Novel microstrip lowpass filters are developed with reduced size and significantly improved stopband characteristics. After introducing quarter-wavelength open stubs, we get one or two transmission zeros in the stopband. By folding the high impedance microstrip lines, we reduce the size of the filter. Three-pole and five-pole lowpass filters are designed, and their measured frequency responses agree well with theoretical predictions.

New explicit formulas for tap-coefficients of halfband low/high pass MAXFLAT non-recursive filters are presented by using their relationship with already presented maximally linear type IV differentiators. These formulas are modified to give a new class of narrow transition band filters, with a performance comparable to that of optimal filters.