Q2Electromagnetics Waves
Question
Q.2. What do you mean by VSWR?
Answer
VSWR (Voltage Standing Wave Ratio) is the ratio of maximum to minimum voltage magnitude along a mismatched transmission line, VSWR = Vmax/Vmin = (1+|Γ|)/(1−|Γ|), ranging from 1 (perfect match) to ∞ (total mismatch).
When a transmission line is terminated in a load not equal to its characteristic impedance Z0, part of the incident wave reflects back, and the forward and reflected waves superpose to form a standing-wave pattern with alternating maxima and minima along the line. The Voltage Standing Wave Ratio is defined as the ratio of the maximum voltage magnitude to the minimum voltage magnitude of this pattern:
where Γ is the voltage reflection coefficient at the load. VSWR = 1 corresponds to |Γ| = 0, a perfectly matched line with no reflection and no standing wave (pure travelling wave); as the mismatch worsens |Γ| → 1 and VSWR → ∞ (total reflection, as with an open or short circuit). VSWR is a dimensionless, always real and ≥1 quantity, and is one of the most commonly measured figures of merit for antenna and RF-system impedance matching, since it can be measured directly with a slotted line or a directional-coupler-based VSWR meter without needing a phase-sensitive measurement.