Standing waves with load terminal open circuited
Standing waves: The forward and reflected waves on the incorrectly terminated transmission line produce an interference pattern known as Standing waves. The concept of Standing wave can be best understood by considering the two cases of impedance mismatch at load or the antenna end of the transmission line.
The waveform below the transmission line shows the voltage and current at each point on the line. We can measure these voltages and current at each point with the help of multimeter. As shown the voltage is zero while the current is maximum because short circuit means zero impedance. All the power is reflected back towards the source. The voltage and current variations distribute themselves according to the wavelength of the signal. The pattern repeats for every one-half wavelength. The voltage and current levels at the source will be dependent on the signal wavelength and actual line.
Standing waves with load terminal short circuited
It means infinite impedance, so that voltage at the end of the line is maximum and the current is zero. All the energy is reflected, thereby setting up this stationary pattern of voltage and current standing waves. Practically, transmission line won’t have a short or open. Instead, the load impedance will not be equal to the transmission line (characteristic)impedence.