Microwave Transmission

Process of sending and receiving data using microwave signals. It is the use of microwave signals to transmit data, voice, television, telephone, and radio signals. For point-to-point communications, microwaves are frequently utilized. The electromagnetic spectrum includes microwaves. Their wavelengths range from 1 mm to 30 cm, and their frequency spans from 300 MHz to 300 GHz. Microwave transmission is the process of sending and receiving data by microwaves. Microwaves are classified as wireless or unguided transmission media.

• A microwave relay network is created by the repeaters.
• However, because to their high cost, these systems are only utilized in specific tasks.
• Wireless networks and broadcast satellites are examples of technology that provide radio and television straight to consumers' homes.
• Wireless power transmission is another application for microwaves.

Features

• It is the wave that radiates electromagnetic energy with a shorter wavelength.
• Microwave links consist of a Transmitting station (Tx), a Relay station or Repeaters (RPT), and a Receiving station (Rx).
• Microwaves travel in straight lines, so stations should be aligned to each other.
• Microwave links require clear LOS (line of sight), so antennas are installed high up to avoid the interference of obstacles in their path.
• Microwaves do not pass through buildings, thus reducing the efficiency of inside receivers.
• Highly directional, but can serve multiple receivers using proper setup
• Repeaters are added to boost the power of the signal so that it can travel a longer distance.
• Microwaves can be refracted by atmospheric layers, causing slight delay compared to direct signals.

General Properties

• Configuration: Arrangement and Setting of Transmission equipment such as antennas, towers, and whole network design is known as configuration.
• Bandwidth: It is a measure of the width of the frequency range. It determines the rate of data transfer.
• Error: Due to interference and obstacles disruptions occur in data transmission. These inaccuracies are known as errors.
• Performance: In microwave transmission, the successful transmission of data in terms of speed, latency, and reliability is known as performance.
• Distance: The maximum span over which microwaves can effectively transmit data without weakening of signals is known as distance.
• Security: Protection of data from unauthorized access or interception in microwave transmission is known as security.
• Cost: The financial investment required for maintaining a microwave transmission system, including equipment, licensing, and operational expenses is known as cost.

Process

• At first, the signal to be transmitted (baseband signal ) is processed or encoded at the transmitting station.
• Then it is used to modulate an intermediate carrier of 70 MHz or 140 MHz .
• Then the modulated signal is up-converted to microwave frequency.
• Then it is amplified before being fed to the antenna for radiation.
• Repeaters placed at several points are used to boost the power of the signal.
• Repeaters can be of two types: Active and passive repeaters.

• Passive repeater: Uses reflectors or antennas to redirect the signal around obstacles without amplification.
• Active repeater: Includes an amplifier for boosting the signal strength. They also have frequency translation circuits to change the frequency of the signal before retransmitting it.

• At the receiving stations, the signal is down-converted to 70 MHz or 140 MHz.
• Then it is demodulated to recover the baseband signal.

Antennas Used for Microwave Transmission

Antennas can be defined as a transducer between guided and unguided media. It transforms energy between free space and a guided media such as cable or waveguide.

Antennas can be divided further as :

• Parabolic Dish Antenna: They are used at the receiving end of the transmission link. They are parabolic in shape. They permit the greatest focus of energy possible in a single beam. Parabolic Antennas are highly directional.

• Horn Antenna: It is a radiating element in the shape of a horn with a stem. Its one end is flared out to improve the efficiency. It is less directional compared to parabolic antennas.

Advantages

• Cheaper compared to wired communication (such as optical fiber) in certain terrains
• Supports larger Bandwidth so more information is transmitted.
• They are used for point-to-point communication.
• Antenna size gets reduced as the frequency is higher.
• Does not require any land for the installation of cables.
• Easy communication over rugged terrain.
• Communication over oceans is also possible.

Disadvantages

• The cost of equipment or installation cost is high.
• Susceptible to weather conditions.
• Eavesdropping
• Operates in the frequency range of 300 MHz to 300 GHz

Applications

• Bluetooth: In Bluetooth, Communication is done through Ultra high frequency (UHF) radio waves .
• Wi-Fi: In Wi-fi , data is transferred using microwave.
• Direct broadcast satellites: Since microwaves are able to pass through the atmosphere layer so communication is done through satellites
• GPS: In order to locate the positions, microwaves are used.
• FM Radio: Microwave links are used in backbone communication to support radio broadcasting networks.
• Satellite T.V: Since microwaves are able to pass through the atmosphere layer so the information passes from Tv to satellite and vice versa.

Types

Microwave Transmission can be of two types:

• Terrestrial Transmission
• Satellite Transmission

Terrestrial Transmission

• They cannot pass through any obstacle.
• They use directional parabolic antenna.
• Signals are highly focused.
• Line of Sight transmission is needed i.e. their path should be free of any sort of obstacle.
• For long-distance transmission signal strength weakens.
• Repeaters are used for every 35-40 km as such.

Advantages

• They are used to carry thousands of voice channels at the same time.
• Data Transmission rate of 16 Gbps.

Disadvantages

• Installation cost is high.
• Maintaining a LOS or obstacle-free path for a long distance is a difficult task.
• EMI effect and jamming affect the signal strength.

Applications

• Used in mobile networks to connect base stations for voice and data transmission.
• Enables long-distance voice communication through microwave links between switching centers.
• Transmits TV signals between studios, relay towers, and broadcasting stations.

Satellite Transmission

• A microwave relay station is placed in space in the form of a satellite.
• A satellite is launched by a rocket or space shuttle.
• Satellite is precisely positioned 36,000 km above.
• Orbit speed matches Earth's rotation speed.
• A satellite is stationary relative to Earth.

Advantages

• Single microwave relay station visible from any point in a large area.
• Transmission and reception costs are independent of the distance between the 2 points.
• The transmitting station can receive back its transmission and check whether the satellite transmitted information correctly.

Disadvantages

• High cost of placing a satellite in orbit.
• The signal is sent to satellite broadcast to all receivers in satellite range.
• Security measures are required to prevent unauthorized tampering of information.

Applications

• Used for Broadcasting and receiving signals.
• Provide internet connectivity in remote and rural areas where wired networks are not feasible.
• Monitors weather conditions, storm tracking, and climate analysis.

Microwave Propagation and Path Losses

When the signal propagates even a slight directional LOS link's beam can cause losses in Transmission. These losses are known as path losses.

• Free Space Path Loss (FSL): Loss due to signal spreading in free space; increases with distance and frequency.
• Atmospheric absorption: Both oxygen and water vapor present in the air attenuate the microwave signals. When the link length increases the loss increases.
• Diffraction: Diffraction is yet another cause of path losses.

Path Reliability in Microwave Transmission

Considering all the path loss factors, we can quantify path reliability, also known as path availability. Due to poor propagation conditions, the path fails to perform and data transmitted from one end is not successfully received at the other end. So Path availability is a measurement of the path's ability to reliably communicate data over year.

Path's performance can typically be improved by :

• Increasing overall system gain by increasing power.
• Reducing losses in transmission lines.
• Increasing the size of the Antenna itself.