Very directional Antennas requiring little power for short distances, high frequency, high gain.These Modules operate between 300-MHz and 433-MHz. The TE11 (kind of propagation) cut-off (chopping/ attenuating the wave)
frequency should be lower than 300-MHz and the TM01 cut-off should be
higher than 433-MHz.
The criteria for cutoff is that the circumference at the midpoint inside the dielectric must be less than a wavelength