摘要:

The identification of wave modes or electromagnetic fields in a multi-mode circular waveguide is a new and complicated problem. At present there is no established method of obtaining the required information, nor is there any simple apparatus which produces it. In the paper, methods and instruments which are used to identify wave modes or measure field components are described, and some of their limitations discussed.

DOI:10.1049/pi-b-2.1959.0014

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper describes an instrument for the measurement of field distribution in a multi-mode waveguide, and shows how the information obtained in this way can be analysed to yield the relative amplitudes and phases of the various wave modes present. The technique of measurement is based on the use of a minute dipole supported by a nylon thread and spinning about an axis perpendicular to its length, so that the electric field incident upon it is scattered with a frequency corresponding to twice the speed of rotation. Arrangements are made to amplify and record this scattered field while the dipole is moved from one point to another over the cross-section of the guide, thus enabling relative values of the field strength, its direction and phase to be obtained. The instrument was employed to examine the mode purity of rectangular-to-circular H01mode waveguide transducers and of the output field distributions from various waveguide tapers and bends terminated in a matched load. By making comparison with the results obtained by other methods, it was concluded that the spinning-dipole technique gave an accurate assessment of the mode content of the fields in the waveguides investigated.

DOI:10.1049/pi-b-2.1959.0015

出版商:IEE    

年代:1959

数据来源: IET

摘要:

A simple method is described for measuring the fraction of power in spurious modes generated by a transducer in the presence of the main mode. This method is applicable when the energy in the spurious mode is small and its guide wavelength is different from that of the main mode. Briefly it involves measuring the input standing-wave ratio as a function of the position of a short-circuiting piston in the multi-mode waveguide. From the pattern of the absorption resonances so obtained, together with their shape and spacing, the modes can be identified and their energy contents calculated. The attenuation coefficients can be derived from the measurements if desired, but this is not essential for the calculation of the coupling coefficient.

DOI:10.1049/pi-b-2.1959.0016

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The characteristics of two 50 m lengths of straight circular waveguide have been measured at 25 and 35 Gc/s. The first line was made from solid copper tube of 50 mm bore by drawing to an overall tolerance, including ovality, of ±0.03 mm. The second line was composed of helical waveguides obtained by winding rectangular copper wire on a precision mandrel and surrounding it by a sheet of plastic material reinforced with glass fibre: the bore and overall tolerances were again 50 mm and ±0.03 mm. With the two lines short-circuited at both ends, measurements were made with 0.02 microsec pulses; for favourable settings of short-circuiting piston, attenuations as low as 0.3 neper/km at 35 Gc/s and 0.6 neper/km at 25 Gc/s have been measured on both lines, these results exceeding the theoretical attenuation by only 25–40%.A third line, made of flexible helical waveguide of 50 mm bore, was bent with radius of curvature extending from 50 to 1000 m; attenuation measurements showed that the losses of the TM11wave were 1 500 times higher than those of the TE01wave at 35 Gc/s, and 500 times at 25 Gc/s.

DOI:10.1049/pi-b-2.1959.0017

出版商:IEE    

年代:1959

数据来源: IET

摘要:

It is the usual practice to use, where possible, the dominant mode in a waveguide, because, by making the cross-section of the tube just sufficient to support that mode, all others can be effectively excluded. For some applications the normal dominant mode is unsuitable, and the paper describes arrangements by which another desired mode can be brought to the dominant role. Thus the H01mode in a circular-section guide can probably be made effectively dominant by employing an anisotropic surface impedance, yielding an inductive reactance to the H modes and a capacitive reactance to the E modes. Advantage is also taken of the conversion of all H modes with the exception of the H0nfamily to corresponding E modes as a result of longitudinal current in the wall of the guide. The net result of this technique is to make the guide effectively larger for the H modes and smaller for the E modes, while virtually suppressing all H modes requiring for their support longitudinal current. The necessary anisotropic surface impedance is provided by transverse and longitudinal corrugations or by coating the metal with a thin layer of dielectric.

DOI:10.1049/pi-b-2.1959.0020

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The experiments described were designed to show that mode conversion, which normally occurs when a hollow tubular metal waveguide supporting a circular H01mode is bent, can be reduced very considerably by the use of an inhomogeneous dielectric filling, having a distribution over the cross-section such as to keep the wavefront radial with respect to the centre of curvature of the bend and thereby to preserve the wave pattern. For this purpose a length of waveguide was filled with thin discs of polystyrene loosely packed together, giving, when straight, what was equivalent to a homogeneous dielectric filling. Subsequently, as the tube was bent the discs separated slightly on the outside of the bend and closed up still further on the inside, giving a good approximation to the inhomogeneous distribution of dielectric required in these circumstances.With a pure H01mode at the input, the content of this mode and of the E11mode was examined at the output for different angles subtended at the centre of curvature of the bend. The results showed that, although there was a considerable fall in the power level at the output due to losses inherent in the dielectric, the conversion to the E11mode which would normally be expected was very substantially reduced. Thus the principle governing this technique was amply demonstrated. It remains now to find more suitable forms of dielectric filling for the purpose.

DOI:10.1049/pi-b-2.1959.0021

出版商:IEE    

年代:1959

数据来源: IET

DOI:10.1049/pi-b-2.1959.0022

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The properties of waveguide modes (phase velocity greater than velocity of light) are investigated for a helix line of finite wire diameter and with an arbitrary surrounding medium. It is assumed that the guide wavelength is always much greater than the pitch of the helix. Use of the helix waveguide as a mode filter in transmitting the H01mode is studied in particular.It is shown that the magnitude of the losses and the angle of pitch of the helix determine whether the waveguide modes are capable of existence. For a given angle of pitch the losses must be larger than a definite value to make waveguide modes possible. If the losses are less than this value, the helix line has only the character of a delay line (phase velocity smaller than velocity of light). On helix lines with an angle of pitch ψ ≪ 0.1 the copper losses in the helix wire alone are sufficient to allow the existence of the H0nmodes.For the Hmnmodes, which interfere with H01mode transmission, a maximum attainable loss exists which can be achieved by correct selection of the wire diameter in conjunction with the surrounding medium. This maximum loss is inversely proportional to the square of the helix diameter and to the frequency. For instance, with a helix diameter of 5 cm and a frequency of 50 Gc/s the maximum attenuation of the H12mode is α = 0.0158 nepers/cm, and hence exceeds by a factor of 3 180 the attenuation in a homogeneous circular copper waveguide having the same dimensions.

DOI:10.1049/pi-b-2.1959.0023

出版商:IEE    

年代:1959

数据来源: IET

摘要:

It is shown that a properly designed 2-section conical taper gives superior performance to a simple linear taper and that such a taper, of minimum length and fulfilling given mode conversion and bandwidth requirements, can be designed with the aid of the graphs and table given.

DOI:10.1049/pi-b-2.1959.0024

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The results of a detailed analysis of the propagation of circular electric modes, H0n, is extended, approximated and eventually adapted to the design of monotonic multi-section conical tapers.The formulae and graphs obtained are directly applicable to the calculation of mode conversion loss encountered when two colinear waveguides are connected together by means of a multi-section taper, and the conversion loss is related to the wavelength and the geometry of the structure.The design procedure is illustrated in detail by several numerical examples. It is thereby clearly demonstrated that, for a given mode conversion loss and bandwidth, a considerable reduction in the overall taper length is possible if a multi-section taper of suitable proportions is used in preference to a simple linear taper.

DOI:10.1049/pi-b-2.1959.0025

出版商:IEE    

年代:1959

数据来源: IET