Radiation from conical horns with large flare angles

Radiation patterns of conical horns with large flare angles excited in theTE_{11}mode are calculated from a simple solution for horn modes using the vector diffraction formula. Radiation patterns are expressed in closed form when the half-flare angle is less than30deg. Patterns obtained by experiment show close agreement with calculated results.     

Radiation patterns of dielectric loaded rectangular horns

The effect of dielectric loading upon theE-plane radiation patterns of rectangular horns is shown to give higher directivity with raised sidelobes. The main beam and first sidelobe can be predicted accurately in terms of radiation from aTM_{y10}mode.     

Mutual coupling between circular waveguide-fed apertures in a rectangular ground plane

A method is presented whereby the infinite ground plane analytical model for the self- and mutual admittances of waveguide-fed apertures can be supplemented (using the geometrical theory of diffraction) to include the edge effects of a rectangular ground plane. TheH-plane coupling between twoTE_{11}mode excited circular apertures is calculated and compared with measurements.     

Sum and tracking radiation patterns of a conical horn

The gain and the radiation patterns of a conical horn excited by a circular waveguide operating in theTE_{mn}andTM_{mn}modes are predicted. The expressions are rigorously derived by using the accurate calculation of the associated Legendre function with the real order and the integer degree.     

E-plane analysis of a modified horn antenna withsuppressed far-out sidelobe level

It is shown that the far-out sidelobes of a horn antenna can be suppressed by curving the edges in the aperture. A three-dimensional uniform geometrical theory of diffraction (UTD) analysis of the E -plane radiation pattern of the modified horn antenna was performed and compared with straight edges. This analysis indicates that the curvature of the edges does indeed influence the sidelobes to the effect that the modified horn antenna has significantly lower far-out sidelobes. The radiation patterns for modified horns were measured and compared with the calculated patterns and were found to be in good agreement     

Radiation patterns of radial waveguides with TM mode excitation

An analysis is presented of the radiation pattern produced by the open-ended radial waveguide with TM mode excitation. Radiation patterns have been computed for TEM,TM_{10}, andTM_{20}mode excitation and comparison is made with measured results.     

GTD analysis of the E-plane patterns of conical horns

An analytical procedure for predicting accurately theE-plane patterns of conical horns with moderate aperture widths (ka < 10), based on uniform geometrical theory of diffraction (UGTD) and supported by measured data, is presented. This analysis predicts theE-plane patterns more accurately (over the main beam) than the one presented earlier.     

Radiation patterns of a mode transducing antenna

Radiation patterns for the general case ofTE_{0n}excitation of Wengenroth's mode transducing antenna are derived. The antenna seems well suited for application as a launcher for electron cyclotron resonance heating (ECRH) plasma heating. Gain and launching efficiency are calculated. Very good agreement is found between predictions and experimental results forTE_{01}mode excitation.     

Aperture fields and gain of open-ended parallel-plate waveguides

The fields at the open end of a parallel-plate waveguide with aTE_{10}mode incident are calculated. For plate spacings greater than about 0.6 wavelengths, these are well approximated by incident and first-order diffracted fields. Consequently single diffraction at the aperture alone is often adequate for pattern calculations and, although no more complicated, is superior to the Kirchhoff result, even for on-axis calculations. Numerical values for Kirchhoff, geometrical theory of diffraction and exact on-axis gain demonstrate this. In contrast, for TEM incidence, both methods yield the exact on-axis gain. Application of these results to the improvement of gain prediction of horns is discussed.     

RCS of a coated circular waveguide terminated by a perfect conductor

The radar cross section (RCS) of a circular waveguide terminated by a perfect electric conductor is calculated by the geometrical theory of diffraction (GTD) for the rim diffraction and by a physical optics approximation for the interior irradiation. The interior irradiation is generally more than 10 dB higher than the rim diffraction fora/lambda geq 1(ais the waveguide radius,lambdais the free-space wavelength). At low frequencies (a/lambda sim 1), the interior irradiation can be significantly reduced over a broad range of incident angle if the interior waveguide wall is coated with a thin layer (1 percent of the radius) of lossy magnetic material. Our theoretical prediction is confirmed by measurements. At higher frequencies (a/lambda sim 3), a thin layer of coating is effective for the case of near axial incidence, provided that a good transition of theTE_{11}mode near the waveguide opening to theHE_{11}mode inside the waveguide is made. A thicker layer of coating is required for the RCS reduction over wider incident angle.     

