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     

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     

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 study of slotline leaky-wave antennas

The results of an experimental investigation of several millimeter-wave slotline leaky-wave antennas at 94 GHz are given. The experimental results show how variations in the transverse slot geometry affect the radiation pattern. Additionally, slot geometry variations also change the polarization performance of the antenna. The narrow transverse slot array was more sensitive to a perpendicularly (E_y-E_z) polarized electric field than the wide slot case. Also, the change in the effective phase constant along the antenna with changing slot dimensions caused a noticeable shift in the angle of the main beams. However, the beamwidths for all cases remained about the same. A simple model is presented to explain this. For designing an antenna of this form, the effective phase constant, β, can be approximately determined using a numerical analysis of the uniform slot problem. Given β and the operating frequency and the scanning ranges, the element spacing can be determined. The attenuation constant does not change much when the transverse slot widths are varied. If greater sensitivity to an E _y-E_z polarized wave is desired, the transverse slots should be narrow     

Dual-beam array of microstrip leaky-wave antennas

The authors present a small series-fed array of microstrip leaky wave antennas (LWAs) operating at 6.85 GHz and showing a narrow dual-beam pattern (17°×22°). The excitation is provided by a slotted coplanar waveguide. This type of antenna could be used as a radar sensor in Janus systems for contactless measurements of velocity and distance     

Broadside radiation from periodic leaky-wave antennas

A double-strip grating leaky-wave antenna consisting of two strips per unit cell is analyzed. The stopband behavior exhibited at broadside scan in the single-strip grating antenna is characteristic of all periodic leaky-wave antennas having a single strip per unit cell, and results in a drastic increase in the attenuation rate of the leaky wave as the beam is scanned to broadside. By nearly eliminating this stopband behavior, the double-strip leaky-wave antenna can scan from backward end fire to forward end fire without any large frequency regions of high attenuation. An approximate design rule for the double-strip antenna is discussed, and results are presented to show how the antenna may be further optimized to achieve the minimum possible variation in attenuation as the beam is scanned through broadside. Although the stopband behavior is never completely eliminated with the addition of the extra strip, the optimum design shows an almost negligible region of rapidly varying attenuation near broadside     

CRLH metamaterial leaky-wave and resonant antennas

Composite right-/left-handed (CRLH) transmission-line (TL) metamnaterials, with their rich dispersion and fundamental right- /left-hand duality, represent a paradigm shift in electromagnetics engineering and, in particular, for antennas. This paper presents an overview of the most practical leaky-wave and resonant CRLH antennas, which all exhibit functionalities or/and performance superior to prior state of the art. The leaky-wave antennas provide full-space dynamic scanning capability, with fan beams, conical beams in uni-planar configurations, pencil beams without any complex feeding network, and actively shaped beams based on the concept of aperture digitization. The resonant antennas offer alternative properties and a solution to beam-squinting when no scanning is required, including multi-band (dual/tri-band) operation, zeroth-order high efficiency, high directivity, and planar electric and magnetic monopole radiators.     

采用介质PBG盖板Fabry-Perot谐振器的宽频带高增益印刷天线

研究了采用介质盖板组成的Fabry-Perot (F-P)谐振器结构的宽频带高增益平面印刷天线.比较了不同结构参数对天线性能的影响,并在此基础上通过引入二维光子带隙(PBG)结构,提出了两种既能提高增益、又能减小背向辐射的新型结构.通过软件仿真计算和实验,都验证了这两种结构的天线具有较好的实际应用性能.     

Analysis of planar strip geometries in a substrate-superstrate configuration

A moment method procedure is used to analyze the behavior of several different configurations consisting of planar strips in a substrate-superstrate geometry. These include the microstrip transmission line, center-fed dipole, the mutual impedance between two dipoles, and the transmission-line coupled dipole. In each case some of the basic superstrate effects are discussed.     

Short leaky-wave antennas of sum and difference patterns

A set of differential feed short (~0.7 λ₀) leaky-wave antennas with sum (Σ) and difference (Δ) patterns is presented. Rigorous field-theory analyses show that the radiation characteristics of these antennas agree well with the measurements. The performance of these antennas is well suited for direction finding applications     

94 GHz dielectric slab-line leaky-wave antenna

A leaky-wave planar antenna for millimetre-wave frequencies is described using a dielectric slab line, fed by a slotted waveguide array. The radiation of the planar antenna is induced by line discontinuities such as metallic discs on the guide surface.     

