Input mismatch of TE11mode coaxial waveguide feeds

The reflection characteristics of the TE11mode in a coaxial waveguide antenna due to mismatch at the radiating aperture are described. Results are presented for conventional coaxial waveguide as well as waveguide whose inner conductor extends beyond the aperture plane. Coaxial wavegulde mismatch is often quite large, particularly for conditions of good pattern symmetry, and some matching is usually required. A broad-band matching technique using annular rings inside the waveguide is described for the case where there is no external conductor. Results presented show excellent agreement between theory and experiment.     

A high power gyrotron operating in the TE041mode

A 35-GHz gyrotron operating in the TE041mode has been built and tested. Output powers of 320 kW at 40-percent efficiency have been obtained. These test results agree closely with theoretically predicted results. Regions of stable operation in the TE041mode were also determined experimentally. These regions could be predicted by a small signal analysis of threshold currents.     

Analytical approximation of the radiation confinement factor for the TE0mode of a double heterojunction laser

An analytical approximation is found forGamma_{0}, the TE0radiation confinement factor in symmetric heterostructures, by using a combination of its asymptotes in the limits of very thin active layers and thick active layers, respectively. The exact expression forGamma_{0}is calculated and compared to the approximation formula. It is found that for any light guiding planar double heterostructure (DH) configuration the approximation is at most -1.5 percent off with respect to the exactGamma_{0}value.     

Mode coupling in coaxial waveguides with varying-radius center andouter conductors

The mode conversion process in a coaxial waveguide with varying-radius center and outer conductors is shown to be described by a system of first-order differential equations-the coupled mode equations. The nondiagonal coefficients of this system are called the coupling coefficients. In this paper, we derive the explicit expressions for the coupling coefficients in a varying-radius coaxial waveguide and discuss some of their important features. These coefficients can be used in determining model conversion in a coaxial cavity with slowly varying walls or designing and analyzing coaxial waveguide tapers and mode converters. Some experimental results of the coupling coefficients for the case of azimuthally symmetric modes, TE_0n modes, are also given     

Selective excitation of high-order modes in circular waveguides

The excitation of very high-order modes in circular waveguides has been performed in a cavity with a connected up-taper with a geometry similar to those used in gyrotrons. A Gaussian beam was coupled to the cavity which was made translucent by an array of holes. With the help of a special optics, the amplitude as well as the phase distribution of the beam was matched to the mode to be excited in the resonant cavity. By simple rotation of one mirror to adjust the phase distribution together with the change of frequency to match the resonance condition, a large number of modes could be produced with one experimental set-up. Field measurements in the output waveguide show a high mode purity of the radiation and confirm the calculations. The method can be used for cold tests of electrodynamic systems operating with these modes, e.g. quasi-optical converters for gyrotrons.     

An analysis of TM11mode beam blowup in linear electron accelerators

The "beam-blowup" phenomenon associated with traveling-wave linear electron accelerators is examined. An equation describing the interaction between the electron beam and the TM¹¹backward-wave mode is developed, and solutions of the equation presented. Computed blowup times as a function of beam current are compared, and show good agreement, with experimental results obtained elsewhere. Possible methods for suppression of blowup are advanced.     

Effective cutoff wavelength of the LP11mode in single-mode fiber cables

The effective cutoff wavelength of the LP11mode is investigated for nylon-coated step-index type single-mode fibers stranded in a cable. It is found from the pulse propagation experiments that the single-mode operation is effectively attained in the two-mode region up to theV-value of 3.0. It is numerically estimated that splice loss, bending loss, and absorption loss due to the OH-ion in cladding are reduced by choosing the operatingV-value as large as 3.0.     

Design of short high-power TE11-HE11 modeconverters in highly overmoded corrugated waveguides

A theoretical parametric study of TE₁₁ to HE₁₁ mode conversion in highly oversized, circumferentially corrugated circular waveguides with different inner diameters is presented for various frequencies in the range of 28 to 140 GHz. The depth of the annular slots is tapered gradually from one half to one quarter wavelength. Computer-aided optimization of converter length, shape of corrugations, and nonlinear slot depth variation has been achieved with a scattering matrix code employing the modal field matching techniques (modular analysis concept). Relatively short mode transducers with matched converter lengths are feasible. The optimum conversion lengths are L₁≈0.5λ_B (short converter) and L₂≈1.2λ_B (long converter), where λ_B is the beat wavelength of the TE₁₁ and TM₁₁ modes in the corresponding smooth-walled circular waveguide. The predicted performances of short and long mode transducers are practically identical. Experimental results taken at 70 GHz (i.d.=27.79 mm) are in excellent agreement with the theoretically predicted performance data. In all cases the HE₁₁ output mode purity is 99% to 99.5%. The maximum cross-polarization and input-reflection levels are below -29 dB and -50 dB, respectively     

Thick circular iris in a TE11 mode circular waveguide

The TE₁₁-mode excitation of a concentric circular iris of finite thickness in a circular waveguide is analyzed by Galerkin's method with even and odd excitation. Agreement between calculated and measured dominant mode scattering parameters is generally within experimental accuracy     

Magnetic dipole excitation of an insulated conductor of finitelength

Excitation of currents on an insulated conductor of finite length and with arbitrary terminations is studied for a magnetic dipole source. For matched terminations, the results agree closely with previous results for an infinitely long conductor, but other terminations produce end reflections that cause standing waves. Specific calculations for a vertical magnetic dipole source are presented, because this source produces the appropriate horizontal electric field and could be used in a borehole-to-borehole configuration. Numerical results for the induced current and secondary magnetic field indicate that long conductors produce a strong anomaly over a broad frequency range for any type of termination     

Performance of an array of circular waveguides with strip-loadeddielectric hard walls

