A research of W band microstrip integrated high order frequency multiplier based on avalanche diode is presented. The associated nonlinear model of avalanche diode driven by external RF signals for high order frequency multiplication is presented and analyzed according to the physical property of avalanche diode. Subsequently the circuit of microstrip integrated high order multiplier is analyzed. In experiment, maximum output power of 6.5 mW with the efficiency of about 0.62% is obtained at output frequency of 94.5 GHz with 15th multiplication order. The phase noise of output 94.5 GHz signal is about −90.83 dBc/Hz and −95.67 dBc/Hz at 10 KHz and 100 KHz offset.
In this paper, Wave Concept Iterative Procedure (WCIP) is used to investigate scattering by multilayered cylindrical structures in free space and to calculate the diffracted far field by adopting a cylindrical coordinate formulation. The WCIP principle consists of alternating waves between the modal and space domains. Its iterative resolution process is always convergent in lossless media case. The proposed technique used for determining the electric far field diffracted by a multilayered cylindrical structure is validated and confronted to literature results.
Circularly polarized superquadric dielectric resonator antenna is investigated. A single coaxial probe is used to excite circularly polarized patterns. Finite element method is used to analyze the problem. Different aspect ratios of the superquadric dielectric resonator cross section for each squareness parameter for circular polarization are calculated.
An approach utilizing a paraboloid photonic crystal structure (PPCS) is proposed in this paper to compensate the polarization discrimination of an antenna's radiation. It is demonstrated by considering a reflector antenna excited by a pair of crossed-dipoles, whose circularly polarized (CP) radiation may be distorted due to the scattering from the finite reflector surface. The proposed approach tends to compensate the discrimination and achieve a wider beamwidth of good axial ratios while, in the mean time, retaining a less gain loss. The advantage of this approach is that the PPCS can be integrated into a radome structure of the antenna without increasing an excess cost. Numerical studies are conducted in this paper and demonstrate that this compensation method can achieve a beamwidth of about 30 degrees at the frequency of 12.45 GHz.
Fields inside the chiral nihility slab which is backed by perfect electric conductor are determined. It is noted that both electric and magnetic fields exist inside the grounded chiral nihility slab when it is excited by a plane wave. Electric field inside the slab disappears for excitation due to an electric line source. Magnetic field inside the slab disappears when geometry changes to corresponding dual geometry. Dual geometry means chiral nihility slab backed by perfect magnetic conductor and excited by a magnetic line source. Using fractional curl operator, fields are determined for fractional order geometries which may be regarded as intermediate step between the two geometries which are related through principle of duality. Discussion is extended for chiral nihility slab which is backed by perfect electromagnetic conductor (PEMC).
A TE/TM wave splitter composed of a gyrotropic slab is proposed. We demonstrate theoretically that, when the working frequency is chosen to be within one of the two ranges, total reflection occurs at the boundary of a slab of gyrotropic medium for either TE or TM component of the incident waves. Tuning can be done by choosing the working frequency band or adjusting the applied magnetic field. Furthermore, within the TE-stop or TM-stop frequency region, if the incident angle is selected appropriately, the other polarized component of the wave is totally transmitted. And we also show that when the slab is thicker, there are more possibilities to satisfy the full-pass condition. Finite-element method simulations verified the theoretical results.
Various isolation improvement techniques for MIMO WLAN card bus applications consisted of three closely spaced loop antennas are presented and investigated both numerically and experimentally in this paper. The proposed techniques are easily implemented and proven effective to achieve high isolation among the antennas which is a must for MIMO terminals to receive uncorrelated signals with good system throughputs.
This paper presents a comprehensive Non Line of Sight (NLOS) localization scheme in a multipath environment where the scatterers with smooth surfaces are aligned parallel or perpendicular to each other. It leverages on the estimation of Angle of Arrival (AOA) and Time of Arrival (TOA) of the omni-directional mobile device's signal received at the reference devices. Unlike the conventional Line of Sight (LOS) localization schemes that rely on the various mitigation techniques to mitigate the multipaths that are mistaken as the LOS signal, our proposed two step localization scheme not only utilizes the LOS path but also any one bound scattering NLOS multipath arriving at the reference devices for localization. Channel experiment coupled with simulation results in a typical multipath environment has demonstrated that our proposed localization scheme outperforms the conventional localization schemes that are coupled with their own mitigation techniques. Robustness in performance of our proposed localization scheme towards different scatterers' orientation where they are not aligned parallel or perpendicular to each other are also investigated.
