An improved calculation procedure for the radiation pattern of acylindrical leaky-wave antenna of finite size

A method is given for calculating the radiation pattern of a finite-size cylindrical leaky-wave antenna structure consisting of a single source near a planar surface that supports leaky-wave propagation. The method accounts for the finite radius of the planar surface by subtracting the radiation from that part of the leaky wave that lies beyond the physical surface, from the exact radiation pattern corresponding to an infinite planar surface. Experimental results obtained for a leaky-wave structure consisting of multiple dielectric layers above a ground plane confirm the improved accuracy of the method, particularly for the part of the radiation pattern away from the peak     

Leaky-wave propagation and radiation for a narrow-beammultiple-layer dielectric structure

Previous work has demonstrated that very narrow beam radiation patterns can be obtained from a simple source embedded within multiple dielectric layers of appropriate thicknesses above a ground plane. The configuration consists of dielectric layers having permittivities ϵ₁ and ϵ₂ stacked in an alternating arrangement, with ϵ₂>ϵ₁. This narrow-beam effect can be attributed to weakly attenuated leaky waves that exist on the structure. Simple asymptotic formulas for the propagation and attenuation constants are derived. The formulas show how the beamwidth varies with the number of layers and the material constants. The exact radiation pattern is compared with the leaky-wave pattern for a specific case to demonstrate the role of the leaky waves in determining the total pattern     

Radiation from one-dimensional dielectric leaky-wave antennas

Dielectric leaky-wave antennas consist of multiple dielectric layers above a ground plane, along with a simple source such as an infinite line current in the one-dimensional case. The layers act as a guiding structure for one or more leaky waves, which are responsible for producing a narrow-beam radiation pattern. Depending on the beam angle, the leaky waves may extend for a considerable distance from the source, and thus experience truncation effects due to a finite-size substrate. One of the purposes of the present investigation is to study efficient methods for calculating the patterns under such conditions. The chirp z-transform (CZT) is shown to be very efficient for this. Simple approximate formulas for calculating the radiation pattern are also investigated. In addition, a study is also made of the different contributions to the total aperture field, including the leaky-wave field, the space-wave field, and the surface-wave field     

Characteristics of guided and leaky waves on multilayer thin-filmstructures with planar material gratings

This paper presents the characteristics of guided (surface) waves and leaky waves on multilayer structures with planar implanted periodic dielectric blocks. A three-dimensional (3-D) integral-equation formulation in conjunction with the method of moments (MoM's) is used to find the propagation constants of the surface-wave and leaky-wave modes. The analysis deals with layered structures with irregular implants. Photonic band-gaps of both guided waves and leaky waves for rectangular air-implants are identified. Anisotropic properties of the surface waves and leaky waves are investigated. The design of leaky-wave antennas with the information of mode characteristics is discussed. The analysis is validated through the comparison with a low-frequency effective-medium approach and results for linear gratings     

Characterization and Design of Cylindrical Microstrip Leaky-Wave Antennas

The spectral-domain approach is applied for the analysis and the design of the cylindrical microstrip leaky-wave antenna. The first higher-order leaky-mode is thoroughly investigated. We perform the well-known spectral-domain approach and Galerkin's method to acquire the complex propagation constants of leaky modes, which are verified with results obtained by the scattering-parameter extraction technique. Two practical antennas are designed and implemented. Measured return loss and radiation patterns show a good performance of these cylindrical antennas, compared to that of the planar ones.      

Multimode network analysis for dielectric leaky-wave antennas consisting of multilayer periodic structure with arbitrary dielectric distributions

The multimode network method is used to analyze the radiation characteristics of the leaky-wave antenna consisting of multilayer dielectric periodic structure with arbitrary dielectric distributions in each layer. The eigenfunction of each periodic layer is determined by Floquet theorem; and the mode matching combining with generalized transverse resonant method are used to derive the dispersion equation of the leaky-wave antenna. The complex transmission constant is calculated by Newton iterative method and the radiation characteristics of the antenna are obtained. Some antenna structures are analyzed and useful guidelines for design of the leaky-wave antennas are suggested.     

