In Microwave Journal March 2017, Sheng Zhang et al published a very nice, narrowband miniaturized band pass filter design, "Miniaturized Bandpass Filter Using Quarter SIW Resonator With Elliptic Defected Structure"
I really like the design, and created an ADS file with a fully scalable layout of that miniaturized band pass filter. This scalable layout cell can be used in ADS for analysis, parameter sweep or optimization with Momentum.