an application, a physically small horn is required. For effective signal penetration, a low frequency of operation (about 1.4 GHz) is selected. An array of these sensors is intended for use in a cylindrical breast imaging system, which is under development in the authors laboratory. The miniaturisation is achieved by loading the double-ridged horn antenna with distilled water (ε_r = 76), a high permittivity, but easily available material. Further size reduction is achieved by reducing the aperture size and flare length in the horn section. The frequency response and both near- and far-field patterns were studied. Two simplified prototypes were fabricated, and as per the system requirements, tested in a cylindrical container filled with distilled water. Measured and simulated reflection and transmission responses are discussed. Measured radiation patterns are compared with the simulated ones to validate the analysis.