Optimization of Profiles of Rectangular Horns for High Efficiency

Realization of high-efficiency rectangular horns is investigated by means of mode generation and profile optimization. Conditions required for maximum efficiency of an aperture array are derived and made specific to a rectangular aperture with twofold symmetry. It is shown that aperture coupling has a significant effect on aperture efficiency through mode coupling. Efficiencies in excess of 100% are predicted for aperture sizes that are slightly greater than an odd multiple of half-wavelengths. The method described here results in more compact horns than obtained by using conventional linear tapers or steps. Results are presented for horns suitable for array feeds or directly radiating array applications that achieve aperture efficiencies close to 100% with horns of aperture size ranging from 1.25 to 3 wavelengths and at the same time have a return loss 20 > dB and cross-polar isolation > 22 dB. Measured results are given for an experimental compact horn that has high efficiency over an 8% bandwidth. The agreement between computation and measurement is within the limits of experimental error and this is obtained without any special surface treatment on the inside surfaces.     

Analysis of diagonal horns through Gaussian-Hermite modes

The radiation characteristics of diagonal horns are investigated by means of Gaussian-Hermite modes. It is shown that, for reasonably long horns, the beamwidths in the principal and 45° planes are equal to within 10%, and all sidelobes are below -15 dB. It is also demonstrated that the phase center of a diffraction-limited horn is close to the aperture, whereas the phase center of a constant-beamwidth horn is behind the throat. The maximum coupling to the lowest order copolar Gaussian mode is 84%, and the total amount of power coupled into the cross-polarized lobes is 9.5%. More significantly, the aperture efficiency of a Cassegrain antenna fed by a diagonal horn has a maximum value of 81%, which compares with 87% for a corrugated horn. The maximum efficiency is achieved when the aperture of a diffraction-limited horn is placed at a confocal tertiary focus, although a secondary focus gives an aperture efficiency that is only 10% lower, suggesting that diagonal horns are suitable for focal-plane arrays     

Aperture efficiencies of large axisymmetric reflector antennas fedby conical horns

It is shown how the radiation patterns of conical horns can be understood in terms of Laguerre-Gaussian beam modes. This approach provides a simple method for calculating the horn radiation pattern as it propagates through a multielement optical system consisting of lenses or offset mirrors with large focal ratio and/or a small angle of incidence, and can be used in quantitatively determining aperture efficiencies for systems where conical horns are coupled to antennas via tertiary optics. The resulting aperture efficiency results and a practical quasioptical system fed by a conical horn are discussed     

Analysis of spherical hybrid modes in a corrugated conical horn

An approximate analysis of fields in a corrugated horn is considered using spherical hybrid modes. Under the special condition where the slots are about a quarter-wavelength deep, the approximations are slight in the far-field region of the horn. Solutions are presented for the lowest-order spherical hybrid modes, and a procedure is described for the determination of the horn radiation pattern. A first step in the procedure involves the calculation of the hybrid-mode field in the horn aperture. Because diffraction will be minimal in wide-angle corrugated horns, the aperture and radiation patterns should be similar when the far-field approximation applies. This feature is verified for a 120° horn making use of experimental results due to Kay.     

Soft and hard horn antennas

Horn antennas with soft and hard boundaries are analyzed. A soft boundary which exists in classical hybrid-mode horns gives zero field intensity at the wall. A hard boundary corresponds to a uniform field distribution over the horn aperture. Soft and hard horn antennas are compared with respect to directivity, sidelobes, and beamwidth. The dependency between the edge taper directivity, and sidelobes is also calculated based on the solution to the spherical hybrid modes in a conical horn with arbitrary wall impedances. This makes it possible to study how to compromise between directivity and sidelobes. Also discussed is how the different wall impedances may be realized, and some preliminary experimental work on hard horns is presented     

Propagation and radiation behavior of dielectric-loaded pluralhybrid mode multiflare conical horn antennas

A dielectric-loaded multiflare conical horn exhibiting the desirable features of low sidelobes and cross-polarization with the additional advantage of increased on-axis gain is reported. This new horn is developed by combining the techniques of multimode operation for low cross-polarization and sidelobe levels, and dielectric loading for aperture efficiency enhancement. The condition for the support of balanced hybrid modes for low cross polar radiation in the dielectric-loaded multimode horn is derived. Also, the equation for the dielectric thickness for maximum aperture efficiency at a given frequency is obtained. This new type of multimode horn is potentially simple to design, analyze, and manufacture, yet it exhibits the desirable features of a corrugated conical horn and hence can be an attractive alternative to corrugated conical horns for communication applications     

