Feed-forward artificial neural networks (ANNs) can provide the adequate model required for the linearization of power amplifiers (PAs) used in wireless communication systems. A common characteristic of previously available ANN-based models for linearization purposes is the use of a single real-valued ANN having two outputs. The contribution of this work is to report the benefits of performing such behavioral modeling based on two independent real-valued ANNs, where each network has a unique output. The proposed ANN-based model is applied to the behavioral modeling of a GaN HEMT class AB PA, and its accuracy is compared to previous approaches in two different scenarios. First, in case of similar number of network parameters, it is observed that the proposed ANN-based model can reduce the normalized mean-square error (NMSE) by up to 1.3 dB. Second, in a situation of comparable modeling accuracy (NMSE = -40 dB), it is observed that the proposed ANN-based model can reduce the number of network parameters by up to 40% (from 62 to 38 real-valued parameters).

A modified generalized memory polynomial model (MGMP) is proposed for RF power amplifiers (PAs). The MGMP model is derived by applying complexity-reduced technique to the generalized memory polynomial model (GMP)， and the least square (LS) algorithm is used for coefficient extraction. The proposed MGMP model is assessed using a GaN Class-F PA driven by two modulated signals (a WCDMA 1001 signal and a single carrier 16 QAM signal with 20 MHz bandwidth). The experimental results demonstrate that the MGMP model outperforms the memory polynomial (MP) model and the generalized memory polynomial (GMP) model. Compared with MP model, the MGMP model shows a normalized mean square error (NMSE) improvement of 2.13 dB in forward modeling, average adjacent channel power ratio (ACPR) improvement of 2.62/2.11 dB in the DPD application with almost identical number of model coefficients. In contrast with the GMP model, the MGMP model can achieve comparable forward modeling and linearization performance results, but reduces approximately 40% of coefficients.

A tunable metasurface composed of multiple resonant units is proposed, with each unit containing a block of SrTiO₃ ferroelectric and a periodical copper-wire structure. The local transmission coefficient of the metasurface is controlled by voltagetuning the permittivity of SrTiO₃ in each resonant unit. The function of this tunable metasurface is demonstrated by simulating beam steering at the angles of 30˚ and 14.47˚, respectively; as well as beam focusing at the focal lengths of 2λ₀ and 4λ₀, respectively.

In this paper, a novel compact dual-band microstrip antenna operating at two different bands namely C-band and X-band is presented and analyzed. The dual ultra wide band is realized by cutting two triangular slots on the right and on the left sides of the patch and a rectangular slot on the top side of the patch. The antenna structure is optimized and simulated using commercial software. The excitation is launched through a 50 Ohms microstrip line. According to simulation and measured results the proposed antenna can provide two separated impedance bandwidths of 500 MHz centered at 7 GHz and 2 GHz centered at 10.7 GHz and stable radiation patterns.

A novel compact wideband inphase multilayer power divider based on slotline-to-microstrip coupling structure is presented in this paper. To improve the isolation between output ports, this power divider breaks the conventional half-wavelength slotline configuration and introduces a lumped resistor. A wideband bandpass filter integrated with the power divider is designed to allow the power divider to reject the undesired signals located in adjacent frequency channels. This filter consists of two E-shape units. In order to improve its performance at low frequency band, a lumped capacitor is bridged between the two E-shape units. As an example, a wideband power divider combining with a filter is designed and fabricated. The experimental results show that the proposed power divider has a low insertion loss, high isolation, good return losses at all ports, good amplitude and phase balance, as well as flat group delay over the wide frequency band from 3.5 GHz to 10 GHz. In addition, the width of upper stopband reaches up to 3.8 GHz (12.9 GHz-16.7 GHz) corresponding to attenuation more than 20 dB.

