New approach of the design and realization of intermediate sampling filter

Many signal processing algorithms aim at complex signals, so it is important to create complex signal from the bandpass real signal. Intermediate frequency sampling technique samples the intermediate frequency signal directly and produces complex signal by digital signal processing. Unlike current intermediate frequency sampling method, the bandwidth of the sampling filter is variable, and the coefficients of the filter are given analytically. Then new filter produces similar results when the sampling rate is 2b (b means bandwidth of signal) or 4b, and works much better when the band of signal is narrow.