Chapter 4 Antenna PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Four Antenna Introduction In Standard Four, you learnt how to use and take care of a radi...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Four Antenna Introduction In Standard Four, you learnt how to use and take care of a radio and LY television. Likewise, in Standard Six, you learnt about the concept of the Internet, which is among the communication networks. In N this chapter, you will learn about the concept of the antenna as a device used in communication. You will also learn about the types O of antennas, quality and uses of antennas. Similarly, you will learn about the materials used in the fabrication of antennas. The competencies developed will enable you to design, fabricate, and choose the right antenna. SE U The concept of antenna Discuss with your fellow: E 1. The meaning of antenna 2. The importance of antennas in communication N LI Radio and television receive communication signals from a device which captures those signals from broadcasting stations. Also, ships N and aeroplanes receive communication signals throughout the journey. This communication takes place through electromagnetic waves. O Communication signals are wirelessly transmitted. The reception and transmission of these signals is done by a device called an antenna. R The meaning of the antenna FO The antenna is a device that receives and transmits electromagnetic waves to communication devices such as radios, cell phones, and televisions. For example, when a radio reporter broadcasts, the sound waves are converted into electrical signals. The electrical signals are then carried to 34 SCIENCE AND TECHNOLOGY STD 7.indd 34 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE the transmitting antenna installed at the broadcast station. The antenna converts electrical signals to electromagnetic waves and transmits them through the air. These waves are received by the antenna installed on the user’s radio. The radio antenna then converts electromagnetic waves LY into electrical signals in an electric circuit connected to this antenna. The waves are received and converted N into sound waves that the radio listener listens to. O Antennas are also mounted on telecommunication system towers as shown in Figure 1 (a). These SE antennas receive and transmit U electromagnetic waves to mobile phones. In addition, air and water transportation vessels are installed E with antennas for communication. Figure 1 (a): Telecommunication system The captain or pilot uses a voice N tower recorder to deliver a message Source: Tanzania Telecommunications that is converted into electrical LI Corporation, TTCL signals. The electrical signals are then conveyed to the transmitting N antenna installed on the aeroplane O or ship for transmission. The antenna converts the electric signals into electromagnetic waves and transmits R them to the other antenna installed FO on radar. Radar is a system used to detect and track the movement of Figure 1 (b): Radar system objects such as aircraft and ships. See Figure 1 (b). Source: www.habarileo.co.tz 35 SCIENCE AND TECHNOLOGY STD 7.indd 35 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Some antennas are capable of both receiving and transmitting waves. Other antennas are capable of either receiving or transmitting waves. Examples of antennas that are capable of receiving and transmitting waves are those used on mobile phone and telecommunication towers. Receiving antennas are similar to those used on radios and televisions. Also, transmitting antennas are similar to those used at radio and television broadcasting stations. LY The importance of antennas Communication devices that are not connected using cables need antennas to communicate. Therefore, antennas enable wireless communication, such N as mobile phone communication. Antennas are used in various devices such as in wireless transmitting and receiving communication, mobile phone, O satellite, radar, and wireless internet communication devices. Exercise 1 Answer the following questions: SE U 1. Explain the meaning of an antenna. 2. Explain the importance of antennas in communication. 3. Name three devices which use antennas. E 4. How will the knowledge of antennas help you in your life? N 5. Which devices use antennas that are capable of both transmitting and receiving electromagnetic waves? LI N Types of Antennas Different types of antennas are grouped based on their structures. Those O groups are as follows: (a) Wire antennas, R (b) Aperture antennas, (c) Array antennas, FO (d) Reflector antennas, and (e) Microstrip antennas. 