Constant k filters , also k @-@ type filters , are a type of electronic filter designed using the image method . They are the original and simplest filters produced by this methodology and consist of a ladder network of identical sections of passive components . Historically , they are the first filters that could approach the ideal filter frequency response to within any prescribed limit with the addition of a sufficient number of sections . However , they are rarely considered for a modern design , the principles behind them having been superseded by other methodologies which are more accurate in their prediction of filter response .