Meaning
Direct conducted measurements on printed circuit boards require the installation of semi-rigid or flexible coaxial interfaces to connect with test gear. The technique known as SMA pigtail integration involves soldering a coaxial cable directly to the board traces after disconnecting the on-board antenna. This connection delivers a low-loss signal path from the RF transceiver directly to the network or spectrum analyzer.
It bypasses any radiative loss to establish a reliable baseline measurement of the device.
Soldering Procedure
Engineers must strip the outer jacket of the coaxial cable to expose the center conductor and the outer shield. For successful SMA pigtail integration, the shield must be soldered to a nearby ground plane while the signal lead contacts the RF pad. Keeping these connections as short as possible avoids introducing parasitic inductance or impedance mismatch.
This step prevents signal attenuation that would corrupt the power calibration.
Testing Accuracy
Calibrating out the cable attenuation is necessary to obtain accurate conducted results. Once the SMA pigtail integration is complete, the reference plane is shifted to the solder joint using vector network analyzer offset functions. This calibration compensates for the insertion loss and phase delay introduced by the added cable.
The resulting measurement accurately depicts the power levels generated by the wireless transmitter.
Impedance Match
Impedance mismatch at the transition point can cause signal reflection and thermal losses on the board. Proper SMA pigtail integration requires careful alignment to prevent impedance discontinuities from skewing power readings.
