The purpose of this paper is to discuss the practical and experimental results obtained from the design, construction, and test of an array of circular microstrip elements. The aim of this antenna construction was to obtain a gain of 12 dB, an acceptable pattern, and a reasonable value of SWR for altimeter system application. In this paper, the cavity model was applied to analyze the patch and a proper combination of ordinary formulas; HPHFSS software and Microwave Office software were used. The array includes four circular elements with equal sizes and equal spacing and was planed on a substrate. The method of analysis, design, and development of this antenna array is explained completely here. The antenna is simulated and is completely analyzed by commercial HPHFSS software. Microwave Office 2006 software has been used to initially simulate and find the optimum design and results. Comparison between practical results and the results obtained from the simulation shows that we reached our goals by a great degree of validity.

In this work, a new design of small microstrip antenna with variable band-notched filtering characteristic for super ultra-wideband (UWB) applications including 5G/IoT networks is presented. In the proposed structure by creating steps with optimized appropriate sizes and angles in the lower edges of the quasi-square patch antenna and by a new technique of modifying the ground plane, more efficient radiation patterns and characteristic impedance are achieved. Moreover, the omnidirectional low cross-polarized H-plane radiation patterns are obtained in frequency band of 3-11 GHz. Also, its radiation patterns are improved between 11 and 14.5 GHz and have better performance especially with tuning capacitors between 14.5 and 20 GHz. In addition, its frequency bandwidth with VSWR < 2 is from 3 GHz to 50 GHz which covers 5G networks and both ultra-wideband (UWB) and super wideband (SWB) communications. A rectangular slot on the patch is used to create an integrated band-notch filter in the structure to avoid interference with other wireless systems like wireless local area networks (WLANs), and this specification can be activated or deactivated by a PIN diode. In addition, the center frequency of the filter can be tuned by just a varactor diode or a variable capacitor and/or by changing the position of the capacitors in frequency range of about 3.5-6 GHz, which rejects interference of all WLANs and even their lower and upper bands, and nulls in the radiation patterns can be changed especially in upper bands as well. The final structure simulation results are in good agreement with measurement ones.

The effects of adaptive genetic algorithms (AGAs) and defected ground structures (DGSs) on performance optimization of tapered microstrip filter are investigated. The proposed structure achieves an ultra wide stopband with high attenuation within a small surface area, as well as 45% smaller size, in comparison with conventional filters. The parameters of the filter are optimized using in-home AGA code. In the proposed AGA algorithm, the crossover and mutation probabilities are adaptively changed according to the value of individual fitness. Then by utilizing the proposed DGS, a compact S-band lowpass filter with ultra-wide spurious free window is obtained. The proposed filter achieves an insertion loss of 0.8 dB from DC up to 4 GHz and 21 dB rejection in the stopband from 4.3 up to 60 GHz. The fabricated and measured results exhibit good agreement with the simulated results. They demonstrate that combining AGA and DGS yields best possible response for this group of filters.

Less efficiency and gain is achieved by existence of aperture blocking phenomena in cassegrain antenna caused by the presence of subreflector or antenna feed. Also, length of feed cables causes delay which is another undesirable problem in antennas, since errors and less precision of detecting targets are created. To overcome these problems, low weight and compact optimized polarization-rotation monopulse cassegrain antenna is designed in this paper. The goal of our proposed rotating antenna is achievement of sum and difference patterns for target tracking in monopulse radar. In our work, left part of hyperbolic subreflector instead of right one has been used for reducing size of the antenna. The antenna is fabricated by grid wires instead of solid sheet metal reflectors and with composite technology for decreasing its weight. Width and volume of the antenna reduce by about 50% in comparison to other reflector antennas. This antenna has been simulated and manufactured in X-band and simulation data are in good agreement with measured ones. The antenna has the average gain of 35 dB from 8.5 up to 9.5 GHz. Also the antenna feed bandwidth is more than 50% and the antenna has efficiency of about 50% from 8 up to 10 GHz.

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