Wide Band mm- and Sub-mm-Wave Dielectric Rod Waveguide Antenna

The design of a dielectric rod waveguide (DRW) antenna for frequencies of 75-325 GHz is presented. The optimal broadband antenna geometry is determined using numerical simulations. A single DRW antenna is matched with metal waveguides of different sizes for different frequency bands. Measurement results agree very well with the simulation results up to 325 GHz; the gain of the antenna stays nearly constant (G approximate to 10 dB) over the whole frequency range measured from 75 to 325 GHz (160% relative bandwidth). The upper limit is due to our limited manufacturing capability to produce sharp antenna tips. The return loss of the antenna is better than 15 dB. The radiation patterns are nearly independent of frequency. The 3 dB beamwidth is 50 degrees-60 degrees, and the 10 dB beamwidth is about 95 degrees. This indicates that the aperture size of this end-fire antenna decreases as a function of frequency, and this observation agrees well with the earlier observation that the phase center of a DRW antenna moves towards the antenna tip as a function of frequency. Also the cross polarization was studied. The cross-polarization level is better than 15 dB at all frequencies.