In this paper, we propose a new way to compact the transmission lines, which has a general application to miniaturization of RF and microwave circuits. In this way, we use Nonuniform Transmission Lines (NTLs) instead of Uniform Transmission Lines (UTLs). To synthesize the desired Compact Length Transmission Lines (CLTLs), the characteristic impedance function of the NTLs is expanded in a truncated Fourier series. Then, the optimum values of the coefficients of the series are obtained through an optimization approach. The usefulness of the proposed structures is verified using some examples.
Fractional solutions of a parallel plate waveguide originally with impedance walls have been derived and fractional impedance of the guiding walls have been investigated. Two distinct ranges ofw all impedance have been found in which fractional impedance behaves in opposite ways. For 0 < α < 1, the fractional impedance is inductive in range 1 and is capacitive in range 2, where α is fractional parameter. For 1 < α < 2, the fractional impedance is capacitive in range 1 and is inductive in range 2. At the boundary ofthe two ranges, the fractional impedance is independent of α and is resistive. This behavior is periodic with period α = 2.
As wireless communication applications require more and more bandwidth, the demand for wideband antennas increases as well. One of the most applicable frequency bands is X-band (8-12 GHz). X-band frequencies are used in satellite communications. Radar applications, terrestrial communications and networking, motion detection and etc. Fractal passive Microstrip antennas are simple and novel structures that attract much attraction recently. In this paper, new Microstrip sierpinski modified and fractalized antenna using multilayer structure for achieving wideband behavior in X-band which in 7-10.6 GHz portion overlaps UWB working range. Using fractal defection in patch, multi higher order modes are inspired for coupling a much wider bandwidth. Roggers TMM3 (εr = 3.38) is used in this antenna as substrate. Working range for this antenna is from 7.7 GHz to 16.7 GHz (BW = 9 GHz). This antenna has simple structure, small size and 4 resonance frequencies. This fabricated and tested antenna is designed by Ansoft Designer software.
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
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 (7.15oN, 5.12oE), 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.
Effects of different optical losses (auger recombination, cooperative up-conversion, excited state absorption (ESA) and Si- Nc induced loss) on amplification parameters including net gain and population inversion in Si-Nc Er doped fibber are studied. Optical loss due to up-conversion effect has critical role in the mentioned optical amplifiers. Simple modeling of this effect can be done by 2CupN22, where Cup and N2 are up-conversion coefficient and population of level 2 respectively. In traditional considered cases Cup are assumed to be constant, but in practical situation this is hard to be realized. In practice distribution of Er ions is inhomogeneous and especially the Gaussian. So, from our point of view the suitable model should consider position dependence up-conversion coefficient. In this paper we considered this subject and by simulation modeling tries to show effect of inhomogeneous distribution of up-conversion coefficient on optical net gain and population inversion. It is shown that life times of first and second excited states are decreased and so the population inversion is decreased too. Thus optical net gain near to center of the Gaussian distribution is deceased strongly. The observed gain lowering is suitable description of the reported experimental results. Also, it is observed that in high level Si-Nc density the obtained optical gain is decreased against traditional description which Cup is assumed to be constant. The core diameter is considered R = 10μm.
A very small patch type RFID tag antenna (UHF band) using ceramic material and proximity coupled feeding structure mountable on metallic objects is presented. The proposed tag size is 25×25×3 mm. Both of the radiating part and the feeding part of the proposed antenna is located in the same plate for easy implementation. The resistive and reactive components of the input impedance of the antenna can be easily matched to the tag chip impedance from the size of the feed loop and the distance between feed loop and radiating patch. The antenna satisfactorily operates on metal plates, so it is applicable in many applications. The proposed design is verified by simulation and measurements which show good agreement.
A compact ultra-wideband (UWB) band-pass filter (BPF) with highly rejected notched band is proposed in this paper. The proposed UWB BPF is composed of two cascaded interdigital hairpin resonator units. Interdigital hairpin resonator unit with different coupling is theoretically analyzed. The working frequency of the proposed UWB BPF is 3.1-10.6 GHz and notched band is 5.7-5.8 GHz. Finally, measured results are presented, which are in good agreement with the simulation results.
