SUMMARY - Continued

1-63 description of the various TE and TM modes. The dominant mode for rectangular waveguides is shown in the figure. WAVEGUIDE INPUT/OUTPUT METHODS are divided into three basic categories: PROBES, LOOPS, and SLOTS. Size, shape, and placement in the waveguide are critical factors in the efficiency of all three input/output methods. WAVEGUIDE/IMPEDANCE MATCHING is often necessary to reduce reflections caused by a MISMATCH between the waveguide and the load. Matching devices called IRISES, shown in the illustration, are used to introduce either capacitance or inductance (or a combination of both) into a waveguide. Conductive POSTS and SCREWS can also be used for impedance matching in waveguides. WAVEGUIDE TERMINATIONS prevent standing waves at the end of a waveguide system. They are usually specially constructed HORNS or absorptive loads called DUMMY LOADS. WAVEGUIDE PLUMBING refers to the bends, twists, and joints necessary to install waveguides. E bends, H bends, and twists must have a radius greater than two wavelengths. The CHOKE JOINT, shown in the figure, is most often used to connect two pieces of waveguide. The ROTATING JOINT is used when a waveguide must be connected to a rotating load such as an antenna.