Why is polar pattern diagram not included on the data sheet for a miniature lapel microphone, like the Shure WL50?
The Shure WL50 is a miniature omnidirectional microphone. Its largest dimension is smaller then the 20 kHz acoustic wavelength. Therefore, in the free field, the polar pattern is a textbook perfect circle. This applies to all professional quality omnidirectional microphones having such small dimensions.