GB719258A - Improvements in or relating to wave guide systems - Google Patents

Abstract

719,258. Waveguides. WESTERN ELECTRIC CO., Inc. May 16, 1952 [May 17, 1951], No. 12438/52. Class 40 (8) Wavepower in a waveguide is converted from the operating mode to another mode by a dielectric transducer comprising dielectric material that is disposed within the guide in predetermined rotation to the characteristic electric field pattern of the wave mode it is required to produce. Thus unwanted secondary modes arising from lack of symmetry in launching the operating mode into the guide, or irregularities in the guide such as bends, elbows and tapers, may be neutralized by converting energy from the operating mode into those secondary modes, but of opposite phase. The dielectric is disposed across a portion only of the cross-section of the wave-guide and preponderantly in one of the co-phasal regions of the secondary mode. Its dielectric constant is preferably greater than unity by not more than 10 per cent and it may be a polystyrene foam. Thus, to convert into the TE 02 mode some of the energy of a TE 01 mode being carried in a circular guide 10 (Fig. 2), which is of such radius a that it is capable of supporting a TE 02 mode, a dielectric cylinder 11 is used having radius p equal to, or approximately equal to, the radius of the inner cophasal zone of the TE 02 mode (Fig 1b). Its length l will decide the amplitude of the generated TE 02 waves. Alternatively, the complementary arrangement of Fig. 3 may be used. Similarly the most efficient disposition of dielectric material for the generation of the TE 02 mode is as shown in either of the complementary arrangements of Figs. 4 and 5. Here p1 and p2 are the radii of the two modes which occur between the three cophasal zones of the TE 02 mode (Fig. 1c). These basic transducer units may be combined together using spacing plugs 18, 19, 20, as shown in Fig. 6, to produce a composite mode transducer, the one shown in Fig. 6 being designed to substantially neutralize the TE 02 <SP> </SP>and TE 03 modes generated by conical adaptor 16 between guides 17 and 18. The method of deciding the various sizes of the spacing plugs 18, 19, 20 (Fig. 6), and the transducers 11, 12, 15 may be either empirical or mathematical, both methods being described. The invention is also applicable to other shaped wave guides (Figs. 1D, 1E, 1F, not shown). In Fig. 7 (not shown) a dielectric transducer is disposed in a 90 degree arcuate bend to cancel a spurious mode TM 11 , generated by the bend from the applied TE 01 mode. In Fig. 8 (not shown) the spurious TE 11 and TE 21 modes, produced by a TE 10 to TE 01 converter used when transforming from a rectangular wave guide to a circular one, are cancelled by a mode transducer. In Fig. 9 (not shown) TE 01 <SP> </SP>mode waves required to be taken through a curved guide of circular cross section are first taken through a mode transducer to convert half or all of their power into a TM 11 mode oriented to conform with one of the natural modes, TE 01 , +TM 11 <SP>11</SP>, TE 01 -TM 11 <SP>1</SP>, or TM 11 <SP>1</SP>of the bend. A second transducer after the bend transforms the wave power back to the TE 01 mode.