Complex bandpass sampling and direct downconversion of multiband analytic signals

The kernel concept of the software defined radio architecture is to eliminate the analogue mixers and to place analogue-to-digital converters as near the antenna as possible. Bandpass sampling can be used for direct downconversion without analogue mixers. In this paper, we report an efficient method to find the ranges of valid bandpass sampling frequency for direct downconverting multiple bandpass analytic signals (single-sideband RF signals). The algorithm results in the ranges of valid bandpass sampling frequency for the complex signals in terms of bandwidths and band positions of the single-sideband RF signals. Compared to real bandpass sampling, the valid sampling frequency ranges are easier to find and the ranges thus obtained having much wider interval than those of real sampling. As a consequence, the complex sampling scheme is more flexible in choosing sampling frequency and more robust to the sampling frequency variation. Furthermore, if spectral inversion is not permitted, then in some cases there will have no applicable sampling frequency under Nyquist rate for real sampling.