5GHz reciever mixer question: what type, what purpose of "U" line.

Hello! This is PCB of 5GHz reciever mixer.

Is it single-balanced mixer? I read some books, but can"t find where is port hybrid junction in this scheme. What is that "U" line between diodes? Also,why thin lines (to GND and to IF output) have so many 90 degree junctions, is it on purpose (somehow reflects RF back to RF part?) Thanks!

The outline shows a typical balanced mixer. The two diodes are fed by LO power so that he "u" line feeds the right diode ~180 degrees out of phase than the left diode directly fed from LO port.
All bends shown have one purpose - to save space on the PCB.
The IF in/out with a thin line indicates that it can only carry a quite low IF frequency, < ~200 MHz due to its high impedance. The LO and RF lines have ~50 Ohms.

Check similar balanced mixers designed e.g. by Minicircuits: they use other balun type and offer a higher IF range that this design.

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One point I would add: the RF port and IF port should have capacitors as DC block to operate correctly; the LO port should be DC-grounded (through 50 Ohms or a coupling loop).

can i say that it is 180 hybrid junction? I can understand why port is isolated in 4-port 180 hybrid junction. But here, does it mean that LO input of diode is isolated from itself (not reflected back to LO, because 180 phase-shifted signal cancel LO (as i understand 4-port hybrid junction, i did it simulation in CST lite edition)?

This is a Single-Balanced Diode Mixer, using a mitered TL to get the right phase shift of the LO signal, a distributed choke to the ground as a DC path (thin TL) otherwise the diode mixer would not work, and a kind of distributed LPF at the IF output.

Can i use two such mixers in this configuration to build quadrature mixer?
Here is idea drawing:

What would be performance compared to classical double balanced mixer with branch-line splitters?

Also have doubt about high-impedance IF output line. Can it be connected to any place: LO port line, 180deg line, RF port line, or only to LO port line as shown on first image in this topic?