Quadrature-modulation-type lowpass and highpass filters

Quadrature-modulation filters, introduced by the author four years ago, can be realised in two different configurations. It is shown that, in the transition bands of the `star¿-structured filters, `unwanted¿ output frequency components (i.e. components not present at the input) are generated, but that, in `lattice-structured¿ filters, semiequivalent to the corresponding star configuration, such unwanted components are (or can be) suppressed.