Electromagnetic transmission of an oblique waveguide array

Transverse magnetic (TM) and transverse electric (TE) wave transmissions of an oblique parallel-plate waveguide array is studied. The scattered wave is represented in terms of continuous and discrete modes based on the Fourier transform and series, respectively. The tangential field continuities at the boundary are enforced to obtain simultaneous equations for the discrete modal coefficients. Residue calculus is utilized to transform the radiation field and reflection coefficient into numerically efficient forms. Numerical computations are performed to illustrate the behavior of wave radiation and reception by an oblique waveguide array.     

Monopole antenna radiation into a parallel-plate waveguide

A rigorous solution of coaxially fed monopole antenna radiation into a parallel-plate waveguide is obtained. The Fourier transform/series representations are used to represent scattered fields and the boundary conditions are enforced to obtain the simultaneous equations for discrete modal coefficients. Fast convergent series of the reflection coefficient is obtained and compared with other existing results     

TM-radiation from an obliquely flanged parallel-plate waveguide

Electromagnetic TM wave radiation from an obliquely flanged parallel-plate waveguide is studied. The Fourier-transform/series and Green's formula is used to represent the scattered wave and the simultaneous equations for the modal coefficients are formulated. Residue calculus is utilized to obtain a fast-convergent series solution. Numerical evaluation shows the behaviors of transmission, reflection, and radiation in terms of junction geometry and operating frequency.     

Radiation from multiple circumferential slots on a conductingcircular cylinder

Electromagnetic wave radiation from multiple circumferential slots on a conducting circular cylinder is theoretically investigated. The Fourier transform/series technique is used to represent the continuous and discrete modes of the scattered field. The mode matching is utilized to constitute a set of simultaneous equations for the discrete modal coefficients. The residue calculus is applied to transform the scattered field integral representations into fast-converging series forms, thereby facilitating the numerical computations. Numerical computations illustrate the behavior of radiation in terms of the slot geometry, the incident mode, and the operating frequency     

Optimization of linear arrays for broadband signals

The effect of broadband signals on the far-zone field of long arrays is investigated in terms of the energy radiation pattern. A generalized directive gain is introduced which depends on the signal spectrum. With maximum directivity as a criterion it is shown that the problem of optimizing a long isotropic array with respect to a given signal can be associated with a classical eigenvalue problem. The concept of array-bandwidth is introduced. Computed curves for directivity and directive gain are given in terms of this parameter and signal bandwidth. It is shown that while little improvement in directivity is achieved by optimizing the distribution coefficients of an array, a substantial reduction in sidelobe level is obtained when the signal bandwidth is comparable to the array bandwidth.     

A hybrid projection method for analysis of waveguide arrays with protruding dielectric elements: 2D problems

A method is proposed for the analysis of an array of parallel-plate waveguides with protruding longitudinally inhomogeneous dielectric elements. The method consists in expansion of the transverse electric (for the case of E polarization) or magnetic (for the case of H polarization) field in the domain containing the dielectric elements in terms of transverse functions of the Floquet channel. This expansion contains unknown variable coefficients. Projection of the Helmholtz equation for the aforementioned fields onto the transverse functions and application of a 1D finite-element method along the longitudinal coordinate in combination with projective matching of the fields in the waveguide apertures and at the boundary with free space reduces the problem to solution of a system of linear algebraic equations. The results of calculation of the reflection coefficient and the radiation pattern of an array element are presented. These results characterize both the efficiency of the proposed method and the possibility of formation of sector element patterns in the studied arrays.     

Mutual Coupling Between Parallel-Plate Waveguides

The radiation field and mutual coupling between two identical parallel-plate waveguides having the same axis of symmetry are investigated. Jones' method of formulation is applied and a modified Wiener-Hopf equation is obtained. Expressions for the radiated field in free space, reflected field in the exciting waveguide, and transmitted field in the coupled waveguide are obtained and the reflected and transmitted fields are expressed in terms of waveguide modes. The reflection coefficient for each mode is represented by three terms, two of which are due to reflections at the open end of the exciting waveguide and are constant along the waveguide. The third term is the contribution from the field scattered by the open end of the coupled waveguide and decays along the waveguide according to the radiation condition. Similarly, the transmission coefficient of each mode is represented by three terms, two of which decay along the coupled waveguide and the third one is constant. The radiation field is also divided into three terms. One of them is due to the radiation from the open end of the exciting waveguide and the other two are the contribution of multiple interactions between the two waveguides. Computed results for the reflection and transmission coefficients and the radiation field are shown for TE/sub 0,1/ excitation and various separation distance of the waveguides. The results for the reflection and transmission coefficients are oscillating functions of period /spl pi/, and approach gradually the well-known final values of a single excited wavegnide.     

