Matching is important when selecting chip antenna. Return Loss and VSWR parameters are used to measure the antenna matching condition. There is a numerical relationship between Return Loss and VSWR.
Return Loss, also known as reflective loss, is a parameter of the reflected signal performance. It indicates that a portion of the incident power is reflected back to the signal source.
- Return Loss = Incident power / Reflected power, in dB
Greater Return Loss means the signal having a higher efficiency in transmission.
VSWR stands for Voltage Standing Wave Ratio. It is the ratio about maximum voltage and minimum voltage in the microwave transmission. There is a relationship between the return loss and the VSWR.
- Return Loss = -20log ((VSWR-1) / (VSWR + 1))
VSWR is usually shown in a figure with the frequency. In below figure, the lowest point is the antenna working center frequency.
In most cases, due to the manufacturing tolerances, perhaps the actual working center frequency is slightly different from the data sheet.
Smaller VSWR will have a better antenna matching performance, and a higher power from the antenna.
The minimum VSWR is 1.0. This is ideal as no power is reflected from the antenna.