Admittance of a waveguide radiating into stratified plasma

A slot covered by a stratified plasma is assumed to radiate into a wide waveguide instead of free space. The slot admittance approximates the free space admittance of the slot for waveguide diameters exceeding 6 to10lambda. For thick plasma layers the computed slot admittance checks with earlier admittance calculations for a laterally unbounded plasma. When approximating a plasma profile of a typical hypersonic re-entry, a multilayer plasma model in a wide waveguide appears to provide a more accurate slot admittance than a single-layer approximation in a laterally unbounded geometry.     

Admittance of a half-wavelength slot antenna radiating into a warm lossy two-layer plasma

The admittance of a half-wavelength slot antenna in a two-layer lossy plasma is shown to be greatly affected by moderate electron temperatures (T_{e} leq 1 eV) when the plasma is overdense. The effects of slot width and electron collision frequency upon the slot admittance also are investigated.     

Admittance of rectangular waveguide radiating from a conductingcylinder

Theory and experiment are compared for the admittance presented to a rectangular waveguide which terminates at an arbitrary angle in the surface of a conducting cylinder. Two methods are described for calculating the admittance: a single-mode approximation from the modal solution and an alternative asymptotic solution. Using these methods, the effect of aperture orientation on admittance, and the results obtained are compared with the experiment. The single-mode approximation is in good agreement with experimental results for the case when the input waveguide supports the TE₁₀ mode only. The accuracy of the approximate formula for waveguide admittance was also verified. The admittance is shown to be weakly dependent on aperture orientation for moderately large cylinders     

Admittance of an isolated waveguide-fed slot radiating betweenbaffles using a spectrum of two-dimensional solutions

An efficient method of computing resonant length and admittance characteristics of an isolated broad-wall shunt slot radiating between baffles of finite height is presented. The outer three-dimensional (3D) field problem associated with this geometry is reduced to a two-dimensional (2D) one via a Fourier transformation with respect to the longitudinal z direction. For each value of the longitudinal wave number k_z an integral equation is solved for the E field in the mouth of the plates using the method of moments. This procedure is repeated for several discrete values of k_z, to obtain a spectrum of 2D solutions which are then inverse-transformed to construct the 3D solution in the spatial domain for the exterior baffle region and the half space. The slot aperture field is determined by the conventional moment method solution to the integral equation that enforces the continuity of the H field across the slot. Scattering properties of the slot are then deduced. Numerical results for the resonant length and resonant conductance are presented. Computer results are found to be in good agreement with experimentally measured data     

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     

非均匀网格FDTD分析波导宽边辐射缝隙特性

波导宽边辐射缝隙被广泛应用于波导缝隙阵列中，为了比较准确地对波导缝隙进行建模，同时考虑到计算资源限制，本文引入一种采用非均匀网格的时域有限差分方法对其S参数特性进行了计算。数值结果表明该方法分析波导辐射缝隙特性问题的有效性。     

Iterative FEM for characterising radiating slot in broad wall ofrectangular waveguide

It is shown that the iterative finite element method with the radiation-type boundary condition can give an efficient and accurate solution to the radiation problem. The proposed method is applied to the characterisation of a radiating slot on the broad wall of a rectangular waveguide. The result is compared with those of other conventional methods, and shows a good agreement     

Impedance properties of a longitudinal slot antenna in the broad face of a rectangular waveguide

The impedance properties of a waveguide longitudinal slot antenna of arbitrary length and offset in guide walls of finite thickness are investigated. These properties are obtained by treating the slot discontinuity as an electromagnetic boundary value problem and the resulting pair of coupled integral equations are solved by numerical techniques. Results are given for slots having lengths from0.35lambdato1.7lambdaand are in good agreement with experimental results.     

Analysis of a centered-inclined waveguide slot coupler

Integral equations are developed for a centered-inclined coupling slot (including the effect of finite wall-thickness of the common broad-wall) and the slot-aperture electric intensity field is found using the method of moments. Numerical results for resonant length, backscattered wave amplitude, and phase variation off-resonance are presented over a range of values of the waveguide b dimension, wall thickness, slot width, and frequency. It is shown that the resonant length is relatively insensitive to slot tilt, &thetas;, for a standard-height X-band waveguide, whereas its dependence on &thetas; is significant for reduced-height waveguides. The phase variation of scattered TE₁₀ waves in both waveguides off-resonance is less for wider slots and smaller b dimensions. Shunt-series coupling slots exhibit greater phase variation off resonance when compared to a centred-inclined coupling slot. Also, the former has a longer resonant length for a smaller b dimension and for a wider slot. Thus the centred-inclined slot coupler possesses superior characteristics. The higher-order mode coupling between a centred-inclined slot coupler and a pair of straddling radiating slots in the branch waveguide is significant     

Form of field in small-offset longitudinal slot in broad wall of rectangular waveguide

A surface-patch moment method approach is used to examine the electric field distribution in longitudinal slots that have small offsets from the host rectangular waveguide centreline. It is shown that the phase of the transverse electric field in the slot may display a large variation across the slot narrow dimension in such instances.<>     

