To apply the power-law to random mixing composites, the power parameter α is defined as the mean depolarization factor along the external field. The formula of α is derived from the effective medium theory and beta function distribution assumption to study the geometrical influence of scatterers. According to the simulation, we prove that α = 1/3 is fit to the composites of randomly distributed spherical dielectric scatterers, whereas α = 1/2 to the flake-like or cylindrical shaped scatterers. This law can be applied to both dilute and dense condition describing the effective permittivity of random mixing composites and extended to aligned cases, which are meaningful to practical applications.

In this paper, we investigate nonuniformly spaced linear arrays (NUSLA) rigorously. Several important problems in NUSLA design are solved with the combination of the Genetic Algorithm and Conjugate Gradient method (GA-CG). The pattern synthesis for the specified beamwidth and minimum achievable sidelobe level (SLL) are performed and for the first time, the graphs which show the relation between the beamwidth, sidelobe level and number of elements for NUSLA are derived. Also, the NUSLA's pattern for the specified directivity and sidelobe level is synthesized. The graphs showing the behavior of NUSLA relative to the increase of its length for a fixed number of elements are derived. These graphs showthe relations between the directivity and sidelobe level of NUSLA with its length. As a practical design, an array of parallel dipoles is designed for specified beamwidth/sidelobe level or specified directivity/sidelobe level. Furthermore, a novel Neural Network based model for the NUSLA is presented for the rapid and accurate computation of Sparameters. The computed S-parameters are used for the computation of coupling among elements. Then the GA-CG method can adjust these values in the synthesis process to achieve desired pattern and bearable coupling among elements.

This paper presents a new design of a compact patch antenna based on the slot matching concept. Switches are integrated with the previously inserted slots into the patch antenna to enhance the performance. The newly designed antenna is a multi-wideband antenna. It is able to achieve a return loss less than -9.54 dB and VSWR≤2 in more than four frequency bands in the range from 2 to 5GHz

This paper proposes the application of the Wiener filter in an adaptive manner in speech enhancement. The proposed adaptive Wiener filter depends on the adaptation of the filter transfer function from sample to sample based on the speech signal statistics (mean and variance). The adaptive Wiener filter is implemented in time domain rather than in frequency domain to accommodate for the varying nature of the speech signal. The proposed method is compared to the traditional Wiener filter and the spectral subtraction methods and the results reveal its superiority.

A new iterative technique based on the T-matrix approach is proposed for the electromagnetic scattering by dielectric cylinders, in particular cylinders with large aspect ratios. For such cases the conventional T-matrix approach fails. We use hypothetic surfaces to divide a cylinder into a cluster of N identical sub-cylinder, for each the T matrix can be directly calculated. Since any two neighboring subcylinder are touching via the division interface, the conventional multiscatterer equation method is not directly applicable. The coupling among sub-cylinder and boundary conditions at the interfaces are taken care of in our approach. The validity of the proposed method is demonstrated through agreement between theoretical predictions and numerical simulations as well as measurements for scattering from dielectric circular cylinders with finite length. The results clearly demonstrate that the new iterative technique can extend regular T-matrix approach to solve cylindrical cases with large aspect ratio.

In the planning and design of microwave communication links, the structure of the radio refractive index in the lower part of the atmospheric boundary layer is very important. In this work, measurements of atmospheric pressure, temperature and relative humidity were made in Akure (7.15^oN, 5.12^oE), South Western Nigeria. Wireless weather stations (Integrated Sensor Suite, ISS) were positioned at five different height levels beginning from the ground surface and at intervals of 50m from the ground to a height of 200m (0, 50, 100, 150 and 200 m) on a 220m Nigeria Television Authority TV tower at Iju in Akure North Local Government area of Ondo State. The measurement of the atmospheric variables was made every 30 minutes everyday. The study utilized the data for the first year of measurement (January-December 2007) to compute the radio refractivity and its refractivity gradient in Akure. From these parameters, the vertical distributions of radio refractivity are then determined. The results obtained show that the propagation conditions have varying degree of occurrence with sub-refractive conditions observed to be prevalent between January-July while Super-refraction and Ducting were observed mostly between August-December.

