Surface-wave phenomena in phased slot arrays with parasitic wirearrays

Blind spots observed in structures consisting of a slot array and parasitic straight wire arrays are investigated. Each blind spot is found to be associated with either a pattern null or the excitation of a surface wave on the corrugated structure consisting of the parasitic wires and conducting screen, with the slots shorted. The plane-wave-expansion technique is used to evaluate the coupling between arrays. It is shown analytically that for structures consisting of a single wire array, the blind spot can exist only at broadside, where there is a pattern null for the parasitic wires. For structures with two-wire arrays, such as an array of Clavin elements, a surface wave can be excited at a particular scan angle provided a certain uniformity condition in the structure is satisfied. The information presented is relevant to the incorporation of parasitic wire arrays for scan compensation     

Mutual coupling between parallel columns of periodic slots in aground plane surrounded by dielectric slabs

Arrays of slots with arbitrary orientation in an infinite conducting plane that are infinitely periodic in one dimension and finitely periodic in another dimension are considered. The plane is bounded on each side of dielectric slabs of finite thickness and infinite extent. Single columns of slots are represented by equivalent magnetic scattering currents, which are solved for by the moment method. The mutual coupling (admittance) between slot columns in the presence of the stratified media is found by the array scanning method, which expresses the admittance as the average of the scan admittance of an artificially constructed doubly infinite array of slots over all real scan angles. The technique avoids the use of Sommerfeld integrals, but still gives rise to singularities at scan angles corresponding to the resonant excitation of surface waves. An analytical approximation removes these surface wave singularities, making numerical implementation of the method practical     

The design of large waveguide arrays of shunt slots

It is shown that the method of moments (MM) solution can determine the active admittance of each slot in a finite array and that the infinite array model is quite accurate for the design of large waveguide arrays of shunt slots. Active admittances computed by an infinite array model agree favorably with that of slots in sufficiently large finite arrays. Measured results verify the MM solution, thereby validating the infinite array model accuracy     

Moment method analysis of infinite stripline-fed tapered slotantenna arrays with a ground plane

A full-wave method of moments solution for infinite arrays of stripline-fed tapered slot antennas is described. The formulation of the problem is sufficiently general to permit performance evaluation of most of the geometries that have been proposed for stripline-fed antennas as well as of several other types of array antennas. Computed results for some well-known antenna arrays are presented to demonstrate the validity and accuracy of the method. Excellent agreement with published results has been obtained for scattering from corrugated surfaces and grounded dielectric slabs and for the input impedance of dipole and monopole arrays. Catastrophic effects such as scan blindness are accurately predicted. A sample result showing the measured and computed input impedance of a stripline-fed tapered slot antenna array is also presented     

Efficient analysis for infinite microstrip dipole arrays

A moment method analysis of infinite microstrip dipole arrays which uses an efficient technique to evaluate the generalised impedance matrix is described. A particularly simple formulation is obtained through the use of the periodic Green function. Results for the reflection coefficient magnitude against scan angle are given for a typical array.     

Analysis of an infinite periodic array of slot radiators withdielectric loading

An efficient numerical procedure for determining the radiation characteristics of an infinite periodic array of slots in a conducting screen is presented. The procedure employs a novel mixed-potential integral equation formulation and is solved by the method of moments. Subdomain-type basis functions are used to provide the flexibility to model arbitrarily shaped slots. Analysis is carried out to account for dielectric layers, ground planes, or cavities placed on either side of the slot. Series acceleration techniques are employed to reduce significantly the computation time required to sum the series representing the periodic Green's function. The numerical scheme developed is applied to obtain quantities such as the slot field distribution and input admittance as a function of the array scan angle. Where possible, numerical results obtained are compared with data available in the literature. Data for the half-space case are found to agree with those of A.Y. Grinev et al. (1978) except for the case of multilayer dielectric loading     

Dipole and slot elements and arrays on semi-infinite substrates

The printed dipole or slot antenna on a semi-infinite substrate and infinite phased arrays of these elements are investigated. The solution is based on the moment method in the Fourier transform domain. The generalized impedance or admittance matrix can be expressed in rapidly converging infinite-integral or infinite-summation forms, allowing the accurate determination of the current distributions. Using the present formulation, the input impedance, resonant length, and radiation pattern for the isolated antennas, and the reflection coefficient for infinite phased arrays, are calculated.     