In this work, a planar monopole ultra-wideband (UWB) antenna with an L-shaped stub on the ground plane is proposed. The novel extended L-stub in conjunction with the UWB radiator achieves an ultra wideband impedance matching with a compact size. The proposed antenna is fabricated and measured showing an ultra wide operating frequency range from 2.3 to over 14 GHz (VSWR < 2) with a unidirectional gain from 3-6.5 dBi and efficiency from 70-85% within the UWB band from 3.1-10.6 GHz. The proposed antenna provides a new way to improve ultra wideband impedance matching other than the frequently used tapered microstrip feed line. It also provides a way to improve the lower frequency bandwidth of the antenna without increasing the antenna's physical size, which is the most common method to use.

An X-band ferrite-loaded half mode substrate integrated waveguide (HMSIW) phase shifter is proposed and fabricated in this paper. A full-height E-plane Yttrium Iron Garnet (YIG) ferrite slab is embedded in the HMSIW to construct the non-reciprocal phase shifter. With the application of a magnetic bias field on the ferrite slab, the phase of the ferrite-loaded HMSIW can be adjusted and controlled. For a magnetic bias field of 1800 Gauss, the insertion loss is less than 3.2 dB from 9.7 to 11.0 GHz. The return loss is better than 10 dB over the same frequency range. The largest differential phase shift can be up to 337°. This circuit is easily integrated with other planar components and also has the capability to handle medium power level.

A novel ortho-mode transducer (OMT) for dual-band dual-polarized communication systems is proposed in this letter. The OMT is loaded with five posts in reasonable positions of the waveguides and a shorted circuit piston in the branch waveguide. Compared with the septum loaded traditional one, the presented OMT is more flexible, simple and easy to fabricate. Both simulations and measurements indicate that the impedance bandwidths of VSWR<1.15 ranging from 6.50 to 7.20 GHz and 8.80 to 10.2 GHz can be obtained. The low insertion losses indicate that the presented OMT can be used in actual project. Moreover, good isolation performance between the two input ports in both bands are obtained because of the inherent existence of cross polarization.

A typical magnetic resonance coupling based wireless Electric Vehicle (EV) charging system consists of a transmitting coil at the charging station and a receiving coil in the vehicle. In order to maintain good energy transfer efficiency of the wireless charging system, the effect of the proximal metallic object in the vicinity of the receiving coil has been investigated. Both from the theoretical simulation and experimental measurement, it has been observed that the resonance based wireless energy transfer system is very sensitive to the nearby metallic objects, leading to significant deterioration in energy transfer efficiency. This effect on the energy transfer efficiency is also seen to be different for different physical spacing between the transmitting and receiving coils. It is also found that the operating resonant frequency for optimum energy transfer efficiency changes with the metallic object in close proximity to the receiving coil. The theoretically simulated results well agree with the experimental results. The analysis will provide future guidelines for designing an efficient resonance coupling based wireless charging system for EVs even in the presence of metallic objects.

The rigorous evaluation of the NRCS (Normalized Radar Cross Section) of an object above a one-dimensional sea surface (2D case) needs to numerically solve a set of discretized integral equations involving a large number of unknowns. Thus, the direct solution of the impedance matrix equation via LU decomposition becomes the most expensive step in the MoM (Method of Moments) procedure. So, in order to minimize the computation cost, the iterative domain decomposition method called EPILE (Extended Propagation-Inside-Layer Expansion) was used and then was combined with the FBSA (Forward-Backward with Spectral Acceleration) to calculate the local interactions on the rough sea surface. The resulting fast method is called EPILE+FBSA. In this paper, we take advantage of the rank-deficient nature of the coupling matrices, corresponding to the object-surface interactions, to further reduce the complexity of the method by using the ACA (Adaptive Cross Approximation). Thus, the coupling matrices are strongly compressed without a loss of accuracy and the memory requirement is then strongly reduced. For a cylinder above a rough sea surface, the results show the efficiency of the accelerated EPILE+FBSA+ACA method.

