Microwave Communication Fundamentals PDF

HOME WHAT IS MICROWAVE? MICROWAVE GENERATION FUNDAMENTALS OF MICROWAVE COMMUNICATION SYSTEM Ms. Chloe Laserna, ECT  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Electromagnetic waves with frequencies ranging from 3 G...

HOME WHAT IS MICROWAVE? MICROWAVE GENERATION FUNDAMENTALS OF MICROWAVE COMMUNICATION SYSTEM Ms. Chloe Laserna, ECT  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Electromagnetic waves with frequencies ranging from 3 GHz to 300 GHz. Wavelength is in the order of 10 cm to 1mm – something in between light waves and radio waves. So, it is also known as millimeter waves. The term “micro” refers to the tinyness of the wavelength. Microwaves behave more like rays of light than ordinary radio waves. Dueto this unique behavior, microwave frequencies are classified separately from radio waves.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Frequency Bands  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Frequency Bands  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Characteristics Microwaves follow a straight path. It is designed to provide a signal connection between two specific points. Also coined as: -Line-of-Sight or LOS communications, - Radio Link - Point-to-Point communications  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Advantages Small antenna size. A 1% bandwidth provides more frequency range at microwave frequencies than that of HF. There is much less background noise at microwave frequencies than at RF.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Advantages Microwave systems do not require a right-of-way acquisition between stations. Underground facilities are minimized Increased reliability and less maintenance.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Disadvantages Requires no obstacle present in the transmission path The cost of implementing the communication infrastructure high. Microwaves are susceptible to rain and snow. Complicated electronics circuitry is being used.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Disadvantages Distance of operation is limited by line-of-sight (LOS) Microwave signals are easily blocked.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Generation The operation of conventional vacuum tubes and solid- state devices is limited by transit time, Inter-electrode capacitance, and lead inductance effects. Thus, the development of new devices was essential to exploit the microwave frequency region. Fortunately, several new principles of operations, such as velocity modulation, the interaction of electrons with electromagnetic fields, transferred electron techniques, etc. have enabled the generation of microwaves. HOME WHAT IS MICROWAVE? MICROWAVE GENERATION MICROWAVE GENERATION MICROWAVE TUBES KLYSTRON MAGNETRON TRAVELLING WAVE TUBE  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION Microwave Tubes Tubes generate and amplify high levels of microwave power more cheaply than solid-state devices. Klystron Tube Types of Klystron tube Reflex Klystron 2-Cavity Multi-cavity  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION KLYSTRON TUBES Used as an oscillator or high-power amplifiers. It makes use of velocity modulation and electron transit time. Electron beam moves down tube past several cavities. Input cavity isthe buncher,output cavity is the catcher. Buncher modulates the velocity of the electron beam. Electric field from microwaves at buncher alternately speeds and slows electron beam This causes electrons to bunch up Electron bunches at catcher induce microwaves with more energy.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION USES OF KLYSTRON TUBES Klystron tubes are primarily used in applications requiring high-power microwave amplification. These include: Radar Systems- Klystrons are used in radar systems for both military and civilian purposes. They generate the powerful microwave signals required for radar detection and tracking. Telecommunications- They are employed in satellite communication systems to amplify microwave signals before transmission.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION USES OF KLYSTRON TUBES Particle Accelerators- Klystrons are used in particle accelerators to provide the high-power radio frequency (RF) energy needed to accelerate charged particles. Broadcasting- High-power television transmitters use klystrons to amplify the signals for broadcasting. Medical Equipment- In certain types of medical linear accelerators (linacs) used in radiation therapy, klystrons amplify the microwave energy needed to accelerate electrons.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION KLYSTRON TUBES  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION HOW KLYSTRON TUBES WORKS? Electron Gun - The klystron tube starts with an electron gun, which produces a stream of electrons. This stream is directed into a vacuum tube. Bunching Cavity - The electrons first pass through a "bunching cavity," which is an area in the tube where the electric fields oscillate at the desired frequency. These oscillations cause the electrons to bunch together at certain points. Drift Space - After leaving the bunching cavity, the electrons travel through a "drift space." In this region, the bunched electrons continue to move together because of their inertia.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION HOW KLYSTRON TUBES WORKS? Output Cavity - The bunched electrons then enter the "output cavity." As they pass through this cavity, their kinetic energy is transferred to the cavity, creating an amplified microwave signal. Collector - Finally, the electrons are collected at the end of the tube, and the amplified signal is extracted from the output cavity.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION MAGNETRONS High-power oscillator Common in radar and microwave ovens. The cathode is in the center, and the anode around outside A strong DC magnetic field around the tube causes electrons from the cathode to spiral as they move toward the anode The current of electrons generates microwaves in cavities around the outside.