Admittance of transverse waveguide slots in cylindrical structures

The self and mutual admittances of transverse slots in arbitrary conducting cylindrical structures are computed. The analysis is performed in the spectral domain, where all fields and currents have been Fourier transformed along the structure. There are, however, no transformations in the transverse directions. A system of integral equations for cylindrical structures are formulated and solved with the moment method. The induced currents on the structure can thus be determined and used to compute the spectral self and mutual admittance of the slots. The spectral admittance is inverse transformed and included in the overall slot antenna analysis. The analysis is rigorous with trigonometric basis function expansions at the inner and outer slot apertures. Computed results on scattering parameters in the waveguide show good agreement with measured data     

Analysis of aperture-coupled microstrip antenna using thesegmentation method

The authors present an original analysis of an aperture-coupled microstrip antenna. The theory is based on the segmentation method, which considers the patch as a multiport network whose impedance matrix is deduced from a hybrid matrix, and the use of analytical expressions of the cavity admittance at the slot centre. The theory is presented for the first time, and the theoretical results are in good agreement with previous published measurements     

双圆柱体结构天线阵列的电流计算方法

在天线的设计过程中,天线表面的电流分布将对天线的性能产生重要影响。本文介绍了一种双圆柱体结构全向天线阵列的表面电流及等效端口导纳矩阵的计算方法,根据这个算法,本文计算了在一定物理尺寸下该天线阵列的电流分布和端口导纳矩阵。数值计算显示这种算法是可行的,结果是令人满意的。     

A 94-GHz aperture-coupled micromachined microstrip antenna

This paper presents an aperture-coupled micromachined microstrip antenna operating at 94 GHz. The design consists of two stacked silicon substrates: (1) the top substrate, which carries the microstrip antenna, is micromachined to improve the radiation performance of the antenna and (2) the bottom substrate, which carries the microstrip feed line and the coupling slot. The measured return loss is -18 dB at 94 GHz for a 10-dB bandwidth of 10%. A maximum efficiency of 58±5% has been measured and the radiation patterns show a measured front-to-back ratio of -10 dB at 94 GHz. The measured mutual coupling is below -20 dB in both E- and H-plane directions due to the integration of small 50-μm silicon beams between the antennas. The micromachined microstrip antenna is an efficient solution to the vertical integration of antenna arrays at millimeter-wave frequencies     

Two-dimensional cylindrical dielectric resonator antenna array

A square 2×2 subarray and infinite phased array of aperture-coupled cylindrical dielectric resonator antennas is investigated experimentally. The return loss, radiation pattern, and antenna gain are studied and compared with those of the single element antenna, and the waveguide simulator is used to measure the return loss of the element in an infinite array environment     

Mutual coupling between slots printed at the back of ellipticaldielectric lenses

This paper presents calculations of the mutual admittance between two slots on a ground plane that are the primary feed of an elliptical dielectric lens antenna. This admittance may also be regarded as the basic constituent of a Galerkin method of moments formulation for the analysis of more complex feeding arrangements of slot antennas and coplanar waveguide circuits, it is found that the contribution of the reflection mechanisms inside the lens significantly affects the mutual admittance especially for H-plane coupling     

Bandwidth enhancement of dielectric resonator antenna by loading alow-profile dielectric disk of very high permittivity

The aperture-coupled cylindrical dielectric resonator (DR) antenna loaded by a low-profile DR disk of very high permittivity is studied experimentally. By using the low-profile parasitic DR disk the antenna bandwidth can be increased from 8% bandwidth to 25%. The characteristics of the new configuration are measured and discussed     

The admittance of the infinite cylindrical antenna immersed in a lossy, compressible plasma

Some numerical results obtained from an analysis of the admittance of an infinite cylindrical antenna excited at a circumferential gap of finite thickness and immersed in a lossy, compressible (warm) plasma are given. The linearized hydrodynamic equations are used for the electrons (ion motion is neglected). A free-space layer, or vacuum sheath, is used to approximate the ion sheath which forms about an object at floating potential in a nonzero temperature plasma. Values for the antenna admittance are obtained by a direct numerical integration of the Fourier integral for the current, and are presented as a function of frequency for plasma parameter values typical of theEregion of the ionosphere. The admittance exhibits a maximum below the plasma frequency unless the electron temperature and sheath thickness are both zero; however, above the plasma frequency, the sheath and electron temperature have relatively little effect on the antenna admittance. The nonzero plasma temperature considerably enhances the antenna conductance below the plasma frequency compared with the zero-temperature case while at the same time reducing the dependence of the conductance on the electron collision frequency. A susceptance zero the location of which is not sensitive to the vacuum sheath thickness occurs near the plasma frequency.     

