A NEW LEAKY WAVE ANTENNA BASED ON CHANNEL GUIDE FILLED WITH LEFT-HAND MATERIAL FOR MILLIMETER-WAVE APPLICATIONS

A new leaky wave antenna based on channel guide filled with left-handed material (LHM), operating in evanescent surface mode of TM polarization, is presented for millimeter wave applications. A transverse equivalent network that yields a dispersion relation in closed form is employed to analyze the leakage characteristics of the antenna. Numerical results are presented for the phase and leakage constants of the antenna in terms of different geometric parameters and dielectric distributions. Besides, the frequency dependences of the leaky characteristics for the present antenna are given, from which the backward radiation is clearly demonstrated.     

A New Dielectric Grating Antenna with Large Leakage Constant for Millimeter-Wave Applications

The leakage properties of a new dielectric grating leaky wave antenna are carefully examined by an approach of combining the multimode network theory with the mode-matching method. A systematic comparison is given for the leaky characteristics of the n?=??1 space harmonic of TM mode polarization between the present antenna and the traditional one. It has been found that the former is not only of lower conductor loss, but also of larger leakage constant than the latter. As a result, the dimension of the antenna could be largely reduced, which is of practical significance for some applications. Extensive numerical results of the radiation characteristics are given to establish useful guidelines for the design of the new grating antenna. Furthermore, special features such as cancellation or resonance effects are high-lighted and discussed. Physical insights for the mathematical findings are also presented.     

Perturbation Analysis of Dielectric Grating Antenna with LHM Substrate

A dielectric grating leaky wave antenna with a substrate consisted of left handed material (LHM) is presented in this paper, the case where the n?=??1 space harmonic of TM mode radiating into the space is carefully investigated through the improved perturbation analysis, which tremendously simplifies the analysis procedure with good calculation accuracy and brings considerable physical insight into the overall behavior of the dielectric grating antenna. It has been found that the new leaky wave antenna is of larger leakage constant than that of the traditional antenna with substrate of the right handed material (RHM). As a result the dimension of the antenna could be largely reduced, which is of practical significance for some applications. Extensive numerical results of the radiation characteristics are given to establish useful guidelines for the design of the new grating antenna.     

Leaky wave antenna based on image NRD guide with staircase-shapeddielectric slab

A leaky wave antenna based on the use of an asymmetric image nonradiative dielectric (NRD) guide has been studied experimentally. By using a staircase-shaped image NRD guide, the gain bandwidth of the antenna becomes three times that of a leaky wave antenna using an ordinary image NRD guide. Moreover, this antenna employs a flared horn in the NRD guide which makes the H-plane beamwidth controllable     

A new leaky wave antenna for millimeter waves using an asymmetric strip in groove guide, Part I: Theory

Traveling wave antennas for the millimeter wave range face two main problems: higher metal loss at the higher frequencies, and fabrication difficulties due to the smaller wavelengths. These two problems are addressed here by a new type of leaky wave antenna, in which the fabrication problem is minimized by employing a longitudinally continuous aperture, and the higher loss reduced by basing the antenna on a low-loss waveguide, the groove guide. A longitudinally continuous asymmetric metal strip provides the mechanism that transforms the initially bound mode into a leaky mode. An accurate analysis, based on a transverse equivalent network, is presented here for the properties of this leaky structure that takes into account the mode conversion from the bound mode to the leaky mode. All the constituents of this transverse equivalent network are obtained in closed form, thus yielding a dispersion relation in closed form. Part I of these two companion papers describes the new antenna and its principle of operation, and then derives the parameters of the complete transverse equivalent network. Part II is concerned with the properties of the leaky mode and their relations to leaky wave antenna performance; design considerations together with a variety of numerical results are contained in Part II.     

A Double-Beam Radiation Leaky Wave Antenna Based on Left-Handed Material Slab with Metallic Strips Periodically Loaded

A new leaky-wave antenna structure is carefully investigated in the paper, which is based on a grounded Left-Handed material (LHM) slab periodically loaded with metal strips. A rigorous formulation similar to the spectral domain method for planar circuits is deduced to analyze the radiation characteristics of the antenna. Theoretical analysis results reveal that at specific frequency region or with proper geometrical parameters chosen, the present structure supports simultaneously two leaky modes corresponding to the forward and backward radiations. The principle of the antenna is due to the peculiar propagation properties of the unperturbed LHM grounded slab waveguide, which is totally different from the phenomenon of double or even more space harmonic mode radiations in normal periodic structures. Extensive numerical results of the leakage characteristics are given to establish useful guidelines for the design of the new type leaky wave antenna.     

