I designed a coaxial lowpass filter for 2.4 GHz. The cutoff frequency is 3 GHz, Order 7 according the book "Microwave Filters, Impedance-Matching Networks, and Coupling Structures" by G. Matthaei, L. Young and E.M.T. Jones. You can see the design here:
The most difficult part is to calculate the fringe capacities at points, where the diameter of the inner conductor changes. Fortunately, in the book you can find diagrams to estimate them.
The next part will be to energize my workshop.