A simple microstrip circular disc antenna to excite circularly polarized radiation is presented. In a single-probe fed circular disc sector patch, the corners are further truncated to obtain circular polarization characteristics. The truncation helps to reduce the ground plane dimensions making the antenna more compact with overall dimensions of 50 mm x 50 mm x 1.6 mm. The lengths of truncation necessary to achieve circular polarization are mathematically expressed. The simulated and experimental results are compared and are found to be in good agreement. Axial ratio bandwidth of 1.3% is obtained. The overall size reduction is 55% in comparison with the original disc sector antenna. The antenna resonates in the UMTS 1900-2170 MHz band and can be employed for Mobile Communication applications.

Small ultra high frequency (UHF) radio frequency identification (RFID) tags of fragment-type structure can be designed for broadband operation and for versatile impedance matching to different chips. The fragment-type tag structure can be optimized by using genetic algorithm. In our design, multi-objective evolutionary algorithm based on decomposition combined with enhanced genetic operators (MOEA/D-GO) is used for optimization searching. The multiple objectives are defined in terms of power transmission coefficients for operation in multiple RFID bands and for impedance matching to several prevailing RFID chips. For demonstration, a fragmented tiny square UHF tag of dimensions of 5.5 mm * 5.5 mm is designed for multi-band operation over the 433 MHz, 869 MHz and 915 MHz RFID bands, and a fragmented round tiny RFID tag of radius of 4.5 mm is also designed for versatile connection to five prevailing RFID chips at 915 MHz. The tiny round versatile tag is tested by connecting two chips, the IMPIMJ Monza-4 chip (11-143j) and ALIEN Higgs-3 chip (27-195j), respectively. Effects of input impedance and adjunct fragments on versatility of the design are further discussed.

A dual-band capacitive coupled planar inverted F antenna is presented. The antenna operates in two bands centered around 1.5 GHz and 2.4 GHz with nearly omnidirectional radiation pattern in the entire operating band. It offers a peak gain of 2.4 dBi at 1.5 GHz and 7 dBi at 2.4 GHz with an average efficiency of 82%, 97% respectively. Effects of key design parameters such as the distance between feed strip and radiator patch, the dimensions of the feed strip on the input characteristics of the antenna and length of slot have been investigated and discussed. The antenna is compact and simple to fabricate. The antenna posses an overall dimension of 10×40×6 mm³ when fabricated on substrate of dielectric constant 4.4 and thickness 1.6 mm.

3D integration using through-silicon-vias (TSVs) is gaining considerable attention due to its superior packaging efficiency resulting in higher functionality, improved performance and a reduction in power consumption. In order to implement 3D chip designs with TSV technology, robust TSV electrical models are required. Specifically, due to the increase of signal speeds into the gigahertz (GHz) spectrum, a high frequency electrical characterization best describes TSV behavior. In this letter, 5x50 μm TSVs are manufactured using a via-mid integration scheme and characterized using S-Parameters up to 65 GHz. At 50 GHz, the measured attenuation constant is 0.35 dB/via with a time delay of 0.7 ps/via.

The purpose of this paper is on the behavioural modelling of surge voltage pulses used in Atom Probe Tomography. After brief description of the atom probe functioning principle, we examine the excitation electrical pulse signal integrity along the electric pulser (E-pulser) feeding line modelling with respect to the IEC1733/04 standard. This feeding electric line is ended by cylindrical via ground to control the ion emission. By using the transmission line (TL) ultra-broadband RLCG model, the propagating pulsed signals degradation is predicted. The signal propagation was analysed in both frequency and time domains by taking into account the substrate dispersion. The wideband frequency behaviours of the surge signal along the feeding line were examined from DC-to-2 GHz. In addition, by considering pulse surge signals with pulse-width and rise-/fall-time parameters (T₁=9 ns, t_r1=t_f1=1.6 ns) and (T₂=30 ns, t_r2=4 ns/t_f2=18 ns), the transient responses from 5 cm to -20 cm length TL are characterized. It was shown that the excitation pulse was significantly distorted. It was emphasized that the operated signal delay varies from 0.3 ns-to-1.5 ns in function of the via capacitor value. The time-dependent radiated E-field on the performance of the atom probe system which enables to characterize the nature of tested materials (ions or atoms) is discussed. The presented analysis approach is particularly useful for E-pulser integrated in measurement scientific instruments as Atom Probe Tomography time of flight optimisation, a nano-analysing technique that uses ultra-sharp high vacuum pulse to induce controlled erosion of samples. In this application, the excitation voltage pulse integrity during the propagation is required in order to improve the measurement instrument performances.