Mode Matching Analysis for a New Millimeter Wave Omni-Directional Antenna Consisting of Circular Rod Corrugations Gloved with a Dielectric Shell

A new millimeter-wave omnidirectional antenna consisting of circular rod corrugations gloved with a dielectric shell is investigated. As an eigenvalue problem, the antenna is analyzed with the rigorous mode matching method. The radiation characteristics of the antenna are calculated in the Ka-band frequency range. A comparison of the leaky characteristics is made between the antennas with and without dielectric shell. It is found that the circular dielectric shell layer greatly affects the leaky characteristics of the antenna and the leakage constant increases considerably. In such a way, the length of the antenna can be reduced tremendously with higher radiation efficiency. This fact indicates that the proposed leaky wave antenna is of essentially practical significance for the case where the limitation in size and weight of system is strictly required. The effectiveness and reliability of the present analysis are verified by the calculated and experimental results given in the literature.     

Leakage characteristics of groove guide having a conductor strip

A full-wave characterization of the groove guide having a conductor strip is made based on the mode-matching procedure. All of the constituents of the structure, including a coupling strip, grooves and a radiating open end, are treated in a concise and rigorous way by using the generalized scattering matrix technique. Numerical results show that a set of channel guide leaky modes is also present in this structure in addition to the groove guide leaky mode. The complex propagation behaviors of both the groove guide leaky mode and the channel guide leaky mode are illustrated for various waveguide geometric parameters, and some conclusions regarding the design of leaky wave antennas using this structure are drawn     

An Improved Perturbation Analysis of a New Omnidirectional Circular Rod Antenna with Double Dielectric Gratings for Millimeterwave Application

The leakage characteristics of a new millimeter-wave omnidirectional circular rod antenna with double dielectric gratings are analyzed by an improved perturbation method. The electromagnetic fields are described in terms of a radial transmission-line network, which brings considerable physical insight into the overall behaviour of the leaky wave antenna. The analysis yields expression for the leakage constant in a closed form so that the design procedure of the antenna becomes very convenient. It is found that under the condition of the same radiation intensity, the double dielectric-grating antenna has relatively smaller dimension than that of the single one. The results obtained by the present analysis are compared with the exact solution based on the mode matching method; it is found that the improved perturbation analysis yields as accurate results as the rigorous method with extreme simplicity of the analysis and calculations.     

一种基于左手介质的新型介质栅漏波天线的理论分析

提出了一种基于左手介质的新型介质栅漏波天线,并采用多模网络与严格模匹配相结合的方法,对该左手介质栅天线的辐射特性进行了仔细严格的分析.文中给出了漏波系数随天线结构参数变化的关系以显示该左手介质天线特有的性质.数值结果表明这种新型漏波天线比传统介质栅天线具有更强的辐射能力.讨论了产生这种现象的原因.     

Radiation modes in circular patch antennas

We have formulated exact solutions of the normal modes in the microstrip patch antenna possessing circular geometry. The theory makes use of a new Green's function in conjunction with current potential analysis. The calculations demonstrate that the magnetic wall confinement boundary conditions as formulated in past theories hold approximately true if the surface wave loss is minimal compared to other losses: dielectric loss, conductor loss, and radiation loss. For practical path antennas the normal modes are not confined locally near the microstrip patch. Rather, they are composed of propagation surface waves which extend far beyond the region containing the patch antenna. We term these normal modes as leaky modes, since they resemble the leaky modes found in dielectric image guides. Measurements by us of the radiation mode frequencies and the intrinsic Q-values of the microstrip patch antennas compared very well with theory     

Propagation Characteristics of a Novel NRD Guide with Double-Layer LHM Slab

A new waveguiding structure based on NRD (Nonradiative Dielectric) guide with a double-layer LHM (Left Hand Material) slab is carefully investigated. Rigorous multi-mode network treatment combining with mode matching method is carried out to analyze the propagation characteristics of the structure. Theoretical analysis results reveal that depending on the choice of permittivity and permeability of the two dielectric slabs, the guiding structure is of series distinct and interesting properties, such as anomalous dispersion, opposite polarization modes coupling, and the existence of complex mode. Besides, the new configuration can also be used as a leaky wave antenna working in the dominant or the first higher order mode. All these particular features create various applications in electromagnetic engineering.     

