Yagi-Uda Antenna: Advantages and Disadvantages

This page explores the pros and cons of the Yagi-Uda antenna. We’ll cover its benefits, drawbacks, and some basic information about what makes it tick.

What is a Yagi-Uda Antenna?

Introduction:

The Yagi-Uda antenna, often simply called a Yagi antenna, is a directional antenna consisting of a driven element, one or more directors (parasitic elements), and a reflector. These elements are arranged collinearly, close to each other, as shown in Figure 1.

The Yagi antenna produces a uni-directional radiation pattern and typically offers a gain of around 7 dB. It’s commonly used in HF and VHF frequency bands.

The spacing between the driven element, director, and reflector is usually about 0.15λ (wavelength). Placing the radiators closer together helps to reduce back lobes in the radiation pattern. The reflector is generally about 5% longer than the driven element, while the directors are about 5% shorter. Dipoles are often used as the driven element.

The design utilizes one reflector and multiple director elements, which may be of equal length or gradually decreasing in length. The larger parasitic element acts as a reflector, while the shorter parasitic elements act as directors, concentrating the radiation in a specific direction.

Benefits and Advantages of Yagi Antenna

Here are the key advantages of using a Yagi antenna:

• Compact and Lightweight: Yagi antennas are relatively small and easy to handle.

• Wide Bandwidth: The use of a folded dipole can provide a wider bandwidth.

• Unidirectional Radiation Pattern: It offers a reasonably good unidirectional radiation pattern.

• Increased Directivity and Gain: Provides a significant improvement in directivity and gain compared to a simple dipole antenna.

• Low Cost and Simple Construction: Yagi antennas are inexpensive and easy to build.

• Easy Mounting: They can be easily mounted on vertical or other poles using standard mechanical fixings.

Drawbacks and Disadvantages of Yagi Antenna

While Yagi antennas have many advantages, they also have some limitations:

• Moderate Gain: Doesn’t offer very high gain. Typically achieves a moderate gain of around 7 dB. Achieving higher gain requires increasing the antenna length.

• Frequency Sensitivity: It’s sensitive to changes in frequency.

• Bandwidth Reduction: Adding more director elements to the array can reduce the bandwidth.

• Obstructive Design: The design can be somewhat bulky and obstructive.