A bandpass filter based on square open loop resonators at 2.45 GHz

A bandpass filter based on square open loop resonator is designed at 2.45 GHz. To enhance the filter selectivity around the pass band two transmission zeros are introduced and also additional tranmission zeros inserted apart from the pass and to guarantee the rejection there. This six pole filter with four transmission zeros is implemented in microstrip technology. The simulation and measurement results show a very well reflection characteristics, whereas they show relative big insertion loss of about 3.6 dB in simulation and 6.3 dB in measurement. The bandwidth obtained by simulation and measurement is about 72 to 86 MHz. Moreover we see a shift of measurement againts the simulation result, which probably due to mechanical tolerances and tolerances of the relative permittivity of the subtsrate used.