Abstract :
The selectivity characteristics of some three-terminal lumped and distributed RC null networks are examined. The lumped networks considered are the bridged and shunted ladders. In the symmetrical configuration, both networks are found to be less selective than the corresponding parallel-T. By tapering the ladder portion and increasing the number of sections, they can be made as selective as, or even more selective than the asymmetric parallel- T. The distributed networks are obtained as logical extensions of the lumped ones and are studied for exponential, proportional and parabolic types of tapering. Proportional tapering is found to offer no advantage over the untapered-line network. The other two types yield better selectivity; the maximum selectivity with parabolic taper is, however, less than that obtained with exponential taper. For both lumped and distributed networks, the selectivity is found to depend upon the direction of taper. For low source and high load impedances, a higher selectivity is obtained if the impedance level increases with distance from the source, while for high source and low load impedances, the reverse case yields a higher selectivity.
