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This paper presents a comprehensive study of a groove gap waveguide (also known as a waffle-iron) bandpass filter at Ka-band (26.5-40 GHz), fabricated using a high resolution polymer jetting (Polyjet) 3-D printing technology. The same filter was previously fabricated using brass CNC milling technology. The metalized Polyjet 3-D printed filter has lower loss, is lighter in weight and more costeffective, when compared to the solid metal case. The filter operates at a center frequency of 35.65 GHz, has a 500 MHz bandwidth (1.4% fractional bandwidth), and has a transmission zero below and above the passband. Without any design iterations, the measured S-parameters for the Polyjet 3-D printed filter are presented and compared with simulated results, showing excellent agreement. A comparison is then made between the measured results and that of its brass machined counterpart. The new Polyjet 3-D printed filter is 85% lighter than the conventional machined version. All these features prove the important potential of 3-D printing technology for millimeter-wave applications, which includes aerospace. INDEX TERMS Printing, bandpass filter, millimeter-wave band, gap waveguide, waffle-iron, Polyjet.