GB842799A - Improvements in or relating to attenuators for guided electromagnetic waves - Google Patents

Abstract

842,799. Microwave attenuators. WESTERN ELECTRIC CO. Inc. May 6, 1958 [May 9, 1957], No. 14449/58. Class 40(8). A microwave attenuator. for co-axial lines, strip lines and other multi-conductor lines using TEM wave modes comprises one or more elements of gyro-magnetic material, e.g. ferrite, magnetically polarized in the direction of wave propagation and occupying only a small part of the cross-sectional area of the propagating structure. It is stated that incomplete filling of the line by the ferrite material causes perturbation of the dominant TEM wave whereby higher modes are generated which are capable of producing gyro-magnetic effects. A section 10, Fig. 1, of coaxial line may be loaded by a ferrite annulus 14 which is either permanently magnetized or polarized by a variable solenoid 15. The annulus may occupy any position between the concentric conductors and the rest of the space may be occupied by a solid dielectric. If the polarizing field is sufficient to saturate the ferrite element, imaginary values of the tensor permeability of the ferrite occur over a certain band of signal frequencies and the device operates as a reflective band-stop filter. A modification (Fig. 3) applicable to strip lines operates in a similar fashion. The line is of the type comprising three conductors 27, 28, 29 and the ferrite element consists of a slab or slabs 30, 31 disposed in any position in planes parallel to the conductors. The propagating structure may be surrounded by a conducting shield. The outer conductor 34 of an input coaxial line is connected to the outer strips 27, 29 and the inner conductor to the centre strip 28. In a further embodiment (Fig. 4), one or more longitudinally polarized ferrite slabs, e.g. 44, 45, 46, 47 are arranged in radial planes between the conductors of a coaxial line 40, the rest of the space being occupied either by air or a solid dielectric. It is stated that this embodiment behaves as a band-stop filter, the rejected frequencies being absorbed rather than reflected. In a modification of this construction for use in a three conductor strip line (Fig. 5, not shown), the ferrite elements are in the form of plates extending in planes parallel to the direction of propagation and at right angles to the strips. They are arranged either symmetrically or asymmetrically on either side of the centre strip. The devices are stated to be effective for either direction of propagation.