A WiMedia compliant CMOS RF power amplifier (PA) for ultra-wideband (UWB) transmitter in the 3.1 to 4.8 GHz band is presented in this paper. The proposed two-stage PA employs a cascode topology on the first stage as driver while the second stage is a simple common source (CS) amplifier. In order to improve the efficiency and output power, the output impedance of the driver amplifier (first stage) is optimized so that it falls on the source-pull contours of the second stage amplifier. On-wafer measurement on the fabricated prototype showed a maximum power gain of +15.8 dB, 0.6 dB gain flatness, +11.3 dBm of output 1 dB gain compression and up to a maximum of 17.3% power added efficiency (PAE) at 4 GHz using a 50 Ω load termination, while consuming only 25.7 mW from a 1.8 V supply voltage. Measurement results obtained are used to create a non-linear powerdependent S-parameter (P2D) model for wideband input and output matching optimizations and co-simulations with the UWB modulated test signals. Using the created P2D model, the PA achieved a maximum output channel power of +3.48 dBm with an error vector magnitude (EVM) of −23.1 dB and complied with the WiMedia mask specifications.

Recent research on the array geometrical configuration shows that the two L-shaped array (TLSA) has a lower Cramer-Rao Low-Bound (CRLB) of two-dimensional (2-D) directions-of-arrival (DOAs) estimation than other array configurations. However, in this array configuration, there are some problems to note: i) three electric angles are independently obtained from three uniformly linear subarrays on three axes, so they must be matched before solving elevation and azimuth angles from them; ii) Similar to other array geometries, the effect of mutual coupling in the TLSA on the estimation performance cannot be ignored; and iii) the conventional elevation estimators may encounter estimation failure. In this paper, we develop a new TLSA-based 2-D DOAs estimation algorithm. The key points of this paper are: i) using some particularly selecting matrices, a trilinear model is constructed to compensate the effect of mutual coupling on three subarrays. In addition, the steering vector is restored using the trilinear alternating least square method; ii) 2-D DOAs are estimated from the properly chosen elements of the restored steering vector to avoid pairing parameters and the severe performance degradation resulted from the failure in pairing; and iii) a new elevation estimator is designed to avoid estimation failure. Simulation results are presented to validate the performance of the proposed method.

A novel printed dipole antenna was designed for the L-band satellite communication system INMARSAT (Downlink: 1525--1559 MHz, Uplink: 1626.5--1660.5 MHz). Several structural parameters were experimentally studied with care to establish a design procedure. The measured results show that the impedance bandwidth for return loss below -10 dB is about 170 MHz and that the half-power bandwidth (HPBW) can be up to 110°. The antenna can be used in high latitudes because of wider HPBW.

Exact formulas for internal impedance per unit length of tubular cylindrical conductors energized by time-harmonic current involve Bessel functions. These functions are defined by infinite series, which yield unstable and often erroneous results for complex arguments of large magnitudes. Although it is well known how to evaluate Bessel functions numerically and many routines are now available to perform the actual computation, the available software routines often fail when computing equations that consist of a product and a quotient of Bessel functions under large complex or real arguments. For such cases, different approximate formulas can be used. In this paper, three types of approximate formulas for internal impedance of tubular cylindrical conductors are compared with respect to numerical stability and accuracy.

We have developed an array antenna consisting of 12 elements of simple square-shaped, corner-truncated patches for circularly polarized synthetic aperture radar (CP-SAR) operated in the L-band. The corporate feed design concept is implemented by combining a split-T and a 3-way circular-sector-shape power divider to excite circularly polarized radiation. The fabricated antenna based on the simulation using moment method gives a good circular polarization at the center frequency of 1.27 GHz with an impedance bandwidth of 6.1% and 3-dB axial ratio bandwidth of 1.0%, satisfying the specification for our circularly polarized synthetic aperture radar intended for use onboard an unmanned aerial vehicle and a small satellite.

