A new design approach based on wave analysis has been implemented in order to derive voltage gain, center frequency and bandwidth of millimeter wave amplifier using parameters of transmission lines (TL). The derived formula allows one to design high frequency amplifier with predetermined bandwidth and centner frequency. It has been shown that in the case of lossy TL or at high frequency, circuit theory cannot predict the amplifier gain behavior while presented wave theory can accurately predict the frequency response of the amplifier in both low and high frequency ranges.

A hybrid mode-matching/compact 2-D finite-difference frequency-domain (MM/compact 2-D FDFD) method is proposed for the analysis of rectangular ridged waveguide discontinuities. In order to apply MM technique, mode spectrum of the ridged waveguide is determined by an improved compact 2-D FDFD method with only two transverse field components at the cutoff frequencies which lead to two independent sets of real symmetric eigenvalue problems for TE and TM modes. Solving these two separate eigenvalue equations, cutoff wave numbers and discrete mode field functions can be obtained respectively from eigenvalues and eigenvectors. Finally, the generalized scattering matrix (GSM) of the rectangular-ridged waveguide step discontinuity can be easily calculated through the transverse field matching procedure. The method is demonstrated at the examples of two waveguide structures, and results are shown to be in excellent agreement with those by the commercial CAD software HFSS.

A novel broadband Van Atta array operating in a broadband with frequency offset characteristic is proposed. A single sideband mixer is introduced to achieve sideband choice without utilizing filters which make this array have excellent performance and wider applications than the conventional Van Atta array. The simulated results of the amplitude and phase of the array show that this antenna array can achieve retrodirectivity with frequency offset and good isolation in a broadband. The experimental performance of the array is observed within the frequency range from 2.8 GHz to 3.4 GHz.

An advanced aspheric and asymmetric large aperture dielectric lens antenna is proposed firstly here for high resolution at W-band frequency. Large aperture and aspheric lens provides minimum focusing error and high resolution in millimeter wave quasi-optics application. To the best of the authors' knowledge we design first time 500 mm large aperture lens for W-band quasi optics application. Near field radiation pattern, beam size and focal length of the lens are obtained theoretically and experimentally as well. Dielectric rod waveguide antenna is also designed and employed as a source antenna for the lens. The measured and simulated results of the DRW antenna also show very good performance at W-band frequency, and it has 15.3 dB gain with -22.5 dB sidelobe levels at 94 GHz.

Existence of backward electromagnetic surface waves at an interface separating a semi-infinite uniform left-handed metamaterial and a 1D photonic crystal composed of alternating layers of two kinds of single-negative (ε-negative and μ-negative) metamaterial is theoretically investigated. Dispersion characteristics of surface states are analyzed for two different cases of ENG-MNG and MNG-ENG layered periodic structures. It was demonstrated that in the presence of metamaterial, surface waves are sensitive to light polarization and there exist only backward TM-polarized (or TE-polarized) surface Tamm states depending on the ratio of the thicknesses of two periodic stacking layers.

A new structure of an ultra-wide bandpass filter is considered. An intelligence method of optimization is applied first for synthesis of three-section filter on dual-mode resonators. An area of fractional bandwidth values and values of dielectric constant of the substrate, where synthesis problem for the filter has a solution, is determined theoretically. Experimental results show good agreement with simulated values.

A cell-vertex based finite volume scheme is used to solve the time-dependentMaxwell's equations and predict electromagnetic scattering from perfectly conducting bodies. The scheme is based on the cell-vertex finite volume integration method, originally proposed by Ni[1], for solution of the two dimensional unsteady Euler equations of gas dynamics. The resulting solution is second-order accurate in space and time, and requires cell based fluctuations to be appropriately distributed to the state vector stored at cell vertices at each time step. Results are presented for two-dimensional canonical shapes and complex three dimensional geometries. Unlike in gas dynamics, no user defined numerical damping is required in this novel cell-vertex based finite volume integration scheme when applied to the time-domain Maxwell's equations.

An extremely compact branch-line coupler operating at 900 MHz is presented without the use of viaholes, multilayered technique, or air-bridged. The technique presented here uses the concept of fractals to load a coupled transmission-line in order to realize a compact quarter-wavelength transmission-line, which forms the couplers arms. It is shown that the proposed branch-line coupler's performance is analogous to a conventional branch-line coupler with the benefit of substantially reduced physical dimensions by a factor of 78%. The measured result of the fabricated microstrip branch-line coupler is compared with the simulation data. The agreement of the measurement and simulated confirms the theory and validates the proposed coupler design.

