A compact ultra-wideband (UWB) bandpass filter (BPF) with improved harmonic suppression using a modified coupling structure is presented in this paper. The modified coupling structure is constructed by taper-connecting two folded open stubs to the traditional parallel-coupled lines, which shows an improved characteristic in harmonic suppression. By integrating the proposed coupling and the stepped-impedance stub loaded resonator (SISLR), a UWB BPF is finally built and tested. The simulated and measured results are in good agreement with each other, exhibiting good wideband filtering characteristic and improved out-of-band performance.

This paper presents the design, simulation and measurement of a dual-band terahertz metamaterial absorber with polarization-insensitivity and wide incident angle. The unit cell of the metamaterial consists of top resonator structures and low metallic ground plane, separated by an isolation material spacer to realize both electric and magnetic resonances. The physical mechanism of dual-band absorption and the sensitivity to the polarization direction and incident direction of the EM wave are theoretically investigated by simulating the x-component and normal component electric field distribution, current distribution on ERRs and metallic ground plane, and distribution of power flow and loss at the resonance frequencies as well as different modes EM waves, based the FDTD calculated method, respectively. The results show that the absorber is not only correctly coupling to the incident electric field and magnetic field, but also can trap the input power into specific positions of the devices and absorb it, besides insensitive to the polarized angle and incident angle. Moreover, the experiment demonstrates that the absorber achieves two strong absorptions of 82.8% and 86.8% near 1.724 and 3.557THz.

Recent studies on artificial materials demonstrate that substantial improvements in electromagnetic response can be attained by combining different materials subject to desired metrics. However, the perfect material combination is unique and extremely difficult to determine without automated synthesis schemes. In this paper, we develop a versatile approach to design the microstructure of periodic materials with prescribed dielectric and magnetic material tensors. The proposed framework is based on a robust material model and generalized inverse synthesis tool relying on topology optimization. The former is derived using homogenization theory and asymptotic expansion applied to Maxwell equations and can characterize the effects of anisotropy and loss of materials with periodic unit cells of arbitrary geometries and multi-phases much smaller than the wavelength. Resulting Partial Differential Equation (PDE) is solved numerically using Finite Element Analysis (FEA) and is validated with results in literature. The material model proves to be fast and numerically stable even with complex inclusions. The topology optimization problem is applied for the first time towards designing the unit cell topology of periodic electromagnetic materials from scratch with desired dielectric and magnetic tensors using off-the-shelf materials, i.e., readily available constituents obtained from isotropic ceramic powders. The proposed framework's capability is demonstrated with five design examples. Design with anisotropic permittivity is also fabricated. Results show that the framework is capable of designing, in an automated fashion, non-intuitive material compositions from scratch with desired electromagnetic properties.

The specific absorption rate (SAR) of a human body exposed to a random field inside a reverberation chamber (RC) has been modeled. The exciting field is simulated using the plane wave integral representation which is numerically solved by a superposition of N plane waves randomly generated and repeated M times to reproduce the same statistics of an RC. An experimental validation, carried out by means of known saline solutions, confirms the reliability of this method. The obtained results at various frequencies for the adopted "Visible Human Body" and for some tissues well highlight the absorption percentage. The frequency behavior of the total SAR reveals the resonance of the human body around 75 MHz, in spite of the chaotic source.

A novel compact design of planar T-shaped monopole antenna with multi-band operation for WLAN/WiMAX system is proposed. By insetting a pair of mirrored L-shaped monopole strips, multi resonant modes close to 2.45/3.5/5.5 GHz band are excited to meet the specifications of WLAN/WiMAX system. And, the obtained impedance bandwidth across the operating bands can reach about 160/1100/2690 MHz for the 2.45/3.5/5.5 GHz bands, respectively. Only with the antenna size of 30×42×0.8 mm³, the proposed monopole antenna has the compact operation with more than 20% antenna size reduction. The measured peak gains and radiation efficiencies are about 3.2/3.5/5.4 dBi and 72/98/96% for the 2.45/3.5/5.5 GHz band, respectively, with nearly omni-directional pattern in the XY-plane.

The radio waves propagating through the earth atmosphere will be attenuated due to the presence of atmosphere particles, such as water vapor, water drops and the ice particles. Meanwhile, the atmospheric gases and rain will both absorb and scatter the radio waves, and consequently degrade the performance of the link. The results of various studies conducted in temperate and tropical regions have been published in research papers. This paper presents the summary of comparative studies on different rain attenuation prediction methods for terrestrial microwave links tropical regions. Basically the models described in this paper include those of the ITU-R, revised Moupfouma, revised Silva Mello and Lin model. The objective of this study is to reveal the most suitable rain attenuation prediction model for the Malaysian tropical region. This paper will provide useful information for microwave engineers and researchers in making decision over the choice of most suitable rain attenuation prediction for terrestrial links operating in a tropical region. Even though the ITU-R model underestimates the rain attenuation at higher frequencies, the test results have clearly indicated that it is most suitable for predicting terrestrial rain attenuation in tropical Malaysia, compared to others.