A new numerical method is presented for the design and optimization of linear arrays of nonuniformly spaced longitudinal slots on the broad wall of rectangular waveguides, based on the Method of Least Squares (MLS). Elliott's design theory for travelling-wave-fed slot arrays is extended to nonuniformly spaced slots. As a common approach in MLS, an error function is formulated according to the design goals (namely the input impedance matching and pattern synthesis) and then minimized with respect to the design parameters (namely slot lengths, offsets, spacings and excitations). Having the slot parameters, one can design a linear slot array which accounts for the desired input impedance matching and array pattern. This approach has the advantage of combining the ``nonuniform pattern synthesis'', which includes the external mutual coupling and element pattern of slots, with ``impedance matching'' and ``calculation of the array parameters''. This procedure increases the design speed as well as synthesizing any desired pattern. The MLS design results and those obtained by HFSS simulation software are in good agreement and verify the accuracy of the proposed method.

This paper presents the calculations of transmission line loss factor by extracting from the Q-factor measurement of the quarterwavelength open stub resonators over the designed frequency and other resonant frequencies. A comparison of the loss factor of the design frequency with other resonant frequencies of each of the stub's quarter-wave resonances is provided in this paper. The radiation and discontinuity losses are undesirably included in the unloaded Q-factor measurement andit shows that the unloadedQ-factor is not repeatable at different designed frequency. The implementation of the loss factor measurement by quarter-wavelength open stub resonators is becoming more andmore important to be consideredwith the increase of using the electronic circuits operating at high frequencies.

The measurement of the field radiated from an antenna placed above a finite ground plane experiences the effects of the field scattered by the edges of the ground plane. A new numerical method to remove these effects from measured data is presented here. It resorts to the image theorem and can be used for both near-field and far-field measurements. A simple and effective algorithm has been developed to apply that method to fields described by means of spherical wave expansion. A numerical validation shows the effectiveness of the method.

This paper reports on an experimental investigation of modes propagating along a conductor-backed slotline: the dominant mode, and the surface leaky mode. The measurement and the numerical experiments performed in the CST Microwave Studio verify theoretical findings of modes obtained by the method of moments applied in the spectral domain. The dispersion characteristic of the dominant mode on the conductor-backed slotline is determined by substituting this line by a flat slotted waveguide.

This paper proposes a motion compensation method to compensate for the inter-pulse phase errors caused by the target movement in stepped-frequency ISAR imaging. For this purpose, genetic algorithm, particle swarm optimization (PSO) and PSO with an island model (PSOI) were applied in the proposed procedure. Simulation results using point scatterers and measured data show that PSOI is the most efficient in the proposed method.

At the University of Liverpool, we are developing prototype free electron maser (FEM) that are compact, powerful and efficient for potential industrial applications. The design, set-up and results of a novel X-band rectangular waveguide pre-bunched free electron maser (PFEM) are presented in this paper. Our initial device operates at 10 GHz and employs two rectangular waveguide cavities (one for velocity modulation and the other for energy extraction). The electron beam used in this experiment is produced by thermionic electron gun which operates at 3 kV and up to 50 μA. The nominal beam diameter is 1mm passing across the X-band cavity resonators. The resonant cavity consists of a thin gap section of height 1.5mm which reduces the beam energy required for beam wave interaction. The results, progress so far and the scope of work for the next couple of months are reported.

Two 60 GHz homodyne receivers dedicated for high-speed short-range communication systems are presented. The receivers are based on six-port and conventional (anti-parallel diodes) mixers, respectively. Comparative bit error rate results, function of local oscillator power, phase, and frequency shift over the operating bandwidth, are presented and discussed.

Application of artificial ground planes in design of compact cavity-resonance dual-band high-gain antennas is presented. The artificial ground plane consists of periodic strip grating on grounded dielectric slab. A code based on method of moment (MoM) is developed to analyze and design such artificial ground planes. The reflection parameters obtained using the MoM code are employed to characterize the surface impedance of the artificial ground plane for different incident angles and both TE and TM polarizations. Then, this impedance surface is used in transverse equivalent network (TEN) model of the cavity-resonance antenna with high-permittivity dielectric superstrate. Using TEN model radiation properties of such antennas are analyzed. Finally, the antenna with the compact size is designed to demonstrate the maximum directivity. An interesting characteristic of this antennas is that when the antenna ground plane acts as an artificial magnetic conductor the height of the antenna is almost reduced by a factor of two, while its directivity is increased by about 1 dB compared to the conventional antennas of this class having PEC ground plane.

