Two novel compact 2.6/5.2 GHz diplexers with high common-mode suppression were designed and fabricated on the FR4 substrate. The diplexers were designed based on two open loop rectangle ring (OLRR) resonators and the two different resonant frequencies could be easily obtained by tuning the lengths of OLRRs. In the past, the traditional balun diplexer needed matching circuit to transfer signal to radio frequency (RF) transceiver with low loss because of the existence of unmatched impendences between the balun diplexer and RF transceiver. In order to improve their efficiency and low down the cost of the fabricated circuits, we would propose a method to tune the output impendence of the balun diplexer and the diplexer could have matching output impendence with the RF transceiver. The proposed balun diplexer had the structure of two stub-loaded microstrip lines, and the needed output impendence could be changed by tuning the widths of microstrip lines and stubs and by changing the length and position of stubs. For that, if the output impendence is well tuned, the designed balun diplexer will have the higher efficiency and low cost because the matching circuit is not necessary.

In stomach tumor imaging, traditional time domain algorithm, i.e., back projection (BP) algorithm, and traditional frequency domain algorithm, i.e., frequency wave number migration (F-K) algorithm, can locate tumor target accurately. However, BP and F-K algorithms perform poorly in identifying tumor sizes and shapes. The algorithms must consider the influence of various tissues in the human body: the attenuation of the signal strength of electromagnetic waves, the decrease in speed and the refraction due to the different permittivities between different organs of the body. These factors will eventually lead to image offset and even generate a virtual image. It is effective to refrain the displacement of image with modifying the time element of the imaging algorithm by iteration. This paper proposes a method based on combination of support vector machine (SVM) with BP and F-K algorithms to solve problems in recognizing tumor shape. The method uses field strength obtained by BP and F-K algorithms as input in SVM to establish the SVM model. Based on BP algorithm, recognition method for SVM includes the following characteristics: short prediction time of SVM and good virtual elimination effect. However, the algorithm requires long periods and possibly misses tumor targets. Except the same characteristics as BP algorithm: short prediction time of SVM and good virtual elimination effect, F-K algorithm also works more efficiently, does not miss any tumor targets, and conforms more with requirements of real-time imaging. When the data are contaminated by noises, the tumor shape in the stomach can still be suitably predicted, which demonstrates the robustness of the method.

In this article, a compact ultra-wideband (UWB) band-pass filter (BPF) with wide upper stopband is presented. The filter is designed with a UWB response from 3.2 GHz to 10.8 GHz with low insertion loss of 0.9 dB and less than 0.19 dB at the center frequency (6.67 GHz). The filter is also designed with a broad upper stopband with high rejection level of 20 dB. The group delay is flat with maximum of 0.4 ns. The proposed UWB filter is constructed by using a pair of parallel coupled lines and two ring resonators. In this design, the ring resonators provide two new excited modes to widen the desired UWB passband and also create two tunable transmission zeros to achieve a wide stopband. Good agreement is observed between simulated and measured performances of the UWB filter.

New generation wireless communications are expected to provide new services over the existing variety of wireless applications in the coming years. In this perspective, advances in utilization of computational electromagnetics (EM) and millimeter-waves (mmW) frequency bands make them as candidates for ultra-high-resolution and ultra-high-speed wireless communications. With the deployment of mmW wireless technologies, brinks of potential mmW induced biological and health effects should be evaluated carefully. The EM exposure is usually measured in terms of absorbed power from any user operating wireless devices. The exposure varies with the part of the body and location of the source that is exposed to the radio frequency waves. The purpose of this study is to observe EM exposure in terms of Specific Absorption Rate (SAR) and temperature elevations at mmWs from the designed Antipodal Linear Tapered Slot Antenna (ALTSA) at 60 GHz on different body parts utilizing EM computations and experiments with Infrared Thermal Camera.

In this paper, a microstrip lowpass filter with -3 dB cutoff frequency of 1.8 GHz composed of two resonators with different polygon patches and six symmetric suppressing cells is presented. To design the proposed filter, the impact of each microstrip transmission line on the scattering parameters of the employed resonators is separately determined by extracting the equations of the insertion loss (S21) and return loss (S11) on the basis of their equivalent LC circuit. The designed filter is fabricated and measured, and a good agreement between the results of simulation and measurement is obtained. In the whole stopband region, a return loss better than -0.35 dB and an acceptable suppression level of -22 dB from 1.87 to 19.75 GHz are achieved. Furthermore, a flat insertion loss in the passband and an acceptable return loss (-19.32 dB) in this band can verify desired in-band performance. The designed lowpass filter has a high figure of merit about 36969.34.

