A 60 GHz image rejection filter manufactured using a high resolution LTCC screen printing process

An LTCC test panel including various mm-wave test circuits has been designed and manufactured using a recently developed screen printing process (Thales Microelectronics) having a highly optimised resolution, here evaluated using a minimum microstrip line width/gap of 2 mil (50.8 μm). In this paper we report on a 60 GHz microstrip coupled lines bandpass filter manufactured on a 3.7 mil (94.0 μm) thick Ferro A6S substrate using a minimum line gap of 2 mil. The electromagnetic effects caused by the top conductor recess were taken into account using direct full-wave simulations (Ansoft HFSS) but also by a circuit simulation methodology based on the use of effective relative permittivity and substrate height parameters. Preliminary measurement results show a 3 dB bandwidth of approximately 5 GHz, a passband insertion loss of 4 dB and a center frequency slightly above the simulated value. This bandpass filter could e.g. serve as an image rejection filter together with the 60 GHz WLAN chipset where it would demonstrate a 55 GHz image suppression of approximately 20 dB.