Bandpass filtering using quadrature modulation

Existing quadrature-modulation systems for bandpass filtering do not make the bandpass filter response have a strictly linear-phase characteristic, even when the equivalent low-pass filter used in the system has a strictly linear-phase response. Simple modifications are proposed to make the bandpass response have a strictly linear-phase characteristic. The modified technique is then extended to obtain an output signal with additional phase shift of 90/spl deg/.