Detailed Study of Millimeter Wave EBG Guide: Broadbanding Techniques, Modal Structure, and Crosstalk Behavior

An electromagnetic band gap (EBG) waveguide using holes drilled in a dielectric substrate is investigated in this paper. A broadbanding technique is suggested and implemented through a detailed study of the modal behaviour of the guiding structure. The stop band of the EBG waveguide was adjusted by changing the width of the waveguide to increase its bandwidth. It is shown that the propagating mode is a quasi-TEM by examining the dispersion properties of the propagating mode. An EBG waveguide of 49.1 mm (equivalent to 19 EBG cells) was designed and fabricated. The simulation results show better than -10dB return loss performance from 27 GHz to 31.5 GHz with insertion loss of better than 2.5 dB over the same bandwidth, and also high isolation in the range of -20 dB with an adjacent similar EBG waveguide. There is a good agreement between the measured data and simulation results. A microstrip line was also fabricated and used as a benchmark for comparison with the designed EBG waveguide. The group velocity of this waveguide is nearly constant across its operating frequency band which implies low frequency dispersion and is also a confirmation of the quasi-TEM nature of the EBG fundamental mode. Also, using the physical insight gained from a careful study of the EBG guide, a simple method is suggested for the calculation of the dispersion characteristic of its fundamental mode.