Radio Wave Propagation PDF

Principles of Communications RADIO WAVE PROPAGATION BS Electrical Engineering Engr. Christopher V. Maglaque, PECE, MEM Associate Professor 3  Radio Wave Propagation the transmission of electromagnetic waves in free space. Radio Wave AM and FM systems are commonly...

Principles of Communications RADIO WAVE PROPAGATION BS Electrical Engineering Engr. Christopher V. Maglaque, PECE, MEM Associate Professor 3  Radio Wave Propagation the transmission of electromagnetic waves in free space. Radio Wave AM and FM systems are commonly used in wireless Propagation communication to transfer information over long distances  AM Transmitter Block Diagram A simple transmitter can be made by an oscillator connected to an antenna. The oscillator is the one that produces the high frequency carrier then fed to an antenna to radiate it in free space. However, a more practical block diagram of a high-level AM transmitter is shown in Figure 1. Radio Wave Propagation Figure 1: Block diagram of a transmitter circuit  Definition of Terms: Microphone. A device that converts the acoustical signal into an electrical signal so that it can be processed by the succeeding electronic circuits of the transmitter. Audio Amplifier. A linear amplifier that increases the signal level of the audio frequency signal. Carrier Oscillator. A circuit that produces a constant peak high- Radio Wave frequency carrier signal. Propagation Modulation Amplifier. A class B/AB amplifier increases the amplitude of the modulating signal. Driver. A linear amplifier that increases the voltage level of the carrier or modulating signal. Final Power Amplifier. A highly efficient amplifier (class C) is designed to significantly increase the power of the modulated carrier signal in preparation for transmission. Antenna. A passive device that is capable of radiating electromagnetic waves.  FM Transmitter Block Diagram Figure 2 shows a typical block diagram of FM/PM transmitter. The parts are almost similar to AM transmitter, but the modulation process is different. A stable crystal oscillator is used to generate the carrier frequency at HF range. For VHF and UHF range, a frequency multiplier is used together with the crystal oscillator. Frequency multipliers can increase the frequency up to 5x of the fundamental frequency. The frequency multiplier also Radio Wave increases the frequency deviation of the modulating signal because Propagation it affects the modulation index of FM. Figure 2: Block diagram of FM Transmitter  Characteristics of Electromagnetic Waves Previous slides have stated that electromagnetic waves can be radiated by an antenna and will propagate through free space. With enough transmit power, the radiated electromagnetic waves would reach the receiving antenna. Radio Wave Propagation Since the signal is unguided (wireless) once it is radiated by the antenna, the electromagnetic waves are affected by several factors such as atmospheric conditions, time of the day, frequency of the wave, trees, buildings, and other tall structures that would hinder the propagation of the electromagnetic waves.  Optical Characteristics of Radio Waves 1. Reflection Radio wave reflection is the same as the principle of light Radio Wave wave reflection. Propagation The angle of reflection is equal to the angle of incidence. A radio wave striking a perfect conductor surface would reflect all the incident waves. A radio wave striking a poor conductor surface would absorb some of the wave energy.  1. Reflection Radio Wave Propagation Figure 3: Diagram of Radio wave Reflection  2. Refraction Refraction is the bending of radio waves. The degree of bending depends on the index of refraction of the medium. Radio Wave Propagation Figure 4: Illustration of radio wave refraction  3. Diffraction Radio Wave Diffraction is the bending of waves around the object and is based on “Huygen’s principle”. Propagation When the radio wave encounters an obstacle, some of the signals are blocked which creates a “shadow zone”  3. Diffraction Referring to Figure 5: Illustration of Radio wave diffraction, the receiver located at the shadow zone would not receive the complete signal. Radio Wave Propagation  Types of Radio Wave Propagation 1. Ground Wave It is also known as a surface wave. Ground waves follow the Earth’s curvature when propagating through free space as shown in Figure 6. Radio Wave Propagation Figure 6: Ground Wave Propagation  1. Ground Wave Radio signals that have a frequency of 30 kHz to 3 Mhz are ground waves. (LF to MF band) Radio Wave The propagation of ground waves depends on the conductivity of Propagation the Earth’s surface. The ground wave propagates best at saltwater and poorest at low moisture surfaces such as dessert.  2. Sky Wave These are waves that go into the ionosphere and bent back to the destination point. The direction and angle of the bending of the waves depend on the level of ionization of the layers and are determined by Snell’s law. Figure 7 shows that the amount of refraction of sky waves Radio Wave depends on the layer of the ionosphere. Propagation Figure 7: Sky wave propagation  2. Sky Wave It can be observed that angle of refraction decreases as the sky wave reaches the higher layer of the ionosphere. The higher the frequency, the smaller the radiation angle required for refraction to occur. Frequencies 3 Mhz to 30 Mhz usually are sky waves. Radio Wave Sky wave can go through several skips or hops. It can reach up to 20 Propagation skips before the sky wave reaches the receiver. Skip or hop is the bouncing of the sky wave back to the ionosphere after it hits the Earth’s surface for the first time. A single hop or skip can reach up to 2000 mi. Skip zone is the area wherein there are no signal during sky wave propagation.  2. Sky Wave Radio Wave Propagation Figure 7: Sky wave propagation  3. Space Wave Space wave propagate through free space by means of “Line of Sight” (LOS). Commonly used by VHF and UHF spectrum. Space wave travels in a straight line from the transmitter to the Radio Wave receiver antenna. Propagation Figure 8: Space wave propagation  3. Space Wave The distance between the transmitting antenna and the horizon is: 𝑑=√2ℎ Where: 𝑑−ℎ𝑜𝑟𝑖𝑧𝑜𝑛 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 in miles ℎ−ℎ𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑛𝑡𝑒𝑛𝑛𝑎 𝑖𝑛 𝑓𝑒𝑒𝑡 Radio Wave d is also called “horizon distance” Propagation For more practical distance, the distance between transmitter and receiver is equal to: 𝐷=√(2ℎ𝑡 )+√(2ℎ𝑟 ) Where: 𝐷−𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑟 𝑎𝑛𝑑 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑟 𝑎𝑛𝑡𝑒𝑛𝑛𝑎 𝑖𝑛 𝑚𝑖𝑙𝑒𝑠 ℎ𝑡−ℎ𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑟 𝑎𝑛𝑡𝑒𝑛𝑛𝑎 𝑖𝑛 𝑓𝑒𝑒𝑡 ℎ𝑟−ℎ𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑟 𝑎𝑛𝑡𝑒𝑛𝑛𝑎 𝑖𝑛 𝑓𝑒𝑒𝑡  Problems in Radio Wave Propagation 1. Fading It is the variation in signal amplitude at the receiver end due the characteristic of the signal path. Fading causes the signal to have smaller amplitude because of Radio Wave the condition of the signal path. Propagation Factors that causes fading: a. Variation in distance between transmitter and antenna b. Change in environmental characteristics c. Presence of multi path signal d. Relative motion between receiver and transmitter. Fading can be also cause of the obstacle between transmitter and receiver. It is called “shadow fading”.  Problems in Radio Wave Propagation 2. Multipath It is also called “Rayleigh Fading”. Because of the optical properties of radio wave, a signal Radio Wave radiated by a non-directional antenna can go on several path. Propagation Some signal goes straight path, some are reflected, and some are refracted. This causes the signal to be received at the different times resulting to a weaker signal. This signal arrives at the receiver at different phase angle that also cause the decrease magnitude of signal power. Radio Wave Propagation QUESTIONS??? Radio Wave THANK YOU & GOD BLESS Propagation STAY SAFE!!!