There are many antennas that can use in radar systems, but In this lecture, we are going to learn about the Yagi Antenna used in radar systems with a very detailed discussion.
Before starting the Yagi antenna in detail you can also learn the Types of the radar antenna and their Parameters of the Radar antenna. The link is given below. Please read first the below post and then start to learn this lecture.
Radar Antenna | Types and Parameters of Radar Antenna
Yagi Antenna
- A Yagi antenna, also known as a Yagi-Uda antenna, is a directional antenna commonly used in radio communication systems. It consists of a driven element, one or more parasitic elements, and a reflector element, all mounted on a common support structure.
- This antenna ( named after its Japanese inventor, Professor Yagi) form has especially been developed for the area of the short wave up to the SHF band. It is used however also in radar units. It employs parasitic elements to improve directivity and gain.
- A reflector behind the dipole and a director in front of the dipole could be employed for achieving an extra gain of about 5.5 dB. This arrangement is known as Yagi Aerial. Folded dipoles are employed usually in place of the normal dipole.
- The director and the reflector in the Yagi Antenna are usually welded to a conducting rod or tube at their centers. This support does not interfere with the operation of the antenna.
- Since the driven element is center-fed, it is not welded to the supporting rod. Using a folded dipole as the driven element can increase the center impedance.
- The Yagi Antenna shown in the figure has three directors. In general, the greater number of parasitic elements used the greater gain.
- However, a greater number of such elements cause the array to have a narrower frequency response as well as a narrower bandwidth. Therefore, proper adjustment of the antenna is critical.
- The gain does not increase directly with the number of elements used. For example, a three-element Yagi antenna array has a relative power gain of 5 dB. Adding another director results in a 2 dB increase. Additional directors have been less and less effective.
- The various elements are shown in the figure. The spacing between the elements is not uniform, It is usually between 0.15 \lambda to 0.25 \lambda. An economic means of obtaining the maximum gain is about 10 dB with an array length of 1.5 \lambda.
- The radiation from the different elements arrives in phase in the forward direction, but out of phase by various amounts in the other direction.
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Specification of Yagi Antenna
- The specifications of a Yagi antenna can vary depending on the specific design and application. Here are some common specifications that are typically used to describe a Yagi antenna:
- Frequency range: The frequency range is the range of frequencies that the antenna is designed to operate within. Yagi antennas can be designed for a wide range of frequencies, from HF (high frequency) to UHF (ultra-high frequency).
- Gain: Gain is a measure of the antenna’s ability to amplify the incoming signal in a particular direction compared to an isotropic radiator (a theoretical antenna that radiates equally in all directions). Yagi antennas are known for their high gain, which can range from a few decibels (dB) to over 20 dB.
- Impedance: Impedance is a measure of the resistance to the flow of electrical current in the antenna. The most common impedance values for Yagi antennas are 50 ohms or 75 ohms.
- Bandwidth: Bandwidth is the range of frequencies over which the antenna can operate while maintaining acceptable performance. Yagi antennas typically have a narrow bandwidth, which means they are sensitive to changes in frequency and may require tuning for optimal performance.
- Front-to-back ratio: Front-to-back ratio is a measure of the ability of the antenna to suppress signals from directions other than the main lobe. Yagi antennas are known for their high front-to-back ratio, which can be 20 dB or more.
- Beamwidth: Beamwidth is a measure of the width of the main lobe of the antenna radiation pattern. The half-power beamwidth (HPBW) is a common measure used for Yagi antennas and represents the angular distance between the points on the main lobe where the radiation power drops to half its maximum value.
- Materials: The materials used for the elements and boom of the Yagi antenna can affect its performance and durability. Common materials include aluminum, stainless steel, and fiberglass.
- These are some of the key specifications that are typically used to describe a Yagi antenna. Other specifications may include length, weight, wind rating, and mounting options, depending on the specific design and application.
How to Design Yagi Antenna with Specification
- Designing a Yagi antenna requires consideration of several parameters, including the desired frequency of operation, gain, beamwidth, impedance, and the number and dimensions of the antenna elements. Here is an example of a Yagi antenna design specification with typical values for a frequency of 433 MHz:
| Sr. No. | Parameters | Specification |
|---|---|---|
| 1. | Frequency range: | 433 MHz |
| 2. | Gain: | 9 dBi |
| 3. | Impedance: | 50 ohms |
| 4. | Bandwidth: | 5 MHz |
| 5. | Front-to-back ratio: | 15 dB |
| 6. | Beamwidth: | 50 degrees (approx.) |
| 7. | A number of elements: | 3 |
| 8. | Element length: | Reflector – 0.5 λ, Director – 0.45 λ, Driven element – 0.48 λ (where λ is the wavelength at the design frequency) |
| 9. | Boom length: | 1.2 λ |
| 10. | Element spacing: | Reflector-Director – 0.25 λ, Director-Driven – 0.15 λ (approximately) |
- Note that these values are just an example and can vary depending on the specific design and application requirements. It’s also important to note that the design of a Yagi antenna may require iterative adjustments to optimize its performance for a specific frequency range and application. Additionally, factors such as construction materials and mounting options may also affect the final design specification of the Yagi antenna.
Advantages and Disadvantages of Yagi Antenna
- One of the main advantages of Yagi antennas is their high directionality and gain. They can be designed to provide high gain in a particular direction, which is useful for long-range communication. Additionally, they are relatively simple and inexpensive to construct, which makes them a popular choice for amateur radio operators.
- However, there are also some disadvantages to using Yagi antennas. One is that they are directional and need to be pointed in the right direction to receive or transmit signals. This can be inconvenient for mobile applications or when the signal source is moving. Another disadvantage is that they have a narrow bandwidth, which means they are sensitive to the frequency of the incoming signal. This can limit their usefulness in certain applications.
Applications of Yagi Antenna
- Yagi antennas are used in a wide range of applications, including:
| Sr. No | Application | Description |
|---|---|---|
| 1. | Television reception: | Yagi antennas are commonly used for television reception, where they can provide high gain and directionality to receive signals from a particular direction. |
| 2. | Radio communication: | Yagi antennas are widely used in amateur radio, citizen band radio, and other radio communication systems, where they can provide high gain and directionality for long-range communication. |
| 3. | Wireless communication: | Yagi antennas are used in wireless communication systems, such as Wi-Fi and cellular networks, where they can provide high gain and directionality to extend the range of the network. |
| 4. | Radar: | Yagi antennas are used in radar systems, where they can provide directionality and gain to detect and track objects at a distance. |
Conclusion
- Yagi antennas are a popular and versatile type of directional antenna that can provide high gain and directionality for a range of applications. They work by focusing and amplifying radio waves in a particular direction while suppressing signals from other directions. While they have some disadvantages, such as narrow bandwidth and directional sensitivity, they are widely used in television, radio, wireless communication, and radar systems
