Design of a microwave channelized active filter for MMIC

The emergence of new wireless communication systems is always increasing the need for smaller, lighter and cheaper components while technical issues are harder to address as higher frequencies are used. We present the design of a fully integrated microwave bandpass filter, using only lumped components and HEMTs, to fulfill the input requirements of a LMDS client. The channelized filter approach has been used, since it has been demonstrated that this approach can achieve high selectivity in high frequency bands. A three branches design is used. All branches must be optimized so that their individual responses are added in the bandpass while they interfere outside to result in a very selective behavior. Each branch comprises two identical amplifiers and a third order Butterworth filter properly optimized. Final design simulations show that the filter is very selective with a 400 MHz bandpass bandwidth centered at 28.1 GHz. The bandpass gain is slightly over 4 dB and the rejection over 80 dB. The resulting circuit would cover an area of about 10 mm². Further study shows that the circuit is somewhat sensitive to component tolerances. However, the sensitivity is associated with the lumped filters components used in each branch and not with the amplifiers´ characteristics. Consequently, manufacturing yield should not be substantially less than the yield of the HEMT process itself