Volume 73, Issue 3-4 -

Reconfigurable reflectarray/transmitarray antennas have found broad applications in wireless communication due to their low cost, small size, flexible design, and superior performance. However, one common drawback of most current designs is the complex reconfiguration operation, which restricts their further applications. In this research, a new design strategy for reconfigurable reflectarray/transmitarray antennas is proposed and shown. Specifically, a circularly polarized 11×11$11 \times 11$ unit-cell graphene-based reflectarray/transmitarray antenna covering an area of 1.1×1.1$1.1 \times 1.1$ mm 2 is designed, with a graphene-based frequency selective surface (FSS) as a ground. By adjusting the electric field, a dynamic change in the complex conductivity of graphene is achieved, which in turn changes the phase and the resonance point of the reflected or transmitted wave at the element. By tuning the size of the patch and changing the chemical potential of graphene, the element of the reflectarray/transmitarray operated at 1 THz can provide a dynamic phase range of more than 360∘${360^ \circ }$. The simulation results show that the designed antenna can be dynamically reconfigured between the circularly polarized reflectarray/transmitarray antenna of the single structure, and has potential applications in emerging terahertz communication systems.

In this paper, a beam-adjustable metasurface (BAM) is realized based on the plasma metamaterial with a dielectric matching layer technique, which is a novel phase compensation method. In order to realize phase compensation from 0° to 360°, the dielectric matching layers are added above the BAM to compensate the phase. The added dielectric layers can have different refractive indices or different thicknesses. Compared with the conventional phase compensation methods, such a method has an universal adaptability, and the phase curve of unit cell does not need to cover 0° ~ 360°. The elements of the BAM can be reconstructed by adjusting the excitation region of the plasma resonance structures to achieve spatial beam scanning. The simulation results show that the proposed BAM has a good performance. It provides that such a novel idea can help to design the novel BAMs to obtain the adjustable and scannable reflective beam in space.

A compact hexagonal nested loop fractal antenna with L shaped slot on the ground plane is presented for multiband applications. In this paper, the effect of fractal iterations and position of L-slot on ground plane are optimized for better performance of the antenna. Multiple hexagon loops excite multiple resonant modes at 1.7, 2.4, 3.1, 4.5 and 6 GHz and an L-shaped slot on the ground plane helps to achieve wide bandwidth response with better impedance matching in the 4.25–6.41 GHz frequency band. An equivalent circuit of the proposed antenna is modelled and the same is verified using ADS. Reflection coefficient and radiation pattern are presented to further confirm the performance of the proposed design for wireless applications. The proposed antenna is fabricated on a low-cost FR4 substrate of dimensions 40×32×1.6 mm 3 and measured results show good agreement with simulation results.

In present work a wide band and high gain cylindrical dielectric resonator antenna working in X-band has been designed and validated experimentally. First the bandwidth of the antenna has been enhanced by placing the thin dielectric layer between antenna and feed network. Next gain of the antenna has been increased by placing a layer of high dielectric material at nearly λ/2 distance as superstrate. The proposed design with impedance bandwidth of 3 GHz and gain nearly 11dBi could be used in satellite communication and other wideband wireless applications operating in X-band.

This paper presents a novel balanced filter with enhanced stopband by using discriminating coupling. The proposed design utilizes third-order quarter-wavelength coupled resonators to obtain the filtering responses. Discriminating coupling is applied between feedline and resonator. The circuit is theoretically analyzed and implemented for demonstration. The operating frequency is located at 2.4 GHz and the common-mode rejection is larger than 20 dB up to 9 GHz (3.75 f 0 ). Due to discriminating coupling, the differential mode out-of-band rejection is larger than 20 dB up to 18 GHz (7.5 f 0 ), which shows wide stopband.

Ring Laser Gyroscopes (RLG) are widely used in Inertial Navigational Systems for detection of body rotation. But the performance is limited by lock- in state of RLG. To avoid this problem the Laser cavity of RLG is mechanically dithered. This process ensures that RLG stays out of the lock- in zone during its operating condition. But the dither signal appears as noise, which must be removed to obtain the true rotation of the body. This can be achieved by the use of digital filters. The required digital filter should have very high attenuation in the dither band and linear phase response in the pass band. Two types of multistage digital filters namely BBB and BCO filters are developed to remove the dither signal to an acceptable level. The BCO combined filter is found to be good and the same filter is implemented in real time using FPGA. The simulated results and the real time results are compared and found to be nearly same in both cases.

Device-to-device (D2D) communication has become one of the major areas of research ever since the industry was advancing to LTE and 5G. In this nascent stage of transformation, this research work characterizes the radio link behavior of D2D communication network in an indoor environment utilizing licensed and unlicensed band experiments and ray-tracing based simulations at frequencies of 2.4, 3.4, 5.2, 28 and 60 GHz. The path loss exponent (PLE) and standard deviation are estimated and compared with free space path loss (FSPL), log normal shadowing (LNS), International Telecommunication Union (ITU) model and also, compared with other research works. This work also studied the impact of indoor environments on D2D communications along with link budget, channel capacities and required performance improvements.

An inverse scattering problem of cylindrical bodies of arbitrary cross section buried in a circular cylinder with resistive boundary is presented. The reconstruction is obtained from the scattered field measurements for a plane wave illumination under the Born approximation. Illustrative examples are presented in order to see the applicability of the method as well as to see the effects of some parameters on the solution.