 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 <unk> 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 ) . 
