Millimeter wave measurement of the TM mode cutoff for EBG structures fabricated in LTCC for antenna applications

This paper presents characterization of low temperature co-fired ceramic (LTCC) based electromagnetic bandgap (EBG) structures, and a test method to measure the TM mode cutoff frequency at millimeter wave frequencies. This test method differs from prior art in that the TM mode surface wave launchers are fabricated in the same LTCC module as the EBG structure under test to realize a compact and repeatable test vehicle. A pair of two port transmission measurements will experimentally yield the TM mode cutoff frequency. This frequency defines the lower bound for the surface wave bandgap. The TM mode cutoff frequency is a very important parameter where EBG structures are integrated into millimeterwave LTCC antennas because this cutoff frequency must be lower than the antenna´s operational frequency range. This proposed test method may be used with any open EBG structure which exhibits a TM mode cutoff frequency.