36 SCIENCE AND TECHNOLOGY STD 7.indd 36 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Wire antennas Antennas in this group are mainly fabricated of wires. Wire antennas come in different shapes and sizes, such as circular, square or rectangular. These antennas are in different shapes because wires can be folded and shaped depending on the needs or appearance. Examples of wire antennas are dipole antennas, loop antennas and monopole antennas. In this section, you will only learn about loop antennas. LY Loop antennas: These antennas are available in different shapes such as circular, oval, rectangular or square as shown in Figures 2 (a) and 2 (b). N O SE U Figure 2 (a): Square loop antenna Figure 2 (b): Circular loop antenna Loop antennas are mainly used for receiving radio waves. The efficiency of these antennas depends on the loop’s circumference. Therefore, loop E antennas with large circumference have higher efficiency than small N ones. Loop antennas can capture waves from any direction because they do not need to be placed at a fixed position. Thus, loop antennas are not LI much affected by environmental noise. N Advantages of using loop antennas O Loop antennas have the following advantages: (i) They do not receive unwanted signals; therefore, they are free from electromagnetic signal interference; R (ii) They have a simple and stable structure; (iii) No need to search the direction of the radio wave; FO (iv) They are suitable for portable devices; (v) They are available in different sizes and shapes; and (vi) They can be fabricated at low cost. 37 SCIENCE AND TECHNOLOGY STD 7.indd 37 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Disadvantages of using loop antennas Loop antennas have the following disadvantages: (i) Small loop antennas are mostly used in short range transmission, and they are less efficient than the larger loop ones and (ii) Antennas with a small loop cause electrical energy loss as heat. Therefore, large loop antennas are more preferred over the small ones. Aperture antennas LY This group includes antennas such as waveguide antennas, slot antennas, and horn antennas. The waveguide antenna is a pipe-shaped antenna with a wide opening on one side and a narrow opening at the other end. N The slot antenna looks like a metallic piece with a hole at the centre. In this part, you will only learn about horn antennas. O Horn antennas: These antennas have a wide opening at the beginning SE and a narrow opening at the end to capture and guide waves. They are used to collect and transmit radio waves from a waveguide. Horn antennas can have square, rectangular or circular surfaces as shown in Figures 3 (a) and 3 (b). U Circular face Rectangular face Waveguide Waveguide E N LI N Figure 3 (a): Pyramidal horn Figure 3 (b): Conical horn O Advantages of using horn antennas Horn antennas have the following advantages: (i) They are simple to fabricate; R (ii) They direct the waves efficiently and effectively; and FO (iii) They produce straight waves, thus travelling long distances. Disadvantage of using horn antennas They cannot receive many signal waves especially weak signals. 38 SCIENCE AND TECHNOLOGY STD 7.indd 38 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Array antennas Array antennas are a combination of multiple antennas that work together as a single antenna. The Yagi-Uda antenna is a well-known and popular antenna in this group. The Yagi-Uda antenna: This name comes from Japanese inventors Hidetsugu Yagi and Shintaro Uda. The Yagi-Uda antenna is often called the Yagi antenna. It is made of the following materials: director elements, LY a feeder, dry pole, a boom, a reflector and a cable for transmitting waves to communication devices such as televisions as shown in Figure 4. The Yagi-Uda antenna is mainly used for receiving television and radio waves N since they require many waves. Yagi-Uda antenna also receives signals O which are in analog format. Boom Driven element Feeder SE Director element U Reflector element E Cable N Dry pole LI Figure 4: The Yagi-Uda antenna N Advantages of using the Yagi-Uda antenna O The Yagi-Uda antenna has the following advantages: (i) It has high efficiency even when signals are weak; (ii) It receives reasonably good un-directional signals; R (iii) It is easy to maintain and repair; FO (iv) It consumes a small amount of electrical energy; (v) It covers a wide range of frequencies; and (vi) It is cheap to handle and maintain. 39 SCIENCE AND TECHNOLOGY STD 7.indd 39 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Disadvantages of using the Yagi-Uda antenna The disadvantages of using the Yagi-Uda antenna are as follows: (i) It is easily affected by interferences from the flow of electric current; (ii) It is easily affected by weather; and (iii) It needs a large number of connected elements to be efficient. Reflector antennas Reflector antennas have a curved surface for reflecting waves. Based on LY their structures, these antennas are likened to the human ear. Reflector antennas are used to transmit and receive electromagnetic waves more N efficiently. They are often used to receive and transmit waves for television and satellites. Examples of these antennas are the parabolic reflector O antenna, known as the dish; corner antenna and plasma antenna. In this section, you will learn about the parabolic reflector antenna or the dish. SE Parabolic reflector antenna or dish: This antenna has a curved surface to direct and capture waves. Also, this