Pattern shaping with hybrid mode corrugated horns

Hybrid modes in a square corrugated waveguide are investigated, and a technique of combining several modes for pattern shaping is described. The mode amplitudes are calculated from a known throat excitation and used to compute radiation patterns. One horn was designed, constructed, and tested. The theoretical patterns were in good agreement with experimental data.     

Coupling of tilting Gaussian beam with hybrid mode in the corrugated waveguide

The mode-conversion loss in the matching between the gaussian beam emanated from the gyrotron and the hybrid mode in the circular corrugated waveguide with the diameter of 2a is discussed. By numerical calculation, it is found that the loss considerably increases and optimum waist sizew ₀ changes when TEM₀₀ mode with the wavelength λ is injected with offset or tilt. By fitting numerical data to the polynomial function, it becomes evident that the scaling formulas of the losses for the off-axis shiftr _d and for the tilt angle θ are derived to be 2.3(r _d /a)² – 2.2(r _d /a)⁴ and 3.9(aα/λ)² – 5.6(aθ/λ)⁴ for fixedw ₀/a=0.643, respectively. To keep the mode-conversion loss ≤1% for the frequency of 168 GHz and 2a=88.9 mm, tilting angle and offset should be less than 0.1 degrees and 2.9 mm, respectively.     

Improved coupled mode analysis of corrugated waveguides and lasers

Corrugated waveguides and lasers in resonant and non-resonant situations are analyzed by an improved coupled mode theory based on a set of the coupled mode equations for guided modes and radiation continuum. The distributed feedback (DFB) coefficient and the radiation loss coefficient are given in closed forms. The formulation can be applicable to arbitrarily shaped gratings and multilayer waveguide structures. The accuracy of the theory is examined by comparing it with Tamir's exact calculation for a nonresonant situation and also with Streifer's one for a DFB structure. Reasonable accuracy is obtained by the proper choice of the unperturbed waveguide parameter. The dependence of the two coefficients on the grating depth, the grating period, the guide layer thickness, and the refractive index difference between core and cladding layers is obtained for all Bragg orders up to the fourth, and for four typical grating shapes, namely, for rectangular, sinusoidal, symmetric triangular, and sawtooth gratings. Both the threshold gain of DFB lasers utilizing higher order Bragg reflection and the output coupling efficiency of grating beam couplers are also calculated for these parameters. A new multilayer structure for controlling the radiation loss is proposed and analyzed. This structure is suitable for the suppression of the radiation loss in DBR reflectors as well as for the improvement of the output coupling efficiency in grating beam couplers.     

Improved coupled mode analysis of corrugated waveguides and lasers--II: TM mode

In the previous paper [1] we proposed an accurate formalism for analyzing corrugated waveguide devices. This formalism, developed for the TE modes, is extended here to TM modes. Characteristics of TM modes in distributed feedback (DFB) lasers, DBR reflectors, and grating beam couplers are investigated with emphasis on the effect of the radiation loss and they are compared with the TE case.     

Gaussian beam mode analysis of the coupling of power between horn antennas

Gaussian beam mode analysis can be applied in an elegant way to study the coupling of power between two horn antennas. Coupling efficiencies are evaluated for a number of horn combinations and the results presented in a straightforward form useful in the design of submillimetre-wave interferometers and astronomical receiver systems. We show that there is a marked variation in efficiency (up to 30%) depending on the coupling optics, even for beams with well matched profiles.     

Gain of corrugated conical horns

The absolute gain of a corrugated horn which is designed as a 100-GHz gain standard for the Crawford Hill 7-Meter offset reflector has been calculated and measured. The measured gain is determined from "three horn" transmission measurements. The other two horns are a TRG Model W869 corrugated horn and a dual mode horn. Correction factors were computed from the near field power transmission formula. The measured gain of the gain standard is30.8 pm 0.16 dB. Comparison between measured and calculated gains indicate very low ohmic loss in a corrugated horn. The condition of maximum gain for a given length has been found to be a half wavelength phase deviation in the horn aperture. Calculated gain data as well as near field correction factors for two identical corrugated conical horns are given here as reference information.     

Design of profiled corrugated horns

The design principles used to realize smoothly profiled corrugated horns are described. The smooth profiling causes power to be converted to higher order HE₁₂ modes which radiate to produce high sidelobes in the copolarization patterns. A computer-aided spherical modal-matching technique is used to study the higher-order mode conversion. The results show good agreement with measurements. A profiled horn using a series of discrete conical sections is proposed to eliminate most of the mode conversion. A horn designed in this way is presented and shown to possess improved performance characteristics in comparison to a smoothly profiled design     

Phase centers of horn antennas using Gaussian beam mode analysis

The power of Gaussian beam mode analysis to accurately describe the propagation of electromagnetic beams and the location of a horn antenna phase-center is illustrated. By way of example, the case of a compensated pyramidal horn fitted with fins to produce a less abruptly tapered E-plane field distribution is discussed, and the results obtained are compared with those from an alternative method published in the literature. Excellent agreement is found     

Bandwidth properties of corrugated conical horns

It is shown that the aperture fields of circumferentially corrugated conical horns remain virtually unchanged over a very wide frequency range, and that the bandwidth improves as the length of the horn is increased. The theory is applicable over a large range of flare angles.     

