I’ve been trying to design a stepped-impedance coaxial LPF for 23cm using the tool at http://www.changpuak.ch/electronics/Stepped_Impedance_Lowpass_Coax.php

Plan is to use ordinary 28mm plumbing pipe with 0.9mm walls, plus 7/8 inch round bar for the low-Z sections and 3mm round brass rod for the high-Z sections as I don’t currently have a lathe.  I chose 28mm pipe to make it easier to fit 7-16 DIN connectors, the idea being that this will fit directly on the output DIN of my hybrid combiner.  Early days in the thought process so far though.

Stepped Impedance Coaxial Lowpass Filter Designer
http://www.changpuak.ch/electronics/Stepped_Impedance_Lowpass_Coax.php
Version : 09. November 2014
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Cutoff Frequency : 1600 MHz
System Impedance : 50 Ohm
Low Impedance : 9.87 Ω , cap.
High Impedance : 129.88 Ω , ind.
Order of Filter : 11
Filter Topology : Chebyshev, 0.0100 dB
Return Loss, S11 : 26.44 dB (approx)
Tube is round. Center is round.
Tube inner diam. / width : 26.20 mm, respectively 1.0315 inch
Overall Length : 154.0 mm, respectively 6.0627 inch
Depending on your connectors, you may need additional length !
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Section #0
Z (Ω): 50.0
Length : as required ...
Diameter : 11.39 mm, respectively 0.4483 inch
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Section #1
Z (Ω): 129.88
β*l (deg) : 18.16
Length : 9.46 mm, respectively 0.372 inch
Diameter : 3.00 mm, respectively 0.118 inch
G[1] : 0.8235
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Section #2
Z (Ω): 9.87
β*l (deg) : 16.34
Length : 8.51 mm, respectively 0.335 inch
Diameter : 22.22 mm, respectively 0.875 inch
G[2] : 1.4442
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Section #3
Z (Ω): 129.88
β*l (deg) : 40.36
Length : 21.02 mm, respectively 0.828 inch
Diameter : 3.00 mm, respectively 0.118 inch
G[3] : 1.8299
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Section #4
Z (Ω): 9.87
β*l (deg) : 19.73
Length : 10.28 mm, respectively 0.405 inch
Diameter : 22.22 mm, respectively 0.875 inch
G[4] : 1.7437
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Section #5
Z (Ω): 129.88
β*l (deg) : 43.13
Length : 22.46 mm, respectively 0.884 inch
Diameter : 3.00 mm, respectively 0.118 inch
G[5] : 1.9555
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Section #6
Z (Ω): 9.87
β*l (deg) : 20.20
Length : 10.52 mm, respectively 0.414 inch
Diameter : 22.22 mm, respectively 0.875 inch
G[6] : 1.7855
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Section #7
Z (Ω): 129.88
β*l (deg) : 43.13
Length : 22.46 mm, respectively 0.884 inch
Diameter : 3.00 mm, respectively 0.118 inch
G[7] : 1.9555
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Section #8
Z (Ω): 9.87
β*l (deg) : 19.73
Length : 10.28 mm, respectively 0.405 inch
Diameter : 22.22 mm, respectively 0.875 inch
G[8] : 1.7437
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Section #9
Z (Ω): 129.88
β*l (deg) : 40.36
Length : 21.02 mm, respectively 0.828 inch
Diameter : 3.00 mm, respectively 0.118 inch
G[9] : 1.8299
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Section #10
Z (Ω): 9.87
β*l (deg) : 16.34
Length : 8.51 mm, respectively 0.335 inch
Diameter : 22.22 mm, respectively 0.875 inch
G[10] : 1.4442
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Section #11
Z (Ω): 129.88
β*l (deg) : 18.16
Length : 9.46 mm, respectively 0.372 inch
Diameter : 3.00 mm, respectively 0.118 inch
G[11] : 0.8235
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Section #12
Z (Ω): 50.0
Length : as required ...
Diameter : 11.39 mm, respectively 0.4483 inch
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