Volume 75, Issue 7-8

In this paper, the solution of the H-polarized wave scattering problem by infinite graphene strip grating is obtained. The structure is periodic except two neighboring strips. The distance between these two strips is arbitrary. In particular, such a problem allows to quantify the mutual interaction of graphene strips in the array. The total field is represented as a superposition of the field of currents on the ideally-periodic grating and correction currents induced by the shift of the strips. The analysis is based on the convergent method of singular integral equations. It enables us to study the influence of the correction currents in a wide range from 10 GHz to 6 THz. It is shown that the interaction between graphene strips is strong near plasmon resonances and near the Rayleigh anomaly.

The electromagnetic scattering characteristics of foam in Marine environment are studied in this paper. The Elfouhaily sea spectrum model is established, and the dielectric constants of seawater/ocean foam are calculated based on the double Debye dielectric constant model, furthermore, the formula relation between them is given. As an important factor affecting ocean electromagnetic scattering, the thickness of foam is proportional to the wind speed above the sea surface. In this paper, the SMCG method based on the surface current equation is mainly used to calculate the electromagnetic scattering coefficient of the environment, and the correctness of the SMCG algorithm is verified by comparing the calculated results with the actual measured data. Based on the computer simulation, the influence of the existence of ocean foam on the environmental scattering is discussed, and the Marine electromagnetic scattering coefficients under different wind speeds, different scrape angles and different radar bands are calculated. Through the analysis of the calculation results, the influences of wind speed, grazing angle and frequency on the electromagnetic scattering characteristics of the Marine environment containing foam are studied, and the general variation rule is obtained: the intensity of electromagnetic scattering increases with the increase of wind speed, the decrease of incident Angle and the increase of frequency. The results of this paper can be used to guide ocean navigation and fishery, and have reference significance in the military field.

The Capon beamformer has excellent resolution and interference suppression capability but due to various attributes of practical environment such as inaccurate and/or insufficient information about the source, transmission medium and antenna array its performance deteriorates. To enhance its performance various efforts have been devoted and one effective method is presented here. In this paper, a novel and efficient robust Capon beamformer is devised which is based on proximal gradient method (PGRCB) and the robustness is achieved through remodeling the optimization problem of standard Capon beamformer (SCB). In the proposed PGRCB, the proximal gradient method is used to formulate a new optimization problem in order to obtain the optimum weights of the robust beamformer. The proposed method can achieve better performance as compared to some recent methods in the literature and its effectiveness is verified by the simulation results.

This article proposes a design and implementation of array Microstrip Patch antenna of configuration 2 × 2 at an operating frequency of 3.5 GHz. The proposed design takes a dimension of 80 mm × 92 mm × 1.6 mm with four radiating elements arranged in rectangular form with an optimized separation between the patches. All the radiating elements were connected through a corporate series network with an inset feed to have better impedance matching. The model gives an efficiency of 90.99% with a bandwidth of 510 MHz and with fractal configuration, the bandwidth further enhances to 1.12 GHz. The maximum gain measured was found as 11.01 dBi at θ  = 10° and ɸ  = 360° and 10.45 dBi with fractal configuration. The designed antenna is proposed to be used in RADAR which will be used in the intelligent transportation system for the detection of nearby (short-range) vehicles in the blind zone. This kind of Radar also finds its application in collision avoidance and activating airbags/break boosting and thus helping mankind by saving lives. The article gives an idea of the use of an array antenna in intelligent transportation system for better gain and efficient results.

Microwave sensing is important to measure the permittivity of the materials or detecting a material. In this current work, a compact antenna for WLAN application with circular polarization is designed. We are supposed to use it as a sensor to determine the permittivity of industrial oil. For calibration of the sensor, the gasoline and petrol are utilized based on Debye theory and also butanol is checked. This antenna is designed based on Microstrip slot antenna with bent feed line and special split-ring resonator (SRR) as a metamaterial (MTM) element for 4 GHz, it is shown that metamaterial can be considered for improving the Q-factor and matching where the return loss is reduced from −16.5 to −33.5 dB and the Q-factor is increased from 2.39 to 32.9. It covers 4–5 GHz with the bidirectional pattern with gain of 4 dBi which makes it useful for putting inside of liquids. The total dimensions of this resonator are 20 × 20 × 1.6 mm and the FR-4 low-cost substrate is used and the experimental results are confirmed the simulations results by HFSS commercial full-wave software. In fact, this method can be used for fast detecting oil condition and longevity by checking the resonances’ shift and permittivity.