Pattern analysis of corrugated horn antennas

The corrugated horn has been established as an antenna with low sidelobes and backlobes, rotationally symmetric patterns (for square pyramidal and conical horn shapes), and broad-band performance [1]-[9]. These properties make this horn useful for many applications. Previous studies have used conventional aperture integration techniques to evaluate the patterns of the corrugated horn. In general, the near axisE-plane radiation pattern of a pyramidal corrugated horn may be adequately predicted from standard analysis established for theH-plane patterns of conventional horn geometries [3]. This method, however, fails to predict the far-out sidelobe and backlobe radiation levels. The work presented here uses a knowledge of the aperture fields to predict the pattern using aperture integration and diffraction theory. The assumptions made concerning the aperture fields were verified by probing the internal fields and aperture fields of anXband corrugated horn. The results of this field probing are contained in the Appendix. The method of solution used in this paper parallels that used in previous publications [10]-[12]. Specifically, the pattern in the main beam region is computed using conventional aperture integration procedures, the contribution of theH-plane edges is found using a slope diffraction analysis, and the contribution of theE-plane edges is found by use of duality.     

Radiation properties of 90° conical horns

A combination of the method of moments and the geometrical theory of diffraction (g.t.d.) is used to predict the radiation properties of 90° semiangle conical horns possessing a number of annular slots in the flange. Computed and measured results show good agreement, and a set of theoretical curves is given for application of the horn as a feed.     

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     

Mutual coupling in a finite planar array of circular apertures

Equations are presented for the calculation of the interelement mutual coupling in a finite size planar array of waveguide-fed apertures in an infinite flat conductor. The general mutual admittance expression is evaluated for circular apertures and the mutual coupling calculations are verified experimentally for twoTE_{11}mode excited apertures. Qualitative agreement between calculations for a 183 element array and an infinite array establishes the validity of the finite array theoretical model.     

Cross polarization caused by perturbed circular cross sections of waveguides and horn antennas

The cross polarization caused by a perturbed cross section of the conical hybrid-mode horn is analyzed. The perturbed cross section is assumed to be slightly elliptical. The theory previously presented for cross polarization in a smooth-walled waveguide supporting theTE_{11}- mode is referred and applied to theHE_{11}-mode as well. Simple analytical formulas which are sufficiently accurate for small ellipticites of the cross-section ellipse are presented. These show that the tolerances on the waveguide diameter are extremely strong, typically on the order of 2 to4 times 10^{-2}mm in the horn throat for typical horn geometries at 12 GHz.     

Radiation patterns of pyramidal dielectric waveguides

The radiation patterns of pyramidal dielectric waveguides excited by pyramidal metallic horns are predicted and compared with patterns measured at 9 GHz. Satisfactory agreement is obtained, especially in the region of the main beam. At wide angles, the pattern corresponds quite closely to that of the launcher alone.     

Gain of a E-plane sectoral horn--A failure of the Kirchhoff theory and a new proposal

Accurate absolute gain measurements on a typical 10-cm bandE-plane sectoral horn are described which demonstrate the conventional gain expression underestimates by 20 percent or more. More refined Kirchhoff expressions give little improvement. A new gain formula, incorporating the exact on-axisTE_{10}mode field of an open-ended parallel-plate waveguide and yielding much closer agreement with experiment, is proposed.     

Temporal frequency spectra of multifrequency waves in turbulent atmosphere

General formulations for temporal frequency spectra of the fluctuations of plane, spherical, and beam waves operating at two frequencies are given based on weak turbulence and frozen-in assumptions. The cross spectra and the coherence are obtained for the amplitude at two frequencies, the phase at two frequencies, and the amplitude at one frequency and the phase at another frequency. The results are examined in detail for plane and spherical waves. For the spectrum of the index of refractionkappa^{-n}in the inertial subrange, the amplitude spectrum behaves ask^{(5-n)/2}foromega rightarrow 0andk^{2}omega^{1-n}foromega rightarrow infty. The phase spectrum foromegarightarrow 0and foromegarightarrowinftybehaves ask^{2}omega^{1-n}with different constants. These results agree well with the experimental work of Janes et al. [11] at 9.6 and 34.5 GHz, and explains the ratio of the spectra at two frequencies. Also noted is the experimental slope of -2.6 as and foromega rightarrow inftywhich may be compared with1-n = -2.66using the Kolmogorov spectrum ofn = 11/3. The amplitude and phase coherence are calculated, and the results agree well with the experimental data. This agreement is indicative of the general validity of the theory for frequencies as low as10sim30GHz and the path length as long as 60 km. It is also shown that using the preceding theory, the wind velocity and the structure constantC_{n}can be deduced from the experimental data. Theoretical wind velocity of 15.6 knots obtained from the propagation data compares favorably with the meteorologically measured value of 14 knots, and two values ofC_{n}obtained independently from the amplitude and phase measurements closely agree with each other.     

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.     

Reflection from the aperture of a longE-plane sectoral horn

The complex reflection coefficient of a longE-plane sectoral horn is derived using the geometrical theory of diffraction. Single diffraction alone is shown to be sufficient to describe the contribution from theE(widely separated) edges, while singly and doubly diffracted fields from theHedges are included by using an open waveguide result derived elsewhere. A relatively uncomplicated expression is obtained for the complex reflection coefficient of the horn which agrees well with experiment for horns with slant wall lengths greater than about3frac{1}{2}guide wavelengths.