Guided radiation by coaxial cable for train wireless systems in tunnels

In railway radio systems and vehicular communications, a very important problem is that of maintaining stable communications at all locations, especially in tunnels and in spaces between buildings. A leaky coaxial cable having a new type of slot as a radiating element combining longitudinal slots with circumferential slots is described, and the desired radiation power or coupling loss can be easily designed by varying the dimensions of the slots and by selecting an appropriate pitch length. The results of the experimental studies at a frequency of 450 MHz are expected to give a satisfactory solution to this problem.     

Analysis and design of coplanar waveguide-fed slot antenna array

A method for analyzing and designing the slot antenna array excited by a coplanar waveguide (CPW) is presented. The slots are etched on the conducting plane of the CPW and placed in the direction perpendicular to the transmission line. Moment-method analysis and matrix-pencil approach are adopted to calculate the scattering parameters and hence the self-admittance of each slot. The mutual admittances between the slots are calculated from the formulas derived for the complementary strip dipoles based on the reciprocity theorem and via Booker's relation. Then the transmission line theory is used to calculate the input impedance of the array, and an iterative process is employed to obtain a matched design for a desired slot-voltage distribution. A four-element slot array is fabricated and measured using this design procedure. Calculated results are in good agreement with measurements     

Multiband Microstrip-Fed Right Angle Slot Antenna Design for Wireless Communication Systems

This paper presents a novel multiband microstrip-fed right angle slot antenna design technique for multiple independent frequency bands. The new technique uses various slot sizes at various appropriate positions. We first propose a tri-band slot antenna consisting of three right angle slots. Then, a quad-band slot antenna is developed with four right angle slots which achieves slant ±45° linear polarization, omnidirectional pattern coverage, good antenna gain, and acceptable impedance bandwidths over all the operating frequency range. Moreover, an open-circuited tuning stub is introduced to achieve good impedance matching. Both proposed antennas are designed on a ground plane of RT/duroid 5880 substrate with a thickness of 1.575 mm. The real measurable results show that the desired frequencies used in wireless communication systems, namely, WLAN and WiMax, are efficiently achieved.     

Analysis of planar slot arrays using magnetic currents andmagnetomotive force

An effective approach to the analysis of planar slot arrays constructed on a metal-coated dielectric slab is suggested. In the framework of the method, radiation and scattering characteristics of such arrays are obtained from treating the problem of guided mode diffraction with a finite number of transverse slots cut in metallization. The idea of magnetic currents and magnetomotive force is used to solve the problem; in doing so, mutual relations between the slots are taken into consideration. Some numerical results in the specific case of a uniform finite-periodic array are given. Moreover, the design problem aimed at reduction of sidelobes using nonuniform quasi-periodic slot arrays is considered. Applying the proposed analysis to the designed array, one can determine the deviation of actual radiation characteristics from the desired ones, thus correcting the design procedure if necessary     

Meandering long slot leaky-wave waveguide-antennas

A theoretical study is made of the aperture field distributions, the far-field amplitude patterns, and the mutual coupling characteristics of several long leaky-wave slot antennas cut on the broadwall of a rectangular waveguide mounted in an infinite ground plane. Straight long slots have high inner sidelobes in the far-field amplitude patterns, which reduces their utility as high-performance antennas. To reduce these sidelobes, a long slot may be meandered from waveguide centerline to sidewall and back to centerline in such a way to produce the desired radiation patterns. Calculated results for antennas of several meander patterns are presented and discussed     

Increased-bandwidth resonant slot array with bidirectional radiation pattern

A resonant slot array with a bidirectional radiation pattern and an impedance bandwidth of more that 15% has been realized by measuring the admittance of a couple of longitudinal shunt slots on the opposite walls of the waveguide, and then optimizing the reflection coefficient of the equivalent network of the array in the desired frequency range.     

An analysis of the radiation from apertures in curved surfaces by the geometrical theory of diffraction

In this paper the geometrical theory of diffraction is extended to treat the radiation from apertures or slots in convex perfectly conducting surfaces. It is assumed that the tangential electric field in the aperture is known so that an equivalent infinitesimal source can be defined at each point in the aperture. Surface rays emanate from this source which is a caustic of the ray system. A launching coefficient is introduced to describe the excitation of the surface ray modes. If the field radiated from the surface is desired, the ordinary diffraction coefficients are used to determine the field of the rays shed tangentially from the surface rays. The field of the surface ray modes is not the field on the surface; hence if the mutual coupling between slots is of interest, a second coefficient related to the launching coefficient must be employed. In the region adjacent to the shadow boundary, the component of the field directly radiated from the source is represented by Fock-type functions. In the illuminated region the incident radiation from the source (this does not include the diffracted field components) is treated by geometrical optics. This extension of the geometrical theory of diffraction is applied to calculate the radiation from slots on elliptic cylinders, spheres, and spheroids.     

