Dipole with"Gamma" match system

[Admin 2579]

The gamma match is often used for providing Yagi impedance matching. It is relatively simple to implement.

As seen in the figure below, the outer of the coax feeder is connected to the centre of the driven element of the Yagi antenna where the voltage is zero. As a result of the fact that the voltage is zero, the driven element may also be connected directly to a metal boom at this point without any loss of performance.

The inner conductor of the coax is then taken to a point further out on the driven element - it is taken to a tap point to provide the correct match. Any inductance is tuned out using the series capacitor.

When adjusting the RF antenna design, both the variable capacitor and the point at which the arm contacts the driven element are adjusted. Once a value has been ascertained for the variable capacitor, its value can be measured and a fixed component inserted if required.