A novel broadband planar rotated cross monopole antenna, which consists of a vertical patch (area A) and a rotated horizontal patch (area B), is proposed. By rotating the horizontal patch, the bandwidth of the proposed antenna can be significantly enhanced. The effect of the rotated angle of the horizontal patch on the bandwidth has been deeply studied. The measured results show that the proposed antenna with compact size of 50×50 mm² can achieve a wide impedance bandwidth (10-dB reflection coefficient) as large as 8.76 GHz (2.33-11.09 GHz) or about 130%, which is nearly two times of what the corresponding conventional cross monopole antenna was.

A Coplanar Waveguide(CPW)-fed monopole loaded with Composite Right/Left Handed Transmission Line (CRLH-TL) unit cell is presented in this letter. Multiband is achieved due to the nonlinear dispersion relation of the CRLH-TL unit cell. The CRLH-TL unit cell supports a fundamental LH wave (phase advance) at lower frequencies and a RH wave (phase delay) at higher frequencies. By loading CRLH-TL unit cells with a conventional monopole, the resonant frequency of higher order mode can be decreased and zeroth-order mode or even negative-order mode can be achieved. As a result, the proposed antenna operates at 1.43 GHz, 2.58 GHz, 3.31 GHz and 4.4 GHz. Finally the modified antenna is fabricated and measured; measurements and EM simulations are in a good agreement that confirms the proposed theory.

A compact ultra wide band (UWB) antenna with dual band notch characteristics is proposed. The antenna consists of a coplanar waveguide (CPW) fed bevelled rectangular patch and a modified rectangular ground plane. A Z-shaped meander line parasitic element and a pair of symmetrical L-shaped quarter-wavelength stubs are employed to realize band-notched functions at WiMAX and WLAN bands respectively. By optimizing the dimensions and positions of these notch structures, the desired notch-bands of WLAN and WiMAX are achieved. Unlike other dual band-notched antennas reported in literature this antenna has a merit of regulating the centre frequency as well as the bandwidth of both the notched bands easily and independently. The measured -10 dB S₁₁ covers the bandwidth from 2.5 to 11.5 GHz, with two notched bands from 3.3 to 3.6 GHz and 5.2 to 5.75 GHz. The proposed antenna exhibits nearly omni-directional radiation patterns with moderate gain and small group delay variations less than 0.5 ns over the entire operating bandwidth except at the notched bands. Moreover, by using antenna transfer function, the time domain characteristic of the antenna is also studied to confirm its suitability for UWB pulse communication.

This work is devoted to a theoretical investigation of the current crowding problem in flat conductors bent at arbitrary angles. Using conformal mapping techniques, we succeed in obtaining an analytical expression for current density distributions in such conductors. It is shown that the current density increases in a small vicinity of the corner and approaches to infinity at its top. In order to eliminate the infinity, the vertex is replaced by an arc of a circle with a small radius. The method has been developed for an arbitrary angle; several specific examples are considered.

A pattern synthesis approach based on a modified alternating projection method for large planar arrays is presented in this paper. In the alternating projection method, pattern synthesis problem is considered as finding the intersection between two sets: the specification set and the feasible set. The former contains all the patterns that want to be obtained, while the latter contains all the patterns that can be realized. An element belongs to both sets is a solution to the problem. In this paper, a modified projection operator which varies with the iteration number is introduced because the conventional alternating projection method is known to suffer from low convergence rate and/or trapping on local optimum depending on the starting point. When the planar array has a nonuniform element layout, the unequally spaced elements are interpolated into virtual uniform elements with an interpolation of the least square sense. Then the synthesis problem is converted to the problem of a uniform array. Finally, several examples are presented to validate the advantages of the proposed method. Results show that the modified method is fast and obtains better results than the conventional one.