Well, the lines of small width are like inductors, the big fat lines on top look like capacitors to ground, and the small pads on the back are series capacitors in parallel with the inductors. In other words, they are trying to make an elliptical function, not a chebychev, lowpass filter.
It's a generalized chebyshev low-pass filter,please refer:
A Novel Class of Generalized Chebyshev Low-Pass Prototype for Suspended Substrate Stripline Filters
Alseyab, S.A.;
Microwave Theory and Techniques, IEEE Transactions on
Volume 82, Issue 9, Sep 1982 Page(s):1341 - 1347