Analysis of pyramidal horn antennas using moment methods

A hybrid numerical technique is developed for electrically large pyramidal horn antennas radiating in free space. A stepped-waveguide method is used to analyze the interior surfaces of the horn transition. The electric field integral equation (EFIE) is employed on the outer surfaces of the pyramidal horn including the radiating aperture. Meanwhile, the magnetic field integral equation (MFIE) is used on the aperture to relate the aperture fields and those in the horn transition The resultant hybrid field integral equation (HFIE) is solved numerically by the method of moments. This formulation is both accurate and numerically stable so that high-gain microwave pyramidal horns can be analyzed rigorously. Far-field radiation patterns, both computed and measured, are presented for three electrically-large X-band horn antennas. The comparisons demonstrate that this method is accurate enough to predict the fine pattern structure at wide angles and in the back region. Computed far-field patterns and aperture field distributions of two smaller X-band horns are also presented along with a discussion on the validity of the approximate aperture field distributions routinely used in the analysis and design of pyramidal horns     

Circularly polarised mode-converting antenna

A novel mode converter that transforms coaxial transverse electromagnetic mode into circularly polarised coaxial TE/sub 11/ mode is proposed by inserting several metal plates into the coaxial waveguide. A circularly polarised mode-converting antenna with length of 36 cm and aperture diameter of 30.8 cm is designed by combining the mode converter with a special conical horn. The antenna has a gain of 19.2 dBi with an aperture efficiency of 50% and an axial ratio of 1.2 at 4 GHz. Measured results agree well with the simulated ones.     

Scattering at Circular-to-Rectangular Waveguide Junctions

A formally exact solution is given for the problem of scattering at a circular-to-rectangular waveguide junction and at a thick diaphragm, with a centered circular aperture, in a rectangular waveguide. The method uses normal TE and TM mode expansions of the waveguide fields and traditional mode matching of the transverse electric and magnetic fields at the junction boundary. Exact closed-form expressions are obtained for the electric field mode-matching coefficients which couple the TE(TM) modes in the rectangular guide to the TE(TM) and TM(TE) modes in the circular guide. Numerical results are presented for the case of TE/sub 10/ mode propagation in the larger rectangular guide with all other modes cutoff. Convergent numerical results for the equivalent shunt susceptances of such junctions are obtained when about 12 modes (eight TE and four TM) are retained in the circular waveguide or in the circular aperture of the diaphragm. The results are graphically compared with formulas and curves due to the quasi-static theory of Bethe and the variational theory given in the Waveguide Handbook [2].     

Radiation of conical horns excited in higher-order modes

Theoretical investigations carried out for the far-field-radiation-pattern prediction of conical horns excited in the spherical TMmn and TEmn modes are applied on the radiation-pattern analysis of TM01 and TE01 modes. The results, valid even for conical horns with large flare angles, provide an optimum horn design for a maximum gain slope near the boresight axis.     

Design of corrugated horns: a primer

Typical example of horn is shown where the inside wall is manufactured in a succession of slots and "teeth". The purpose of the corrugated surface is to provide the means to support the propagation of hybrid modes within the horn. Hybrid modes are basically a combination of TE and TM modes. Some basic information for the inexperienced horn designer to get started in designing their corrugated horn is provided. The class of circularly symmetrical corrugated horns and the parameters in designing are considered. As an example a standard Ku-band operation from a typical Earth station is also considered.     

Improved Selectivity in Cylindrical TE/sub 011/ Filters by TE/sub 211/TE/sub 311/ Mode Control

A new method is presented for the design of low loss cylindrical TE/sub 011/-mode resonators whereby transmission nulls can be placed near the TE/sub 011/, resonance by controlling the TE/sub 211/, and TE/sub 311/, modes that are naturally excited in the same resonator. The frequencies at which the nulls occur are controlled by the angular offset of the sidewall coupling apertures and the relative amplitude of the TE/sub 011/ mode compared to the TE/sub 211/ and TE/sub 311/ modes. It is also shown that a lumped constant circuit model can be used to accurately represent the multimode response of the resonator.     

Gyrotron-traveling wave-tube circuits based on lossy ceramics

The gyro-traveling wave tube (gyro-TWT) is a microwave amplifier with simultaneous high power, high frequency, and broad bandwidth capabilities. Techniques for providing a controlled loading of the TE/sub 01/ cylindrical-guide operating mode of a 35 GHz gyro-TWT using monolithic, lossy ceramic structures are presented. The loading scheme, which also suppresses spurious backward-wave oscillations in the TE/sub 11/, TE/sub 21/, and TE/sub 02/ modes, is based on a sequence of alternating ceramic cylindrical shells and metal rings to form the electron beam tunnel. Design techniques for achieving optimal performance and methods for reducing the sensitivity to temperature-induced variations in ceramic dielectric properties are presented.     

