Crossed monopole array for single mode excitation of ventilation duct communication channels

This work presents a novel antenna array for exciting a single mode of propagation in common ventilation ducts with a circular cross-section that are overmoded waveguides in the 2.4 GHz frequency band. By inverting the phase of one driven element with respect to the other, one of two modes can be selected for excitation, but in either case only a single mode is excited. We present the design technique and advantages of such an antenna array for use with IEEE 802.11g access points.