Rectangular waveguide bends are either E-plane bends or H-plane bends. The
standard bend angles are 90, 60, 45, or 30 degrees. An E-plane bend is
along the electric field (E- field) plane, which is along the shorter
walls of the rectangular waveguide section. An H-plane bend is along the
magnetic field (H-field) plane, which is the longer walls of the
rectangular waveguide section. An easy way to remember which way is the E- or H-plane bend
is:
For an E-Plane
bend, think of the word "Easy". This is a bend in the
easier direction, which is along the shorter walls of the rectangular waveguide (see Photo
1).
For an H-Plane
bend, think of the word "Hard". This is a bend in the
harder direction, which is along the longer walls of the rectangular waveguide (see Photo
2).
Frequently Asked Questions
Q:
Why is this important?
A: If you specify the wrong type of bend (E / H), when you receive your
new waveguide bend it will point in the wrong direction when the waveguide sections are
attached together. If the bend was originally intended to turn upward or downward, instead
it will turn to the left or right, and vice versa.
Q:
If I accidentally ordered the wrong bend, why can't it just be turned so it points in the
right direction?
A: The waveguide flanges are keyed so they will only connect in the
proper orientation (common-polarization, or co-pol) and cannot be turned 90 degrees
(cross-polarization, or cross-pol) because this would result in an almost total loss of
signal.
Flange
Keying
If the waveguides have circular flanges, these flanges have guide pins that only allow the
flanges to fit together in the proper (co-pol) plane. If the waveguides have rectangular
flanges, the spacing of the flange screw holes is made slightly rectangular (not square)
so that the sections only fit together in the proper (co-pol) plane.
 |
 |
| D |
E |
...and the screws are carefully tightened so no gap is visible between the
two mating surfaces in the center. |
|
Wrong
way (cross-pol) to connect circular flanges: |
 |
 |
 |
If the rectangular centers of the waveguides are turned the wrong way
(cross-pol) as above, the flange keying pins will not line up with the holes on the
opposite flange. |
|
Rectangular
Waveguide Keying |
 |
 |
 |
| 11 |
12 |
13 |
To reduce the possibility of cross-pol connections on rectangular flanges the
spacing of the flange screw holes are made to form a slight rectangle (in photo 11 compare
the vertical distance of the holes on the left flange with those on the right flange). If
the waveguide sections are cross-pol, when a screw is inserted in one of the four sets of
holes it will cause a small misalignment on the other three sets of holes. This
misalignment is enough that it makes the screws for the other three holes fit very tightly
or not fit at all, depending on variations in parts and materials (see photos 12 and 13). |
|
