On Sun, May 18, 2025 at 04:13 PM, Roger Need wrote:
You also need a good test jig because stray capacitance and inductance can
affect the results.
An ideal test fixture would maintain a 50¦¸ impedance right to the device body. The Keysight high-frequency SMD fixtures come close to this ideal, the device interface center conductor is a disk, coaxial to and coplanar with a grounded ring which is the outer conductor, with an insulated gap between.
The calibration standards and device under test are placed across this gap to make measurements; there is also a shielding cap which bayonets on during calibration and measurements, to stabilize the stray capacitance and add shielding from interference.
In the photo the brass thing is the outer ring and the inner electrode is indistinguishable as it is 1 or 2mm across.
It would not be to difficult with someone with a lathe, etc. to fabricate a pretty good one. Even a piece of .250" semirigid cable sanded flush would be pretty darned good for small SMD devices or it could be soldered into a ground plane plate flush with the shield for larger components.
Other Keysight accessory links, for inspiration:
Lower frequency:
I used this one a lot for UHF and below:
73, Don N2VGU
Donald S Brant Jr