This paper furnishes a compact modified hourglass-shaped aperture-coupled antenna for radar applications. The effect of slots of various shapes and various slot lengths on the input impedance, radiation pattern, and gain of the antenna are analyzed. The proposed antenna, designed using a modified hourglass-shaped aperture, offers a gain of 8.214 dBi for an compact antenna with a dimension of 20.4 × 20.4 × 1.041 mm3 and an aperture area of 2.495 mm2. Implementation of this proposed modified hourglass-shaped aperture offers a high gain per unit radiating patch area of 40.26 dB/$\lambda _g ^2$ and a high gain per unit aperture area of 1324.84 dB/$\lambda _g ^2$. The proposed aperture feeds a circular patch which radiates at its resonant frequency of 10.5 GHz. The proposed design is fabricated and the simulated results are verified experimentally. Equivalent circuit analysis is also done. A measured gain of 7.2 dBi is observed at 10.5 GHz. The physical area of the antenna is reduced without compromising the gain by judiciously choosing the shape of slot with more degree of freedom for impedance matching. The proposed antenna is well suited for the unit cell of phased array antennas for X-band missile radar applications.

A simple closed-form analytical formula is proposed to compute the probe reactance of an equilateral triangular patch antenna. The variation of the probe reactance with the variation of antenna dimension, substrate electrical parameters, and probe location is examined thoroughly. The computed values employing the present model show excellent agreement with experimental and simulation results.

A meandered-dual-antenna structure is proposed for UHF radiofrequency identification (RFID) tag. It is composed of two independent antennas printed on the one side of the substrate board. One of the antennas is exclusively used for receiving and harvesting sufficient energy to the tag chip having the complex conjugate impedance of the receiving antenna. The other is for backscatter to enhance maximum differential radar cross-section with purely real input impedance, to enhancement the read range. The receiving antenna is formed by a rectangular loop and a parasitic meandered line. The rectangular loop is used as a feeding element for the meandered line. The backscattering antenna is made using a meandered dipole along with a thin rectangular strip. The input impedance of the receiving antenna is designed to be conjugate matched to the chip impedance (13.5-j110 Ω), whereas the input impedance of backscattering antenna alternatively switched to open and short circuit for modulating the backscattered field. The input impedance of receiving and backscattering antennas is measured using differential probe technique. The simulated and measured results are found in good agreement. It is also demonstrated that the read range of UHF RFID system increased considerably by using the dual-antenna structure.

We evaluated the physical characteristics of the pulmonary trunk in 32 patients with complete transposition after the arterial switch operation, calculating the pulmonary input impedance. In 6 of the patients, the characteristic impedance was equal to, or less than, the value in patients with ventricular septal defect. In those patients with an intact ventricular septum, or those with a ventricular septal defect who had undergone the arterial switch operation or banding of the pulmonary trunk before 3 months age, the frequency of the first modulus minimum also agreed with the values obtained in patients with ventricular septal defect. The value was high, however, in patients with complete transposition with ventricular septal defect who had undergone an arterial switch operation or banding of the pulmonary trunk after 4 months of age. Our data suggest decreased distensibility of the proximal pulmonary trunk after the arterial switch operation, and mild changes in the pulmonary vasculature in patients with complete transposition with ventricular septal defect who had undergone either an arterial switch operation or banding of the pulmonary trunk after 4 months of age. Long-term follow-up is needed clarify whether or not these features affect right ventricular function by means of an increase in afterload.