SWR bridge

This bridge is a resistive wheatstone bridge with a balun in the middle of the symmetric bridge to adapt and connect to the asymmetric detector.

I used a MA-com MABAC-t-0079 50 Ohm SMD balun and 3 50 Ohm SMD melf type resistors.

(Melf indicates a small cylindric formfactor)  It is important to use resistors that show almost no parasitic capacitance and inductance. Small parts are normally the best choice.

 Here the heart of the bridge is seen. The 3 resistors and balun are assembled on a small brass part I made . The M3 screw gives an idea of the size.

The brass part has a diameter of 6mm.

Most of the time is spend designing the mechanical dimensions of the body.

See picture below.

The hole is not in the middle and rather deep. In this way the 3 bridge connections are in line with the 3 center pins of the connectors.

The tiny brige before final assembling.  First the connectors are removed and the center pins are equipped with small tapered wires to adapt to the small pads of the SMD parts.

Then the bridge is put on place and fixed with the M3 screw. ( actually I first did some milling for the closing lid and the surface of the body )

And finally the bridge is ready for use.

The result is quite satisfying,  20 dB returnloss @10MHz,  My spectrum analyser stops at 1.5 GHz and the result is still acceptable as you can see.

I have to optimize a bit for parasitics and can possibly improve the performance in the high end.