H. Idei

K. "Ohkubo

M. Sato

S. Kubo

T. Shimozuma

T." Watari

Y. Takita

National Institute for Fusion Science (NIFS-Repository)

§ 12. Development of Miter Bend with Mov-able Corrugated Waveguides Ohkubo, K., Kubo, S., ldei, H., Sato, M., Shimozuma, T., Takita, Y., Watari, T. The outdoors transmission system should absorb expansion and constriction of the waveg-uide due to the change in atmospheric tem-perature. From an economical viewpoint, we develop a 90-degree miter bend with movable circular corrugated ( CC) waveguide slided into arm with the circular smooth (CS) waveguide instead of the corrugated bellows which is flex-ible. A schematic view of miter bend for 53.2 GHz developed is shown in Fig. 1. The end A-A'( or C-C") of CC-waveguide with 88.9 mm in diameter has the interface at the CS-waveguide (A-A' to B-B' or C-C" to E-E'). CS 1'1/G . E Figure 1. Schematic view of the miter bend with movable corrugated waveguide arms. The length of the CS-waveguide ls is varied by sliding the CC-waveguide. The standard ls is 3 em for both arms. When the pure hybrid mode HEn is injected into the interface at A-A' plane, HEn mode is decomposed into TE1n and TM1n in the CS-waveguide with different diameter of 110 mm. At first, we compute the mode purity at the A-A' by using the mode matching technique. Amplitude patterns of Ey and Ex at the inter-face A-A' between the CC- and CS-waveguides are shown in Fig. 2. Each TE- and TM-mode in the CS-waveguide propagates with different propagation constant and the field pattern at B-B' is obtained by superposing all the modes. The radiation patterns at the various positions 82 z = pl::iz from the waveguide aperture at B-B' are calculated by using FFT -superposition of plane wave (SPW). Here, l::iz is the distance be-tween samplings and p the integer. We choose sampling points of ms in x-direction and ns in y-direction for a waveguide mouth so as to sat-isfy m; + n;:::; (L/ A)/{1 + (2z/ L)2}, where, L is the sampling size ( L x L) of B-B" plane. Figure 2. Ey (upper) and Ex (lower figure) at the various planes. (a) A-A' in the CC-waveguide. (b) B-B', (c) E-E' in the CS-waveguide. Each contour is plotted by 5 db. The phase correction ~ is obtained by compensating the sum of wave phase at the flat mirror injected from each inlet of the bend; ~(x,y,z) = -a.rg[Ey(x,y,R- y)] -arg[Ey(x, y, R + y)] where, R is the radius of the CS-waveguide. From the calculated ~, we can easily determine shape of the surface on reflector. The field component, for example Ey at the reflector is multiplied by exp(i~). The corrected field represents the source field at the reflector with phase correction. Because the reflector plane is non-parallel with the bend output in the configuration, we adopt the new method to calculate the radiation pattern at the bend output by SPW. Radiation patterns at position of the bend output from the source plane ( Q-Q' plane) being made up of sampling points with the same z on the reflector are cal-culated. All the radiation patterns are linear-superposed and we obtain field patterns at the outlet of bend. It is shown trhat 98.8% of the HEn-mode injected is transmitted to the final output. The ramain part is the higher modes including the HE12-mode. 

Development of Miter Bend with Movable Corrugated Waveguides

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