Semiempirical formula for the end-coupled bandpass symmetric stripline filter

It is shown that the equation for the series susceptance of the gap in the centre conductor of a symmetric stripline can be modified to extend its range of validity. This is achieved by empirical determination of a correction factor, in the equation, which is practically constant for given ratios of strip width and thickness to ground-plane spacing. It is also shown that the shunt susceptances of the gap can usually be neglected in the determination of bandwidth for an end-coupled filter.