A novel type of ultra-wide band (UWB) crossed semi-ring monopole antenna with band notched characteristics is presented. The proposed antenna consist a wideband crossed semi-ring monopole and four L-shaped slots, producing band-notched characteristic. Effects of the various parameters for antenna performances are discussed. The central frequency and bandwidth of the notched band can be controlled easily by adjusting three key design parameters. The time domain responses are simulated and studied. A prototype is constructed and measured finally.

A theoretical study of optical properties of phase shift defects in one-dimensional asymmetrical photonic structures consisting of two rugate segments with different periodicities at both normal and oblique incidence is presented. Using the propagation matrix method we numerically calculated transmittance spectra, defect wavelengths, energy density distributions, and group velocities for TE and TM waves, respectively. Our study shows that by adjusting the periodicity of one rugate segment, the defect wavelengths can be shifted toward either a shorter wavelength or a longer wavelength. The differences of the energy density distributions of TE and TM waves at different angles of incidence are explained with the help of group velocity. Effects of the change of the period of one rugate segment on the peak energy densities of defect modes and minimum group velocities at different angles of incidence are also investigated.

Recently, the use of the particle swarm optimization (PSO) technique for the reconstruction of microwave images has received increasing interest from the optimization community due to its simplicity in implementation and its inexpensive computational overhead. However, the basic PSO algorithm is easily trapping into local minimum and may lead to the premature convergence. When a local optimal solution is reached with PSO, all particles gather around it, and escaping from this local optima becomes difficult. To overcome the premature convergence of PSO, we propose a new hybrid algorithm of particle swarm optimization (PSO), simulated annealing (SA) and tabu search algorithm (TS) for solving the scattering inverse problem. The incorporation of tabu search (TS) and simulated annealing (SA) as local improvement approaches enable the hybrid algorithm to overleap local optima and intensify its search ability in local regions. Reconstructions of dielectric scatterers from experimental inverse-scattering data are finally presented to demonstrate the accuracy and efficiency of the hybrid technique.

The characteristics of guided modes in the four-layer slab waveguide containing chiral nihility core have been investigated theoretically. The characteristic equation of guided modes is derived. The dispersion curves, energy flux and normalized power of guided modes for three cases of chiral metamaterial parameters are presented. Some abnormal features are found, such as the existence of fundamental mode and surface wave mode, unusual dispersion curves, positive energy flux in the chiral nihility core, and zero power at some normalized frequencies.

In this paper, a large signal equivalent circuit empirical model based on Anglov model for ceramic packed high power AlGaN/GaN HEMT has been proposed. A temperature-dependent drain current model, including self-heating effect, has been presented, and good agreement is achieved between measurement results and the calculated results at different temperature. The nonlinear capacitance models are modeled by the directly measured microwave scattering (S) parameters and multi-bias small signal equivalent model (SSECM) of packed device. A power amplifier based on large size AlGaN/GaN HEMT with a total gate periphery of 36 mm has been designed by using the proposed model for validation purpose, and the simulated results fit the measurement results well at different temperature.

This paper studies the surface modes at the interface of finite size Electromagnetic Band Gap (EBG) woodpile structures. The impact of different types of woodpile terminations on the properties of these surface modes is analyzed. For all the studied terminations there exist surface modes which must be taken into account when designing components based on this EBG structure.

A simple finite difference time domain (FDTD) scheme is proposed for modeling three-dimensional (3D) nondispersive chiral media. Based on the recently reported new BI-FDTD mesh method and rearranged curl equations, this scheme implements a simple leapfrog algorithm. By adding the mirror layer, the perfect electric conductor (PEC) condition is implemented in the BI-FDTD mesh method of 3D problem. Results of this scheme are presented for the scattering coefficients of discontinuity in waveguides, which are partially filled with chiral or achiral media. The validation is performed by comparing the results with those obtained from the literature and software simulation.

