t the effect which is seen is that of two phased dipoles. The region in which this occurs is called the active region of the antenna. Although the example of only two dipoles is given, in reality the active region can consist of more elements. The actual number depends upon the angle a and a design constant. The elements that are not 'active' still contribute to the operation of the antenna. The larger elements behind the active region are longer than the resonant length and appear inductive. Those in front are shorter than the resonant length and appear capacitive. These are exactly the same criteria that are found for reflectors and directors in a Yagi. Accordingly those elements behind the active region act to reflect the power they receive and those in front act as directors. This means that the maximum radiation is towards the feed point of the antenna. The feed arrangements of the log period antenna are important. The input impedance is dependent upon a number of factors. Fortunately the overall impedance can be determined to a large degree by the impedance of the inter-element feeder. However, the main problem to overcome is that the impedance will vary according to the frequency in use. Fortunately this can be compensated to a large degree by making the longer elements out of a larger diameter rod. Even SO the final feed impedance does not normally match a convenient 50 ohms on its own. It is normal for some further form of impedance matching to have to be used. This may be in the form of a stub or even a transformer. The actual method employed will depend to a large degree on the application of the antenna and its frequency range. A log periodic antenna provides modest levels of gain when compared to a Yagi. Typically this is between about 4 to 6 dB and over an operating frequency range of about 2:1. As such it enables wideband operation to be achieved with some gain and the use of only a single feeder. This is a significant advantage in many applications, especially at VHF and Vertical antenna Vertical 