For experimenting with 23 and 13 cm antenna’s I needed a Return Loss Bridge covering above 1 GHz. Searching the internet I found several designs but I liked the one of Wolfgang Wipperman, DG0SA. He also sells the small ferrit parts.
I build the bridge and I measured good results. An Insertion Loss of 13 dBm and Directivety of -45 to -55 dBm. It’s very imported to use SMD’s very close to 50 ohm (0.1%). I used small pieces of semi rigid cable for the connections between the N-connectors.