In this paper, a novel microwave bandpass filter structure is proposed. By introducing a metallic via hole, the filter structure operates as one λ/2 and two λ/4 uniform impedance resonators and consequently form a triplet coupling scheme. The equivalent circuit model is analyzed in detail, which shows that there is a transmission zero in the low stopband. Based on that concept, three microstrip filters are designed, fabricated and measured, respectively. The first filter has no source/load coupling and only one transmission zero is created. By introducing source/load coupling, the second filter can create three transmission zeros. The third filter can create a controllable transmission zero in upper stopband. The simulated and measured results agree very well.

Perfect electromagnetic conductor (PEMC) is a novel concept in electromagnetic fields of interesting properties and many potential applications. This paper introduces a new technique to design an artificial surface that has equivalent PEMC properties. The proposed PEMC boundary is based on a periodic structure composed of two conducting patches on a grounded dielectric slab. One of them is embedded inside the substrate and the other lies on the surface of the substrate. A conducting via is used to connect the two patches. In the resulting PEMC boundary, the polarization of the reflected wave is controlled by the tilting angle between the two patches.

In this paper a new method based on the complex images technique has been presented to efficiently compute the Green's functions required in a Mixed Potential Integral Equation (MPIE) analysis of a periodic structure located in a layered medium. This method leads to a closed-form representation for these slowly convergent series valid for sub-wavelength as well as super-wavelength cell sizes for all source point to field point distances. Comparison between the results obtained by the proposed method with ones obtained from other numerical approaches verifies its accuracy. Fast convergence, simple final form and versatility of the proposed method are its main advantages which make it suitable for the analysis of the periodic structures using the integral equation techniques.

We report on free space transmission experiments carried out on stacked split ring resonator (SRRs) arrays operating at microwave frequencies. We start from the case of a single frequency selective surface which exhibits a rejection at the SRR resonance frequency. By stacking SRR arrays in the propagation direction, we then show experimentally the possibility to induce a transmission band just below this resonance frequency. Full wave analysis shows the role played by the longitudinal and transverse coupling effects in the electromagnetic properties of such bulk metamaterials, with the appearance of a transmission band resulting from an artificial magnetic activity.

This paper presents a printed dipole with left-handed loading and electrically small dimensions. Uniform currents are obtained at 750 MHz, proving zero order (i.e. n=0) mode operation. Comparisons are made with other left- and right-handed antennas. Good agreement is achieved between simulation and measurement. The antenna has various applications in RFID systems and wireless environments.

A novel wafer-dipole printed antenna fed by balanced micro-strip line is proposed, and the adoption of the balanced micro-strip line can effectively solve the feeding problem of the UWB dipole antenna. The wafer-dipole and a branch of the balanced microstripline are printed on one side of FR-4 substrate (1mm thickness), and the later is connected to a wafer directly, while the other branch is printed on the back side of the substrate and connected the other wafer with a via-hole. The measured results show that the antenna impedance bandwidth is from 3.0 GHz to 15.0 GHz with VSWR < 2, and the ratio bandwidth is about 5:1. Moreover, the antenna size is just 40 mm×20 mm with simple structure, which is well suited for short-distance UWB communications.

This paper presents the design and test results of a 20-GHz transmitter front-end implemented in the TSMC 0.13-μm CMOS process. The chip consists of a voltage-controlled oscillator (VCO), an RC phase splitter, and two differential switches. To realize the K-band transmitter function, the two different switches are designed to serve the purpose of frequency doubler and phase modulator, respectively. These two features are verified in the implemented chip and, as a result, the chip can serve as a transmitter front-end. The measured total current consumption of the chip core circuit is 26 mA under a DC supply voltage of 1.2 V. The chip size is 1.03×0.93 mm².

In this work we propose a new class of optical pressure sensors suitable for robot tactile sensing. The sensors are based on a tapered optical fiber, where optical signals travel, embedded into a PDMS-gold nanocomposite material. By applying different pressure forces onto the PDMS-based nanocomposite we measure in real time the change of the optical transmittivity due to the coupling between the gold nanocomposite material and the tapered fiber region. The intensity reduction of the transmitted light intensity is correlated with the pressure force magnitude.