DOI:10.1049/ji-3-1.1944.0002

出版商:IEE    

年代:1944

数据来源: IET

摘要:

In this paper is calculated the energy radiated by a long current filament which is screened by a squirrel cage of equally spaced thin wires. It appears that the screening ratio depends on two distinct factors; one is the peripheral spacing between the wires of the cage and the other is the radius of the wires themselves. If the peripheral spacing is not greater than about about λ/10 then the radius of the wires is likely to be much more important than the space between them. If the wires are not too thin the screening effect is out of all proportion to the space blocked up by them: this is reminiscent of the properties of the grid of a triode valve, a problem which is a particular case of the present one.To obtain good screening effect the radius of the wires should not be less than about λ/100. Provided this condition is fulfilled then the energy radiated from the screened filament will be only of the order of 2% of that from the unscreened filament even when the peripheral distance between wires is as much as λ/10, whatever the radius of the cage. Thus a comparatively open cage is found to be a very effective screen, provided the radius of the screen wires is not excessively small. The analysis will not be exact when the radius of the wires is comparable with the distance between them, for then the current distribution round each wire will not be uniform: the wires must be thin in this sense. This analysis should form a useful qualitative guide to the screening effect of the screens of finite dimensions used in practice.The equations required to solve this problem lead readily to a resonance condition for a coaxial chamber: it is shown that this condition tends very rapidly to the radial distance between the inner and outer conductor of a coaxial box being one half of a wavelength.As a final example theQis calculated of a cylindrical chamber having no inner conductor.

DOI:10.1049/ji-3-1.1944.0005

出版商:IEE    

年代:1944

数据来源: IET

摘要:

This paper starts by calculating the electric field of an infinite sheet of cophased current and also the field of a flat grating ofNequally spaced wires of infinite length. It shows that the field of the grating approximates closely to that of an infinite sheet at near-by points and approximates to that ofNconcentrated currents at distant points: thus the wave front starts nearly plane and merges gradually into a cylinder. Section 4 shows that the field close to a single Franklin aerial approaches rapidly to that of a filament of infinite length and Section 5 shows that the field close to a “broad-side curtain array” approaches rapidly to that of a grating of filaments of infinite length.Having established that a broad-side array, having the dimensions commonly used in practice, can be validly represented by an idealized grating the author shows that the total output of such an array can be measured by means of a single monitor aerial. The monitor aerial may be placed at any distance less than a wavelength from the plane of the array, but it should be near the ground and near the middle of the panel and in a plane mid-way between two consecutive wires.Then the problem is considered of using a monitor aerial to test whether successive members of the curtain are carrying similar currents: it is shown that the response of a monitor aerial is unduly sensitive to phase and insufficiently sensitive to the magnitude of the current in the member to which it is closest. It is shown that equality of loading should be tested by a monitor loop and not by a monitor aerial, though it is recognized that the use of a loop involves serious instrumental difficulties at wavelengths less than, say, 5 metres. An example is given to show how maladjustments of phase can be located by systematic analysis of the inequalities in response of a monitor aerial which is moved parallel to the plane of a curtain array. In short, a monitor loop is a suitable device with which to test equality of loading, and a monitor aerial to test equality of phase.

DOI:10.1049/ji-3-1.1944.0006

出版商:IEE    

年代:1944

数据来源: IET

DOI:10.1049/ji-3-1.1944.0007

出版商:IEE    

年代:1944

数据来源: IET