Geometrical analyses of basic equations of electromagnetics waves propagation in anisotropic dielectric materials with magnetic isotropy are presented in two complementary papers (Part I and Part II). In the present one, analysis arises from quadrics associated with relative dielectric tensor (ε) compatible with conical surfaces that represent the general plane wave equation (relation of dispersion). This study systematizes rays propagation in left-handed materials (LHMs) exhibiting dielectric anisotropy and magnetic isotropy. In particular, indefinite dielectric media where dielectric permittivities are not all the same sign, have been investigated. Graphical alternative procedures for ray tracing in these media are presented.
Geometrical analysis of basic equations of electromagnetics waves propagation in anisotropic dielectric materials with magnetic isotropy are presented in two complementary papers (Part I and Part II). In this paper, analysis arises from local properties of dielectric permittivity tensor and Mohr's plane graphical construction compatible with circumferences that represent general plane wave equation. This theoretical study allows to know how rays propagate in left-handed metamaterials (LHMs) exhibiting dielectric anisotropy and magnetic isotropy. Geometrical analysis yields plane graphical procedures for ray tracing, that are extremely easy. In particular, indefinite dielectric media, where dielectric permittivities are not all the same sign, has been investigated and a joint study of materials having the same eigenvalues of ε, but with opposite values of μr is performed. The opposite sense of propagation of rays in "opposite media" (media with opposite values of εi and μr) has been also shown. It must be pointed out that the presented method always allows graphical plane constructions, even when dealing with biaxial media.
A technique for natural frequency extraction without a prior knowledge of the number of natural frequencies is proposed. The proposed scheme is based on the GPOF method with the overestimated number of natural frequencies, and it has been shown from simulation result that the proposed method is superior to the GPOF method. The method is applied to the extraction of the natural frequencies of the thin wires whose exact natural frequencies are known. While the absence of the true natural frequency has much effect on the transient response reconstruction, the absence of the spurious natural frequency has little effect on the transient response reconstruction. Using the above property, true natural frequencies and spurious natural frequencies can be discriminated.
In this paper, we present a new domain decomposition technique which considers the effect of multiple reflections between the subdomains. This method has the ability to simulate accurately large electromagnetic problems that are difficult to handle using the direct application of the FDTD method. The results for the test examples considered in this paper compare well with the direct FDTD solution, and serve to validate the proposed scheme.
A class of linear derivative constraints, which provides robustness to the conventional narrowband uniform linear array configuration so as to handle broadband and moving jammer sources problem is presented. The robust modification of linear constrained minimum variance (LCMV) algorithm is given to broaden the null widths in the jammer directions. Numerical results show that the proposed algorithm has a better performance in broadband and moving jammer scenarios in terms of maintaining beamwidth broadening and capability of rejecting interferences.
In this paper we formalizes a new discrete time model of digital array based MIMO radar in which the combined effects of the transmit filter, physical MIMO multi-path channel fading, and receive filter. It has the same sampling period as that of the MIMO receiver. Apart from this, SNR value and target detection are different in compared to the continuous domain nature. Orthogonality is introduced using OSTBC (orthogonal space time coding) including interelement spacing at the transmitter is greater than the target beam width coverage. For space and temporal diversity we have considered distributed source model. and modulation schemes respectively. Frequency diversity is achieved using N point IFFT (N = 32, 64, 256, 1024) at the base band. Thus, three dimensional analysis with respect to diversity and selective nature of fading channel in digital array based MIMO radar are now used for performance analysis based on probability of detection, symbol error rate, model error, power spectral density at the receiver and SNR value at the detector.
Planar multilayer structures have found several applications in electromagnetics. In this paper, an equivalent model based on the bi-characteristic-impedance transmission line (BCITL) is employed to model planar multilayer structures effectively for both lossless and lossy cases. It is found that the equivalent BCITL model provides identical results, for both perpendicular and parallel polarizations, as those obtained from the propagation matrix approach.
A fast analysis of aperture-coupled reflectarrays is presented in this work in terms of transmission line model. The circuital approach is adopted to derive the phase design curve as a function of the current flowing on the equivalent impedance of the single radiating element. Computational costs are drastically reduced with respect to standard full-wave methods. Numerical and experimental validations are discussed on slot-coupled reflectarray configurations working at different operating frequencies.