Return Loss vs. VSWR in chip antenna selection


#1

Matching is important when selecting chip antenna. Return Loss and VSWR are both parameters used to measure the antenna’s matching condition. There is a numerical relationship between Return Loss and VSWR.

CSWR

Return Loss, also known as reflective loss, is a parameter of the reflected signal performance. It indicates what 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 has a higher transmission efficiency - you’re losing less power and signal strength to your transmission gear.
return loss

VSWR stands for Voltage Standing Wave Ratio. It is the ratio between 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 figures with the antenna’s frequency. In the below figure, the lowest point is the antenna working center frequency.
VSWR

In most cases, due to manufacturing tolerances and the vagaries of production, the actual working center frequency may be slightly different from the antenna’s data sheet.

Smaller VSWR indicates 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.