 The inverted-F antenna is an evolution of the basic quarter-wave monopole antenna. The wire F-type antenna was invented in the 1940s. In this antenna the feed is connected to an intermediate point along the length of the antenna instead of to the base. The base is connected to ground. The advantage of doing this is that the input impedance of the antenna is dependent on the distance of the feed point from the grounded end. The portion of the antenna between the feedpoint and the ground plane is essentially behaving as a short-circuit stub. Thus, the designer can match the antenna to the system impedance by setting the position of the feed point (RF systems commonly have a system impedance of 50 Ω whereas a λ / 4 monopole has an impedance of 36.5 Ω).