A modal-expansion method is proposed for the analysis of a monopole antenna in a vibrating reverberation chamber. Inside the chamber, electromagnetic fields are expanded using modal functions. Mode matching process is applied to enforce the boundary conditions at regional interfaces. Boundary conditions on the four side walls of the chamber are imposed by the point matching method. Combining these two matching processes, a set of matrix equations are obtained and the expansion coefficients can then be determined accordingly. The loss from the chamber walls is accounted for through homogeneous material filling. The input impedance and scattering parameter of a monopole in a reverberation chamber are computed and statistical analysis of the scattering parameter is conducted when one of its walls is vibrating.
This paper explores the feasibility of microwave imaging a buried object by the GA and using the S11 parameter of a radiation antenna rather than data of the scattered electromagnetic field. To improve the efficiency of the GA-based algorithm, a technique of limiting the location of the buried object prior to the implement of the GA is proposed, and the GA is parallelized and executed on a PC cluster. A few numerical examples are presented, in which the dimension and location of a 3-D object buried in the earth are recovered. Results validate the proposed GA-based microwave imaging algorithm.
A new class of microstrip filter structures are designed, optimized, simulated and measured for ultra-narrowband performance essential to the wireless industry applications. More accurate model of the coupling coefficient is outlined and tested for narrowband filter design. Two sample filters are fabricated and measured to verify the simulations and prove the concept. The idea behind the new designs is based on minimizing the parasitic couplings within the resonators and the inter-resonator coupling of adjacent resonators. A reduction of the overall coupling coefficient is achieved even with less resonator separation which is a major issue for compactness of such filters. The best new designs showed a simulated fractional bandwidth (FBW) of 0.05% and 0.02% with separations of S = 0.63 mm and S = 0.45 mm, respectively. The measured filters tend to have even narrower FBW than the simulated, though its insertion loss deteriorates, possibly due to mismatch at the interface with external circuitry and poor shielding effect of the test platform. The investigated 2-pole filters are accommodated on a compact area of a nearly 0.6 cm2. An improvement of tens of times of order in narrowband performance is achieved compared to reported similar configuration filters and materials. A sharp selectivity and quasi-elliptic response are also demonstrated with good agreement in both simulations and measurements. In all filters, however, the study shows that the narrower the FBW, the larger the insertion loss (IL) and the worse the return loss (RL). This is confirmed by measurements.
Circular arrays of log-periodic (LP) antennas are designed and their operational properties are investigated in a sophisticated simulation environment that is based on the recent advances in computational electromagnetics. Due to the complicated structures of the trapezoidal-tooth array elements and the overall array configuration, their analytical treatments are prohibitively difficult. Therefore, the simulation results presented in this paper are essential for their analysis and design. We present the design of a threeelement LP array showing broadband characteristics. The directive gain is stabilized in the operation band using optimization by genetic algorithms. We demonstrate that the optimization procedure can also be used to provide beam-steering ability to LP arrays.
This paper presents an ultra-wideband rectangular ring fed by stepped monopole antenna. The initial parameters of rectangular ring are first considered to obtain the bidirectional pattern with the desired resonant frequency. Subsequently, the parameters of stepped monopole for enhancing impedance bandwidth are investigated. To study the impedance and radiation behaviors, the simulations of the proposed antenna have been carried out. It is found that this antenna offers a bidirectional beam with the impedance bandwidth (return loss lower than -10 dB) covered the frequency range from 3.1 to 10.6 GHz. At the desired direction along this frequency band, the gain of 2.33-5.21 dBi is achieved. Furthermore, the prototype antenna was fabricated and measured to verify the simulated results. Obviously, the simulation and measurement are reasonably in good agreement.
The analytical formulae based on the generalized reflection and transmission coefficient matrices for cylindrically stratified media are used to simulate the borehole effect on multicomponent induction logging responses in various ratios of mud conductivity and formation conductivity and to investigate the tool's eccentricity effect on the responses of coplanar coils and coaxial coils. The simulated data show that the borehole effect and the tool's eccentricity effect on the response of coplanar coils is greater than that on the response of coaxial coils in most cases. Then we give an algorithm for the correction of borehole effect on multicomponent induction logging responses, and the algorithm is based on the above-mentioned formulae to build forward model and regularized Newton method. Finally we correct borehole effect on the apparent conductivity responses of two different models with the algorithm, and the results demonstrate the effectiveness of the algorithm.
