A picture says a 1000 words.. this is an ancient mixer on e-bay recently, I have one for experimentation. It looks well designed (baluns to keep the mixer balanced, and tight twists), and is from a military device (UFT 721 or 771). Only thing missing is resistors in series with the diodes, to improve the linearity.
The pictures below are detailed, because from them it is really clear how transmission lines should be wound.
A snippet of the circuit diag is also below.
Front of the board:
Back: 
Circuit diagram: 
Layout: 
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