Analysis of dielectric loaded hybrid mode coaxial horns

This article presents a numerical solution for radiation from a novel coaxial horn with a partial dielectric loading. The horn is represented as a set of three-layer dielectric loaded coaxial waveguide sections. Characteristic equation has been obtained to calculate phase coefficients for hybrid modes in each section. Applying mode matching technique generalised scattering matrices for each junction between the sections have been obtained, besides that power coupling integrals for each of three different type of junctions have been found in closed-form solutions. Cascading these scattering matrices with transmission matrices of each section yields a generalised scattering matrix of the horn. For the given excitation at the throat of the horn, amplitude and phase of eigenmodes at the aperture of the horn have been determined. Finally, Fourier transform integral of the aperture electric field has been applied to solve radiation problem of the horn. Numerical results on propagation and radiation characteristics of the first four hybrid modes of the horn are presented and it is validated that this solution can be successfully used for full-wave electromagnetic analysis and optimisation of multiband dielectric loaded coaxial feeds.     

Radiation and matching characteristics of a novel dual-band dielectric loaded coaxial horn

Copolar and crosspolar radiation as well as matching characteristics of a novel dual-band coaxial hybrid-mode feed horn with partial dielectric loading [1] for reflector antennas have been numerically and experimentally investigated. In comparison with dual-band corrugated horns this horn has higher crosspolar level, but provides larger band separation and rather good electrical performances over a wide frequency range (20% and more) within each operational frequency band. Furthermore, the main concept of the coaxial feed system can be easily extended for multi-band cost-effective applications in reflector antennas with polarization diversity.     

Scattering by a lossy dielectric cylinder in a rectangularwaveguide

Electromagnetic fields in a rectangular waveguide containing a lossy dielectric cylinder are investigated by means of the orthogonal expansion method. The calculated results are provided by measurement. Resonance effects become visible through the frequency responses of the scattering parameters and understandable by patterns due to magnetic fields and Poynting vectors. The lowest resonance is nonsymmetric and can be used to realize tunable bandstop filters with a relative 3-dB bandwidth of about 0.04 and an attenuation of more than 40 dB     

Eigenmode analysis of dielectric loaded top-hat monopole antennas

Eigenmode expansions are used for computing the currents on a dielectric loaded top-hat monopole radiating above an infinite conducting ground plane. The approach is facilitated by adding a parallel ground plane above the antenna, thus allowing use of cylindrical harmonic field expansions in each of three regions. Expansion coefficients are found by enforcing boundary and continuity conditions at conducting surfaces and regional interfaces. Convergence and accuracy are assessed using comparisons with three other methodologies, namely an integral equation solution, a quasi-static analysis, and multi-octave experimental measurements     

A monopole antenna loaded by a hemispherical dielectric resonator

The input conductance, radiation pattern, and radar cross section (RCS) of a monopole loaded by a hemispherical dielectric resonator (DR) are studied. The effects of the DR on the monopole characteristics are investigated. Measurements were carried out to verify the theory. It is found that the input conductance, radiation patterns, and RCS are strongly affected by the DR.     

Quick accurate design of a frequency-stabilised coaxial dielectric resonator

A numerical study of a composite dielectric resonator of coaxial type is proposed. It consists in finding a simple equivalent structure on which the influence of electrical and geometrical parameters on frequency are well known. A knowledge of the thermal drifts of these parameters can be used for the design of a temperature-stabilised composite resonator. The validity of the method is tested experimentally.     

Mode-matching analysis of top-hat monopole antennas loaded withradially layered dielectric

A top-hat monopole antenna with homogeneous or inhomogeneous dielectric loading over a ground plane is considered. Mode-matching analysis with proper enforcement of edge conditions is applied to the problem. The results of this technique are verified through independent calculations of admittance as well as by comparison of fields across matching regions. Measurements were also taken for comparison with the results from the model. It is shown that dielectric loading can reduce the electrical size necessary for self resonance, but only at the expense of a large increase in radiation Q     

Radiation from a flanged coaxial line into a dielectric slab

The radiation from a flanged coaxial line into a dielectric slab is investigated in this paper. The Hankel transform and mode-matching technique are used to obtain simultaneous equations for the modal coefficients. The residue calculus is utilized to represent the solution in rapidly convergent series. Numerical computations are performed to illustrate the behavior of reflection in terms of the slab permittivity, frequency, and coaxial-line geometry     

Excitation of an untilted narrow-wall slot in a rectangularwaveguide by using etched strips on a dielectric plate

We propose a novel excitation technique of an untilted slot in the narrow wall of a rectangular waveguide. The excitation is realized by inserting into the slot a dielectric plate on which there are etched conducting strips. The strip excitation can control the coupling more easily and accurately than a conventional excitation using tilted wires. We analyze the coupling to the slot by using the dyadic Green's function for the waveguide with the dielectric plate, derived by Seki's (1984) virtual cavity method. A double resonance due to the strip and the slot results in large coupling as well as small variation of the phase of the transmitted wave, both over a wide frequency band. Some results are verified by measurements. The coupling can be tuned by varying the distance between the slot and the strip     

阶跃阻抗同轴介质滤波器的研究

为了有效减小均匀阻抗同轴滤波器的尺寸,并优化性能参数,设计了阶跃阻抗同轴滤波器。该滤波器基于一种BaO-Nd2O3-Sm2O3-Al2O3-TiO2(BNSTA)五元系高介电常数、低损耗、近零温度系数的微波介质材料,提出阶跃阻抗同轴滤波器的设计流程和方案,采用HFSS高频仿真软件对该滤波器的传输特性进行了整体仿真。结果表明所制滤波器通带特性优异:中心频率为2.01 GHz,带宽为15 MHz,插入损耗小于1.15 dB,带内纹波为0.23 dB。     

