This study presents the implementation of a waffle-iron filter in multi-layered substrate integrated waveguide technology, together with an approximate technique for measuring the stop-band scattering parameters of such a multi-mode waveguide filter. Two filters are designed for different stop-band widths, and tested. Two measurement techniques are presented – one utilising a set of measurements with different probe positions, and one using a radiating horn. Measured results for the two prototypes, show better than 12 dB pass-band return loss over 8.5–10.5 GHz for both, with stop-band attenuation in excess of 70 dB over the harmonic bands 15–43 GHz for one and 15–48 GHz for the other.