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.     

Scattering and radiation from finite thick slits in parallel-platewaveguide

The problem of TE-wave scattering and radiation from a finite number of thick slits in a parallel-plate waveguide is solved. The Fourier transform is used to express the scattered field in the spectral domain. The boundary conditions are enforced to obtain a series solution which is amenable to numerical computation. The numerical computations are performed to illustrate the behaviors of scattering, transmission, and reflection in terms of incident angle, slit size and operating frequency. The solution presented is computationally very efficient so that it is useful for slotted-waveguide leaky-wave antenna applications     

The optimum transient radiation from an arbitrary antenna

Bounds on the optimum transient radiation from an arbitrary antenna enclosed by a spherical surface of specified size are presented. The optimization criterion is either maximization of the radiated electric field amplitude at a specified time and far-zone position, or maximization of the radiated energy density in a specified time interval for a particular far-zone position. The latter optimization results in the prolate spheroidal wave functions. In both cases, the total energy radiated by the antenna is constrained to be 1 J, and the antenna excitation is assumed to be bandlimited. The performance of the optimum arbitrary antenna is compared to that of optimized practical antennas, such as dipoles and arrays of dipoles. The effect of a sidelobe constraint is also studied.     

Hankel transform domain analysis of dual-frequency stackedcircular-disk and annular-ring microstrip antennas

A theoretical and numerical analysis of the dual-frequency stacked circular-disk and annular-ring microstrip antennas is discussed. The problem is formulated in the Hankel transform domain. First, the Green's function is derived, relating the transformed electric surface currents on the patches and the transformed tangential electric field components on the substrates. Galerkin's method is used with Parseval's relation for Hankel transformation to solve for the resonant frequencies and the unknown currents. The far-zone radiation patterns are expressed in terms of the transforms of the currents. Numerical results obtained for the resonant frequencies and radiation patterns are found to be in excellent agreement with the experimental data available in the literature     

Analysis of a centre-driven antiphase dipole in a warm plasma†

The radiation properties of a thin dipole in a warm plasma, fed with currents in opposite phase, have been theoretically investigated using linearized hydrodynamic theory. Expressions for the far-zone electromagnetic and electroacoustie fields are derived in terms of general propagation constant β. The values of fields and of the radiation resistance are computed using β = β_e and compared with those of a standard dipole. It is found that tho eradiation of the electromagnetic mode is partially suppressed, whereas that of plasma mode remains almost unaltered, suggesting that the antenna could be used for launching electroacoustic waves.     

Optimization of pulse radiation from dipole arrays for maximum energy in a specified time interval

The optimum solution for maximized radiated energy in a specified time interval from anN-element dipole array at a specified farfield position is presented. The solution is obtained in terms of time-domain dipole terminal voltages which are constrained in bandwidth and total input energy, with the currents on the dipoles satisfying Pocklington's integral equation. The orthogonality of characteristic terminal modes is used in the derivation of the optimum solution, and the far-zone field is expanded as a finite sum of characteristic modal fields with unknown mode coefficients. The optimum mode coefficients are found in terms of prolate spheroidal wave functions. An additional constraint can be used to find the optimum solution with a reduced sidelobe level. The effects of signal bandwidth and time interval specification on the peak field intensity and energy density in the direction of optimization are shown and limiting cases are found to agree with previous results.     

