In recent few years fractals have been employed in conjunction with antennas to develop new applications. In this work, novel fractal geometry is introduced as a miniaturized microstrip patch antenna. Compared to a square patch antenna, the antenna shows an improvement of 68% size reduction. Furthermore, by applying of a new feeding method, refereed to here as the sleeve feeding, up to 27% impedance bandwidth is achieved as shown in the experiments.

Conventional monopulse radar cannot detect the direction of two closely-spaced targets in one resolution cell by utilizing the monopulse ratio. In this study, virtual amplitude-comparison monopulse signals are generated from the received phase-comparison monopulse signals, then a solution for estimation of the angles of two unresolved targets using a single snapshot of four independent channels is presented. If both targets have the same azimuth or elevation angle, the proposed scheme cannot detect their angles; an additional antenna is required, to detect such targets' angles. In this study, the antenna array is divided into multiple overlapping sets, to detect the direction of two targets at generalized positions in two different coordinates. Combining the outputs from multiple antenna sets improves the angle estimation performance and accuracy. The impact of SNR, the angle difference between the targets, and the phase difference of target signals on the accuracy of angle estimation have also been explained. The effectiveness of the proposed method is validated by comparing the exact solutions and simulations.

In all types of satellites, communication systems are utilized for data transmission between satellite and ground stations. pointing the communication antennas to the ground is necessary for the correct mission transmission information. The vibration of the satellite antenna leads to deforming antenna pattern, creating noise and reducing connection quality. Moreover, working the attitude control actuators near the antenna's natural frequency leads to its resonance and large amplitude vibration in the antenna and satellite structure. Thus it is necessary to identify the satellite antenna dynamic behavior as natural frequency and damping ratio. In this paper, the satellite antenna is intended as a smart beam, based on the free vibration of clamped-free beam shape of satellite antenna and sensing its vibration by the piezoelectric sensor, its dynamic characteristic as damping and frequency is identified and verified by comparing the results with experimental ones. The considered mathematical model is very accurate and this model can be used to determine the dynamic behavior of the antenna in different satellite secondary structures.

This paper presents the results of a study on the radiation characteristics of a plasma triangular antenna in the VHF band (30-300MHz) applying the method of moment. Deriving the current distribution of the antenna, it shows the relationship between radiation characteristics of the plasma antenna and the plasma parameters. Both theoretical and numerical results indicate that if the plasma frequency is sufficiently higher than the operating frequency and the collision frequency is correspondingly low, the radiation treatment of the plasma antenna will be close to a metal one. Also the consequence of simulations reveals the proposed plasma antenna has better peak gain than the conventional plasma column on the operating band. The results of the current study are checked by using full wave HFSS simulator.

The class of Hybrid Linear and Circular Antenna Arrays is presented. The properties of linear and circular antenna arrays are combined to obtain hybrid array types: concentric circular, cylindrical, and coaxial cylindrical antenna arrays. These three types are defined, the expressions of their array factors are derived, their directivities and half power beam widths (HPBW) are simulated. The obtained plots are approximated by curve fitting. Different combinations of excitation currents (e.g. uniform, Chebyshev, Bessel, …) can exist on the elements of the same antenna array.

In this paper, a new CPW (Coplanar Waveguide) fed printed UWB antenna integrated with a narrowband antenna is designed and analyzed for cognitive radio applications. The ultra-wideband (UWB) and narrowband (NB) antennas provide bandwidth from 2. 2 GHz to 11GHz and from 4. 8 GHz to 5. 7 GHz respectively and reasonable isolation between the antennas. A prototype of the integrated antenna was fabricated and its performance was verified. The dimensions of the FR4 substrate are 40 × 48 × 1. 6 mm3. The antenna represents good radiation characteristics, stable gain and good time domain manner to deliver the requirements of the current wireless communication standards. Also, two external tuning circuits were designed to show the ability of the narrowband antenna for reconfiguration.

A novel approach to ultra-wideband (UWB) antenna design is presented which is based on a general description for the geometry of monopole antennas. This general description is capable of producing almost all possible shapes for monopole antennas and it is compatible with different optimization methods. The general description is used for the optimization of rotationally-symmetric monopole antenna with finite ground plane. The optimization of antennas is performed by applying a hybrid procedure, which begins with a global search and completes with a local optimization. The optimization procedure aims at minimizing the reflection from antennas while reducing the distortion of radiated pulses. In some cases, the reduction of variations in the energy pattern is also considered. The numerical results show the reliability and effectiveness of the whole process and considerable improvement in comparison with similar antennas reported in the literature.