Analysis of two aperture-coupled cavity-backed antennas

The feasibility and performance of an aperture-coupled cavity-fed microstrip patch antenna and an aperture-coupled cavity antenna are demonstrated using reciprocity and moment method analyses, followed by practical design guidelines and equivalent circuit models. Each antenna incorporates a thick ground plane that can be useful as a heat sink for active MMIC circuitry and as structural support for thin substrates. Prototype antennas show good experimental agreement with the analyses in each case. The resonators of the aperture-coupled cavity-fed patch antenna are optimized to achieve a prototype having a measured 2:1 bandwidth of 26%. The size of the aperture-coupled cavity antenna can be easily reduced for array applications by filling the cavity with a dielectric material     

一种新型星载SAR宽带双极化微带天线研究

提出了一种新型宽带双极化微带天线：天线单元采用层叠结构,下层为正方形辐射贴片,上层为圆形寄生帖片。同时给出了常见的正方形寄生贴片的结构参数,计算结果表明：采用圆形寄生贴片的新型天线与一般的正方形寄生贴片天线相比,在带宽、隔离度和交叉极化电平等性能上均具有优势,尤其是交叉极化特性,优于正方形寄生贴片结构-5dB左右,具有重要的工程应用价值。     

Input admittance of a multilayer insulated monopole antenna

An efficient numerical technique based on the modal-expansion method in conjunction with a recursive algorithm is developed for a multilayer insulated monopole antenna fed by a coaxial transmission line. The modal-expansion analysis is facilitated by introducing a perfectly matched boundary (PMB) at a variable height over the ground plane of the monopole. The current distribution and input admittance are computed by finding the expansion coefficients of the electromagnetic field expressions. Numerical results for the input admittance of a dielectric-coated monopole antenna and an air-insulated monopole are compared with experimental ones available in the literature. Good agreement is achieved. Calculated results for the effects of various parameters on the input admittance of an air-insulated monopole antenna are presented and discussed     

Experimental and theoretical investigations of new compact largebandwidth aperture-coupled microstrip antenna

The authors propose an efficient amelioration of the concept of large bandwidth aperture-coupled microstrip antennas by coupling a CPW line-fed slot to a microstrip antenna. The CPW fed aperture-coupled microstrip antenna investigated has a large bandwidth with high gain and low crosspolarisation levels, is compact with only one substrate, and may be easily connected to both passive and active components. A numerical model has been developed and the theoretical results are in good agreement with the experiments     

Dielectric spectroscopy using monopole antennas of general electrical length

A procedure is developed for measuring the complex dielectric permittivity of a material over a broad range of frequencies using a monopole antenna. No restrictions are placed on the electrical size of the antenna. The antenna is calibrated one time by measuring the input admittance in a standard medium with known permittivity, such as air. Next, the admittance is measured with the antenna immersed in a material with unknown permittivity. These two sets of admittances are then used to determine the permittivity of the material. As an application of the procedure, the complex permittivity of the alcohol 1-butanol and saline solutions were measured using a cylindrical monopole antenna. The measured permittivities are in good agreement with those determined by previous investigators.     

A High Gain and Broadband C-Band Aperture-Coupled Patch Antenna

A aperture-coupled patch antenna is designed with parasitic elements connecting to the rectangle ring on the bottom of antenna substrate through metal vias, which lead the current induced by patch radiator to the top surface of antenna substrate. Therefore, the effective radiation is enhanced and higher gain is achieved. The bandwidth is broadened simultaneously due to the structure of aperture-coupled patch antenna with parasitic elements. Compared to the conventional aperture-coupled patch antenna, the antenna gain increases averagely 2 dB due to the novel structure. Compared to patch antenna of electromagnetic band-gap, the dimensions of novel patch antenna greatly decreases, which can be used as element in the array antenna. Two kinds manufactured antenna are both measured in an anechoic chamber. The good agreements between numerical simulation and experimental prototype have been obtained.     