Scanning characteristics of infinite arrays of printed antennasubarrays

The analysis and scanning characteristics of several different types of infinite arrays composed of subarrayed printed dipole and microstrip patch elements are presented. The analysis is based on full-wave moment method theory, and includes mutual coupling between elements in the subarray as well as between subarrays. The effect of subarraying on scan blindness is demonstrated for arrays using two-element subarrays of printed dipoles and microstrip patches. Results are also given for the amount of power radiated in grating lobes. The effect of a subarray composed of one driven element and one parasitic element, and the use of a four-element synchronous subarray of microstrip patches to generate circular polarization are also considered. Data are given for impedance mismatch, power radiated into grating lobes, and the axial ratio; both square and rectangular patches area considered. Results are also shown for an infinite array of seven-element hexagonal subarrays of printed dipoles, and it is found that the large spacing between subarrays leads to a limited scan range     

A hybrid moment method solution for TEz scattering fromlarge planar slot arrays

This paper develops a hybrid moment method (MM) based numerical model for electromagnetic scattering from large finite-by-infinite planar slot arrays. The model incorporates the novel concept of a physical basis function (PBF) to reduce dramatically the number of required unknowns. The model can represent a finite number of slot columns with slots oriented along the infinite axis, surrounded by an arbitrary number of coplanar dielectric slabs. Each slot column can be loaded with a complex impedance to tailor the array's edge currents. An individual slot column is represented by equivalent magnetic scattering currents on an unbroken perfectly conducting plane. Floquet theory reduces the currents to a single reference element. In the array's central portion, where the edge perturbations are negligible, the slot column reference elements are combined into a single basis function. Thus, one PBF can represent an arbitrarily large number of slot columns. A newly developed one-sided Poisson sum formula is used to calculate the mutual coupling between the PBF and the slot columns in the presence of a stratified dielectric media. The array scanning method (ASM) gives the mutual coupling between the individual slot columns. The hybrid method is validated using both numerical and experimental reference data. The results demonstrate the method's accuracy as well as its ability to handle array problems too large for traditional MM solutions     

Analysis of finite parallel-plate waveguide arrays

An analysis has been carried out to determine the edge effects in finite parallel-plate waveguide arrays. The method used in the evaluation is to compare the element patterns and reflection coefficients versus scan for finite arrays with the corresponding results for hypothetical infinite arrays. It is found that, in arrays of empty waveguides, an element has to be about four or five elements removed from the edge in order to be regarded as being in an infinite array environment. On the other hand, when the waveguides are loaded with dielectric plugs having suitable combination of parameters, considerably more elements are needed for the simulation of an infinite array environment due to the appearance of the resonant null in the array transmission coefficient. It is found, moreover, that even though there may be substantial variation in the radiation properties from element to element in finite arrays, particularly so in the case of moderately sized arrays, this variation does not seem to severely degrade the array performance in terms of beamwidth and sidelobe levels.     

平面FSS阵列的一维截断效应

基于互导纳法进行有限频率选择表面(FSS)计算分析,研究狭缝阵列一维截断时磁流分布、散射方向图及传输特性的变化,考察了单元列数、入射角等因素的影响.与无限平面阵列相比,截断导致边缘单元磁流分布起伏,部分频率产生表面波,散射方向图波束展宽且副瓣电平升高,功率透射系数发生变化,仅谐振频率和传输带宽与无限平面阵列基本相同.     

Radiation and scattering analysis of infinite arrays of endfireslot antennas with a ground plane

A Green's function moment-method analysis of infinite arrays of endfire slot antennas is described that includes the constant width slot antenna (CWSA) and the linearly tapered slot antenna (LTSA), with a ground plane. The method utilizes an application of equivalence at a plane in front of the array which facilitates the extension of this analysis to antennas printed on protruding dielectric sheets and/or the addition of a radome. Numerical calculations are compared with waveguide simulator experiments for CWSA and LTSA arrays as well as several less complex problem. Relevant numerical considerations and convergence issues are also discussed     

Electronic scanning of linear slot arrays using diode irises

Semiconductor diodes were employed as electronic iris control elements to scan linear slot arrays atX-band. An iris cluster of four varactor diodes mounted inside the waveguide around each slot provided360degof phase control for slot coupling levels up to -15 dB and a reduced range of phase control for couplings up to -8 dB. Two linear arrays were fabricated with different iris cluster configurations: 1) A ten-slot array, with vertically mounted diodes, electronically scanned sum and difference patterns up to90deg; 2) a five-slot array, with horizontally mounted diodes, scanned sum patterns up to120deg. Both iris configurations had an RF power handling capability of about 0.1 mW.     