antenna is known as a dish or a bowl antenna because it looks like a dish as shown in Figure 5. Large U antennas of this type are built together with horn feed and disk attachment to increase their efficiency. E The quality of the parabolic reflector antenna depends on the size of the dish. Large dish antennas are more efficient than small ones. These N antennas are most popular Parabolic reflector LI and widely used to receive and transmit radio waves Horn feed N in the air. For example, Disc a dish receives signals O from satellites, rockets, and aeroplanes. Similarly, R dishes are used to receive weather forecasting FO information signals at the meteorological station. Figure 5: Parabolic reflector antenna 40 SCIENCE AND TECHNOLOGY STD 7.indd 40 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Advantages of using parabolic reflector antennas Parabolic reflector antennas have the following advantages: (i) They can be efficiently used to transmit and receive signals over long distances; (ii) They can be made in different ways depending on use; and (iii) The production cost is relatively low considering its good efficiency. Disadvantages of using parabolic reflector antennas LY The following are the disadvantages of using parabolic reflector antennas: (i) They need a horn feed to operate properly; (ii) The horn feed reduces a certain amount of signals from the main N antenna; (iii) The process of fabricating a parabolic reflector antenna is complex; O (iv) Some signals from a horn feed may interfere with the signals from the main dish; and (v) It is difficult to align the horn feed and the main antenna during its installation. SE Microstrip antennas U A microstrip antenna is a type of antenna that is light and flat. This antenna is fabricated of two flat metals, which are small and large flat metals. A small flat metal called a patch is placed on top. A large flat metal called E ground plane is placed down as a base. The ground plane and the patch are separated by a substrate as shown in Figure 6. N Patch Key: LI W = width of the patch metal w h = height of the substrate N L = length of the patch metal L O h Substrate Ground plane R Figure 6: The structure of the microstrip antenna FO The ability to receive and process electromagnetic waves depends on the distance between the patch and ground plane metals. The greater the distance, the better the performance and vice versa. However, a 41 SCIENCE AND TECHNOLOGY STD 7.indd 41 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE moderate distance is required to eliminate the possibility of having a big device that uses this antenna. Microstrip antennas are used in wireless devices such as mobile phones, satellites, the Global Positioning System (GPS) and aeroplanes. Such devices require small and light antennas as shown in Figure 7. LY N O Antenna SE Figure 7: A microstrip antenna on the mobile phone U Advantages of using microstrip antennas Microstrip antennas have the following advantages: E (i) They are light and portable; (ii) They do not require mesh support to increase their efficiency; and N (iii) They can work in parallel waves operation. LI Disadvantages of using microstrip antennas N Microstrip antennas have the following disadvantages: O (i) They require complex systems to operate efficiently; and (ii) They require high care when mounting on the device. R Activity 1: Observing the antennas which are found in your surroundings FO Study the antennas that can be found around the school or home areas. Then, identify the uses of each device. 42 SCIENCE AND TECHNOLOGY STD 7.indd 42 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Exercise 2 Answer the following questions: 1. Name four types of antennas based on their structure. 2. Distinguish between the loop antenna and the parabolic reflector antenna. 3. Explain with examples the use of microstrip antennas, parabolic reflector antennas and Yagi-Uda antennas. 4. Name three challenges of using parabolic reflector antennas. LY Quality of antenna N Various characteristics determine the quality of antennas. These include the shape of the antenna, transmitting frequencies and efficiency, depending O on the use. (a) The shape of the antenna SE The antenna’s shape significantly contributes to its quality. Parabolic reflector antennas: The best parabolic reflector antenna is the one that has a smooth surface, an edge made of iron ore and a similar U surface edge throughout the dish. If the dish is made of woven cables or aluminium, it should have a small hole to reduce the loss of waves. Wire antennas: The quality of these antennas, especially loop antennas, E depends on the size of its loop. An antenna with a larger circumference is N better than the one with a smaller circumference. Array antennas: The quality of the array antenna especially the Yagi- LI Uda antenna, depends on the length of its boom. That length provides an opportunity to have many pieces of metal forming it. These pieces give N these antennas the ability to capture even weak signals. See Figure 8. O Pieces