A varactor-tuned microstrip bandpass filter (BPF) with independently tunable center frequency and bandwidth is proposed in this paper. The proposed BPF with a simple configuration is composed of a half-wavelength transmission line with both ends short-ended and a T-shaped transmission line. Meanwhile, two varactors are inserted symmetrically in the middle section of the half-wavelength transmission line to adjust the resonant frequency. The T-shaped transmission line is connected to the half-wavelength transmission line by a lumped capacitor. In addition, two inductors loaded symmetrically in the feed line are employed to control the coupling coefficient. It is convenient to adjust the frequency and bandwidth of the filter independently by using only three varactors, which simplifies the circuit structure greatly. The predicted results on S parameters are compared with the measured ones, and a reasonable agreement is achieved.

This paper presents a new hybrid switching technique for enhanced pulse mode solid-state power amplifiers (SSPAs). In the proposed technique, pulse timing for bias stabilization is effectively decoupled from pulse amplification. The decoupling allows fast pulse switching by reducing the pulse width and increasing the pulse repetition frequency (PRF). The new switching method is applied to an X-band SSPA using GaN HEMT. The advantage of the proposed method is demonstrated by its excellent pulse characteristic. The proposed technique achieves a fast PRF of 100 kHz and a narrow pulse width of 1 μsec. The measured rise/fall time (RFT) is 12.5/11.1 nsec, which is more than four times less than that of previous works. In addition, an excellent pulse droop of 0.43 dB is achieved with an output power of 51.3 dBm at 9.9 GHz. The fabricated SSPA shows a maximum output power of 135 W, a small-signal gain of 47 dB, and power added efficiency (PAE) of 28.2% at 9.9 GHz. These results show that the proposed pulse switching technique provides a promising solution for SSPAs using a high-power GaN HEMT.

The Weibel instability of intense and collimated MeV fast electron beams in multi-layer structure is investigated. It is found that the electromagnetic instability of fast electron beams can be significantly suppressed by this structure. A strong magnetic field will be created at the interfaces between materials with different resistivities as these fast electrons are injected into this structure. It obstructs the transverse movement of the fast electrons and confines them to propagate along the interfaces. In consequence, the positive feedback loop between magnetic field perturbation and electrons density perturbation is broken, and the Weibel instability is thus weakened. Furthermore, the calculated results for Au/Si multi-layer structure by a hybrid Particle in Cell code have proven this weakening effect on the Weibel instability of intense fast electron beams. Because of the high energy-density delivered by the MeV electrons, these results indicate applications in high-energy physics, such as radiography, fast electron beam focusing, and perhaps fast ignition.

In this paper we focus on multi-objective optimization in electromagnetic problems with given priorities among the targets. The approach proposed in this paper is able to build a proper cost function capable to correctly implementing the design criteria and their priorities avoiding the evaluation of the Pareto front of the solutions, which is a very time consuming task required in the classic a-posteriori methods. The resulting function, named Quantized Lexicographic Weighted Sum (QLWS), can be used as cost function in a very large class of electromagnetic problems. In this paper we demonstrate its usefulness in two common situations in antenna array design: the synthesis of a sparse linear array and a sparse isophoric ring array.

This paper proposes a novel planar beam tracking antenna and brings a new prototype antenna in wireless communication systems. The proposed antenna consists of a magic-T, two antenna elements and two phase shifters. The main idea for the antenna is to adjust the phase shifter using the difference of the signals received by the two antenna elements to tilt the beam in the direction of the arrival wave. Theoretical discussion is presented to explain the concept. Both-sided MIC technology is effectively used to integrate the magic-T and the phase shifters with the antenna elements in a simple structure. A prototype antenna of the new design for E-plane beam tracking is fabricated, and the radiation pattern and return loss are measured. Simulated and experimental results of the beam direction vs. applied voltage are successfully compared, and the proposed concept is experimentally demonstrated. An antenna structure for beam tracking in H-plane is also demonstrated in this paper.