This paper presents an image reconstruction approach based on the time-domain and steady state genetic algorithm (SSGA) for a 2-D perfectly conducting cylinder buried in a half-space. The computational method combines the finite difference time domain (FDTD) method and the steady state genetic algorithms (SSGA) to determine the shape and location of the subsurface scatterer with arbitrary cross section. The subgirdding technique is implemented in the FDTD code for modeling the shape of the cylinder more closely. In order to describe an unknown 2-D cylinder with arbitrary cross section more effectively, the shape function is expanded by closed cubic-spline function instead of frequently used trigonometric series. The inverse problem is reformulatedin to an optimization problem and the global searching scheme SSGA with closedcubic-spline is then employed to search the parameter space. Numerical results show that the shadowing effect for the inverse problem in a half space results in poor image reconstruction on the backside of the cylinder. We propose the two-step strategy to overcome the shadowing effect. It is found that goodimaging quality could be attainedbasedon the proposed strategy.
We have studied the problem of diffraction of an electromagnetic spherical wave by a perfectly conducting finite strip in a homogeneous bi-isotropic medium and obtained some improved results. The problem was solved by using the Wiener-Hopf technique and Fourier transform. The scattered field in the far zone was determined by the method of steepest descent. The significance of the present analysis was that it recovered the results when a strip was widened into a half plane.
We present a novel outdoor-indoor radio wave propagation model. It predicts the electric field envelope Cumulative Distribution Function (CDF) in a room placed near a radio communication emitter. The experimental CDF obtained from the simulation, fits the experimental CDF obtained from a measurement campaign carried out over 19200 sampling points inside the room. The maximum deviation found between these CDFs is less than 1%. Kolmogorov-Smirnov test is employed to analyze the goodness of fit. P-values around 99% are reached. A comparison is made with other classical methods reported in the literature as ray-tracing (RT) and a hybrid method employing finite-difference time-domain (FDTD) together with RT. The proposed model significantly improves the results achieved in those previous investigations. Although we study the problem in three dimensions, the repetitive nature of the algorithm allows us to parallelize the computation process speeding the calculations.
A narrowband trisection substrate-integrated waveguide elliptic filter with coplanar waveguide (CPW) input and output ports is proposed and demonstrated for X-band applications. The filter is formed by incorporating metallized vias in a substrate (RT/Duroid) to create cross-coupled waveguide resonators. The result is an attenuation pole of finite frequency on the high side of the passband, therefore exhibiting asymmetric frequency response. The fabricated trisection filter with a centre frequency of 10.05 GHz exhibits an insertion loss of 3.16 dB for 3% bandwidth and a return loss of -20 dB. The rejection is larger than 15 dB at 10.37 GHz.
In this paper we study on the one hand under delayedacknowledgement (Dly-ACK) mechanisms the option of using ACK Request to improve system robustness, and on the other hand the incorporation of effective retransmission schemes such as hybrid automatic repeat request (HARQ) to improve system throughput for an IEEE 802.15.3 compliant system. An expression of throughput is derived in terms of system parameters and channel conditions. A constrained optimization problem for system throughput is formulated. It is then solved numerically due to the high degree of nonlinearity in the payload size. Our results indicate that under poor channel conditions, the optimal throughput under HARQ scheme is significantly higher than that with ARQ, and larger payload size is proposed to further improve the performance.
A basis function with the traveling wave phase factor, called as the phase extracted (PE) basis functions in this paper, has been applied for efficient solution of scattering from 3 dimensional (3- D) electrically large objects. In this paper, a rigorous derivation is given as a physical insight of this basis function. Defined on large patches and containing propagating wave phase dependence, this kind of bases exhibits very strong directivity, leading to a highly sparsed impedance matrix. Based on such observation, a matrix sparsification technique and an impedance prediction technique have been developed in this paper. The total memory requirement and computational time could be reduced significantly with methods proposed in this paper. The basic requirements of basis functions, i.e., current continuity and absence of charge accumulation are demonstrated, and the excellent behavior of PE basis functions in wideband applications has been summarized briefly. Several numerical examples have been given to show its good accuracy and high efficiency in solving scattering from electrically large complex objects.
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.
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.
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.