 Direct synthesis avoids many of the problems of the image parameter method . Not only does it take better account of the terminal impedances but the designer has additional degrees of freedom allowing improved matching . The size and gaps of the teeth are tapered in this method of design . That is , the teeth can be different sizes according to their position in the filter , compared with an image design where all sections are identical . With this approach , the original specification for passband and stopband can be kept while simultaneously improving the impedance matching . The stepped impedance transformers can be dispensed with , or at least significantly reduced in size . 
