Measuring VSWR and Gain in Wireless Systems

Introduction Measurement and control of gain and reflected power in wireless transmitters are critical auxiliary functions that are often overlooked. The power reflected back from an antenna is specified using either the Voltage Standing Wave Ratio (VSWR) or Reflection Coefficient (also referred to as Return Loss). Poor VSWR can cause shadowing in a TV broadcast system as the signal reflected off the antenna reflects again off the power amplifier and is then rebroadcast. In wireless communications systems, shadowing will produce multi-path-like phenomena. While poor VSWR can degrade transmission quality, the catastrophic VSWR that results from damage to co-axial cable or to an antenna can, at its worst, destroy the transmitter.