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION USES OF MAGNETRONS Magnetrons are devices that generate microwave radiation and are used in a variety of applications, including: Microwave Ovens - The most common use of magnetrons is in microwave ovens, where they generate the microwaves that cook food by heating water molecules within it. Radar Systems - Magnetrons are used in radar systems to generate the high-power microwave pulses required for detecting objects and determining their speed and distance.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION USES OF MAGNETRONS Industrial Heating - In industrial applications, magnetrons are used for processes like drying, curing, and melting materials, where microwave energy can be used for efficient heating. Medical Equipment - Magnetrons are employed in some types of medical devices, particularly in cancer treatment for hyperthermia therapy, where localized heating of tissues is required. Plasma Generation - In scientific research, magnetrons are used to generate plasma for various experimental purposes.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION MAGNETRONS  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION HOW MAGNETRONS WORKS? Cathode and Anode - At the center of the magnetron is a cylindrical cathode (negative electrode) surrounded by a coaxial anode (positive electrode). The anode has resonant cavities cut into it, which are crucial for generating microwaves. Magnetic Field - A strong magnetic field is applied perpendicular to the plane of the electron flow (from cathode to anode). This magnetic field causes the electrons emitted from the cathode to spiral outward toward the anode rather than moving directly.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION HOW MAGNETRONS WORKS? Electron Motion and Cavity Resonance - As the electrons spiral around due to the magnetic field, they pass by the resonant cavities in the anode. The movement of the electrons induces oscillating electric fields within these cavities, and these oscillations are at microwave frequencies. Bunching of Electrons - The oscillating fields within the cavities cause the electrons to bunch together at specific points in their circular path. This bunching of electrons enhances the oscillation of the fields in the cavities, effectively amplifying the microwave signal.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION HOW MAGNETRONS WORKS? Microwave Output - The energy generated in the resonant cavities is then extracted as microwave radiation through a waveguide or antenna. This microwave energy is what is used in various applications, such as heating food in a microwave oven or generating radar pulses. Collector - After the microwaves are generated, the remaining electrons are collected, and the process continues with new electrons being emitted from the cathode.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION TRAVELLING WAVE TUBE (TWT) Generates frequency in the range of 0.5 GHz to 95 GHz. It has high gain, high power, larger bandwidth & low noise. Used as low noise amplifier in microwave receivers, repeaters, communication satellites, and RADAR (airborne, shipborne & ground-based). Uses a helix as a slow-wave structure. Because of the helix, electrons interact longer with the electric field. Hence, it produces high continuous power of 2-5 KW and large bandwidth. Microwaves input at the cathode end of the helix, output at the anode end Energy is transferred from electron beams to microwaves.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION USES OF TRAVELLING WAVE TUBE (TWT) Traveling Wave Tubes (TWTs) are widely used in applications requiring high-power amplification of microwave and radiofrequency (RF) signals. These include: Satellite Communications - TWTs are commonly used in the transponders of communication satellites to amplify uplink signals before they are downlinked to Earth. Radar Systems - TWTs are used in radar systems, particularly in airborne radars, where high power and wide bandwidth are essential for detecting and tracking targets.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION USES OF TRAVELLING WAVE TUBE (TWT) Electronic Warfare - TWTs are used in electronic warfare systems for jamming and deception, as they can amplify and transmit a wide range of frequencies at high power levels. Scientific Research - In particle accelerators and other research applications, TWTs are used to amplify RF signals that drive the acceleration of particles. Broadcasting - TWTs are used in television transmitters and other broadcasting equipment to amplify the signal before transmission.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION TRAVELLING WAVE TUBE (TWT)  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION TRAVELLING WAVE TUBE (TWT) Electron Gun - The TWT begins with an electron gun that emits a beam of electrons. These electrons are accelerated and directed into a vacuum tube. RF Input - The RF signal that needs to be amplified is fed into the TWT. This signal is introduced into a helical structure (slow- wave structure) that runs along the length of the tube.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION TRAVELLING WAVE TUBE (TWT) Helix or Slow-Wave Structure - The helix is a coiled wire that acts as a slow-wave structure, allowing the RF signal to travel at a slower phase velocity, close to the speed of the electron beam. This slow- wave structure ensures that the RF signal can interact with the electron beam over an extended distance. Interaction between Electrons and RF Field - As the electron beam travels through the tube, it interacts with the RF field in the helix. The electric fields of the RF signal cause the electrons to bunch together and transfer their kinetic energy to the RF signal. This process amplifies the RF signal as it travels down the tube.  