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This paper explores subband processing of complex (I/Q) signals which finds various important applications especially in communications signal processing. Instead of using traditional DFT based systems, the filter bank based systems are very interesting choices when high selectivity in the subchannels is required. We present a novel efficient complex modulated critically sampled filter bank structure which is based on a combination of cosine and sine modulated filter banks. We show that in case of critically sampled analysis-synthesis filter bank system with complex input signal and highly selective channel filters, perfect reconstruction can be achieved only if the low-rate subchannel signals are real.