Broad-band transition from a coaxial-line to a rectangular waveguide with reduced-height

A transition from a coaxial-line to a rectangular waveguide with reduced-height is proposed. By increasing the height of the waveguide near the coaxial probe, which is opposite to the situation when standard waveguide is used, a broad-band transition can be realized. A transition has been simulated, designed, and tested. Simulation shows that the return loss is lower than -20 dB from 5.7 GHz to 11.1 GHz, with a relative bandwidth of 64%, comparing with a relative bandwidth of 54% tested from an initial design.