The equivalent parameters for the radiating slot on a sectoralwaveguide

Formulas for the field components of the TE_pq, mode and the dominant mode TE₁₁ in a sectoral waveguide are given. Using the equivalence principle, the electric field distribution on the aperture surface of a narrow longitudinal slot cut in the curved broad wall of a sectoral waveguide is solved by the moment method (Galerkin's method). Important results such as the scattering parameters, the equivalent shunt admittance, and the resonant conductance and length are studied. The method used in this paper has good precision and has been adopted in the design of a linear slot array     

Power deposition of a microstrip applicator radiating into alayered biological structure

The power deposited by a microstrip antenna into a layered biological structure is presented. The solution is based on an integral equation for the surface current density on the antenna and on an electric Green's dyadic for the fields inside a planar stratified medium. The integral equation is solved using the method of moments in conjunction with the point-matching technique. The modeling of the surface current takes the edge conditions into account. Special attention is devoted to a correct modeling of the excitation of the antenna by a coaxial feed. The numerical results focus on the power deposition as a function of depth     

Admittance calculation of a slot in the shield of a multiconductortransmission line

The admittance calculation for a narrow slot in the conducting shield of a multiconductor transmission line (MTL) is presented. An approximate calculation is given for the admittance seen looking into a slot in the shield of a multiconductor transmission line when a uniform magnetic current is placed over the slot. The calculation presented is approximate in that only the transmission line mode is used in the calculation. All higher-order waveguide modes are neglected. This allows the magnetic current to be replaced by a point voltage source at the slot location. The admittance calculation then corresponds to calculating the driving point admittance of a point voltage source located in the shield of an MTL     

Admittance of a rectangular slot which is backed by a rectangular cavity

The rectangular cavity backed slot is excited by a current source connected across its center. The longitudinal voltage variation across the slot is obtained from the variational solution of an integral equation. For shallow and narrow cavities the slot appears inductive and the voltage is rapidly attenuated along the slots. The slot may resonate for deeper and/or wider cavities, when the voltage along the slot is approximated by a half-cycle of a sine wave. The resonant cavity depth and the antenna bandwidth are examined for various cavity and Slot parameters. Dielectric cavity loading is shown to decrease both the resonant cavity depth and the antenna bandwidth.     

Efficiency of a radiating element in circular cylindrical arrays

The general theory interrelating active reflection coefficient and element efficiency or realized gain for arbitrary antenna arrays is applied to circular cylindrical arrays. An upper bound corresponding to the exclusion of supergain is obtained.     

Effect of ground plane absorption coefficient on the admittance of a slot antenna radiating into a warm lossy plasma

The effects of the ground plane electron absorption coefficient on the admittance of a half-wavelength slot antenna radiating into a warm lossy plasma are examined for a range of plasma conditions and slot widths. The ground plane absorption coefficient is observed to have significant effects on the admittance of a thin slot when the plasma is greatly overdense, even when the plasma is only mildly warm (T_{e} leq 1 eV).     

Asymmetric ridge waveguide radiating element for a scanned planararray

A novel linear array radiating element for use in a large low-sidelobe, planar slot array electronically scanned in azimuth is described. The planar array consists of many vertical resonant linear array elements; i.e. single ridge waveguides with broadwall shunt slots, closely spaced to avoid array grating lobes when the array is scanned in azimuth. Traditional linear broadwall slot arrays require alternating slot displacement from the waveguide centerline, which generates undesirable secondary beams in skewed directions during electronic scan. To eliminate the secondary beams, a design has been devised in which all slots are exactly collinear and lie on the waveguide centerline. The methods considered to achieve the required waveguide asymmetry, the design procedure used in the successful approach, and the experimental results obtained with a demonstration model are presented     

Compound radiating slots in a broad wall of a rectangular waveguide

An analysis is presented of the characteristics of a broad wall radiating slot, offset from the center line and tilted with respect to the longitudinal axis of a rectangular waveguide. Pertinent integral equations are developed, taking into account finite wall thickness, and are solved for the slot aperture E-field using the method of moments. Compound slot characteristics are then deduced, including resonant length and dominant mode scattering. Numerical results for the scattering from resonant slots are presented over a range of offsets, tilt angles, frequencies and waveguide dimensions. For resonant compound slots, offset and tilt are shown to control the aperture electric-field amplitude with a phase variability of 360°. The results have significant applications in the design of compound slot arrays     

Equivalent-circuit representation and characteristics of a radiating cylinder driven through a circumferential slot

The problem of an infinitely long coaxial cylinder with a single circumferential slot in the sheath is investigated analytically. When the slot width is small compared with the radius of the outer cylinder, an exact integral equation for the aperture field is formulated and subsequently solved by a quasi-static technique. Equivalent circuit representation of the coupling between the outside antenna and the inside coaxial line is obtained in closed form. Due to the highly localized nature of the coupling, the result thus obtained is applicable to finite cylindrical antenna with multiple feed slots.