of metal R FO Figure 8: A pair of Yagi-Uda antennas showing the difference in the length of boom 43 SCIENCE AND TECHNOLOGY STD 7.indd 43 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE (b) The transmitting frequencies The quality of the antenna can also be measured based on the frequency of the waves. The unit for measuring frequency is Hertz (Hz). For example, both horn and Yagi-Uda antennas can receive and transmit high frequency waves with more than one gigahertz (GHz) equal to 109 Hz or one billion Hz. However, horn antennas are more efficient because they transmit straight waves in longer distances while Yagi-Uda waves spread. The Yagi-Uda antenna is more efficient than the loop antenna because it can capture even the weakest signals. Thus, it is preferred to transmit LY and receive “FM” radio waves and long-distance television broadcasts between 88.1 to 108.1 MHz. N (c) Antenna efficiency The choice of the antenna depends on its efficiency and the task it O performs, such as transmitting and receiving waves. Considering this criterion, the horn antenna is better than other antennas because it can transmit and receive waves from a distance. However, this antenna cannot SE receive many waves, especially weak ones. The ability to receive waves is enhanced by connecting the horn antenna with the parabolic reflector antenna. These antennas are mostly used in satellite communications, U weather forecasting, and space observations. Fabrication of antennas E Antenna fabrication involves the following steps: N (a) Identify the use of the antenna Antennas are made depending on their use. They can be designed to LI receive waves, transmit waves, or both. For example, the antenna for receiving radio waves is different from the radar antenna. N (b) Select the type of the antenna O After identifying its use, you can select the most suitable type of the antenna. The choice also depends on the efficiency and position to put R the antenna. FO (c) Antenna design This is a stage in which an antennas sketch is designed. The antenna sketch guides you through fabricating the antenna. When designing an antenna, such as the Yagi-Uda antenna, you should know that it has two 44 SCIENCE AND TECHNOLOGY STD 7.indd 44 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE main parts. Those parts are the element and the boom. The elements are of three types: reflector, driven element, and directors. The reflector is behind the antenna, followed by the driven element and then the directors. The director element is installed in front of the driven element to get the direction of the broadcasting station. The driven element is the part where the dipoles are often folded. The feeder receives waves and transmits them to the television or radio via wire. These elements help each other to capture electromagnetic waves. The antenna’s boom is directed to the source of the waves as shown in Figure 4. LY (d) Selecting materials N Antenna fabricating materials should be capable of conducting electricity and resisting rust. They should also be durable. Thus, antennas are made O using metals such as copper, aluminium, and stainless steel. Copper is preferred when fabricating antennas because it allows the flow SE of electricity more easily. However, most antennas are not made of copper because of its high cost and weight. Aluminium is mostly suitable for fabricating antennas because it is light and rust resistant. Thin stainless U steel wires are also suitable for fabricating antennas due to their high strength. Stainless steel wires are mostly used to create mobile whip antennas where strength and flexibility are needed due to the motion of the vehicle. These wires are not used in fabricating normal antennas used E in homes due to their poor ability of conducting electricity. N (e) Making an antenna LI After you have a sketch and all the required materials for your antenna, you can make your antenna. Follow the next activity to create the Yagi- N Uda antenna by studying Figure 9. O Activity 2: Making an antenna using materials available in the surrounding R Materials: wire, a piece of board or bamboo, straight dry poles, screws, glue, pegs and the pieces of aluminium or devices with the FO characteristics mentioned in the material selection section, as well as the device to receive communications such as a radio or television 45 SCIENCE AND TECHNOLOGY STD 7.indd 45 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Steps: 1. Cut four pieces of aluminium based on the dimensions shown in Figure 9. 2. Tie the pieces of aluminium to the boom by leaving spaces between the pieces based on the dimensions shown in the antenna diagram. 69 cm 60 cm 67.5 cm LY 30 cm 18.75 cm 52.5 cm 84 cm N O Boom Director elements Driven element Reflector SE Figure 9: Measurement for making the Yagi-Uda antenna 3. From the materials you have, take two insulated wires. If you have U a large cable with three wires inside, remove the outer plastic. Do not peel the plastic of the inner wire. Use two wires with a plastic cover. Insert the wires in the space between the reflector and the E driven element and glue them together. Make sure the wires reach N the driven element for connecting. 