A compact tunable notch band ultra-wideband (UWB) antenna is implemented. The band notch characteristics have been obtained by placing a square-shaped metallic loop in the upper ground plane connected via PIN diode. The obtained notched frequency bandwidth can be altered by changing the states of the PIN diode. UWB response with narrow-band notch operation is observed when PIN diode is in ON state. When the PIN diode is in OFF state, the bandwidth of the obtained band notch widens by suppressing the first higher-order resonance and thus a narrow dual-band response is obtained. Moreover, the ratio of the frequency of first higher-order to the fundamental mode in the pass-band can be tuned with the different values as 1.584 and 2.20 in the ON and OFF state of the PIN diode, respectively. Furthermore, the antenna structure offers a compact geometry for the operation with the UWB response with band notch characteristics.

In this paper, a bandpass filter (BPF) has been designed using bent and coupled-line structure. The design process of the filter to achieve a BPF with good characteristics is completely explained. Therefore the LC equivalent circuit of The BPF is presented as the analytical description. The proposed filter can pass frequencies between 2.2 and 3.6 GHz with an insertion loss <0.4 dB, which is suitable for wireless applications. The fractional bandwidths (FBW) of the filter is about 48%. Some characteristics such as small size, low insertion loss, high return loss wide upper stopband bandwidth, and good suppression level in stopband are among the advantages of this study to be mentioned. Finally, the presented filter was fabricated, and the measured results have a proper agreement with the simulation results.

In this paper, a novel four-band diplexer using defected ground structures with compact size, low insertion loss and high isolation is presented. To begin with, there are 16 defected ground stepped impedance resonators (DSIRs) controlling four passbands characteristics. Every four DSIRs can generate one passband. Then, four different DSIRs use the same feeding line. According to the group delay, we can determine the relative physical position of the first resonator. For the demonstration, a four-band diplexer operating at 2.45/4.2 and 3.5/5.2 GHz with the fractional bandwidths of 10, 7, 6.2 and 5% is designed and fabricated. Finally, measured results agree well with simulated results.

This paper communicates the design and experimental validation of dual-band SIW power dividers (single-stage and double-stage) with arbitrary power division. The dual-band power dividers are developed for WiMAX (3.5 GHz) and WLAN (5 GHz) applications. The proposed SIW power dividers are realized by a rectangular cavity, two rows of metallic-vias and one pair of unequal complementary split-ring resonators (CSRRs). Two resonating frequencies are produced below the waveguide cut-off frequency due to the unequal CSRRs etched-out on the top-surface of the cavity, which results in size reduction. To realize arbitrary power division, two output-ports are configured asymmetric with respect to input-port. The power division is varied by altering the distance between the two output-ports. Finally, two compact dual-frequency power dividers (single-stage and double-stage) working at 3.5 and 5 GHz are designed and validated through fabrication and measurement. The fabricated prototype exhibits dual-band operation, compact size (0.027λg2${\lambda }_{g}^{2}$), good magnitude imbalance, return loss and isolation.

In this paper, a new reconfigurable power divider (PD) is proposed to improve the efficiency of the three-way Doherty power amplifier (DPA). The conventional λ/4 transmission line is replaced by the proposed reconfigurable PD in the input of peaking amplifier, where the 90° phase shift and impedance matching can be achieved. Furthermore, the output power distribution ratio (PDR) can be continuously adjusted in a large range by adjusting the reverse voltage of the varactor diodes. Therefore, the reconfigurable PD with the best PDR can assign input power to the peaking amplifier. Experiment results show that the maximum measured power added efficiency (PAE) of the proposed three-way DPA is 49%, which is improved by 5% compared with conventional three-way DPA.