Two port frequency reconfigurable antenna for cognitive radios

A two port frequency reconfigurable antenna for cognitive radios is presented. It is composed of a disc monopole with two ports that excite at opposite sides; one port is very wideband and consists of a coplanar feed line and the other port is tunable narrowband and consists of a microstrip feed line with defect slots in its ground plane. The slots act as a filter that suppresses frequencies outside the desired band, its operating frequency band can be tuned by varying the length of the slots. The two ports are decoupled by at least 10 dB through the considered frequency range. It is believed that the proposed antenna can be a good candidate for cognitive radios in generic small base stations where the narrowband port is used for operation and the wideband one is used for sensing the spectrum. For accuracy, it is important that the sensing (measurement of the interference noise) is made with the same polarisation as the operation and the proposed antenna achieves this by having the two collinear ports. To examine the presented approach, simulated and measured results are presented and good agreement is reported.     

基于动态优先级表的TDMA时隙分配

Ad Hoc网络组网效率提升的一个重要方面就是研究高效的时隙分配算法,动态TDMA时隙分配机制已经成为提高组网效率的一个热门研究点。这里基于动态优先级表提出一种新颖的动态时隙分配算法,该算法能在时间维上保证各节点对空闲时隙资源竞争使用的公平性。仿真结果表明基于动态优先级表的时隙分配算法能高效利用时隙资源,提高信道利用率。     

一种小型具有双阻带特性的超宽带天线设计

提出了一种具有双阻带特性的共面波导馈电超宽带天线。通过在辐射单元上开E型槽实现了3.75 GHz的第一个陷波结构,并在地板上开两条对称槽实现5.5 GHz的第二个陷波结构。文中提出的具有阻带特性超宽带天线的实测结果与仿真结果吻合较好。除了两个期望的阻带外其他超宽带频段内,该天线满足VSWR<2。同时给出了仿真辐射方向图和增益图。     

Numerical and experimental corroboration of an FDTD thin-slot modelfor slots near corners of shielding enclosures

Simple design maxims to restrict slot dimensions in enclosure designs below a half-wave length are not always adequate for minimizing electromagnetic interference (EMI). Complex interactions between cavity modes, sources, and slots can result in appreciable radiation through nonresonant length slots. The finite-difference time domain (FDTD) method can be employed to pursue these issues with adequate modeling of thin slots. Subcellular FDTD algorithms for modeling thin slots in conductors have previously been developed. One algorithm based on a quasistatic approximation has been shown to agree well with experimental results for thin slots in planes. This FDTD thin-slot algorithm is compared herein with two-dimensional (2-D) moment method results for thin slots near corners and plane wave excitation. FDTD simulations are also compared with measurements for slots near an edge of a cavity with an internal source     

Additional degree of freedom in phased-MIMO radar signal design using space-time codes

In this paper, an additional degree of freedom in phased multi-input multi-output (phased-MIMO) radar with any arbitrary desired covariance matrix is proposed using space-time codes. By using the proposed method, any desired transmit covariance matrix in MIMO radar (phased-MIMO radars) can be realized by employing fully correlated base waveforms such as phased-array radars and simply extending them to different time slots with predesigned phases and amplitudes. In the proposed method, the transmit covariance matrix depends on the base waveform and space-time codes. For simplicity, a base waveform can be selected arbitrarily (ie, all base waveforms can be fully correlated, similar to phased-array radars). Therefore, any desired covariance matrix can be achieved by using a very simple phased-array structure and space-time code in the transmitter. The main advantage of the proposed scheme is that it does not require diverse uncorrelated waveforms. This considerably reduces transmitter hardware and software complexity and cost. One the receiver side, multiple signals can be analyzed jointly in the time and space domains to improve the signal-to-interference-plus-noise ratio.     

Isolation enhancement for dual‐band MIMO antenna system using multiple slots loading technique

In this paper, a novel multiple slot loading technique is studied in detail for the isolation enhancement of the dual‐band MIMO antenna system. The proposed MIMO antenna design consists of the microstrip patch loaded with T‐shaped slots parallel to the non‐radiating edge of the patch. The frequency tuning could be achieved by varying the length of the T‐shape slot arm. The proposed MIMO antenna system is optimised for operation in WLAN and WiMAX applications. The isolation enhancement is achieved by providing simple multiple slots loaded in the ground plane between radiating elements. The length of the slots is λ/4 . The system is fabricated and tested using a vector network analyser and anechoic chamber. The reduction in mutual coupling up to ?29.16 dB and ?24.09 dB for the 2.4 GHz and 3.4 GHz, respectively, is achieved. The bandwidths are 62.3 MHz (3.33–3.39 GHz) and 55.5 MHz (2.37–2.42 GHz), respectively. The total gain obtained in this case is 1.8 dBi at 2.4 GHz and 1.2 dBi at 3.4 GHz, respectively. The dimensions of the proposed designed antenna are 70 mm × 60 mm × 1.6 mm. The results were also verified through mutual coupling parameters like envelope correlation coefficient (ECC) and channel capacity loss (CCL) at the desired frequencies.     

