What is Microwave Communication System : Working, Advantages and Disadvantages

Microwave communication system is a wireless system which uses high frequency electromagnetic waves to transmit voice, video, and data over long distances through line of sight (LOS) links, typically in the frequency range of 1 GHz to 100 GHz. It is widely used in telecommunications, satellite systems and wireless backhaul networks. Advantages include high bandwidth and fast deployment, while disadvantages include weather sensitivity and strict alignment requirements.

Microwave Communication System Block Diagram and Working

There are different transmission methods such as satellite, fiber optic communication and coaxible cable based transmission. Microwave based communication system is alternative method. Frequencies ranging from 1 GHz to 30 GHz are classified as Microwaves. These microwave frequencies have wavelengths measured in centimeters. The microwave band is further divided into UHF, SHF, EHF, and others. It occupies the upper portion of the radio frequency spectrum.

Microwave communication system consists of two parts viz. transmitter and receiver. The transmitter consists of information source, multiplexer, baseband processing, microwave up-converter, rf power amplifier and directional antenna. The receiver consists of directional antenna, low noise amplifier (LNA), microwave down-converter, baseband processing, demultiplexer and information retrieval.

Microwave communication system generally requires clear line of sight, proper antenna alignment and fresnel zone clearance.

Microwave Transmitter Part

• The information source generates message signal to be transmitted which can be voice, video, data, internet traffic, television signals etc. This information exists initially in electrical form.
• The next block is multiplexer which combines several low speed signals into high speed composite signal before transmission. By combining multiple input signals multiplexer improves bandwidth utilization.
• Baseband processing unit various operations. Major ones include source encoding, error correction coding, digital modulation (BPSK, QPSK, 16-QAM, 64-QAM, 256-QAM) and signal formatting (packet or frame formation).
• Up converter converts process electrical signal into high frequency microwave signal suitable for transmission. It generates modulated RF frequency from input IF/baseband signal and locally generated carrier frequency.
• RF Power Amplifier increases microwave signal power before feeding it to the transmitting antenna. Common amplifier technologies include SSPA and TWTA.
• Directional antenna converts electrical RF energy into electromagnetic microwave waves. The common antenna types used are parabolic dish antennas and horn antennas as they provide high gain, narrow beamwidth and excellent directivity.

Channel

The communication channel is the atmosphere through which microwave signals propagate. The propagation can be affected by rain attenuation, fog, snow, atmospheric absorption, multiple fading etc. Typically terrestrial microwave links cover approximately about 30-50 Kms before requiring repeaters, which depends on terrain, frequency and system link budget design.

Microwave Receiver Part

• At the other end, receiving antenna captures microwave signal in the form of electromagnetic waves. It converts these waves into electrical RF signals.
• The received microwave signal is usually very weak and requires amplification to boost. LNA is used for this purpose to amplify desired signal and introduce minimal additional noise. LNA enhances signal to noise ratio (SNR).
• Down converter converts microwave frequency to IF/baseband and demodulates it to recover original message signal.
• Demultiplexer separates combined signal into its original individual channels and delivers to respective users.

Devices or user equipments which utilize microwave communication system include telephone exchange, computer network, television receiver, cellular base station, internet router etc.

Benefits or Advantages of Microwave Communication System

1. Large Bandwidth: The microwave spectrum offers a wider bandwidth, enabling the transmission of a larger amount of information.
2. Spectrum Management: With the increasing congestion of the radio frequency spectrum, microwave technology provides solutions through the use of highly selective receivers, advanced modulation techniques (SSB, PSK, QAM, etc.), spread spectrum techniques, and data compression.
3. Channel Allocation: The microwave spectrum is divided into different channels based on specific applications. The center frequencies for these channels are carefully allocated with gaps to prevent overlapping and interference between adjacent channels.
4. Line of Sight Communication: Microwave communication has long been used as a Line of Sight (LOS) communication method, particularly in hilly and remote areas where wired communication infrastructure is difficult to install. Microwave and satellite communications are excellent choices for these locations.

Drawbacks or Disadvantages of Microwave Communication System

1. Complex Circuit Analysis: Unlike frequencies below 30 MHz where standard circuit analysis applies, microwave frequencies require E-H wave analysis, adding complexity to the design and analysis process.
2. Component Limitations: Traditional lumped components like resistors, inductors, and capacitors exhibit different characteristics at microwave frequencies compared to their behavior at lower frequencies. This makes implementing these components challenging in microwave circuits.
3. Transit Time Issues: At microwave frequencies, the transit time of current carriers (electrons) is significant, representing a substantial portion of the signal period. Consequently, conventional transistors may not perform optimally at microwave frequencies compared to lower frequencies.
4. Line of Sight Restriction: Microwave communication is limited to line of sight propagation. This means that communication is only possible if there is a clear, unobstructed path between the transmitting and receiving antennas. Other communication modes are not possible.

Applications

Microwave communication systems are widely used in:

• Cellular network backhaul (4G/5G)
• Television and radio broadcasting
• Satellite earth stations
• Military communication
• Radar systems
• Enterprise private communication networks
• Emergency and disaster recovery communication
• Internet service provider (ISP) backbone links

Summary

A microwave communication system is a high capacity wireless transmission system that employs microwave frequencies to carry voice, data and video over line of sight links. Owing to its high bandwidth, rapid deployment and cost effectiveness, microwave communication remains a critical technology for modern telecommunications, broadcasting and wireless network infrastructure.