An infinite planar periodic antenna array of radiating open-ended circular waveguides is considered. The conducting waveguide walls are covered with dielectric layers loaded with longitudinal conducting strips for providing the hard wall boundary condition. Analysis of the array is carried out by the mode-matching method. The waveguide modes involved in the method are calculated by using the asymptotic strip boundary condition. It is shown that they are split into an independent subsystem of TE modes for the whole cross section and two independent subsystems of TM modes: one is for the central region and another is for the layer region. The calculations show that the operation of the hard waveguides in an array with small element spacing is similar to that of the multimode smooth wall waveguides completely filled with dielectric. For large diameters and element spacing, the hard waveguides have significant advantages over the smooth ones. It is shown that unlike an individual hard waveguide, the aperture efficiency of such a waveguide in the array has a nonmonotonic dependence on the waveguide radius. The results characterizing the behavior of the aperture efficiency and cross-polarization level in a frequency band as well as the contribution of certain waveguide modes in the reflected power are presented and discussed. The examples of the element patterns corresponding to minimal cross polarization are also given     

Vibration-vibration energy transfer in the v3mode of CO2

The vibration-vibration energy transfer of CO2gas initially excited to the first asymmetric stretch level (00⁰1) has been observed. Collisional pumping to the (01¹1) combination level is measured by monitoring the fluorescence due to the (01¹1) → (01¹0) band. The rate constant for the process: CO2(01¹1) + CO2(00⁰0) → CO2(00⁰1) + CO2(01¹0) is found to be(5.3 pm 1) times 10^{6}s^-1torr^-1.     

Optical waveguides with low pulse dispersion over an extended spectral range

A class of index profiles is described which can be used to minimise pulse dispersion over an extended range of wavelengths or at several different wavelengths. These profiles are compatible with standard waveguide compositions.     

Galerkin solution for the thin circular iris in aTE11-mode circular waveguide

An integral equation for the transverse electric (TE) field in the aperture of a concentric circular iris in a transverse plane of a circular waveguide is approximately solved using Galerkin's method. The aperture field is represented by a finite sum of normal TE and TM (transverse magnetic) circular waveguide modes that fit the circular aperture. The numerical convergence of the Galerkin solution is demonstrated using the resultant aperture field distributions and equivalent shunt susceptance for the case of dominant TE₁₁-mode excitation. The resultant aperture electric field distribution closely resembles that of the TE₁₁ aperture mode alone, except for edge contribution behavior at the edge of the iris. A resonant or capacitive iris is possible over a restricted range of frequencies     

Effect of gap length on the input admittance of center fed coaxial waveguides and infinite dipoles

The input admittance of a coaxial waveguide fed by a gap of length2din the center conductor is evaluated using the dyadic Green's function of the guide and a band of equivalent magnetic surface current proportional to the gap's axial electric field via the equivalence principle. The axial electric field is expressed in terms of a rapidly convergent series of ultraspherical polynomials whose weighting function satisfies the edge conditions at each end of the gap. If the inner and outer radii of the coaxial guide areaandb, respectively, then the limiting case ofb rightarrow inftyis an infinite dipole in free space. Numerical results for the admittance are given as a function ofka (0.01 leq ka leq 0.50)with parameterb/a = 2, 5,10and 50 for the coaxial guide. For the infinite dipole the admittance is presented as a function ofd/a (10^{-3} leq d/a leq 10)withkaas a parameter (0.001 leq ka leq 0.1).     

New theoretical developments in nonlinear guided waves: Stability of TE1branches

We determine the stability of TE1, nonlinear, stationary wave solutions in planar optical waveguides with nonlinear substrate and cladding bounding media. Our numerical scheme involves propagation of the transverse field distribution corresponding to a standing wave solution on the appropriate branch of the nonlinear dispersion curve. The results indicate that large regions on the TE1branches are unstable. Limited results are also given for a TE2branch with a power threshold.     

Optical propagation of the HE11 mode and Gaussian beams in hollow circular waveguides

The propagation of the HE₁₁ mode and Gaussian beams in hollow oversized circular waveguides is analyzed using optical theories. Different types of waveguides are considered : hollow dielectric or conducting waveguides, dielectric-lined waveguides, corrugated waveguides. General formulas are derived which give the power transmission through these different guides. The best wall materials and structures are determined from a comparison of the waveguide transmissions, at the infrared and millimeter wavelengths. The question of the coupling between the HE₁₁ mode and Gaussian beams is discussed and from a review of coupling coefficients derived before, an optimum value is pointed out. The problem of matching a Gaussian beam into circular waveguides in order to achieve the maximum power transmission is analyzed. These results are of interest for infrared lasers or waveguide applications and for Electron Cyclotron Wave (ECW) systems at the millimeter wavelength.     

On the characteristic impedance of a coaxial line with elliptic cone outer conductor and angular strip inner conductor

The expressions of the characteristic impedance of a new kinds of transmission lines—elliptic cone coaxial line are derived. The formulas are based on the TEM and the transformation of the sphero-conal coordinate into two dimension plane. Also themethods using the graphical approximation and taking the geometrical average of the upper and lower bounds to the size of the line are put forward to calculate the characteristic impedance — of the elliptic cone coaxial line.     

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.     

Aperture matching for an infinite circular polarized array of rectangular waveguides

This paper studies the polarization of the main beam radiated from an infinite array of rectangular waveguides, and in particular, illustrates the matching procedure for the design of a circularly polarized array. It is demonstrated that the use of resonant irises at the waveguide openings together with a conventional matching junction inside the waveguides can improve both the power and the axial ratio of the main beam in a circularly polarized array. In general, a good matching design is the one which gives a proper compromise between the power and the polarization, and is not necessarily the one minimizing the reflection.