The method of lines for mutual coupling analysis of a finite array of patch antennas on a cylindrical stratified structure

We present an application of the method of lines (MoL) for the analysis of a finite array of microstrip patch antennas loaded with dielectric layers on a cylindrical structure. New formulas are given in cylindrical coordinates to describe multiple, stacked layers without causing an increase in the difficulty or complexity of the analysis. We show that this model is not only numerically efficient, compared with other numerical methods, but also, shows a very good accuracy with respect to experimental results and has no limitation on antenna array geometry and excitation. Finally, some numerical results for both radiation and mutual coupling are presented.     

On the empirical optimization of antenna arrays

Empirical optimization is an algorithm for the optimization of antenna array performance under realistic conditions, accounting for the effects of mutual coupling and scattering between the elements of the array and the nearby environment. The algorithm can synthesize optimum element spacings and optimum element excitations. It is applicable to arrays of various element types having arbitrary configurations, including phased arrays, conformal arrays and nonuniformly spaced arrays. The method is based on measured or calculated element-pattern data, and proceeds in an iterative fashion to the optimum design. A novel method is presented in which the admittance matrix representing an antenna array, consisting of both active and passive elements, is extracted from the array's element-pattern data. The admittance-matrix formulation incorporated into the empirical optimization algorithm enables optimization of the location of both passive and active elements. The methods also provide data for a linear approximation of coupling as a function of (nonuniform) element locations, and for calculation of element scan impedances. Computational and experimental results are presented that demonstrate the rapid convergence and effectiveness of empirical optimization in achieving realistic antenna array performance optimization.     

Active aperture-coupled leaky-wave antenna

An active aperture-coupled leaky-wave antenna which is integrated with a varactor-tuned high electron mobility transistor voltage-controlled oscillator (HEMT VCO) is presented. To excite the first higher mode of the microstrip, the aperture-coupled structure is used and a sequence of covered wire is added at the centre of this antenna to suppress the dominant mode. The measured H-plane main beam can be continuously scanned 10° as the HEMT VCO frequency is varied from 9.05 to 9.5 GHz. This feeding structure is very suitable for active phase antenna array applications     

Maximum electromagnetic coupling to a nearby conducting strip through narrow and wide slits in a parallel-plate waveguide

The problems involved in electromagnetic coupling to a nearby conducting strip through narrow and wide slits in a parallel-plate waveguide (PPW) are discussed as simplified models of the two-dimensional (2-D) problems of aperture-coupled and proximity-coupled microstrip structures while focusing on radiative coupling mechanisms and perfect matching methods. These matching mechanisms exemplify general matching methods for use in small flush antenna structures. Finally, the similarity between the role of the nearby strip and the phasing unit of the recently reported crossed-field antenna structure is also discussed.     

A formula for efficient computation of radiation from a current source in proximity to cylindrical scatterers

A systematic and efficient two-dimensional method is presented for calculation of the three-dimensional radiation field from current sources which are located in proximity to long cylindrical scatterers. The method is applied to the calculation of the isolated-element pattern of a linear array of crossed dipoles (i.e., current sources) mounted above a long and narrow ground plane. Computed and measured results are given. The results are subsequently applied to the problem of prediction of the radiation characteristics of a cylindrical reflector antenna fed by such a linear array.     

An analysis of antenna coupling between arrays on a polyhedronstructure

Antenna coupling between arrays on a polyhedron structure is investigated. First of all, a high-frequency asymptotic closed-form formula is derived for the mutual admittance between two linearly polarized circular microstrip antennas located on the different faces of a perfectly conducting wedge. The microstrip antennas are modeled by the cavity model, and the mutual coupling caused by the wedge-diffracted field is analyzed by the EMF method using Keller's GTD diffraction coefficients for the diffracted field. Next, the antenna coupling between arrays is calculated and compared with an experimental result. Good agreement between them supports the theory. Finally, the properties of the antenna coupling are described by some numerical simulations