4. Connect the wires to the driven element at Points A and B as shown LI in Figure 10. Connect the other end of the wire to the “Bayonet Neill Concelman” (BNC) connector which is connected to a communication N device such as a television. O Antenna A B R FO BNC Figure 10: The Yagi-Uda antenna 46 SCIENCE AND TECHNOLOGY STD 7.indd 46 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE 5. After completing Step 4, drill a 10 mm hole in the antenna’s boom. Connect the boom to the straight dry pole using a 10 mm bolt as shown in Figure 11. At this point, your Yagi-Uda antenna will be ready for use. Antenna LY N Television Cable O Figure 11: The appearance of an antenna connected to a television Exercise 3 SE U Answer the following questions: 1. Name three characteristics of the materials used to make the antenna. 2. Why is aluminium used more than copper in fabricating antennas? E 3. Why are the director elements fixed at the front part of the Yagi-Uda N antenna? LI Uses of antennas N Antennas are used in various communication systems. Some of the uses of antennas are O (a) capturing and transmitting electromagnetic waves, such as television broadcasting, radio communications, radar, and space communications; (b) providing underwater communication or through the ground at short R range frequencies; FO (c) transmitting and receiving communication waves on ships, aeroplanes, satellites, cell phones, rockets, radios, televisions, radar and radio calls; (d) capturing weather forecast indicators; and (e) enabling a global location reporting system. 47 SCIENCE AND TECHNOLOGY STD 7.indd 47 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Exercise 4 Answer all questions in Sections A and B. Section A Choose the most correct answer and write its letter in the box provided. 1. Which of the following is the best antenna for capturing weather forecasting signals? (a) Microstrip antenna (b) Yagi-Uda antenna LY (c) Parabolic reflector antenna (d) Loop antenna 2. Which of the following antennas can effectively protect itself from N noise? (a) Microstrip antenna O (b) Yagi-Uda antenna (c) Parabolic reflector antenna (d) Loop antenna (a) May communicate without antennas SE 3. Which of the following is correct about wireless communication devices? (b) Cannot communicate without antennas U (c) Can communicate with un-directional antennas (d) Cannot communicate without a loop antenna 4. The microstrip antenna is commonly used on one of the following pairs of devices: E (a) satellites and dishes N (b) radio receivers and ships (c) cell phones and aeroplanes LI (d) televisions and mobile phones 5. Which of the following are the two main components of the Yagi-Uda N antenna? (a) Antenna’s elements and director elements O (b) Antenna’s boom and director elements (c) Antenna’s elements and antenna’s boom (d) The reflector element and the director element R 6. Which of the following materials is effective for antennas due to its ability to conduct electricity? FO (a) Copper (b) Stainless steel (c) Aluminium (d) Wood 48 SCIENCE AND TECHNOLOGY STD 7.indd 48 26/07/2021 12:00  FOR ONLINE USE ONLY DO NOT DUPLICATE Section B 7. Name four communication devices that use antennas. 8. Where can antennas be used apart from radio broadcasting stations and marine or air transport vessels? 9. Which type of antennas is used on mobile phones? 10. List the types of antennas that can be used on a television. 11. Explain three advantages of using the parabolic reflector antenna. LY Vocabulary Circuit a connection of components that can conduct electric current N Communications device any type of device capable of transmitting data, instructions, and information between a sending O device and a receiving device Communication system a model describing a communication exchange between two stations, transmitter and receiver Electromagnetic wave SE waves that are created as a result of vibrations between an electric field and a magnetic field Element is a metallic conductor connected to the boom U Meteorological station a station where regular observations of atmospheric conditions are made Radar a device for detecting the presence, direction, E distance, and speed of aircraft, ship, and other objects, by sending out pulses of radio waves N which are reflected off the object back to the source LI Radio wave an electromagnetic wave having a wavelength between 1 millimeter and 30,000 meters, or a N frequency between 10 kilohertz and 300,000 megahertz O Signal an electrical or electromagnetic current that is used for carrying data from one device to another R Sound wave mechanical wave that results from the back and forth vibration of the particles of the medium FO through which the sound wave is moving Waves disturbance that travels through a medium, transporting energy from one location to another location without transporting matter 49 SCIENCE AND TECHNOLOGY STD 7.indd 49 26/07/2021 12:00