An overview of state-of-the-art frequency tunable technologies in the realization of tunable radio frequency (RF) and microwave tunable circuits is presented with focus on filter designs. Those enabling techniques and materials include semiconductors, micro-electro-mechanical systems (MEMS), ferroelectric and ferromagnetic materials. Various performance indicators of one-dimensional tunable filters are addressed in terms of tunability, losses, signal integrity and other aspects. Fundamental limitations of the classical onedimensional tuning method are discussed, which makes use of only one type of tunable elements such as either electric or magnetic tuning/controlling of circuit parameters. Requirements of simultaneous electric and magnetic two-dimensional tuning techniques are highlighted for achieving an unprecedented and advantageous wider modal tuning. It is believed that this emerging scheme will lead its way in the realization of future highly efficient and tunable RF and microwave components and devices.

In this paper, a behavioral model with multi-status is represented to describe electrothermal memory of power amplifiers. In the model, a multi-point linearity approximation method is introduced to estimated the model coefficients at random status. The parameters of the new model can be identified by traditional identification algorithms such as recursive least square (RLS) with the input and feedback data at predetermined status points captured by the digital predistortion (DPD) system. Compared with traditional models, the coefficients estimation speed for the new model at new status is very fast. The final experiment result proves that the multi-status model can efficiently ameliorate the performance deterioration caused by electrothermal memory in the the DPD system, and at the same time it still keeps very high DPD performance.

In this paper, the electromagnetic scattering from two scatterers is analyzed from a rigorous integral formulation solved by the method of moments (MoM). G. Kubicke has recently developed the E-PILE (Extended Propagation-Inside-Layer Expansion) method to calculate the scattering from an object above a rough surface for a two-dimensional problem. This method allows us to calculate separately and exactly the interactions between the object and the rough surface. The purpose of this paper is to extend the E-PILE method to a three-dimensional problem. Such a 3-D problem involves a large number of unknowns and can not be solved easily with a conventional method of moments by using a direct LU inversion. Thus to solve this issue, the E-PILE method is combined with the physical optics (PO) approximation to calculate the local interactions on both the object and the rough surface. By using this hybrid method, the requirements of memory and CPU time can be reduced significantly.

We present the design, characterization, and experimental verification of a dual-band metamaterial absorber (MA) in the microwave frequencies. The proposed MA consists of a metallic gammadion-shaped structure and a complete metal layer, separated by a dielectric spacer. The results show that the proposed MA has two absorption peaks at nearly 5.6 GHz and 6 GHz with absorption rates of 97% and 99%, respectively. The interference theory is used to investigate the physical mechanism of the proposed MA. The experimental results are in good agreement with the theoretical predictions.Furthermore, it is verified by simulations that the absorption of the proposed MAis almost insensitive to the incident wave polarization and oblique incident angle for the both TM and TEmodes. This MA has broad prospect of potential applications.

This paper presents a novel design of an egg curve based wide-slot antenna for various wideband applications. The proposed printed antenna consists of an egg curved slot with a similar tuning stub. The egg curve is obtained by introducing an egg shaping parameter into standard elliptic curve equation. The effect on the impedance bandwidth through the variations in antenna design parameters has been investigated and analysed in detail. To validate the theoretical design, various egg curved slot antennas were designed, fabricated and measured. Good agreement between the simulated results and the measured ones is observed. An empirical formula is also proposed to approximately determine the frequency corresponding to the lower edge of -10 dB operating bandwidth. The results demonstrate that the proposed egg curved slot antenna (ECSA) can obtain a measured bandwidth (BW) of 164.46% (1.95-20.0 GHz) for |S₁₁|≤10 dB. A stable realised gain of about 4.1-5.1 dBi with consistent radiation patterns are measured over more than the entire ultrawideband (UWB) bandwidth (3.1-10.6 GHz) which makes it a suitable candidate for wideband and UWB wireless system applications.

In this paper, we present the measurement methodology and results for a low voltage Power line Communications (PLC) network under different configurations. Based on the measurements, a correlation of the channel transfer characteristics to the network topology is established and a deterministic model based on two-wire transmission line theory for transverse electromagnetic (TEM) wave propagation is proposed. The channel frequency response in frequency range of 1-30 MHz is determined, where the model results agree well with the measurements.

