since I've read that wave guide bends should have a radius of greater than two wavelengths, I was wondering why the bend radius limits of wr75 and most other sizes of flexible waveguide are less than two wavelengths, and I can't find any specifications addressing this. Shouldn't the flex waveguide bend adhere to the two wavelength radius standard?
Here I will "paste" some of the literature I've read. This literature can be found at http://www.tpub.com/content/et/14092/css/14092_78.htm
and many other places. It is from the NAVY Training guide (the "figures" did not copy and paste):
Waveguide Bends The size, shape, and dielectric material of a waveguide must be constant throughout its length for energy to move from one end to the other without reflections. Any abrupt change in its size or shape can cause reflections and a loss in overall efficiency. When such a change is necessary, the bends, twists, and joints of the waveguides must meet certain conditions to prevent reflections. Waveguides maybe bent in several ways that do not cause reflections.
One way is the gradual bend shown in figure 3-48. This gradual bend is known as an E bend because it distorts the E fields. The E bend must have a radius greater than two wavelengths to prevent reflections. Figure 3-48.—Gradual E bend.
Another common bend is the gradual H bend (fig. 3-49). It is called an H bend because the H fields are distorted when a waveguide is bent in this manner. Again, the radius of the bend must be greater than two wavelengths to prevent reflections. Neither the E bend in the “a” dimension nor the H bend in the “b” dimension changes the normal mode of operation. Figure 3-49.—Gradual H bend. 3-22