Near-field radiation characteristics of corrugated horns

The amplitude and phase patterns of corrugated feed horns are predicted in the near-field region by means of a spherical-mode-expansion method which has been previously applied only in the far field. Excellent agreement has been observed with experimental patterns, and typical results for horns with flare semiangles of 12° and 70° are described.     

High-Q resonances due to surface waves and their effects on theperformances of corrugated horns

We present a study of high-Q resonance phenomena that occur in corrugated horn structures. It is found that high-Q resonances occur within certain frequency bands where two types of modes, i.e., space-wave and surface-wave modes, simultaneously propagate. A simple model is presented to explain the resonance mechanism. The model yields the conditions for resonance, explains the Q of the resonance, and provides the associated resonant frequency. Approximate formulas for the upper and lower bound frequencies of a resonant band are obtained. It is found that the high-Q resonances deteriorate the gain and crosspolar performances of a horn even if the return losses are acceptable at some resonant frequencies. Rectangular corrugated horns are more susceptible to these resonances than circular corrugated horns, and the reasons for such a difference are explained     

Design of wide-band compact corrugated horns

It is shown that a specially profiled corrugated horn with a ring-loaded input converter section is capable of operating over bandwidth ratios of up to 2.4: 1. The cross polarization across the band is relatively low, and the change in beamwidth and phase-center position with frequency is acceptable for many applications. This "compact" horn is significantly smaller than the conventional wide-band corrugated horn, and is particularly recommended as a feed in a dual-reflector antenna where space is limited.     

Simulation of corrugated horns and exciters for circular corrugated waveguides

A method is proposed for simulating the problem of radiation from a finite-length corrugated horn joined with a regular corrugated waveguide. Obtained with the help of the factorization method, a solution to the problem of radiation from the open end of a circular waveguide is applied to formulate the conditions of radiation from the horn.     

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.     

VSWR properties of E-plane dihedral corrugated horns

A moment method solution is used to evaluate the VSWR of dihedral corrugated horns in terms of the various contributors. Knowledge gleaned in this fashion is then used to control these reflections, and in turn reduce the horn VSWR. Use of an appropriate curved horn waveguide geometry in conjunction with a tapered corrugation input yields a very small VSWR over a reasonable band.     

Propagation and radiation characteristics of corrugated horns

A new method for predicting the radiation pattern of a corrugated horn is described which is especially relevant to horns with oblique semi-flare angles. Experimental and theoretical results are compared for a horn with a semi-flare angle of 110°. The solution of the characteristic equation is described in the throat region of the horn, and results are presented for the four lowest modes of propagation with 30° < ?1 < 160°.     

Shielding effectiveness of corrugations in corrugated horns

A moment-method solution is used to obtain new design data for corrugated horns. The current density on the walls of corrugated dihedral horns is evaluated as a function of such corrugation parameters as the tooth density, and the ratio of the gap to the period (of the corrugations). The shielding effectiveness or the capability of the corrugations to prevent the edge of the horn from being illuminated is discussed, as is the question of the efficiency of corrugated horns.     

Profiled corrugated circular horns analysis and synthesis via anartificial neural network

In many reflector and lens antennas profiled corrugated circular horns constitute one of the best feed solution thanks to their polarization purity and small size. In this paper, a method for the design of these feeds by using an artificial neural network (ANN) approach is described. The results obtained with such an approach are investigated both for the analysis and for the synthesis problem, and compared with the standard methods. This unconventional solution gives a good level of accuracy and shorter processing times especially for the synthesis problem, where there is still a lack of affordable and fully automated procedures     

Gaussian beam-mode analysis and phase-centers of corrugated feedhorns

The notion of phase center for a feed-horn is critically examined, and, using Gaussian beam-mode analysis, several variously-defined phase centers, including a maximal-gain phase center, are investigated in detail for corrugated feed-horns in balanced hybrid mode. Expressions for the locations of these phase centers are derived which are applicable for a wide range of corrugated horn dimensions and for near-field as well as far-field distances     

Broadbanding of corrugated conical horns by means of the ring-loaded corrugated waveguide structure

Broadbanding of corrugated conical horns is investigated with the ring-loaded corrugated circular waveguide (RCWG) structure devised by the authors. The useful frequency bandwidth in which the corrugated horn is effective for the improvement of antenna properties is limited by the frequency characteristics of the horn-aperture field and input VSWR of the horn. By the precise analysis of the RCWG, the maximum frequency range in which the desirable field is obtained is much wider than that in the conventional corrugated circular waveguide, and is achieved almost independent of ring thickness, when ring width is about 20 percent of slot depth. The characteristic impedance of the RCWG is nearly equal to that of the homogeneous circular waveguide when ring thickness becomes large. Therefore, a good transformer between the RCWG and the homogeneous circular waveguide is achieved by increasing ring thickness from the RCWG toward the homogeneous waveguide. From the above investigations, it is found that in the ring-loaded corrugated horn, the useful bandwidth is 1.35 times broader than that in the conventional corrugated horn. The theoretical results are verified by the experimental results.