Singular integral equation analysis of flange-mounted rectangularwaveguide radiators

The authors analyze rigorously single and twin radiating waveguides by means of a singular integral equation approach which includes the edge condition on the apertures from the start. The above inclusion has an important bearing on convergence and matrix size, enabling highly accurate solutions to be obtained with few test functions, typically two to four. This becomes particularly important in the case of multiple coupled radiators, where matrix sizes increase as the product of the number of radiators times the number of test functions. Theoretical and experimental results are compared for the two important cases of two radiators with parallel narrow walls and with parallel broad walls and are found to be in very good agreement     

Aperture matching of a dielectric loaded circular waveguide elementarray

An X-band phased array with dielectric-loaded circular waveguide elements was investigated. The aperture was designed to provide balanced scan characteristics for both the E- and H-planes. The results of an experimental study are presented in which the active impedance of the radiating element was matched by introducing a circumferential groove onto the dielectric plug. Both the aperture junction and the matching groove were measured to derive their respective equivalent circuits for `look-in' and `look-out' impedance transformations. The groove size and its location from the aperture were then optimized by a hybrid approach wherein the measured data and computer simulations were used to greatly reduce the shop time, lab tests, and the number of trials in the hardware development     

Cherenkov radiation in a plasma-filled coaxial cylindrical dielectric slow-wave structure

In this paper, a new type of plasma-filled coaxial cylindrical dielectric slow-wave structure that is very beneficial to the beam-wave interaction of the high-power microwave source is developed. The Cherenkov radiation in the plasma-filled coaxial cylindrical dielectric slow-wave structure is examined by use of the self-consistent linear field theory. The dispersion equation and the synchronized condition as well as the wave growth rate of the beam-wave interaction are derived. The dispersion equation clearly shows that the Cherenkov radiation excited in the plasma-filled coaxial cylindrical dielectric slow-wave structure results from the coupling between the slow electromagnetic wave, TM-modes, propagated along the slow-wave structure and the negative-energy space-charge wave propagated along the relativistic electron beam. The numerical results indicate that the dispersion curves are divided into two branches due to the presence of the background plasma in the coaxial cylindrical dielectric slow-wave structure for the identical electromagnetic wave mode, and the radial distributions of the longitudinal fluctuating electric field corresponding to the two dispersion curve branches are completely different. Injection of the background plasma into the slow-wave structure can enhance the output frequency and the wave growth rate of the beam-wave interaction and enables the high-power microwave source that utilizes this kind of slow-wave structure to gain more output power of the microwave with higher output frequency.     

Multiply driven and loaded coaxial circular loop arrays

Characteristics of single- or double-loaded coaxial loop arrays with arbitrary circumferences are studied when the sources or loads are located diagonally on the loops. For finite gaps at the deriving points and finite lengths of the loads, integral equations for the loop currents are obtained. These integral equations are then reduced to a matrix one by expanding the currents and the kernel in Fourier series of the azimuthal coordinate. For the special case of loaded Yagi arrays numerical results for the gain and the input impedance are presented. These results reveal that a capacitive loading of the array generally broadens the gain bandwidth of the array over which the gain remains essentially constant. A resistive loading of the exciter, on the other hand, yields a broadband characteristic for the driving-point admittance.     

Unipolar pulse transmission by a coaxial cable loaded with a tunnel-diode-pair unilateral regenerator

An application of a tunnel-diode-pair unilateral pulse regenerator to unipolar pulse transmission is described. An experiment performed at around 10-MHz repetition rate showed that an arbitrary unipolar pulse pattern was regenerated and transmitted unilaterally over a coaxial cable with an error rate of 10^-11per section.     

An X-ray free-electron laser loaded with a periodic dielectric

When a periodic medium is inserted along the axis of a free-electron laser (FEL), the synchronism condition between the electron beam and the electromagnetic wave is changed. This alteration permits a wider parameter selection than the conventional FEL, and provides for the possibility of X-ray operation. The device is a hybridization of the FEL and the stimulated-transition-radiation laser. Photon absorption by the periodic medium and scattering of the electrons limit the interaction length, but calculated gains are still high enough for oscillation. The analysis shows that ultrarelativistic electron beams and low-density foil materials give the most physically realizable parameters. Higher order resonant transition modes (r>1) should be used to maximize gain     

Radiation by a corner reflector with dielectric loaded edges

The first part, of this paper deals with the electromagnetic scattering by a cylindrical dielectric shell with an azimuthal permittivity profile and an internal E-polarized line source or an externally incident plane wave. The integral equation for the resulting scattered electric field is solved approximately by the method of moments and the results for the echo width and polar radiation pattern are displayed graphically for typical geometrical dimensions, frequency and permittivity profiles.

The second part of this paper deals with the cylindrical dielectric shell terminating a conducting strip with one edge coinciding with the axis of the cylinder. The results for the scattered field due to a line source excitation are presented and extended to the case of two such strips whose unloaded edges intersect to form a corner reflector antenna. The resulting radiation pattern is shown to improve for specific dimensions and complex permittivity profiles of the dielectric caps.     

Application of inhomogeneous dielectric loading to coaxial resonators

A technique for improving the Q factor of air-filled coaxial resonators by inhomogeneous dielectric loading is reported.     

Radiation from dielectric sphere loaded horns

The measured radiation pattern of a dielectric sphere fed from a conical horn is given. An appropriate matching device is shown to be a circular dielectric rod in the horn. Improvements in gain and circularity of the beam obtained by dielectric loading are demonstrated.