Patent GB-1052037-A (GB)
IPC: H01S1/02
Abstract: 1,052,037. Masers. WESTERN ELECTRIC Co. Inc. Aug. 29, 1963 [Sept. 12, 1962], No 34169/63. Headings H1C and H1W. In a travelling wave maser amplifier in which the fingers of a conductive comb-like slow-wave structure are disposed adjacent to a slab of maser material, uneven displacement of the fingers due to different contractions of the comb structure and the maser material when the amplifier is cooled to a low operating temperature is avoided by providing insulating spacers in contact with and between adjacent fingers, the spacers being attached to the slab. As shown in Fig. 1, the amplifier comprises a cavity 13 formed by a length of rectangular waveguide 10 terminated by conductive members 11, 12, pumping power being applied by way of a waveguide 14 and aperture 15. The signal power is applied through a coaxial transmission line 20 and the output power is extracted through a coaxial line 21, these lines being extended into the cavity by respective posts 18, 19. Movable blocks 25, 26 are provided for fine adjustments of the impedance match. The slow wave comb structure is disposed within the cavity and comprises a conductive base member 16 along which is disposed an array of copper-plate tungsten rods or fingers 17. Optionally the fingers may be secured directly to the waveguide wall. Composite slabs 30 and 31 of negative temperature material such as chromium-doped aluminium oxide are located on opposite sides of the fingers, and alumina spacers 38, 39 are bonded to respective slabs in the positions shown in Figs. 4 and 8 with the spacers 38 forming the teeth of an alumina comb 40. An alternative method of maintaining equal spacing between the fingers 17 is shown in Fig. 7 in which a plastic thread 62 is laid in a groove 60 in the maser slab 61, indentations 70 and ridges 71 being formed when the fingers 17 are pressed against the slab which serve to keep the required finger spacing. Each slab is formed as a composite structure consisting of 90 degrees material 121 adjacent the fingers, Fig. 12, and a superimposed layer of 0 degree material 122. With 90 degrees material the crystalline C-axis 121 is perpendicular to the C-axis 123 of the 0 degree material, the axis 123 being parallel to the longitudinal axis of the slow-wave structure. The use of a composite maser slab having a proportion of 90 degrees material of about 5 to 35% of the total volume provides optimum gain, since maser gain with transmission in the forward direction tends to decrease with increasing frequency if 0 degree material alone is used and conversely for 90 degrees material. Broad band isolation in the reverse direction of transmission is effected by a gyromagnetic isolator comprising discs 28, 32 of gyromagnetic material inserted in respective apertures 27, 29 of ceramic strips 23, 24. The isolator is spaced from the wall of a rectangular waveguide 10 by a further ceramic strip 22. More discs are inserted in strip 23 than in strip 24. A biasing field H dc  is applied in the direction 26 by a source not shown. Suitable gyromagnetic materials are stated to be ferrite; and the rare earth iron oxides having a garnetlike structure of the form A 3 B 5 O 12  where O is oxygen, A is at least one element from the group comprising yttium and the rare earths having an atomic number in the range 62 to 71, and B is iron optionally containing gallium, aluminium, scandium, indium or chromium.