X-band TM/sub 01/-TE/sub 11/ mode converter with short length for high power

A mode converter for X-band located between a generator and an antenna to convert TM/sub 01/ to TE/sub 11/ mode with high efficiency for a high power transmitting system is presented. The proposed mode converter has extended radius and excessive curvature with symmetric structure in order to convert between two modes efficiently with short length. The measured and simulated results of the return loss, mode patterns and efficiency of the proposed mode converter with 200 mm length are provided.     

纵向槽和径向槽组合波纹喇叭馈源的优化设计

研究了纵向槽和径向槽组合的波纹喇叭馈源的优化设计方法.基于旋转体时域有限差分算法分析波纹喇叭的性能,结合协方差矩阵自适应进化策略,以天线口径效率为目标,优化设计了一款Ku频段波纹喇叭馈源,并加工和测试了馈源样机.计算与实测结果表明,在10.7~12.75 GHz频带内,该喇叭具有良好的阻抗匹配和辐射特性,应用于标准卡塞格仑天线时,天线口径效率优于78%,验证了这种优化设计方法的有效性.     

An improved multimode horn for Gaussian mode generation at millimeter and submillimeter wavelengths

An improvement on the dual-mode horn for Gaussian mode generation has been developed. Previous designs have used a sudden transition or linear taper to generate the required TE/sub 11/ and TM/sub 11/ mode mixture. In the improved design presented here, an optimized nonlinear taper is used to generate multimodes, which have a fundamental Gaussian mode power fraction of 99% that exceeds that of the corrugated horn (98%). The bandwidth and return loss are both improved over other dual-mode horn designs.     

A new multimode rectangular horn antenna generating a circularly polarized elliptical beam

A multimode circularly polarized rectangular horn antenna generating an elliptical shaped beam is described. This antenna operates in two orthogonal mode sets, namely the TE10+ TE/TM12and TE01+ TE/TM21modes. By virtue of the higher order TE/TM modes, the apertureE-field distribution can be tapered such that the effectiveE-plane far-field beam width is approximately equal to theH-plane beam width of the other orthogonal set of modes, resulting in low off-axis polarization axial ratio. Because of the tapered aperture distribution, the radiation patterns also have low sidelobes. The elliptical cross section beam is a direct result of the rectangular shaped aperture. This antenna, used in conjunction with a spacecraft to illuminate an elliptical zone on the earth surface, offers high edge-of-coverage gain, low sidelobes, low edge-of-coverage (EOC) axial ratio, less RF sensitivity to the space environment, and low cost. The performance of this antenna has been evaluated experimentally.     

Scattering Coefficients for Wall Impedance Changes in Waveguides

The Wiener-Hopf tectilque is used to obtain an exact solution to a two-dimensional scattering problem. In the problem solved, an incident TE/sub 10/ mode, traveling from z= -/spl infin/ in the positive z direction, is confined by infinite bounding planes; these planes have infinite conductivity for z<0 and an impedance Z/sub 1/, for z>0. The scattering from the junction at z=0 gives rise to reflection and transmission coefficients that are exactly determined. An approximate solution for the reflection coefficients is also given when the TE/sub 10/ mode is incident from the opposite direction. Finally, a table is presented which lists some transmission and reflection coefficients for rectangular and circular waveguides with discontinuities in the wall impedances.     

Gaussian mode analysis of Cassegrain antenna efficiency

Gaussian mode analysis is a convenient way to characterize long focal length systems, such as the Cassegrain antenna at the secondary focus. We use multimode Gaussian optics to derive several interesting results concerning the aperture efficiencies of Cassegrain antennas fed by corrugated conical horns. The highest efficiency is obtained when the antenna is illuminated by a wide-band, wide-angle horn which has its phase center at the secondary focus, or equivalently by a narrow-band diffraction limited horn with its phase-center located at a confocal tertiary focus. In both cases this corresponds to placing the horn aperture at a position where the incoming fields are frequency-independent and have limited spatial extent. We generalize these results to show that a true image of the aperture distribution can always be formed on the spherical cap in the aperture of any arbitrary scalar horn, by using a single refocusing tertiary lens or mirror. Since both the incoming fields and the horn aperture fields on this surface are frequency independent, it follows that the aperture efficiency is also independent of frequency with either of these arrangements. We suggest that devices for shaping the aperture illumination, such as shaped lenses or dual shaped subreflector systems, should, in general, be installed near an image of the telescope aperture distribution.     

Mutual coupling between sectoral horns side by side

The mutual coupling between two sectoral horns side by side is formulated in terms of the rays, modes, and mode caustics excited in each horn. The coupling term is attributed to the multiple interaction between the aperture edges of both horns and is calculated using Keller's geometrical theory of diffraction. It is shown that this asymptotic method leads to an excellent agreement with experiment and is a considerable improvement over more complicated solutions based on the Huygens' principle.