新型NRD波导漏波天线特性分析

本文利用多模网络理论结合模匹配技术对任意横截面NRD波导漏波天线的辐射特性作了系统的分析,这些天线可以作为低成本的实用天线应用在毫米波系统中.文中着重研究了结构参数的变化对天线辐射特性的影响.这些计算结果对这类新型漏波天线的设计和确定NRD波导作为传输结构时的制作容差有重要的指导意义.     

Analysis and measurement of NRD-guide leaky wave coupler in Ka-band

A new structure for a nonradiative dielectric (NRD) waveguide directional coupler has been developed. The structure combines two NRD guides and a dielectric slab guide in order to utilize a leakage mechanism for coupling. The coupling depends on this leaky mechanism, but not on field interactions as in a conventional proximity coupler. A theoretical formula for calculation of the decay constant is derived. The field along the NRD guide and the decay constant are measured at Ka band (35 GHz) and compared with the theoretical data. Reasonable agreement between the measured and theoretical data is found     

Investigation on a Novel Leaky Wave Antenna with Double Radiation Beam Composed of Left-handed Slab Loaded Hybrid Waveguide using Planar Technology

A novel leaky wave antenna with double radiation beam composed of left-handed slab loaded hybrid waveguide using planar technology is proposed in this paper and its leaky characteristics are investigated with a method that the multimode network theory is combined with mode-matching method. The study of dispersion curves reveals that the proposed antenna structure supports two leaky modes corresponding to the forward and the backward radiations respectively. It demonstrates that the proposed antenna is of desirable property that can radiate both forward and backward directions simultaneously with quite simple and flexible configuration. Extensive numerical results of leaky characteristics with different structural parameters of the antenna are given to provide useful guidelines for the design of the new antenna.     

On the Existence of Leaky Waves Due to a Line Source Above a Grounded Dielectric Slab

The existence of a particular type of leaky wave is verified experimentally. The leaky wave considered is that due to an electric line source above a dielectric slab. Since such a leaky wave cannot exist by itself, it must be detected in the presence of the remainder of the continuous spectrum and often in the presence of a surface wave (or waves). This was done by probing the fields and observing an interference pattern between the leaky wave and the existing surface wave, as predicted by the theory. These results emphasize a need to take leaky waves into account in the design of surface wave components and antennas.     

Theory of line-source radiation from a metal-strip gratingdielectric-slab structure

This paper describes the fundamental theory of line source radiation from a source on a dielectric slab backed by a metal-strip grating. A continuous phased-array (CPA) method is applied to treat the analytic and numerical problems of antenna interaction with periodic structures. Both TE and TM mode cases for a one-dimensional strip grating are investigated. It is found that the strip grating on the dielectric surface may result in surface wave elimination and may also be used to support leaky waves. It is shown that high-efficiency and high-gain antennas on a dielectric substrate are possible with such metal-strip gratings     

一种新型多层介质悬置微带线漏波特性的分析

提出了一种多层介质悬置微带线天线结构,以改善天线的频扫特性.分析表明:该结构不仅可以确保天线工作在效率较高的天线模工作区,而且它的泄漏常数在相当宽的范围内随频率都能平坦地变化.对频率扫描天线能保证当波束扫描时,可以保持一个相对稳定不畸变的辐射方向图.     

Radiation from cylindrical leaky waves

Formulas are derived for the far-infrared radiation pattern of cylindrical leaky waves propagating on a planar surface. The formulas can be used to predict the radiation pattern of a general class of leaky-wave antennas, consisting of a finite-size source which excites a radially propagating leaky wave on some planar surface. Leaky-wave antennas consisting of antenna elements embedded in dielectric layers (microstrip elements) fall into this category. Using the equivalence principle, formulas are derived for both transverse electric (TE) and transverse magnetic (TM) leaky waves with arbitrary propagation constants. The formulas allow for radiation from cylindrical apertures of arbitrary size, so that the effect of truncating the supporting planar surface with an absorbing material can be determined. Particular attention is devoted to the case of a leaky wave for which the real and imaginary parts of the complex propagation constant are equal, since this type of wave has been shown to be responsible for broadside radiation in certain leaky-wave antennas comprised of dielectric layers