https://0xfred.wordpress.com/2018/12/07/nfc-antenna-tuning-without-a-vna/

These practical tips outline an efficient way to perform impedance matching with a PC-based vector network analyzer combined with analysis software.

Properly matching an antenna to a transceiver is one of the easiest ways to extend the signal range and battery life of a smartphone, laptop, or any other wireless device. According to the inverse square law of radio waves, only a 6-dB improvement in path loss from improved matching results in a device that transmits and receives at twice the range. A spectrum analyzer with a tracking generator can check an antenna match by looking at the voltage standing wave ratio (VSWR). But the best tool to make the impedance measurements needed to effectively design a matching network is a vector network analyzer (VNA).

Until recently, many engineers tasked with integrating an antenna into a wireless device had limited or no access to a VNA due to the historically high cost of these instruments. In fact, some have not been trained on how to use them. However, the advent of low-cost, portable VNAs coupled with intuitive PC software has made it easier and more affordable to perform antenna matching to improve the performance of wireless devices.

To combat circuit losses, the impedance-matching network in most cases consists of one or more low-loss inductors and capacitors or transmission line stubs. These components are used in a network design chosen to meet the goals of matching impedances, as well as any filtering and bandwidth (or multi-band) specifications as needed.

Step 1: Calibrate the VNA as close to the measurement plane as possible, ideally at the matching-network location.

Step 2: If necessary, align the calibration plane with the measurement plane by using a port extension.

Step 3: Measure the unmatched impedance at the frequency of interest.

Step 4: Determine the matching-network component values and integrate the components.

Step 5: Confirm the matched impedance and adjust if needed.

By following these five steps and using a portable VNA coupled with analysis software, anyone can improve their wireless device’s performance without breaking the bank.

Using RIGOL Spectrum Analyzer and VSWR Bridge to Measure Antenna
https://www.youtube.com/watch?v=INHslyjBxH0

Return Loss Bridge Basics !!
https://www.youtube.com/watch?v=v94csA9fuHE

In this informational video, Jim Beck at Eagle guides you through the proper procedures for taking antenna measurements using the Eagle Return Loss Bridge.