Figure 83. TE and TM modes in circular waveguide.
a. Some waveguide systems are terminated with an antenna that must be rotated. These systems use a
rotating joint between the waveguide and the antenna system. A simple method for rotating part of a waveguide
system is the use of a mode of operation that is symmetrical about the axis. This requirement is met by a circular
waveguide. In this method a choke joint is used to separate the sections mechanically and to join them
electrically, as shown in figure 84. As explained previously, no actual mechanical connection is needed in a
choke joint. The electrical connection is made because of the low impedance that exists between the two sections
Figure 84. Rotating choke joint.
b. A system using both rectangular and circular waveguides is shown in figure 85. A rectangular
waveguide transfers the energy from the