Patent GB-986928-A (GB)
Title: Improvements in microwave structures
IPC: H01P1/16
Filed: 1961-06-08
Abstract: 986,928. Waveguide ferrite devices. COMPAGNIE FRANCAISE THOMSONHOUSTON. June 8, 1961 [June 9, 1960; Nov. 23, 1960], No. 20721/61. Heading H1W. Various narrow band reciprocal and non- reciprocal transmission effects are obtained in a ferrite device by arranging the ferrite element near a portion of the wall of a waveguide where the electric intensity is zero and applying a magnetic field at right angles to the plane of polarization. In the device shown in Fig. 6, the ferrite element 14 has the form of a rectangular prism and is arranged near or on a narrow wall of rectangular waveguide 12 with its longitudinal axis parallel to and equidistant from the broad sides. By means of a variable electromagnet 18 a magnetic field having an axis of symmetry at right angles to the plane of polarization of the guided wave is applied to the ferrite element, the axis of the magnetic field being arranged to intersect the longitudinal axis of the element. Under these conditions, a longitudinal position of the electromagnet may be found for which the whole of the incident energy within a narrow band of frequencies is reflected by the ferrite element. Energy outside this frequency band is transmitted without loss and the effect is reciprocal. The magnetic field intensity required is of the order of several hundred oersteds and determines the frequency at which reflection takes place. Elements and electromagnets may be arranged on both sides of the waveguide. In an application of this device (Fig. 9, not shown), a pair of ferrite elements are arranged in the branches of an H-plane T-junction. In the absence of any magnetic field, energy is divided equally between the branches. By energizing the solenoid of one of the elements, the whole of the energy may be directed along either one of the branches. If the two elements are effective at different frequencies, the arrangement can be used as a band-separating filter. In the device shown in Fig. 10, a permanent magnet 32 is held by a support 33 which enables it to be displaced parallel to a narrow wall of the waveguide 31. A ferrite element 34 is shaped and positioned as described with respect to Fig. 6 and the whole of the device is surrounded by a soft iron shield 35. The magnetic field intensity is below 100 oersteds and the axis of symmetry of the field is arranged so that it does not lie in the median line of the waveguide. Under these conditions, in certain longitudinal positions of the magnet near the ends of the ferrite, complete absorbtion of incident energy within a narrow band of frequencies may be obtained. Energy outside this frequency band is transmitted without loss and the effect is non-reciprocal. The Specification also briefly describes a construction in which two axially spaced magnetic fields are symmetrically applied to the ferrite element. This construction is stated to behave as a phase-shifter. In a further construction, one field is applied asymmetrically and continuously, and the other is applied symmetrically and is pulse controlled. It is stated that the construction behaves as a modulator.