Most wireless channel models assume fixed scatterers with specific geometrical distributions in the propagation environment. In reality most scatterers move with random movements on the azimuth plane. In this paper, the effects of such scatterers' random movements on the cross correlation function (CCF) of wideband (WB) and ultra-wideband (UWB) non-isotropic multiple-input multiple-output (MIMO) channels are characterized. The CCF of WB/UWB MIMO channels is calculated not by assuming a specific geometry for scatterers in space but based on specific mathematical relationships between physical parameters of the wireless channel along with appropriate assumptions on their probability density functions (pdfs). The CCF is used to determine the inuence of moving scatterers, in a stationary scenario, on the power spectral density (PSD) and the coherence time of WB and UWB multiple-input single-output (MISO) channels, as a particular case of MIMO channels. Unlike the fixed scatterers case, the PSD is not a band-limited process, it decays with frequency.

In this paper, design and simulation of optimized MEMS spiral inductor are presented. The effects of design parameters on characteristics of inductor have been considered. The suspended spiral inductor was designed on silicon substrate using MEMS technology to reduce the metal and substrate losses of inductor. The results show that the quality factor of the inductor is 27 at 5.23 GHz and that the maximum Q-factor is 42 at 26.56 GHz. The dimension of the inductor is 185×200 μm², which occupies less area on chip than other works. In this work, the high quality factor inductor with small size is obtained.

This work aims to provide a physical interpretation of the ``Maxwell's displacement current'' and generalize the use of the derivative function of the electrical flux ``dΨ/dt'' in the magnetic field calculation. The innovative contribution of this study is a mathematical model to describe the origin of magnetic field as a variation of electric flux. By this approach, it follows that only the function ``dΨ/dt'' can generate a ``magnetic tension'': this leads to an interesting unification of electrical phenomena. Displacement current and conduction current are interpreted as complementary aspects of the same phenomena. It is shown how the use of the ``dΨ/dt'' allows the recovery of a formal symmetry in Maxwell's relations of electromagnetic induction law and circuit magnetic law. Included also is a generalized expression of the function ``dΨ/dt''.

In this paper, frequency reconfigurable slot-patch antenna with reflector at the back of an antenna is presented. The proposed antenna consists of a microstrip patch antenna and a microstrip slot antenna where the slot antenna is positioned at the ground plane underneath the patch. Three switches are placed in the slot. The antenna is capable to reconfigure up to six different frequency bands from 1.7 GHz to 3.5 GHz. The microstrip patch antenna produces three different frequency bands with directional radiation pattern while the microstrip slot antenna produces another three frequency bands with bidirectional radiation pattern. Due to the reflector placed at the back of the antenna, the radiation pattern is directional at all frequency bands. Simulated and measured results are used to demonstrate the performance of the antenna. The simulated and measured reflection coefficients and radiation patterns are presented and compared.

In this paper, complementary split ring resonators (CSRRs) as band-stop elements are used in combination with coupled microstrip lines as high and low pass elements to design and fabricate very compact bandpass filter (BPF) having controllable characteristics. The proposed filter provides several advantages such as compactness (occupying area less than 0.1λ_g × λ_g in which λ_g is calculated at center frequency of pass band), sharp rejection, low insertion loss (IL less than -8.5 dB in all of the bandwidth), good return loss (RL 3-dB bandwidth of roughly 2 GHz from 0.7 GHz to 2.7 GHz i.e. more than 115% FBW) and low cost. Defected Microstrip and Ring Resonator Structures have been used for eliminating the created spurious pass band in upper frequencies. The simulation results have been done with full-wave softwares i.e. CST and HFSS by time and frequency domain solvers, respectively. Also, the equivalent lossless lumped circuit of total structure has been obtained and simulated by ADS software. These simulated results show good agreements with experimental ones.

A new ultra-wideband antenna based on a uniform narrow slot is proposed. The slot radiator is fed by a pair of differential microstrip-lines, to implement a balanced and vialess antenna. The multiple-mode resonances of the radiator are excited simultaneously to form an ultra-wideband radiation, by optimizing antenna dimensions and port impedance. Comparing with other ultra-wideband slot antennas, this antenna has improved radiation patterns and low cross polarization due to its symmetry in structure. Antenna samples are designed and fabricated for verification. The measured impedance bandwidth has successfully achieved a fractional bandwidth of 106% (VSWR < 2.5). The radiation patterns are also measured and agree well with the prediction.

We present a simple and straightforward approximate approach to removing resonant artifacts that arise in the material parameters extracted near half-wavelength resonances that arise from transmission/reflection (T/R) measurements on low-loss materials. In order to determine material parameters near one such λ/2 resonance, by means of the 1st-order regressions for the input impedance of the sample-loaded transmission line, we approximate the characteristic impedance of the sample-filled section that is, in turn, dependent either on the relative wave impedance in a coaxial transmission line or on the relative permeability in a rectangular waveguide case. The other material parameters are then found, supplemented with the refractive index obtained from the conventional T/R method. This method applies to both coaxial transmission line and rectangular waveguide measurements. Our approach is validated by use of S-parameters simulated for a low-loss magnetic material, and is also applied to determine the relative permittivity and permeability from S-parameters measured for nylon and lithium-ferrite samples. The results are discussed as compared to those from the well-known Nicolson-Ross-Weir (NRW) method and are experimentally compared to those from the Baker-Jarvis (BJ) method as well.

