It is called an E-type T junction because the junction
arm extends from the main waveguide in the same
direction as the E field in the waveguide.
Figure 3-62, view B, illustrates cross-sectional
views of the E-type T junction with inputs fed into
the various arms. For simplicity, the magnetic lines
that are always present with an electric field have been
omitted. In view K, the input is fed into arm b and
the outputs are taken from the a and c arms. When
the E field arrives between points 1 and 2, point 1
becomes positive and point 2 becomes negative. The
positive charge at point 1 then induces a negative
charge on the wall at point 3. The negative charge
at point 2 induces a positive charge at point 4. These
charges cause the fields to form 180 degrees out of
phase in the main waveguide; therefore, the outputs
will be 180 degrees out of phase with each other.
In view L, two in-phase inputs of equal amplitude are
fed into the a and c arms. The signals at points 1 and
2 have the same phase and amplitude. No difference
of potential exists across the entrance to the b arm,
and no energy will be coupled out. However, when
the two signals fed into the a and c arms are 180
degrees out of phase, as shown in view M, points
1 and 2 have a difference of potential. This difference
of potential induces an E field from point 1 to point
2 in the b arm, and energy is coupled out of this arm.
Views N and P illustrate two methods of obtaining
two outputs with only one input.
H-TYPE T JUNCTION. An H-type T junction
is illustrated in figure 3-63, view A. It is called an
H-type T junction because the long axis of the b
arm is parallel to the plane of the magnetic lines of
force in the waveguide. Again, for simplicity, only
the E lines are shown in this figure. Each X indicates
an E line moving away from the observer. Each dot
indicates an E line moving toward the observer.
Figure 3-63.E field in an H-type T junction.