| 摘要 |
<p>1467233 Channel-dropping filter POST OFFICE 18 Feb 1974 [19 Feb 1973] 7937/73 Heading H1W A channel dropping filter comprises frequency-responsive directional couplers formed from all-dielectric waveguide. Each coupler provides total coupling of wave energy in a certain band from an input terminal to an output terminal, energy in other bands being propagated to a second output. Fig. 3 shows a self-explanatory scheme for channel-dropping or combination using such couplers. Each coupledline filter (Fig. 1) consists of dielectric waveguides 2, 5 coupled over such an interval and having dielectric constants relative to the medium in which they are immersed such that, at a certain frequency, the whole of the wave energy coupled into one guide appears totally in the other guide at the end of the coupling interval. The condition that the whole of the input energy will appear wholly on one or the other of the two guides at the end of the coupling interval can be stated as where L is the length of the coupling interval and C is the coupling coefficient which is frequency-dependent. If n is even, the output appears on the guide to which it was originally applied, and if n is odd, the energy appears on the other line. Thus the coefficient C may be adjusted to cause the coupler to separate one group of frequencies from another where both groups are applied in common to the same input of the coupler. According to the invention, the cross-sectional dimensions of each waveguide is chosen such that the ratio #g/# 2 lies in the range from where #g is the wavelength of energy in the guides remote from the coupling region, # 2 is the TEM wavelength, E 1 is the dielectric constant of the guides and E 2 the dielectric constant of the medium in which they are immersed. The wavelengths are those associated with the frequency at which total coupling from guide to the other occurs. The dielectric waveguides may be associated with a single ground plane, or two such planes one on either side of the waveguide.</p> |
