MIL-HDBK-660B
1. SCOPE
1.1 Scope. This handbook is intended for the electronic installations technician to be used as a guide for fabricating rectangular waveguide bends and twists used in the microwave region of the electronic spectrum.
a. Where bends and twists are required in equipment, it may not always be possible to obtain bends and twists of the exact lengths or radii required because they are not standard, and therefore are not carried in supply, or manufactured by industry as a stock item. By using the techniques described in this handbook, such bends and twists can be fabricated in the field, and the equipment for which they are intended can be placed in service in a shorter time than purchased parts could be supplied.
b. This handbook describes the assembly and finishing of components fabricated from the two most commonly used materials, brass and aluminum. The processes and methods used in the fabrication of waveguide assemblies from other materials are similar to the procedures described herein. Careful attention should be paid, however, to brazing only the components made from similar metals to prevent the possibility of galvanic action between parts.
1.2 PURPOSE OF HANDBOOK
1.2.1 Purpose of handbook. For purposes of this handbook, the term twists means a waveguide configuration similar to those shown in figures 23 and 24. These illustrations should enable a technician to differentiate between twists and those waveguide assemblies that are constructed by ready-made elbows and sweep bends.
1.2.2 Design. Waveguides are supplied in straight lengths of from 6 to 14 feet, but usually the length is 10 feet. The number of joints or couplings in a run should be kept to a minimum in order to obtain the most efficient electrical transmission. In an installation, there will be a need for bends, twists, and off-sets. Since all conditions cannot be met with standard fittings, it is desirable to be able to form bends and twists in the straight sections of the waveguide.
These can be formed in the full straight lengths by the methods described in this handbook.
a. Bending of corrosion-resisting steel or magnesium waveguides is not permissible.
b. Ordinarily, bends and twists should not be sharper than those given in table I, but it is possible to make
sharper bends and twists than specified herein without causing excessive attenuation, provided that reflections are avoided. This is done by forming the bend so that its electrical length (mean "L" in figure 2) is exact multiple of waveguides half wavelengths, and preferably at the midband of the frequency at which it is to operate. This will cause the reflection at either end of the bend to cancel out. Similarly, twists may be so designed that their length is an exact multiple of waveguide half wavelengths.
1.2.3 Part or Identifying number (PIN). Proper identification of waveguide bends referenced herein is provided in figure 1.
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