``Curve-fitting'' method is an important method to extract dielectric parameters of substrate materials from planar transmission lines. At gigahertz frequencies, effective conductivity concept is adopted to model the conductor's surface roughness effects in planar transmission lines, and differential extrapolation method is used to remove surface roughness effects. However, such a concept and method lose their accuracy at extremely high frequency such as terahertz waves. This paper details some new limitations in the terahertz regime and proposes corrections in calculating effective conductivity with rough conductor and curve-fitting method for transmission performance characterization in eliminating the effects of surface roughness. The proposed method is validated by simulation data for conductivity with parallel plate waveguide model, and the corrected method presented here can effectively extract dielectric parameters with an error less than 7% .

Metamaterial absorber (MMA), as a kind of new-style artificial absorption material, has been extensively researched and discussed. Currently, however, the research focuses mainly on the development and application of the novel structure MMA, and only little work is aimed at the physical mechanism of the MMA. In order to deeply understand the absorption mechanism, in this paper, the numerical simulation results of an MMA are given. Then, based on the reflection theory modal, the numerical simulation results are well discussed and explained in detail. It is found that the theoretical results agree well with that of the simulation, which suggests that the reflection theory modal is effective for analyzing the absorption mechanism of the MMA. The main contributions of this paper are to quantitatively discuss and explain the absorption mechanism of the MMA by using the reflection theory and thus offer a consultation in design and fabrication of the advanced MMA for engineers.

A novel structure of a near-field communication (NFC) loop antenna for mobile phones with a metal back case is proposed. The proposed structure of the metal back case itself can operate as an NFC loop antenna through the design of a simple single turn loop antenna on the top portion of the metal back case, so that the simple structure of the proposed NFC loop antenna can reduce the overall thickness of the NFC antenna for slim mobile phones. Since a sintered ferrite sheet with generally higher relative permeability (μr ≈ 200) must be used to reduce the performance deterioration of the conventional NFC loop antennas due to the eddy current in the battery pack of a mobile handset, the cost of these conventional NFC antennas is high, and they are considerably fragile. In this paper, the proposed NFC antenna is designed without the ferrite sheet and in the optimal location to ensure minimum interference from the adjacent metallic components.

A novel method for further wideband RCS reduction on metasurface (MS) is proposed in this paper. By introducing a phasor interference element to the original MS composed of two elements, RCS of the proposed MS constructed by three elements can be further remarkably decreased in broadband. The measurement procedure on scattering performances of samples is conducted in an anechoic chamber, in which the experimental results indicate that the proposed MS can achieve further 3-dB RCS reduction from 6.94GHz to 15.35GHz compared to the original MS, and the maximum further reduction reaches 24.9dB. As a result, compared with a same-size metallic plate illuminated by a normal plane wave, RCS of the proposed MS can be reduced by more than 8.5-dB from 6.68GHz to 15.38GHz with the relative bandwidth of 78.9%.

In the paper, the electromagnetic scattering (EM) from a one-dimensional (1-D) perfectly electric conducting (PEC) randomly rough sea surface with large windspeed is investigated by the iterative physical optics (IPO) algorithm. In this method the multiple coupling interactions among points on sea surface are considered. To improve computational efficiency, the local coupling technique is adopted to accelerate the iterative process. In numerical results, the EM scattering by 1-D sea surface for different polarizations is calculated and compared with that by the conventional method of moments (MOM), as well as the computing time and memory requirements. In addition, the influence of some parameters on the scattering of sea surface are investigated and discussed in detail, such as the threshold of coupling distance, iteration numbers, and windspeed.

As ultra high frequency (UHF) radio frequency identification (RFID) technology, a smart recognition technology, has been gradually spreading to various applications, and several sub-1 GHz wireless technologies are being standardized and developed. As such technologies operate at a specific frequency band (902-928 MHz industrial, scientific, and medical (ISM) bands), the impact of RF interference due to performance degradation of UHF RFID technology on the interference signal is emerging as a new obstacle. In this paper, we investigate the interference analysis and experimental results of passive UHF RFID systems in sub-1GHz wireless communications systems. By considering interference signal frequency and power, interference deployment, antenna polarization, RF system-level analysis, and experimental verification are conducted to evaluate the impact of performance degradation in the UHF RFID system on the interference signal.

