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A printed elliptical monopole antenna operating at 1–4 GHz frequency for biomedical imaging applications is presented in this article. To reduce the reflection of the microwave signal from breast, glycerin is used as the coupling medium (εr = 9, σ = 0.4 S/m, tan δ = 0.28) whose electrical properties are close to those of breast tissue. Directional patterns and reduced back radiations are achieved using a reflector. The antenna has wide impedance bandwidth from 1 GHz to over 6 GHz (over 140%), suitable for radar‐based imaging. The antenna demonstrates S21 > −60 dB from 1 to 4 GHz in the coupling medium. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:808–813, 2014

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.

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This paper reviews the concept of an engineered conductor, introduced by the authors in order to reduce ohmic losses of miniaturized microstrip antennas [1][2][3][4]. Because of the miniaturization, the ohmic losses of microstrip antennas increase, which essentially signifi cantly reduces their gain and effi cien cy. By the use of the engineered conductor concept, these two important parameters of such antennas can be improved without altering the antenna's geometry. The concept is based on using multiple laminated thin conductors, rather than one thick conducting layer, to form the microstrip antenna. The technique is applied to several miniaturized microstrip antennas in order to reduce their ohmic losses. The concept is explained using a microstrip line to demonstrate that the conductor loss can be reduced by increasing the number of layers in the lamination, while keeping the total thickness constant. Using conventional metallized substrates, the lamination reduces the thickness of each conductor layer to approximately or less than the skin depth in that conductor. Studies of two miniaturized antennas -namely, the square-ring antenna and the modifi ed open-ring antenna -have respectively provided about 4.6 dB and 1.5 dB improvements in the gain, and from 30% to 40.7% improvement in the effi ciency. Experimental investigations are also presented that confi rmed the simulated results.