Signal Microwave and GigaProbes have developed a line of 40 and 70 GHz test boards for verifying VNA calibration (cal) and checking for measurement drift. To check a cal, many operators use only a low loss through adapter; however, this only verifies that the system noise was removed. A “golden unit” with a known response over frequency should be used to verify that the cal was successful.
The standard test board design includes a 50 Ω line, a 50 Ω line with a 25 Ω “Beatty” line section to verify time domain measurements and a 100 Ω differential line. Many variations of the board can be created, including differential probe lines with both probe-to-connector and probe-to-probe lines.
The test boards are designed for high performance and ruggedness. The edge-launch connectors, manufactured by Signal Microwave, were designed using 3D modeling and RF transmission line analysis. The board launch, the transition from the board to the connector, has a grounded coplanar waveguide (GCPWG) section incorporating a top ground launch that transitions the ground to an inner layer as it transitions to a microstrip line. Rogers’ RO4003 with a thickness of 8 mils and ½ oz. copper is used for the board. The finish on the board is electroless nickel with a top layer of immersion gold (ENIG). The RO4003 is processed by itself, including drilling vias and plating, and is then laminated to an FR4 backer for mechanical stiffness. The board incorporates a custom design standoff with magnets at the end to hold the board securely to a magnetic plate.
San Carlos, Calif.