A leaky-wave analysis of the high-gain printed antennaconfiguration

A leaky-wave analysis is used to explain the narrow-beam resonance-gain phenomenon in which narrow beams may be produced from a printed antenna element in a substrate-superstrate geometry. It is demonstrated that the phenomenon is attributable to the presence of both transverse electric and transverse magnetic-mode leaky waves, that are excited on the structure. Asymptotic formulas for the leaky wave are compared with the exact patterns to demonstrate the dominant role of the leaky waves in determining the pattern. Results are presented as a function of frequency, the scan angle, and the permittivity of the superstrate     

A uniform asymptotic evaluation of the field radiated from collinear array antennas

A uniform asymptotic representation of the electromagnetic field radiated from arbitrary collinear array antennas is presented. The asymptotic field is obtained applying the saddle-point technique to the radiation integrals after expressing the current excited along the array axis by means of a Fourier spectral representation. The resulting electromagnetic field is expressed in terms of propagating and evanescent truncated Floquet waves (FWs). The leading asymptotic term of the FWs exhibits an optical behavior and is responsible for the slow decay of the array near-field, which can be described as cylindrical in character. The transition toward the spherical wave propagation regime is due to the interference of the cylindrical field with the relevant scattered field from the array truncations, while the reactive energy storage is due to the evanescent FWs, as well as to the progressive inductive and progressive electrostatic FWs excited close the antenna axis. Using the asymptotic field representation, prediction formulas for the spatial locations where the array near-field exhibits peak deviation from the cylindrical decay, and where the transition from cylindrical to spherical wave propagation regime takes place, have been derived. The proposed analytical technique can be adopted to analyze the spatial field distributions and the radiation mechanisms of periodic and nonperiodic linear arrays.     

Leaky and surface waves in anisotropic printed antenna structures

The behavior of the leaky- and surface-wave modes supported by single- and double-layered grounded anisotropic dielectric structures is investigated. Simple low-frequency and high-frequency asymptotic formulas are derived for the wavenumbers. The effects of dielectric anisotropy and losses on the cutoff frequency of the TM and TE surface waves and on the H-plane radiation pattern of a leaky-wave antenna are examined     

Fundamental properties and optimization of broadside radiation from uniform leaky-wave antennas

In this paper, radiation at broadside is studied for a general class of leaky-wave antennas (LWAs) comprised of a grounded slab covered with a partially reflecting surface, on the basis of a simple transverse equivalent network model of the structure. The analysis of the one-dimensional (1-D) version of such a LWA excited by a line source shows that a central role in establishing the features of broadside radiation is played by the condition that the phase and attenuation constants of the leaky mode responsible for radiation are equal. When this happens, a beam with a single peak at broadside is on the verge of splitting into two distinct peaks, and maximum power density is radiated at broadside. Design formulas to achieve such an optimized condition, as well as approximate expressions for the frequency bandwidth and pattern beamwidth of the antenna and for the leaky-wave phase and attenuation constants are derived, both in the absence and in the presence of losses; in addition, an optimal-beamwidth condition (which gives the narrowest broadside beam) is derived. Finally, all the results are extended to the practical case of a 2-D LWA excited by a horizontal dipole.     

Microstrip leaky-wave antenna fed by short-end CPW-to-slottransition

Single and dual-beam microstrip leaky-wave antennas fed by a short-end coplanar waveguide (CPW)-to-slot transition are presented. The radiation bands of the antennas are deduced from the leaky-wave propagation characteristics of the microstrip line first higher order leaky mode. The measured reflection coefficients of the radiation band confirm the predicted leaky band and the measured radiation patterns exhibit the frequency-scanning feature of the leaky-wave antenna. The short-end CPW-to-slot transition feeding method simplifies the circuit layout and is more suitable for different band design than the CPW-fed microstrip first higher order leaky-wave antennas presented in the literature     

Finite-element solution of planar arbitrarily anisotropic diffused optical waveguides

The finite-element method for propagation in planar anisotropic diffused optical waveguides with arbitrary permittivity tensor is presented. A Galerkin procedure has been introduced to the finite-element formulation, to study both the nonleaky and leaky surface waves. The complex propagation constants are determined as a function of frequency for possible modes of propagation. The accuracy of the method has been checked by calculating the nonleaky and leaky surface waves of Ti-diffused LiNbO3waveguides with Gaussian index profiles. The numerical results of Ti-diffused LiNbO3waveguides with dielectric overlays are also presented and the effects of dielectric overlays on the propagation characteristics for the nonleaky and leaky surface waves are examined.     