A wide slot antenna with a Y shape tuning element for wireless applications (GSM 1800, WiMAX, PCS and ITM-2000) is presented. The proposed antenna is fabricated on an FR-4 substrate (tan(δ)=0.02, εr=4.3) with the thickness of 1.6 mm. On the top layer of the substrate, a 50 ohm microstrip line is fabricated which is terminated in Y shape tuning element. On ground plane, an irregular wide slot and triangular notch are etched. In addition, for performance improvement two triangular shaped parasitic slots are embedded on the ground plane. The proposed antenna is energized by the microstrip line. It exhibited the bandwidth of 127.55% from 1.15 GHz to 5.2 GHz for |S11| < -10 dB. Surface current distribution and radiation pattern at resonating frequencies 1.15, 1.25, 1.9 and 4.2 GHz are analyzed. Impact of parameters on S11 characteristic is also studied to know the behavior of the antenna.

In this paper an ultra-wide bandwidth double-layered Vivaldi antenna (DLVA) integrated in Radome housing is proposed. First the conventional Vivaldi antenna is designed with bandwidth extended from 1.8 to 6 GHz at VSWR (3:1). Then for wider bandwidth, two slots are etched in the antenna ground plane to extend the antenna bandwidth from 1.7 to 9 GHz. For more improvement in antenna bandwidth, circular slots as electromagnetic band-gap structure (EBG) are etched to further extend the antenna bandwidth from 1.45 to 10 GHz. For gain enhancement double layers of Vivaldi antenna ground plane are designed with the same feeding line to reach 29 dBi peak. High frequency structure simulator (HFSS) ANSYS is used to design to simulated all the design steps. The proposed antenna is fabricated and measured. Finally, DLVA is integrated inside the Radome to improve the antenna gain and protect the proposed antenna from environmental factors. The antenna is fabricated and tested, and a good agreement between simulated and measured results is found.

The ionospheric GPS signal delay which is a function of TEC plays a major role in the estimation positional accuracy of satellite based navigation systems and detrimental to position estimation especially in strategic applications. Ionospheric TEC is a function of geographical location (Latitude, Longitude), time, season, etc. In this paper, we propose a system theory based Grey Model (GM(1,1)) which uses past and present data for forecasting TEC (GPS signal delay). In this model, data of nine sequential days data from five stations of a GPS Aided Geo Augmented Navigation (GAGAN) system network located at different places representing different latitudes, longitudes and equatorial anomaly regions are used to forecast the 10th day TEC values of each of these stations. The performance of the model is assessed by comparing the statistical parameters such as Standard Deviation (SD) and Mean Square Deviation (MSD). The forecasted results are very encouraging. For all the considered five stations, forecasting is better for post sunset time than day time. Also, the results indicate that SD and MSD values are comparatively more for Trivandrum (near geomagnetic equator) and Ahmedabad (near the crest of the equatorial anomaly region). These results indicate that the proposed model is useful for forecasting of GPS signal delay both for civil aviation and strategic applications.

This paper presents a wide-angle polarization independent triple-band absorber based on a metamaterial structure for microwave frequency applications. The designed absorber structure is the combination of two resonators (resonator-I and resonator-II). The proposed absorber is ultra-thin in thickness (0.012λo at lowest resonance frequency and 0.027λo at highest resonance frequency). The proposed absorber structure offers three absorption bands with peak absorptivities of 99.95%, 95.32% and 99.47% at 4.48, 5.34 and 10.43 GHz, respectively. Additionally, it also offers the full width at half maximum (FWHM) bandwidth of 167.2 MHz (4.40 - 4.56 GHz), 178.1 MHz (5.25 - 5.43 GHz) and 393.8 MHz (10.24 - 10.63 GHz), respectively. The metamaterial property of the designed absorber structure has been discussed by using dispersion diagram plot. The designed absorber structure exhibits wide-angle absorption at various oblique incidence angle for both TM and TE polarizations. The absorption mechanism of the designed absorber structure has been analyzed through electric field and surface current distribution plots. The input impedance of the designed absorber (375.67 Ω at 4.48 GHz and 346.73 Ω at 10.43 GHz), nearly matches the free space impedance. The proposed absorber structure is fabricated and measured. Simulated and measured results are in good agreement with each other.