Filter prototypes derived from Gegenbauer polynomials can represent a useful trade-off between amplitude and phase behavior. This paper discusses the main features of this prototype through a comparison with the more classical Chebyshev and Butterworth solutions; it shows, in the case of an X-band waveguide realization, how its intermediate characteristics, with respect to both amplitude and phase responses, can be very useful in satisfying particular filter performance requirements without increasing filter order.
"On the Use of Gegenbauer Prototypes in the Synthesis of Waveguide Filters," Progress In Electromagnetics Research C,
Vol. 18, 185-195, 2011. doi:10.2528/PIERC10102502