It's a precision microwave "hybrid" ferrite transformer with 50 Ohm resistor stable to 6GHz with 1 Watt RF maximum input.
This is basically a 6dB directional coupler with 4dB insertion loss, so essentially a DC-10.
Let's review a bi-directional coupler schematic which is a fractional RF splitter with one port not used and terminated internally.
simulate this circuit – Schematic created using CircuitLab
Teflon (Rogers subst.) Transmission Losses are more significant when you span > 2 decades to 6 GHz
When output is disconnected or RL=0 dB , -10dB power is reflected back into internal termination.
Given the extreme sensitivity to material quality and tolerances for high Return loss values >40dB, $50 is cheap compared the precision aluminum cavity versions.
I poured Red to highlight the signal ports with that were hidden from green solder-mask that otherwise covers the green signal ground plane.
Many SMD passive components are used to normalize the 50 Ohm impedance and balance the ports to ground and couple to output port for directivity.
The PCB is milled out to fit the component flush and held in place with 4 red PU plastic drops. The ends are rigid coaxial tubes with RF plastic insulation. It is hard to imagine this 3 port DC -10 has a clever coaxial splitter port at one end that has up to 40 db directivity at 5GHz but rated at 23 dB min.
This was just a quick SWAG.