What's this length-tunned shape in this circuit?
It is a special transmission line filter topology, called "hairpin filter" because the line sections look like hair pins.

It is most likely used as a band-pass filter of some sort in this circuit. 

More on these filters can be found on the wikipedia page for distributed element filters: https://en.wikipedia.org/wiki/Distributed_element_filter

The following document shows a few examples for hairpin band-pass filters:

http://www.w1ghz.org/filter/Recipes_for_Printed_Hairpin_Filters.pdf