An Improved Square-Root Nyquist Shaping Filter

A Nyquist filter can have any odd symmetric taper as a transition between its pass band and stop band. The most well known taper is the raised cosine (RC) taper specified in most communication standards. The square root (SRRC) Nyquist filter formed from this prototype exhibits high spectral side lobe levels that fail to meet severe spectral mask requirements. This paper presents a SR Nyquist filter with an alternate taper that, for the same length filter, achieves side lobe levels between one and two orders of magnitude below those obtained from a cosine tapered square root filter. This alternate filter also offers up to an order of magnitude reduction in residual ISI levels.