HOME WHAT IS MICROWAVE? MICROWAVE GENERATION TRAVELLING WAVE TUBE (TWT) RF Output - The amplified RF signal is then extracted from the end of the helix and fed out of the tube as the output signal. Collector - After transferring energy to the RF signal, the spent electrons are collected at the end of the tube. This collector is often designed to dissipate the heat generated by the high- energy electrons. HOME Microwave Transmission Microwave Transmission Two-wire transmission line used in conventional circuits is inefficient at microwave frequencies. The most common transmission lines are coaxial cable, microstrip lines, and waveguides. Microwave Transmission Coaxial Cable Consists of inner conducting wire made of copper, over this conducting wire the coating of polyethylene or Teflon material is carried out. Then it is enclosed in the braded wire in the shape of mesh. The outer surface of this wire is enclosed in a plastic jacket. Coaxial Cable-Merits The possibility of external interference is minimized & output at the load end will be less noised. It is used for high frequency transmission. The conductor is protected from dust, rust etc due to proper insulation. Coaxial Cable-Demerits Costly than two wire line. Complex design Handles low power transmissions. Microwave Transmission Microstripline A micro strip line is simply a copper track running on a side of the PCB while the other side is the ground plane. There is thick coat of insulating material over the copper plate which is made of fiber glass or polystyrene. This insulator works as a dielectric in micro strip line. At the top of the insulated plate one or more than one strip of the best conducting material are plated which is made of gold, aluminum etc. Microstripline-Merits Very high frequency. Small size Low weight Losses are minimum. Used in IC’s where the distance between source and load is very short. Microstripline-Demerits Costly than coaxial. Cannot be used when the distance between source and load is long. Cannot be used in twisty path. Microwave Transmission Waveguide A Hollow metallic tube of uniform cross section for transmitting electromagnetic waves by successive reflections from the inner conducting layered walls of the tube is called waveguide. At microwave frequencies (above 1GHz to 100 GHz) the losses in the two line transmission system will be very high and hence it cannot be used at those frequencies. Hence microwave signals are propagated through the waveguides in order to minimize the losses. Waveguide Two types of Waveguide: a) Rectangular & b) Circular Waveguide Waveguides are generally used to couple transmitter power to antenna and microwave signal from antenna to receiver. Dimensions of the waveguide determines the operating frequency range. Microstripline-Merits Large surface area Low losses Better power handling capability Microstripline-Demerits Size Difficult to install because of its rigid structure. Costly Microwave Transmission Microwave Antenna The antenna is a passive device that radiate or receive the modulated signal. Itis fed by direct connect of the RF unit, coaxial cable, or waveguides at higher frequencies. In two-way communication, the same antenna can be used for transmission and reception. Types of antenna; Horn Antenna, Parabolic Dish Antenna, Slot Antenna, Microstrip-patch or Printed Antenna Microwave Antenna Horn Antenna Parabolic Dish Antenna Microwave Antenna Slot Antenna Microstrip-patch or Printed Antenna Horn Antenna Horn antennas are widely used for transmitting and receiving microwave signals. The shape of the antenna resembles a horn. It functions as a waveguide to direct electromagnetic waves. Waves are radiated into free space through the open end (aperture). Horn Antenna Horn antenna is a directional antenna efficient in radiating and receiving microwave signals It transitions from a waveguide to free space, focusing energy in a specific direction and achieving high gain Simple design and effective performance make it a popular choice for high-frequency communication and measurement applications Parabolic Dish Antenna Parabolic dish antenna is a directional antenna using a parabolic reflector to focus electromagnetic waves. Widely used for high gain and narrow beamwidth applications like satellite communication and radar. Commonly used in radio telescopes and television broadcasting. Parabolic Dish Antenna A parabolic dish antenna is a high-gain, highly directional antenna. It uses a parabolic reflector to focus and direct electromagnetic waves. Ideal for long-distance communication like satellite links, radar, and radio astronomy. Its precise shape ensures that signals are focused at the antenna's focal point for efficient transmission and reception. Slot Antenna A slot antenna is a type of antenna with a narrow rectangular slot in a metal surface. The slot in the metal surface functions as the radiating element, like a dipole antenna. Slot antennas are preferred for applications requiring a low-profile, durable, and planar antenna design. Slot Antenna Slot antennas use a slot cut into a metal surface as the radiating element. They function similarly to dipole antennas but with the radiating element as the slot. Slot antennas are low-profile, durable, and versatile. Suitable for radar, communications, and broadcasting applications. Popular due to its simple construction and predictable radiation patterns. Microstrip-patch or Printed Antenna A microstrip patch antenna, also called a printed antenna, uses a flat, rectangular metal patch on a dielectric substrate. It is backed by a metal ground plane and is compact, lightweight, and low-profile. Widely used in applications like mobile devices, GPS units, and satellite communication systems. Microstrip-patch or Printed Antenna A microstrip patch antenna uses a flat metal patch on a dielectric substrate for radiation. Known for being low profile, lightweight, and easy to integrate. Commonly used in modern communication systems like mobile phones, satellite communication, and wireless networks. Although they have narrow bandwidth, their design flexibility and compact form make them versatile for various applications. HOME THANK YOU!!!!