Millimeter-wave double-dipole antennas for high-gain integratedreflector illumination

A double-dipole antenna backed by a ground plane has been fabricated for submillimeter wavelengths. The double-dipole antenna is integrated on a thin dielectric membrane with a planar detector at its center. Measured feed patterns at 246 GHz agree well with theory and demonstrate a rotationally symmetric pattern with high coupling efficiency to Gaussian beams. The input impedance is around 50 Ω and will match well to a Schottky diode or SIS detector. The double-dipole antenna served as the feed for a small machined parabolic reflector. The integrated reflector had a measured gain of 37 dB at 119 μm. This makes the double-dipole antenna ideally suited as a feed for high-resolution tracking or for long-focal-length Cassegrain antenna systems     

复合左右手传输线结构漏波天线优化设计

针对目前复合左右手(Composite Right/Left Handed,CRLH)结构漏波天线设计上的难题,提出了一种共面波导(Coplanar Waveguide,CPW) CRLH结构漏波天线的优化设计方法.为了妥善处理元件尺寸带来的寄生效应,基于Matlab软件,开发了一款天线结构参数优化计算机辅助设计(Computer Aided Design,CAD)软件,减少了CRLH结构设计过程中反复调试的次数,加快了开发速率.利用该软件和快速遗传算法(Accelerated Genetic Algorithm,AGA),设计了一个小型化CPW-CRLH结构宽带漏波天线,通过仿真计算、制作加工和实验测量,验证了该文设计方法的正确性,为CRLH结构的广泛应用提供了技术支持.     

A leaky-wave antenna in nonradiative dielectric waveguide

A leaky-wave mechanism in a nonradiative dielectric (NRD) waveguide is described. The antenna used in the analysis consists of a long slot in one ground plane of the NRD guide; the currents present in the side walls cause the slot to radiate as a traveling-wave antenna. The antenna was designed to operate at 9.5 GHz to reduce the costs involved in working at high frequencies. The analysis of the slot follows the procedure outlined by L.O. Goldstone and A.A. Oliner (1959). A simple expression for the amount of coupling from the guide is derived under certain assumption made because information on the reactances necessary to model the slot is not as yet available. The theoretical coupling values verified by measurement and the design, construction, and performance of both leaky-wave antennas are described     

Approximate analytical evaluation of the continuous spectrum in a substrate-superstrate dielectric waveguide

In this paper, an original closed-form approximate evaluation is performed for the continuous-spectrum field excited by an infinite line source in a dielectric substrate-superstrate configuration, optimized for leaky-wave radiation. By means of a suitable approximate asymptotic representation obtained via Watson's lemma, the continuous-spectrum field has been expressed as the sum of the contributions of two leaky-pole singularities, each weighted by a transition function that depends on both the frequency and observation distance. The validity of these results is shown in the near and far fields at different frequencies, including the frequency range in which the leaky wave is physical and the entire transition region through the spectral gap. This new closed-form result explicitly shows the nature of the continuous-spectrum field in the transition region, and provides insight into the nature of the fields on more complicated structures in microwave integrated circuits.     

FDTD analysis of a metal-strip-loaded dielectric leaky-wave antenna

The finite-difference time-domain (FDTD) method is used to analyze a dielectric leaky-wave antenna comprising metal strips etched on a rectangular dielectric rod. The radiation patterns of the leaky-wave antenna with and without the transition are determined by using FDTD. The effects of the launching discontinuity on the performance of the antenna are discussed. In addition, the application of the perfectly matched layer (PML) technique to the three-dimensional (3-D) dielectric waveguide and its performance, compared to those of the Mur's (1981) first-order and super-absorbing Mur's first-order absorbing boundary conditions (ABCs) are described. In addition, the effects caused by perturbation on the wave propagation characteristics of dielectric waveguide are also discussed. The FDTD results are verified by a W-band experiment and found to be in good agreement     

A leaky-wave antenna using an artificial dielectric medium

A narrow-beam antenna using an artificial dielectric medium with effective permittivity less than unity has been investigated theoretically and experimentally. Complex propagation constant for a wave propagating along the structure is evaluated by solving the dispersion relation. The analysis indicates the presence of a leaky-wave mode. The radiation pattern is calculated by using Kirchhoff-Huygens integration method. Experimental results for an antenna of this type designed for operation atXband are reported and compared with theoretical calculations. Beam position varies from17degto47degwhen the frequency is changed from 8.6 to 11.5 GHz. Over this frequency range the half-power beamwidth varies from5.6degto4.8deg. An expression for the half-power beamwidth of a leakywave antenna of finite length has been derived and discussed in the Appendix.     

Perforated dielectric resonator antennas

A dielectric resonator antenna (DRA) is formed by perforating a dielectric substrate with a lattice of holes. The performance of several perforated DRA prototypes is compared to a conventional DRA and the results demonstrate better gain and cross-polarisation levels. This technique of fabricating DRAs using perforations is intended for array applications, eliminating the need to position and bond individual elements.     

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.     

Effects of a dielectric coating on leaky-wave long-slot waveguideantennas

A theoretical and experimental study is made of the effects of a dielectric of arbitrary thickness, permittivity, and loss tangent upon the aperture field distributions and the far-field radiation pattern characteristics of long-slot leaky-wave antennas cut on the broadwall of a rectangular waveguide and mounted in an infinite ground plane. The relevant integral equations for determining the aperture fields are developed and then solved using the moment method. Expressions for the far-field radiation patterns and isolation responses are developed. Calculated and experimental results for several antennas are presented and discussed