In this paper, an application of artificial neural network based on multilayer perceptron (MLP) model is presented for predicting the slot size on the radiating patch for improvement of the performance of patch antenna. Several performance affecting parameters like resonance frequencies, gain, directivity, antenna efficiency, and radiation efficiency for dual band frequency are observed with the variation of slot size. For validation of this work, a prototype X-shaped patch antenna is fabricated using glass epoxy substrate and its performance parameters are measured experimentally and have been found in good agreement with ANN and simulated values.

We present a flat lens design that provides focusing with no aberration. By profiling the refractive index of the lens to generate a spherical wavefront at the exit side of the lens, the transmitted fields converge at a specified focal point. The focusing is achieved using primarily the dispersion phenomenon. We show through numerical examples that focusing without aberration can be achieved at a specific frequency and that focusing is possible over a narrow range of frequencies providing that the dispersion is minimal. Additionally, we show that the same principle used to design the lens can be used to design flat reflectors with a focal point focusing.

For the GSOLT calibration algorithm of n-port vector network analyzers (VNA), the sensitivity coefficients for the S-parameters of the n-port device under test (DUT) are developed as functions of the S-parameter deviations of SOLT standards. By introducing the generalized flow graph of the 3n-term error model, analytic formulas for the S-parameter deviations of the n-port DUT with respect to the error terms have been deduced. In addition, expressions for the deviations of the error terms in regard to the nonideal calibration elements are given by a series of matrix operations. Finally, the analytic expressions of the sensitivity coefficients are concluded, which can be used for establishing the type-B uncertainty budget for S-parameter measurements.

This paper proposes a fusion technique of feature vectors that improves the performance of radar target recognition. The proposed method utilizes more information than simple monostatic or bistatic (single receiver) algorithms by combining extracted feature vectors from multiple (two or three) receivers. In order to verify the performance of the proposed method, we use the calculated monostatic and bistatic RCS of three full-scale aircraft and the measured monotatic and bistatic RCS of four scale-model targets. The scattering centers are extracted using one-dimensional FFT-based CLEAN and then used as feature vectors for a neural network classifier. The results show that our method has better performance than algorithms that solely use monostatic or bistatic data.

A low-cost dual-wideband active global navigation satellite system (GNSS) antenna is proposed for vehicle applications. An inverted shorted annular ring (ISAR) and a shorted annular ring (SAR) are used as radiation patches for low-angle multipath mitigation and operated respectively at 1164-1279 MHz and 1559-1610 MHz. To reduce the effect of the mutual coupling between the ISAR and SAR, meanwhile broaden the impedance bandwidth of the ISAR, defected ground structures are etched under the microstrip feed lines of the ISAR. Two trans-directional couplers are adopted to form orthogonal dual-feed networks of the ISAR and SAR for wideband circularly polarized reception. A combiner is adopted to merge two way signals into one way amplified by a wideband low noise amplifier with the proposed DC and RF collinear transmission technology. The experimental results show that the proposed antenna is better than the NovAtel GPS-703-GGG pinwheel antenna in terms of signal reception.

This paper critically reviews the electromagnetic advantages of altering the dielectric substrate section of the antenna as opposed to the conducting elements. Changing the dielectric has been used to improve the bandwidth, efficiency and gain of antennas. Heterogeneous substrates have also been employed to lower the effective permittivity, suppress surface waves for high indexed substrate materials and reduce mutual coupling. In the second half of this paper, 3-D printing has been used to create substrates with reduced material consumption for a lightweight flexible wearable antenna.

The imaging of targets embedded in a planar layered background media has been an important topic in subsurface and urban sensing. In this paper a fast and efficient tomographic algorithm for the imaging of targets embedded in a multilayered media is presented. The imaging algorithm is based on the first-order Born approximation and exploits the spectral multilayered media Green's function. The exploding reflection model is employed and then the Green's function is expanded in the spectral form to facilitate the easy implementation of the imaging algorithm with fast Fourier transform (FFT). The wave propagation effect due to the presence of the layered subsurface media is automatically taken into account in the imaging formulation through the multilayer media Green's function. The linearization of the inversion scheme and employment of FFT make the imaging algorithm suitable in several applications concerning the diagnostics of large probed domain and allow real-time processing. Representative examples are presented to show the effectiveness and efficiency of the proposed algorithm for radar imaging through multilayered media.