A phenomenological theoretical model of grain dielectric properties is presented for radio and microwave frequencies. On the bases of this model, an inverse problem is solved to determine the dielectric permittivity of bound water inside kernels of winter wheat using results of complex permittivity measurements for bulk grain carried out by other authors. The character of the water complex permittivity dependence on frequency and kernel moisture content is studied. For this, the permittivity was considered as a sum of five different functions, depending on moisture content explicitly, and with coefficients being subject to determination. The frequency dependence of these coefficients was analyzed, and the regions typical for the ionic conductivity and for the dipole-orientational polarization mechanism were detected. For this polarization mechanism, the relaxation frequencies are differ from those of free water. It was concluded that water microparticles inside kernels are formed not by pure water, but by aqueous solution of four different substances coming from the kernel solid phase. It is shown that bound water, for the most part, is in a state that is intermediate between that of free water and that of molecules in the monomolecular water layer on the solid phase boundary.

Deterministic blind beamforming algorithms try to separate superpositions of source signals impinging on electromagnetic vector sensor array by using deterministic properties of the signals. This paper links electromagnetic-vector-sensor-array beamforming problem to the parallel factor (PARAFAC) model, which is an analysis tool rooted in psychometrics and chemometrics. Exploiting this link, it derives a deterministic blind beamforming algorithm. The blind beamforming algorithm doesn't require DOA (direction of arrival) information and polarization information. The simulation results reveal that the performance of the blind beamforming algorithm for electromagnetic vector sensor array is close to nonblind MMSE method, and this algorithm works well in array error condition.

In the present communication, we investigate theoretically and study a different type of photonic structure called metallic star waveguide (SWG) structure. The proposed structure, having single homogenous metallic material, is composed of a backbone (or substrate) waveguide along which finite side branches grafted periodically. In order to obtain the dispersion relation and hence the photonic band gaps (PBGs) of the SWG structure the Interface Response Theory (IRT) have been applied. Such types of structures show the band gaps without the contrast in the refractive index of the constituent materials. We also show that the range of forbidden bands can be tuned to different value by varying the number grafted branches of the SWG structures, without changing the other parameters. Moreover, the effects of variation of absorption of metals and plasma frequency on the band gaps of the proposed structures have been investigated.

This paper presents a circularly polarized (CP) GPS/DCS loop-like antenna with a microstrip feed. The proposed antenna comprised of a quasi-C antenna, an inverted-L sleeve strip connected with the ground plane and an L-shaped slit embedded in the ground plane. The C-like antenna generates a resonant mode with a poor impedance matching condition. The inverted-L grounded strip and the embedded L-slit are not only capable of modifying two orthogonal electric fields with equal amplitude and phase difference of 90 degree for radiating circular polarization at 1.575 GHz, but the impedance characteristics is also improved and the operating frequency is reduced. Both simulated and measured results are provided to validate the impedance and CP performance of the proposed antenna. For the optimized antenna case, the measured bandwidth with an axial ratio (AR) of less than 3 dB is larger than 19% and the measured impedance bandwidth of reflection coefficient S₁₁ < −10 dB is about 30.1%.

In this paper, a new compact circular monopole ultrawideband antenna with multiple narrow bands notched is proposed, which is implemented by using the existing techniques, such as loading a L-type band-stop filter, inserting a split ring resonator (SRR), and the method we proposed that connecting L branches on the radiation disk. Four sharp notches at 2.4GHz, 3.5 GHz, 5.5 GHz, and 7.6 GHz are achieved separately. The measured VSWR shows a good agreement with the simulation results. The radiation patterns are obtained from Ansoft HFSS simulations and verified by CST Microwave Studio. The results prove that this kind of antenna can be applied in the UWB communication systems to avoid interference with other wireless systems, such as the 2.4GHz WLAN, 3.5 GHz WiMax, and 5.8 GHz WLAN etc. The parameters determining the antenna's band notched characteristic are discussed.

In this paper a novel ultra-thin radar absorbent material (RAM) using HIGP is presented and investigated. Owing to the high impedance property of the HIGP, the thickness of the RAM is about several tenths of the centre wavelengthof the absorption band, considerably thinner than conventional absorbers. The absorption band of the RAM is about several hundred megahertz. In the new RAM, lumped resistances are soldered between the patches of mushroom-like high-impedance surface (HIGP). And the metal ground plane of waveguide slot antenna is covered by this new type of RAM. As compared to the slot antenna with a metal ground plane, the measured results show that the radar cross section (RCS) of waveguide slot antenna reduces significantly. This proves that the new HIGP RAM has a good radar absorbing characteristics. The simulations and experiment results have shown that the RCS of antenna is reduced by 7.9 dB and gain is only reduced by 0.9 dB.