Understanding a Five Element Yagi
A five element Yagi antenna is a focused directional antenna. It uses one reflector, one driven element, and three directors. The reflector sits behind the driven element. The directors sit in front of it. This layout increases forward gain and reduces rear radiation.
Why Dimensions Matter
Small length changes can shift resonance. Small spacing changes can alter impedance. That is why this calculator keeps every factor visible. You can start with proven ratios. Then you can tune the design for tubing size, boom style, mounting method, and local construction limits.
Main Design Idea
The wavelength comes from the selected operating frequency. Each element is a fraction of that wavelength. The reflector is usually longest. The driven element is near a corrected half wave. Each director is shorter than the driven element. This gradual shortening encourages energy to travel forward along the boom.
Boom Spacing
Spacing controls gain, bandwidth, and feed resistance. A short boom can be compact, but it may reduce front to back ratio. A long boom can improve gain, but it needs stronger support. The default layout gives a balanced starting point for VHF, UHF, and experimental amateur designs.
Practical Building Notes
Use straight elements and accurate center marks. Keep the boom square to every element. Insulate the driven element when needed. Check all hardware before outdoor use. Element diameter affects end correction, so thin wire and thick tube may need different trim values. Always cut slightly long, measure carefully, and trim in small steps. Use weatherproof joints, strain relief, and noncorrosive fasteners for stable outdoor service in rain.
Using the Results
The calculator reports total element lengths, half lengths, element positions, boom length, estimated gain, feed impedance, front to back ratio, and wavelength. These values are planning numbers. Real antennas also depend on ground height, nearby metal, cable routing, weather sealing, and test equipment.
Testing and Tuning
After assembly, test the antenna at safe power. Use an antenna analyzer when possible. Adjust the driven element first. Then make small changes to directors only when you understand the effect. Record each change. Exporting CSV or PDF helps keep a build log. A careful log makes the next antenna easier, faster, and more repeatable.