K-pulse techniques for short-pulse radiation from dipole arrays

An investigation of K-pulse techniques to transmit short-time duration pulses from dipole arrays is presented. The array is analyzed from a radiation standpoint using the singularity expansion method. The analysis also makes use of the method of moments to express the array's radiation in terms of the terminal voltages and pole singularities. Following a numerical search in the complex frequency plane (from which the dominant singularities of the array are located), the time-domain waveform of the approximated K-pulse voltage is constructed. Calculated plots of the far-zone radiated electric field resulting from applying these voltages at the array terminals are presented, and their energy concentrations are compared to those of the optimum solutions     

Numerical Solution of Coupling Between Two Collinear Parallel-Plate Waveguides

The problem of coupling between two collinear parallel-plate waveguides is investigated numerically using moment methods. The exciting mode in the waveguide is assumed as the incident field, and the integral equation for the induced current is expressed in terms of the reflected, transmitted, and evanescent currents on the waveguides. The integral equation is then solved numerically by a point-matching method and the reflection and the transmission coefficients and the radiated fields are obtained. To examine the accuracy of the results, the special case of a semi-infinite exciting waveguide coupled to a finite coupled waveguide is also considered and is solved numerically by treating the singularities of the induced currents using a transformation method. For a TE/sub 0,1/ excitation of the exciting waveguide, the results of both numerical methods are compared with the analytical results obtained previously using the Wiener-Hopf technique, and are found to be in good agreement. The methods are then used to study the effect of the coupled waveguide on the radiation field.     

Radiation from a Rectangular Waveguide Filled with Ferrite

This paper presents an approximate analytical solution to the problem of radiation from a ferrite-filled rectangular waveguide. The field distribution at the mouth of the guide is assumed to be unaffected by the termination of the guide. The vector Huygens' principle is applied to find the far-zone radiation field from the determined aperture field. The solution to the problem is found in this manner for the cases of longitudinal and transverse magnetization of the ferrite. The transverse magnetization case is supplemented with a discussion of a specfic numerical example which includes plots of the aperture field distribution and the phase angle as well as plots of the far-zone radiation field. The experimentally known phenomenon of the effect of the applied magnetic field upon the shift of the main lobe is demonstrated and verified analytically.     

Internal reflections at the open end of a semi-infinite waveguide

The reflection coefficients of those waveguide modes, with propagation constants near cutoff, which are excited at the open end of a semi-infinite parallel-plate waveguide for frequencies from the microwave to the optical region are discussed in this paper. The reflection coefficients are obtained from a recently developed form of the factorization formula for the Wiener-Hopf kernel associated with this problem. This particular formula is suitable for numerical processing over the complete frequency spectrum. Results of representative calculations are presented graphically as functions of the ratio of waveguide size to wavelength.     

Analysis for a dielectrically filled parallel-plate waveguide withfinite number of periodic slots in its upper wall as a leaky-waveantenna

A dielectrically filled parallel-plate waveguide (PPW) with finite number of periodic slots in its upper plate is analyzed as a leaky-wave antenna structure for E-polarization case. The characteristics of the finite periodic structure such as input impedance matching, antenna efficiency, gain, and radiation pattern are investigated. In particular, phenomena such as total reflection and transmission occurring in the practical finite periodic structure, associated with the coupling point and the real solution (propagation constant), respectively, in the fast wave region observed for the infinite open periodic structure case, are described in detail     

Least Squares Boundary Residual Method for the Analysis of Step Discontinuities in Open Chiral Waveguides

We analyse the reflection, transmission and radiation characteristics of a step discontinuity in a grounded chiral slab and we show that the step radiation can be enhanced due to the effect of the chirality. The analysis is performed using a mode matching technique. The fields are expressed in terms of the discrete modes and the continuous spectrum using two subsets of hybrid radiation modes: incident transverse electric (ITE) and incident transverse magnetic (ITM) modes. The scattering matrix of the step is determined by minimizing the boundary residual error in the sense of the least squares. The influence of chirality on the characterization of the step is demonstrated and we show that control of the radiation pattern is achieved, including angle and width of the radiation beam.     

Finite element method analysis of discontinuities of multi-dielectric rods embedded in a parallel-plate waveguide

We have analysed various discontinuities inside a parallel-plate waveguide embedded with multi-dielectric rods by using an eight-node, isoparametric finite element method (FEM). The proposed FEM technique is very efficient and requires only small amounts of computer memory and computation time. In order to investigate the reflection and transmission properties of the structures, we have constructed diverse discontinuity configurations by choosing one, two or four dielectric rods inside a parallel-plate waveguide. The research results indicate that both the reflection and transmission coefficients of the structures are highly dependent on the geometrical dimensions, namely the height of the dielectric rods, the slot size of the slotted rods, as well as the total number of the dielectric rods.