It's called the 'S-match' and is designed for use with balanced antennas eg tuned feeder dipoles.
A description appears on the website of one of our radio clubs in Melbourne.
It's based on ideas from PA0FRI and RZ3AE.
I've not yet tried it. Have you? If so please let me know in the comments below.
PS: Want to learn about portable antennas? You'll find many ideas and projects in the top-selling Hand-carried QRP antennas.