渐变开槽相控阵天线的FDTD分析

对UHF波段无限大开槽阵列天线进行了时域分析,应用Floquet原理对阵列的结构进行区域划分,同时采用时域有限差分法（FDTD）进行数值仿真,研究了作为相控阵天线应用时的频率和空间扫描特性,给出了数值计算结果,得到一些有参考价值的结论。     

On the asymptotic decay of coupling for infinite phased arrays

The asymptotic decay of coupling with distance from a single excited element it an infinite linear array has been analyzed for several special cases and is shown to behave according to exp (-jkr)/r^3/2where r is the distance from the excited element. This behavior is also characteristic of propagation over a lossy surface. By geometric extrapolation one would expect an asymptotic decay of coupling for planar arrays to behave according to exp (-jkr)/r². This extension is carried out for an arbitrary infinite periodic planar current sheet with the expected result. In addition, this behavior is shown to be valid for an infinite parallel plate array immersed in a magnetized cold plasma. In all cases, the asymptotic behavior is shown to depend on the form of the singularity of the derivative of the reflection coefficient with scan angle. This singularity occurs at grazing incidence of the radiated beams.     

Modal analysis of periodic planar phased arrays of apertures

A general method is established for the evaluation of the driving point admittance of a radiating aperture, fed by a waveguide of the same cross section as the aperture, in an infinite periodic planar phased array. The array may have an arbitrary element lattice and it may be covered by a dielectric layer. The coefficients of the waveguide modal expansion and of the Floquet series representing the electromagnetic field in the waveguide and in the radiation half-space, respectively, are determined by approximately enforcing the boundary conditions in the array plane through an application of Galerkin's method. By eliminating from the set of equations thus obtained the complex amplitudes of the waveguide modes and of the Floquet harmonics, the driving point admittance can be expressed as the ratio of two determinants of order N and N-1 (N being the number of the waveguide modes utilized), whose elements contain truncated bidimensional series, structurally similar to the well-known grating-lobe series. The expression allows relatively simple numerical computations if the Fourier transforms of the waveguide vector mode functions are known in closed form (as they are for rectangular or circular elements). The variation of the power reflection loss with scan angle has been numerically calculated for various array configurations. The results are in some cases substantially different from those predicted through the conventional grating-lobe series technique, which is based on the assumption of one-mode elements.     

Radiation from dielectric-loaded arrays of parallel-plate waveguides

The problem of calculating the reflected and transmitted fields as a function of scan angle in an infinite phased array of parallel-plate waveguides is studied on an analytical basis. Two infinite sets of simultaneous linear equations are derived for the scattered fields internal and external to the waveguides. These sets of equations are attacked by a newly developed modified residue calculus method. Application of the results to the problem of designing rectangular waveguide arrays with improved impedance performance over a wide range ofH-plane scan angles is discussed. It is indicated that the present analysis may serve as a first step toward investigating the more general problem of phased arrays scanning at an arbitrary angle.     

A 3-D hybrid finite element/boundary element method for the unifiedradiation and scattering analysis of general infinite periodic arrays

We present a rigorous frequency domain variational 3-D electromagnetic formulation for the general nonself-adjoint infinite periodic array problem. The hybrid method described combines the vector finite element and Floquet boundary element techniques. It is general in the sense that it is applicable to infinite periodic arrays of the open or aperture-types. It is thus effective for modeling both the scattering and radiation performance of diverse FSS, absorber, and phased-array structures. The technique accurately handles arbitrarily complicated 3-D geometries, lossy inhomogeneous media and internal as well as external excitations. These analyses can be applied to general skewed grids under arbitrary scan and polarization conditions     

Analysis of finite phased arrays of printed dipoles

The problem of a finite array of printed dipoles is treated, and results are presented in the form of reflection coefficient magnitudes, element patterns, and efficiency (based on power lost to surface waves). Various sized arrays are considered, and are compared with infinite array solutions. The excitation of surface waves is discussed in relation to the scan blindness phenomenon and the transition to an infinite array. Techniques for computational efficiency are also presented.