GB1345576A - Electrical high frequency devices - Google Patents

Abstract

1345576 Aerials; microwave oven HUSQVARNA VAPENFABRIKS AB 19 April 1971 [4 March 1970 10 March 1970] 22929/71 Headings H4A and H5H [Also in Division H1] A backward-wave slow-wave structure 1, and adjacent conductor 5, operated in the frequency range over which the structure supports a pair of coupled waves propagated in opposite directions with increasing and decreasing amplitude, respectively, is employed as an antenna, or as a choke (see Division H1) in microwave apparatus. For a wave propagated towards the left between conductors 3 and 4 in the antenna arrangement of Fig. 1, the structure 1 produces a decreasing amplitude, together with a wave of increasing amplitude propagated in the reverse direction, which is coupled out through the transmission line 6, 7. Conversely, a wave coupled into the structure 1 through line 6, 7 suffers a decreasing amplitude, an increasing amplitude wave being generated to propagate in the reverse direction between conductors 3 and 4. If line 6, 7 is omitted, the arrangement operates as a simple choke. In the microwave furnace of Fig. 15, waves from antenna 46 are propagated around the oven surfaces 42, 43, 44, and 45, the propagation being further restricted to this path by a conductive helix, or closed conductive loops 52-formed by photo etched conductive strips on a dielectric basespaced and insulated from the oven walls, and acting as the conductive surface 4 of Fig. 1. The material to be heated may be placed upon a conductive surface 48, disposed above the antenna, insulated therefrom by dielectric legs 49, acting as the surfaces 2 and 3 of Fig. 1, and in the form either of an aluminium plate, or of a plastics or ceramic material bearing conductive strips which either form closed loops or a continuous helix extending parallel to the strips 52. If in the form of a helix, the antenna can be coupled to its end turn adjacent the back of the oven, and energy not absorbed by the goods to be heated can be absorbed by a further antenna adjacent the oven opening 41, or reflected either by a further slowwave structure acting as a choke, or by forming the end turn of the helix as a closed loop. The plate 48 can be attached to the oven door, so that it is automatically moved away from the antenna 46 upon opening the oven, thereby preventing the transmission of energy into the oven. A conveyer microwave furnace employing slow-wave structure antennae and chokes is also described (Figs. 13 and 14, not shown), and suitable forms of slow-wave structure are disclosed (see Division H1).