Tamara Wilhite is a technical writer, industrial engineer, mother of two, and published sci-fi and horror author.
What Is a Yagi Antenna?
Yagi antennas, more formally known as Yagi-Uda antennas, are named after their two Japanese inventors. These devices are commonly used in TV reception, ham radio, and as a bridge antenna to connect a site to a Wi-Fi access point.
Yagi antennas have a dipole as the main radiating or “driven” element. A “reflector” is usually located behind the driven element. The reflector usually adds 4 dB to 5 dB of forward gain. However, not all devices have a reflector. If any extra directors are added to the antenna, the antenna gets an average 1 dB of gain.
Parasitic elements which don’t radiate signal can be added to the main element to alter its performance. The amplitude and phase of the signal depend on the size and spacing of these parasitic elements and their location relative to the driven element.
What are the pros and cons of these antennas? When should you use this antenna?
Advantages of Yagi Antennas
Yagis are directional antennas. Most of these antennas have a 50° to 70° beam width. Because they focus all their input in one direction, they put out high gain relative to omnidirectional antennas. This makes them ideal for receiving lower strength signals.
Their high gain gives these antennas relatively good range. They have the most gain for their physical size compared to antennas like log periodics.
The antenna’s design filters out almost all signal noise coming from the opposite direction. This makes Yagis a good choice when you have a high demand application like telecommunications.
It is easier to aim a Yagi antenna than some arrays. And their construction makes them easy to mount on vertical towers or any other type of structure.
Because Yagi antennas are simpler than log periodic antennas, they usually cost less than a comparable LP antenna. While printed circuit board Yagis are available, others can be built from simple rods properly positioned.
Disadvantages of Yagi Antennas
Bandwidth or frequency range is somewhat limited.
If you want a high gain level, the antenna will need to be very long. And even then, gain is limited to around 6-9 dB unless you have more than one Yagi antenna assembled in an array.
These antennas experience a degradation of their electrical characteristics (gain, feed point impedance, front to back ratios) as you move away from the frequency range the Yagi is designed for. This is because these antennas are based on resonant elements, and off-resonant operations introduce reactance that cause the SWR to increase.
Yagi antennas are designed to be balanced but can be unbalanced if a balun is placed at the feed joint line where it connects to the drive element. Depending on the design of the driven element, they can be balanced or unbalanced. Note: Cheap Yagis are balanced, so no balun needed.
Adding elements to this type of antenna increases its directionality. It essentially becomes narrower in its focus, but it then receives signals from that direction even better than before because the signal to ratio improves. In short, the interference levels are reduced, especially from the sides.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: Why do we use folded dipoles?
Answer: It is easier to match impedance. There's less noise on the received signal.
Question: Is a long high gain Yagi antenna suitable for digital TV?
Answer: Yes, but it is difficult to make a Yagi with both high gain, and enough bandwidth to cover all the UHF channels.
If you are interested in only one channel, then it is quite easy.
Question: Can a yagi-uda antenna and Omni directional antenna be built into one and used together?
Answer: No. Yagi uda antennas are directional. Omni-directional antennas like wheel antennas can't be combined with a directional antenna. In theory, you could create an array of directional antennas like a dozen yagi uda antennas pointing in a circle. However, connecting these together is unnecessarily complex. Just use a wheel or bow tie antenna.