小张角环加载波纹喇叭中表面波的传播及辐射特性

本文利用空间谐波法导出了小张角环加载波纹圆锥喇叭中表面的传播文程，利用数值方法求解该方程，并分析了表面波在喇叭内的传播及辐射特性。数值计算结果与实测值吻合一致。结果表明，喇叭内激励的表面波主要影响喇叭的Ｅ面辐射场和交叉极化辐射场。     

A time domain theoretical method for the analysis of microstrip antennas composed by slots

In this paper, a time domain method is introduced for analyzing microstrip antennas having thin slots. The present method is based on a resolution of Maxwel?s. equtions using the finite difffreence time domain method. A particular investigation has been made for taking thin slots into account, this avoids a prohibitive grid to represent the slots. Two kinds of antennas have been analyzed by this method: the slot antennas and the radiatins patch fed by a line through a slot.     

ASAF ALOHA Protocol for Dense RFID Systems

RFID tags are used for varied applications in large numbers. Human Tracking is one such important application wherein the RFID system detects the presence of a tag in a dense tag environment. Quick estimation of the number of tags in the field at a desired level of accuracy is one of the most common requirements in the present scenario. Identification of tags has become a critical area which need more time and unsuitable in many situations; especially where tag set is dense. We introduce a novel medium access control (MAC) protocol for Radio Frequency IDentification (RFID) systems which exploits the statistical information collected at the reader. The protocol, termed Adaptive Slot Adaptive Frame (ASAF) ALOHA protocol, is motivated to significantly improve the total read time performance of the currently suggested MAC protocols for RFID systems by minimizing the collisions of the tags. In order to perform this task, ASAF estimates the dynamic tag population and adapts the frame size and number of slots simultaneously in the subsequent round via a simple policy that maximizes an appropriately defined function. We demonstrated that ASAF is better than the current RFID MAC protocols. We also considered the case where suddenly if the number of tags increases, the running frame with adapted slots gets flushed away and new frame with increased number of slots gets adapted automatically by the system showing the robustness in this case as well.     

基于哈希算法的动态TDMA时隙分配研究

动态时隙分配机制是Ad Hoc网络提高组网效率的重要方面。提出了一种基于哈希算法的动态时隙资源分配机制-HP_TDMA算法。该算法将节点的时隙需求划分为3种情况:节点不需要使用时隙、只需要使用主时隙和需要竞争额外时隙。在时隙竞争阶段采用哈希算法获得节点对时隙使用的优先级顺序表,按照优先级表配置节点对时隙的使用。经过仿真分析得出采用哈希算法的时隙分配策略能够高效地利用时隙资源,提高信道利用率。     

Development of the Fel’d’s concepts on the slotted waveguide devices in the works of researchers from the Karazin National University

The development of the Fel??d??s concepts on the slotted waveguide emitters in various slot systems is presented. Various narrow slots (slots with coordinate boundaries and tilted slots whose length is comparable with one half of wavelength, electrically long slots whose length is no less than one hundred wavelengths, slots in waveguides that are uniformly or partially filled with insulator, infinite slots, slots with reflecting walls, and slots that are uniformly or partially filled with insulator) are considered. The analysis of the effect of the waveguide wall thickness, the selection of the approximating function for the electric field in the slot, the correctness of the representation of the tensor Green function, and the application of the potential vector eigen-functions of the Helmholtz equation in the study of the magnetic field in the slot region are discussed.     

Transition From Perturbed to Coupled-Cavity Behavior With Asymmetric Spectral Emission in Ridge Lasers Emitting at 1.55 μm

We have investigated a series of ridge waveguide lasers with deeply etched slots in the ridges. The slots do not penetrate the active region, but are deep enough to strongly perturb the longitudinal modes. By the addition of slots, a transition between perturbed-mode and coupled-cavity behavior is crossed. With a group of four or more slots, the below-threshold amplified spontaneous emission spectrum from each end of the laser has different periods and the facet-facet oscillations are suppressed indicating that the different sections have become quasi-independent. A model using a distributed emitter in the cavity reproduces this behavior. Above threshold, the single contact coupled cavity lasers are single mode with greater than 30-dB sidemode suppression ratio over a wide range of currents     

有限元\边界元混合算法分析波导裂缝阵列天线

研究了一种分析波导裂缝阵列天线的方法。将有限元-边界元混合算法(FE-BI)应用于波导裂缝阵列天线的计算中,建立理论分析模型,计算波导裂缝上的等效磁流,进而求解整个天线阵列的远场辐射特性。为了检验这种方法的正确性,将所得的数值计算结果与测试值进行了比较,结果表明:FE-BI法可以作为计算波导裂缝阵列天线的一种有效的方法。