A Triband Parasitic Vertical Directional Array

Original scanned PDF "A Triband Parasitic Vertical Directional Array" Article

written by Walter J. Schulz | K3OQF

Excerpt:

Vertical directional arrays are employed in AM broadcast stations to protect other radio stations that share the same frequency from interference. In other instances, they are used to direct radiation to a specific target area. It is with that purpose in mind that as radio amateurs we are interested in this type of array. Much of this work was completed during the 1930s on the broadcast band in the United States, based on the research of Dr. George H. Brown and Carl E. Smith. 1,2

We have occasionally seen directional arrays in Amateur Radio articles with all the vertical elements driven. Sometimes the array is constructed with one driven element and one parasitic element. This type of array is a much simpler system to employ. However, when the number of array vertical elements is increased beyond two, the difficulty increases. I was perplexed on how to solve this problem in a simple way and felt that by using an array where each element was driven would prove a difficult task to maintain in adjustment, especially with an inadequate ground radial system. One of the other associated problems is sustaining the correct phase relationships and current ratios between array elements. Therefore, something less complicated was needed to overcome the problems noted. The answer occurred to me in the form of a triband Yagi-Uda dipole array conforming to the configuration of a vertical tribend parasitic array placed on the earth's surface.