For array beampattern synthesis, it is possible to simplify the model and reduce the computational load by formulating it to be a Quadratic Programming (QP) problem. The QP method is conceptually simple and imposes no restriction on array geometry. In the QP method, a key component is the template function which describes the desired beampattern as a deterministic function of direction. In this paper, the template functions in the form of Hypergeometric Function corresponding to Legendre arrays and Dolph-Chebyshev arrays, namely Legendre Hypergeometric Function (LHF) and Dolph-Chebyshev Hypergeometric Function (DCHF), are derived and the synthesis procedures are also presented. The simulation results show that the DCHF and LHF work in the QP method and provide the exactly synthesized beampattern. Moreover, another synthesis method using a Gegenbauer polynomial to synthesize the beampattern of a Uniform Linear Array, is proposed. This method gives rise to the Gegenbauer arrays. Gegenbauer arrays are very generalized and Legendre arrays and Dolph-Chebyshev arrays are considered as its special cases. Using the Gegenbauer array synthesis method, one is able to further adjust the beam efficiency and the directivity when the Side-Lobe Level and the element number are specified. As well as Dolph-Chebyshev arrays and Legendre arrays, its template function for the QP method, Gegenbauer Hypergeometric Function, is also derived.

The berthing of large ships in inclement weather with frequently poor visibility presents a challenge. To assist with this application, it may be beneficial to utilise standard radar imaging. Whilst this may be achieved using a mechanically-scanned system, reliability, cost and weight issues, coupled with the need to primarily image only a 120º sector on the port and starboard of the ship, make phased array radar an attractive possibility. Multiple-Input Multiple-Output (MIMO) radar, with its ability to enhance the resolution available from a given number of elements, is particularly suited to a short-range application such as this in which there is sufficient time to switch between antenna elements as an alternative to more complex implementations. This paper describes a system of this nature from its basic architecture to development and validation, including some artefacts of the particular topology employed.

The magnetic properties of the metamaterial composed of both periodic and aperiodic closed rings are studied. Experimental results validate that metamaterials with 0 < μ < 1 can be non-dispersive in a wide frequency range. The magnetic properties are insensitive to disorders of the closed rings, e.g., the position disorders and the size disorders. The related causality issue is also discussed.

In this paper, a novel maximum likelihood algorithm for joint angle and delay estimation is developed to identify the specular components of channel fading for uniform linear array based on the physical propagation channel model. Frequency domain presmoothing is applied to the structured frequency transfer matrix before the estimation procedure in order to utilize substantial observations. Iterative Gauss-Newton method is used to solve the multidimensional optimization problem, and a new compact matrix form is presented. Further simplification of the iteration is derived based on the assumption of independent channel parameters. Both simulations and measurement results are investigated for performance analysis. The simulations reveal that the proposed algorithm leads to higher performance with appropriate complexity. Also, a comparison with other algorithms is carried out to validate the accuracy of algorithm by using the power delay profile measured in a real environment, and the results show the proposed algorithm performs well.

The goal of this work is to look for a technique of optimization making it possible to improve the optical performances of materials with photonic band gap by reducing of the Kiessig fringes. The techniques of apodization and smoothing were used. The combination of these two techniques made it possible to reduce the Kiessig fringes up to 95%.

This paper presents a method for extracting the coupling matrix and the unloaded Q from the measured (or electromagnetic simulated) S-parameters of a narrow band cross-coupled resonator bandpass filter with losses. The Cauchy method is applied to determine the characteristic polynomials of the S-parameters of a filter in the normalized low-pass frequency domain. A five-parameter optimization method is proposed to obtain the unloaded Q and remove the phase shift of the measured S-parameters, which is caused by the phase loading and the transmission lines at the input/output ports of a filter. Once the characteristic polynomials of the S-parameters with the phase shift removed have been determined, the coupling matrix of a filter with a given topology can be extracted using well established techniques. Two application examples are given to illustrate the validity of the proposed method.

This paper introduces a novel technique for efficiently combining implicit space mapping (ISM) with method of moments (MoM) for the synthesis of antenna arrays and explores several example applications of the ISM approach. The antenna arrays geometric parameters are extracted to be optimized by ISM, and a fitness function is evaluated by MoM simulations to represent the performance of each candidate design. A coarse-mesh MoM and a fine-mesh MoM solver are used for the coarse and the fine models, respectively. To achieve the parameter extraction, the auxiliary parameter is selected and the approximation between the two models is accomplished by particle swarm optimization (PSO). The results show that the running time of the ISM algorithm is 2~3 times faster than that of other optimization algorithms (e.g. PSO).