This paper presents the microwave characteristics of thin film microstrip line (TFML) under dc-bias conditions. The proposed TFML with 20 μm thick polyimide layer is used as a thin dielectric supporter on low-resistivity silicon (LRS) substrate. Measured frequency-dependent microwave characteristics and equivalent lumped elements are evaluated for the dc-biased TFML over 1-50 GHz. This work presents acceptable attenuation of 0.561, 0.563 and 0.565 dB/mm at 50 GHz with dc-bias conditions, showing that the TFML can be used for high frequency interconnects for any 3D-based microwave devices and monolithic microwave integrated circuits (MMICs).

This work presents the derivation of high frequency electromagnetic field expressions for two dimensional Gregorian system embedded in a chiral medium. Two cases have been analyzed. Firstly, the chirality parameter is adjusted to support positive phase velocity (PPV) for both left circularly polarized (LCP) and right circularly polarized (RCP) modes traveling in the medium. Secondly, the chirality is adjusted in such a way that one mode travels with PPV and other with negative phase velocity (NPV). Method proposed by Maslov is used, for finding the field expressions, to overcome the problem of Geometrical Optics (GO) because GO fails at caustics. The results for both the cases are given in the paper.

Analytical expressions for the average intensity, mean-squared beam width and angular spread of partially coherent standard and elegant Laguerre-Gaussian (LG) beams propagating in turbulent atmosphere are derived. The properties of the average intensity, spreading and directionality of partially coherent standard and elegant LG beams in turbulent atmosphere are studied numerically and comparatively. It is found that the beam parameters and structure constant of turbulence together determine the properties of the beams in turbulent atmosphere. Partially coherent standard and elegant LG beams with smaller coherence length, larger beam orders and longer wavelength are less affected by the turbulence. A partially coherent elegant LG beam is less affected by turbulence than a partially coherent standard LG beam under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant LG beams, equivalent fully coherent standard and elegant LG beams, equivalent Gaussian Schell-model beams that may have the same directionality as a fully coherent Gaussian beam both in free space and in turbulent atmosphere. Our results will be useful in long distance free-space optical communications.

This paper applies the recently introduced electrical engineering approach to investigate room temperature THz metal shielding, using the accurate classical relaxation-effect frequency dispersion model. It is shown that, with the simplest case of a uniform plane wave at normal incidence to an infinite single planar shield in air, all figure of merit parameters for the shield can be accurately characterized. The errors introduced by adopting the traditional and much simpler classical skin-effect model are also quantified. In addition, errors resulting from adopting well-established approximations have also been investigated and quantified. It is shown that the engineering approach allows analytical expressions to be greatly simplified and predictive equivalent transmission line models to be synthesized, to give a much deeper insight into the behaviour of room temperature THz metal shielding. For example, it is shown that figures of merit and associated errors (resulting from the use of different classical frequency dispersion models) become essentially thickness invariant when the physical thickness of the shield is greater than 3 normal skin depths.

An analytical approach is developed in the present paper to investigate the interaction between two non-magnetic particles migrating in a conductive fluid due to an imposed strong magnetic field (e.g., 10 Tesla). The interaction between the conductive fluid and a single particle migrating along the magnetic lines is influenced by the magnetic field and can be represented by an additional fluid viscosity. Thus the effective fluid viscosity is discussed and the magnetic field effect on the particle migrating velocity is examined. For two particles, two kinds of magnetic forces are induced: namely, the attractive force due to the magnetisation and the repulsive force caused by the conductive fluid flow around the non-magnetic particles. The forces are then evaluated with the consideration of the magnetic field effect on the particle migration and become significant with the increase of the magnetic flux density. The counteracting behavior with a critical particle size of the interparticle magnetic forces is discussed and compared with different magnetic field densities and gradient values.

A geometrically based channel model is proposed to describe radio propagation in an indoor environment with directional antennas. In conventional geometric channel models (GCMs), distribution of scatterers does not take into account the antenna properties. A different approach is taken here for directional channel modeling. The locations of scattering objects are defined using non-Cartesian coordinates comprising an auxiliary geometric parameter ρ and angle-of-arrival (AOA) φ. Subsequently, we present a systematic method to study the influence of antenna pattern on scatterer distribution by applying two heuristic rules, which underpin the connection between the physical wave-propagation process and its canonical GCM. Provided with model preliminaries, important channel parameters including power azimuthal spectrum (PAS), power delay spectrum (PDS), mean effective gain (MEG), and antenna-decoupled PAS are derived and compared against the published data in the existing literature to demonstrate the usefulness of the proposed model.

