Radar System Engineering

402 R-F COMPONENTS m-c. 11.3
Contact-type unions have also been used successfully. The flanges
are relieved so that the bolts bring maximum local pressure to bear near
the junction of the waveguide walls. Abrasion of the mating surfaces
is much more serious in such a union than in the choke-type joint.
.
FIG. 11.11 .—Waveguide elements. (a) Long-radius bend in waveguide. (b) Miter elbOw.
(c) Short-radius bend, electroformed fitting. (d) Flexible waveguide, corrugated wall.
Bends in waveguide such as those in Fig. 11.1 la cause inappreciable
mismatch if the inside radius is greater than twice the free-space wavelength.
Short-radius bends are well matched if the length along the
center of the guide is half a guide wavelength. Such elbows as those
shown in Fig. 11“1lc, are produced by electrof orming—that is, plating
copper or other metal on a soft metal mold which is later melted out.
Two-cut miter elbows, such as those shown in Fig. 11.1 lb, are well
matched if the distance between cuts, measured along the center of the
guide, is a quarter of the guide wavelength. Flexible waveguide can be
made by winding It up out of metal strip in the same way that certain