In this paper we develop an empirical approach to the design of Ultra Wideband (UWB) antennas employing the Inverse Parabolic Step Sequence (IPSS). The relationships developed can be used to miniaturize the antenna and achieve a good impedance match over the UWB bandwidth. The overall aim of this process is to give a good starting point for detailed numerical optimizations. We will illustrate the use of these formulae in three different designs of IPSS-based antennas. A low loss duroid substrate of loss tangent, tan δ, 0.0009, relative permittivity 2.2 and thickness 1.575 mm is used to simulate these planar monopole antennas in Ansoft High Frequency Structure Simulator (HFSS).

A new four-parameter modified refractivity profile (M-profile) model for the evaporation duct is introduced in this paper. In the estimation of radio refractivity structure from sea clutters, a parametric M-profile model is normally employed. The conventional M-profile model for evaporation ducts is the one-parameter log linear model, which has some potential disadvantages in describing the observed M-profiles which would result in rough results of evaporation duct estimation. Based on this model, three new parameters are introduced and a four-parameter M-profile model is proposed here. This model has the ability to (a) more accurately match real-world M-profiles, (b) well replicate the observed clutter field, and (c) show clutter power or path loss sensitivity to each model parameter. All these abilities are necessary for robust refractivity estimations. The performance of this model is tested and validated through the estimation for two truly measured M-profiles.

Bandwidth enhancement technique of circularly polarized square slot antenna is presented in this paper. A square slot antenna with the components of L-probe separated could achieve an axial ratio (AR) bandwidth of 33.84%. Placing Stubs in the slot by studying the electric field behaviour could enhance the AR bandwidth by around 10%. Creating an L-shaped slot on the ground plane, where the electric field rotates in the desired clockwise direction, can further enhance the bandwidth by 7%. A < -10 dB S₁₁ bandwidth of 46.15% and < 3 dB AR bandwidth of 50.35% could be achieved with the present design. Unidirectional patters are obtained by having a cavity at the wide slot of the antenna and shows a measured bandwidth of 41.79% in S₁₁ and 44.97% in AR. Both antennas show a cross polarization discrimination of more than 15 dB on a wide azimuth range. The measured results well comply with the simulated results.

Reflection of electromagnetic plane wave from a planar chiral nihility-chiral nihility interface is calculated as a special case of two different chiral media by assuming that permittivities and perme-abilities of the both media approach to zero. That is, ε_i→0, μ_i→0, and chiralities κ_i≠0, i=1, 2. These results are used to find the geometrical optics reflected fields of a cylindrical chiral nihility-chiral nihility interface, when it is excited by a plane wave. Using the Maslov's method, field expression which yields finite values around the focus of cylindrical interface is also determined.

We investigate numerically the collision of nonlinear envelope pulses in composite right- and left-handed transmission lines with regularly spaced Schottky varactors. Because of the nonlinearity caused by the Schottky varactors, the dispersive distortion of envelope pulses is well compensated. We find that when two nonlinear envelope pulses traveling in the opposite directions collide, two envelope pulses are newly developed. The carrier wave frequency of the newly developed pulse is the harmonic of the colliding pulses that satisfies the phase-matching condition.

The design and measured results of a compact, low cost, low conversion loss microstrip single balanced Schottky diodes mixer is proposed. This mixer is designed for Ka-band satellite transponder simulator to convert the 30 GHz radio-frequency (RF) signal down to the 20 GHz intermediate-frequency (IF) signal with 9.8 GHz local oscillator (LO) frequency. This design takes full advantage of the frequency relationship of the RF, IF and LO, which is 3 : 2 : 1. A microstrip rat-race ring is designed at the LO frequency, which also functions as a 180-degree hybrid coupler at the RF frequency by its intrinsic multi-band characteristic. The amplitude and phase balance at both LO and RF frequency are analyzed, which guarantee the state-of-art performance of this single balanced mixer. The multi-function open/short stubs and a lowpass filter (LPF) with bonding wires across the rat-race ring are optimized to realize this low conversion loss mixer. The measured results show that the conversion loss is less than 9 dB at the IF frequency from 20.0 to 21.6 GHz, and the power of the second harmonic of LO is -45dBm with +6.5dBm LO drive power. The 3rd order inter-modulation products (IMD3) could be lower than -50 dBc with LO power higher than +7.8dBm at the input RF power of -15 dBm.

A set of characteristic basis functions of the energy radiation pattern for a true-time-delay array of equi-spaced elements radiating a pulsed/transient wave-field was derived. This set is determined by the array layout and by the set of excitation waveforms that can be used to expand the actual excitation pulse. It is established that the characteristic basis function set spans the mapping of the square amplitudes of the discrete Fourier transform of the excitation coefficients to the energy radiation pattern. This mapping is further used to analyze array performance and re-examine the term array sparsity. Additional use of this set can be found in synthesizing an array radiation pattern to meet prescribed requirements.