This paper presents a very flexible and generic design of a diode-based RF predistortion linearizer that can correct for the dual-inflection point type compression characteristics found in the gain profile of metal semiconductor field effect transistor (MESFET) based and Doherty power amplifiers. It consists of a circuit configuration that has the head-tail configuration of Schottky diodes, complemented with a p-intrinsic-n (PIN) diode in parallel, at two ports of a 90° hybrid coupler for improving the performance of the linearizer. The use of a PIN diode in the linearizer provides it with an extra level of freedom in achieving the desired characteristic. Overall, the linearizer is equipped with three degrees of freedom and hence possesses the capability to achieve output characteristics that can be employed in linearizing various types of power amplifiers. The proposed linearizer has been shown to simultaneously improve the third- and fifth-order intermodulation distortions of a commercial ZHL-4240 gallium arsenide field effect transistor (GaAs FET) based power amplifier over a 10 dB power range.

In order to improve measurement efficiency in electromagnetic test facilities (compact range or near-field range), testing probes are required to have ultra-wideband (UWB) radiation characteristics, dual-polarization capability, and interchangeable E- and H-plane far-field patterns. In this context, we propose a new type of UWB antenna that satisfies these requirements in the frequency range of 4 to 18 GHz. For the proposed antenna, a low-loss dielectric material is loaded over pairs of balanced feeds to overcome radiation performance degradation addressed in purely metallic antennas. Also, radiation patterns are further improved by employing a lens aperture and shielding structures. The measured results of the final antenna design demonstrate broad and stable far-field patterns (half-power beamwidth > 45^◦), low voltage standing-wave ratio (< 2), similar E- and H-plane patterns, and large cross-polarization isolation (> 23 dB).

The programmable graphics processing unit (GPU) is employed to accelerate the unconditionally stable Crank-Nicolson finite-difference time-domain (CN-FDTD) method for the analysis of microwave circuits. In order to efficiently solve the linear system from the CN-FDTD method at each time step, both the sparse matrix vector product (SMVP) and the arithmetic operations on vectors in the bi-conjugate gradient stabilized (Bi-CGSTAB) algorithm are performed with multiple processors of the GPU. Therefore, the GPU based BI-CGSTAB algorithm can significantly speed up the CN-FDTD simulation due to parallel computing capability of modern GPUs. Numerical results demonstrate that this method is very effective and a speedup factor of 10 can be achieved.

The primary requirement for maximum power transfer and minimum power loss is matched impedance in a transmission system. However, static design variations in system such as parasitics and dynamic variations such as changes in transmission frequency will result in reflections. A redesign or reconfiguration of complex systems is neither easy nor cost effective. A noble technique for compensating reflections in a communication system is presented here. The proposed methodology adapts the system to change without any modification to the system physical configuration. In this methodology compensation signals are added by I/O drivers with programmable phase delay and drive strength adjustments to cancel reflections. The concept application is demonstrated for a narrow bandwidth antenna system. An operating frequency off the antenna frequency results in a degraded received message eye. Using the proposed technique, without modifying the antenna, reflections were compensated and a significantly improved data eye was produced, as measured by the enhancement of critical performance parameters. The architecture of an expanded driver to implement the concept is outlined here. An algorithm and flow chart to dynamically identify and compensate for reflections are also presented.

Three novel shapes of mushroom-like electromagnetic band-gap (EBG) structures are presented in this paper. The three shapes are based on rectangular metal strip with different combinations. The performances of the three-shape structures are studied by using both incident plane wave method and transmission coefficient approach. The effect of height and via location are also studied to achieve multi or wide band gap. These shapes are embedded in microstrip patch antenna substrate. The performance of the MPA is improved as increasing the antenna gain by 5 dBi, decreasing the surface current so improving the antenna radiation pattern as well as reducing the antenna size by more than 70% compared to the original size. The new shapes of EBG structure are integrated with MPA as a ground plane, where the conducting ground plane is replaced by a high impedance surface EBG layer. Parametric studies are conducted to maximize their impedance bandwidth and gain. It is found that the antenna bandwidth increased by about four times than original band and its gain is similarly increased. Sample of these antennas are fabricated and tested, to verify the designs.

Compact dual-band bandpass filter (BPF) with wide and narrow bands simultaneously is presented. By using the stepped impedance resonators (SIRs) in multilayered structure, the dual-band responses with wide and narrow bands simultaneously can be obtained. The filter has 3-dB fractional bandwidths (FBWs) of 45% and 10% for 2.4 GHz and 5.2 GHz, respectively. The circuit size is compact due to the multilayered structure. Moreover, multi-path propagation inside the multilayered structure generates transmission zeros at each skirt of the passbands for improving the passband selectivity. Measured results of the filter are in good agreement with the full-wave electromagnetic (EM) simulation.