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     

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.     

基于特异材料微带漏波天线辐射特性研究

分析复合左右手特异材料微带漏波天线的辐射原理,建立复合左右手材料微带漏波天线仿真模型,通过仿真计算得到微带漏波天线的辐射特性。制备与仿真参数相同的实物天线,测量天线S参数、方向图和天线各单元电容瞬态电压。最后,对仿真试验结果和实物天线测量结果比较,吻合较好。在固定工作频率下,复合左右手特异材料微带漏波天线工作在左手区时,电磁波辐射主要发生在天线结构前几个单元,且电磁波以指数形式快速衰减,工作在右手区时,电磁波沿整个天线辐射,且电磁波衰减较慢。     

Guided-Wave Experiments with Dielectric Waveguides Having Finite Periodic Corrugation

A planar dielectric waveguide having finite periodic rectangular corrugation is investigated analytically and experimentally, in case of surface waves propagating at an angle to the corrugation. In analytical considerations, a finitely corrugated guide is regarded as consisting of many step discontinuities connected by a length of uniform slab waveguide, and its propagation characteristics in the Bragg interaction region are derived from a cascaded connection of the transmission matrix expressing a step discontinuity. Although the present method takes only surface wave modes into account and neglects the wave with continuous spectrum, the calculated results show an excellent agreement with experimental ones which are performed for art H-guide in the microwave region.     

Radiation of millimeter waves from NRD leaky wave antennas withtapered transition and tuning aperture

The radiation of millimeter waves from the nonradiative dielectric (NRD) leaky wave antennas with the tapered transition and the tuning aperture is investigated. An accurate theory for the leakage constant and the phase constant of the antennas is presented, which is based on the generalized scattering parameters considering the higher-order mode interactions at the discontinuities. The associated transverse equivalent network involves the characterization of the mode couplings at two air-to-dielectric interfaces, the coupled mode analysis of the tapered transition, and the calculation of the radiation fields at the tuning aperture via the extended spectral domain approach. The interesting behavior of the present modified configuration of NRD leaky wave antennas is illustrated by typical examples. The validity of the theory is confirmed by the comparison of the theoretical results with experimental data for the limiting cases     

Resonant type leaky-wave antenna using image NRD guide

A novel leaky-wave antenna constructed from an image non-radiating dielectric waveguide (INRDG) is presented. Unlike conventional leaky-wave antennas, the broadside radiation is realised by utilising the resonant characteristic of the leaky INRDG waveguide mode. Experimental results measured at Ku band confirm the effective performance of the antenna.     

Helix Leaky Waveguide

The propagation characteristics of leaky waves in a helix waveguide covered with a slitted cylinder are presented by a method of transverse network representation. The main interest is in helix waveguides with small pitch angles, characterized by a hybrid mode consisting of TE/sub 01/, and a small amount of TM/sub 01/ modes. The leaky wave discussed in this paper may then be regarded as a perturbation of the TM/sub 01/ wave by the slitted cylinder outside the helix. The radiation, metal, and dielectric losses are calculated numerically at a frequency of 50 GHz. The relation between the radiation loss and aperture angle of slit is very different from that of an ordinary leaky waveguide composed of a slitted cylinder without helix, especially when the distance between the helix and shield cylinder is about a quarter of the radial wavelength. The metal and dielectric losses are the same order as radiation loss, however the dielectric loss decreases as the power factor /spl epsiv/"/ /spl epsiv/' increases. The measured total attenuation constant averages about 5 dB/km, almost twice the theoretical value.     

Leaky NRD guide as a feeder for microwave planar antennas

Although leaky wave antennas have been studied extensively in the literature, their practical use is still limited. This work proposes a novel and unique application of leaky NRD guides as feeding systems for microwave planar antennas and shows their substantial possibilities of practical use. At first a new leaky waveguide is introduced based on a periodic array of grooves on the upper side of the dielectric strip in the NRD guide. Then, leaky waves issuing from this configuration are used to feed a slot array cut on the upper metal plate of the NRD guide. Design examples of linearly and circularly polarized planar antennas were constructed, and their characteristics were measured at 23 GHz. The obtained results show the validity for this application of the leaky waveguide