A Modification of Brune´s Method for Narrow-Band Filters

If a given driving point immittance represents a narrow-band filter it can be developed into a ladder network without closely coupled coils by a modification of Brune\´s method. The method is applicable to filters with phase or amplitude characteristic which are not symmetric with respect to the band center frequency. is represented by the ratio of two polynomials in with complex coefficients. A fictitious low-pass equivalent network is developed, which contains frequency independent imaginary components. This network becomes realizable after a low-pass, band-pass transformation is made. It then represents a narrow-band approximation to the exact solution.