GB1207511A - Improvements in dielectric heating apparatus - Google Patents

Abstract

1,207,511. R.F. couplings; microwave heating apparatus. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 3 Jan., 1968 [4 Jan., 1967], No. 464/67. Headings H4A and H5H. Microwave heating apparatus comprises a source 10, Fig. 1, such as a klystron or a magnetron, of nominal frequency (f n ), two resonators 1, 2 for different frequencies (f 1 ), (f 2 ) within a range extending above and below the frequency (f n ), a load 11, and interconnecting means 21 for the said source, resonators, and load. Dielectric material to be heated is drawn through the resonators 1, 2 in turn. As described, each resonator is a section of rectangular-section waveguide and a sheet of dielectric material is drawn through slots in the sides of each section in a direction which is at an angle of less than 90 degrees to the axes of the sections. The resonators may, however, be of other forms of waveguide, such as coaxial lines, strip-lines, parallel-plate lines. The interconnecting means 21 is a 4-port hybrid, but may be a 3 dB coupler, or be of the rat-race or magic-T type. The load 11 is resistive. The frequencies (f 1 ) and (f 2 ) may be equally disposed below and above the frequency (f n ) and it is arranged that when the actual frequency of the source 10 is outside the band between them energy reflected from one resonator is out of phase with energy reflected from the other resonator at the port A of the hybrid connected to the said source. In that case, the reflected energies at the port B connected to the load 11 are in phase. When the actual frequency of the source 10 is inside the band between (f 2 ) and (f 1 ) reflected energies from the resonators 1, 2 are in phase at the port A, but are kept at predetermined low levels by suitable choices of (f 2 ) and (f 1 ). In another embodiment, the output port B of the hybrid 21, which was connected to the load 11, is instead connected to a port A of a second hybrid 22, which has ports C, D connected respectively to two further resonators 3, 4. The said resonators have frequencies (f 3 ) and (f 4 ) equally spaced about the frequency (f n ) and respectively smaller and greater than the frequencies (f 1 ) and (f 2 ). The output port B of the hybrid 22 is in turn connected to a port A of a third hybrid 23, which has ports C, connected respectively to two further resonators 5, 6. The said resonators have frequencies (f 5 ) and (f 6 ) equally spaced about the frequency (f n ) and respectively smaller and greater than the frequencies (f 3 ) and (f 4 ). The output port B of the hybrid 23 is connected to a load 31.