 Synthesis methods allow better control of the precise filter response . A common response function used by filter designers is the Chebyshev filter which trades steepness of the transition band for passband ripple . However the Chebyshev response is not always the best choice for waffle @-@ iron filters . Low @-@ pass waveguide filters do not pass frequencies all the way down to zero because of the waveguide cutoff effect . A better choice is the <unk> @-@ Zolotarev filter . This filter is based on Zolotarev polynomials ( which include the Chebyshev polynomials as a special case ) discovered by Yegor Ivanovich Zolotarev . The Zolotarev response has a stopband at low frequency , the cutoff of which can be controlled by the designer so it is not detrimental in a waveguide filter . The advantage of the Zolotarev response is that it results in a filter with a better impedance match to the connecting waveguides compared to the Chebyshev filter or image @-@ parameter filters . 
