Microwave Radio Relay Systems: How They Work & Why They Matter

Microwave radio relay systems are one of the oldest yet still highly relevant technologies for point-to-point wireless data transmission. Despite the widespread adoption of fiber optics, satellite systems, and cellular networks, microwave links remain a vital component of telecom infrastructure. They are used for backbone channels, backup connections, communication in mountainous or forested areas, on operator towers, and in places where laying cable is either impossible or prohibitively expensive.

What Are Microwave Radio Relay Systems and How Did They Emerge?

A microwave radio relay system transmits data via a narrow, focused radio beam between two or more stations located far apart. For a link to operate, there must be a clear line of sight between antennas, with signals transmitted in frequencies ranging from several gigahertz up to dozens of gigahertz. Unlike mobile networks or Wi-Fi, microwave relay systems are designed exclusively for point-to-point or chained connections, not for serving many subscribers.

Microwave relay lines first appeared in the mid-20th century, originally for military communication over long distances without cables that could be easily damaged. Later, telecom operators adopted the technology for creating trunk lines between cities, stations, and towers. Before the advent of mass fiber optics, microwave relay was the backbone of long-distance telephony, broadcasting, and the first digital data channels.

The uniqueness of microwave relay systems lay in their ability to provide communication in the most challenging terrains: mountains, forests, steppes, and deserts. Antennas were installed on elevated points and towers, creating chains of stations stretching hundreds of kilometers-a revolutionary, cable-free solution at the time, protected from most types of damage.

Over time, microwave systems transitioned to digital standards, offering higher speeds, improved equipment reliability, smaller antennas, and reduced power consumption. Today, they are used as fiber backups, primary links in difficult landscapes, and as transport technology for cellular operators.

How Microwave Radio Relay Systems Work: A Simple Explanation

A microwave relay line operates by transmitting a radio signal as a narrow, focused beam from one antenna to another. The antennas are precisely aligned so the radio energy travels in a nearly straight line-much like a flashlight, but invisible to the eye. This setup requires direct line of sight: any obstruction such as mountains, trees, buildings, or towers can weaken or disrupt the signal.

Each relay station performs two functions: it receives the signal and retransmits it further. If the distance is too great or terrain interferes, intermediate repeater stations are installed. These do not alter the data; they simply receive, amplify, and forward the signal, forming a long chain.

Communication occurs on microwave or millimeter-wave frequencies-from 1 to 80 GHz. Higher frequencies offer greater data rates and narrower beams, but are more affected by rain, snow, and fog. Lower frequencies allow data transmission over tens of kilometers per hop; higher ones cover only a few kilometers but with much greater capacity.

Antennas, usually parabolic dishes ranging from 30 cm to 3 m in diameter (sometimes flat panel antennas), focus the signal tightly. The larger the antenna, the narrower and longer-range the beam, and thus the more stable the connection. Alignment must be precise to fractions of a degree-any shift can reduce signal quality or break the link.

Modern microwave transmission uses digital technologies such as QAM modulation, compression, and error correction. This enables reliable, high-volume data transfer even over long distances. Essentially, a microwave relay line functions as an "invisible cable," using a directed radio beam instead of glass fiber.

This principle makes microwave links versatile: they can be deployed quickly, do not depend on cable installation, and require minimal infrastructure. That's why they are chosen where fiber is impractical or too expensive.

Key Components of a Microwave Relay System: Stations, Antennas, and Equipment

A microwave relay system consists of several key elements, each playing a crucial role in delivering stable and long-range connections. Despite differences in models and manufacturers, the structure of most systems is similar.

Microwave Relay Station (MRS)

This is the hub that receives, amplifies, digitally processes, and retransmits the signal. A typical station includes:

Radio unit (radio module)
Modem for forming data streams
Power supply
Monitoring and control system
Synchronization and network interface equipment (Ethernet/SDH)

Stations are placed on towers, building rooftops, masts, or elevated terrain, where clear line of sight is available.

Antenna

The core component is the parabolic dish antenna, which focuses the radio signal into a tight beam. The larger the diameter, the narrower the beam and the greater the range. For urban links, antennas are typically 30-60 cm; for tens-of-kilometers links, 1-3 meters.

Inside, a feed horn directs the signal, while the radio unit is connected via waveguide or short coaxial cable to minimize losses.

Outdoor Unit (ODU)

Mounted near the antenna, usually outside, the ODU:

Handles signal transmission and reception
Amplifies the signal
Performs modulation/demodulation
Filters and suppresses interference

The closer the ODU is to the antenna, the lower the losses and the higher the connection quality.

Indoor Unit (IDU)

Housed in a server room or indoor facility, the IDU is connected to the ODU by cable and:

Processes digital data
Forms Ethernet or SDH data streams
Controls frequency, modulation, and power
Performs diagnostics and monitoring

Feeder System

This consists of cables or waveguides between antennas and radio units. At higher frequencies, coaxial cables are rarely used due to excessive losses; waveguides are preferred.

Repeaters

If there is no direct line of sight or distances are too great, intermediate stations (repeaters) are installed. These receive and forward the signal unchanged, acting like a mirror for radio waves.

These components work together to build both short urban links for mobile operators and long, complex routes through mountains, forests, and remote regions.

Microwave Frequency Bands and Their Features

Microwave relay systems operate in microwave and millimeter-wave radio frequency bands-from 1 GHz to 80 GHz. Each band has its own advantages and limitations, determining range, signal stability, and throughput.

Low Bands (1-6 GHz)

Used for long-distance trunk lines. These frequencies are less affected by rain, snow, and fog, allowing links of 30-50 km between stations.

Pros: Long range, high stability
Cons: Wider beams increase interference risk, less available spectrum

Mid Bands (7-13 GHz)

The classic "workhorse" frequencies for microwave. They offer a good balance of range and data rate. Typical link distances: 10-25 km. Commonly used by mobile operators, railways, and utility companies.

High Bands (15-23 GHz)

These frequencies deliver higher speeds-up to hundreds of megabits or even gigabits per channel-but with a reduced range of 5-15 km. Signal attenuation from heavy rain is noticeable but generally manageable.

Millimeter-Wave Bands (24-38 GHz and 60-80 GHz)

The highest frequencies, supporting multi-gigabit speeds (5-10 Gbps and beyond), but extremely sensitive to weather. Range is 1-5 km. Such links require highly accurate antenna alignment and are used where high traffic is needed but fiber is not feasible.

Terrain and Atmospheric Effects

Higher frequencies create narrower beams but are more affected by:
- Rain
- Snowfall
- Fog
- Humidity
- Multipath reflections from mountains, buildings, or water

Choosing a frequency band is a trade-off between speed, range, and local conditions. For example, low bands are used in mountains, while high bands are favored in cities for greater capacity over short distances.

Advantages of Microwave Radio Relay Systems

Despite the rapid growth of fiber optic networks, microwave relay systems remain in demand thanks to a set of unique benefits. These features make them ideal where cable infrastructure is impossible, too expensive, or needs backup.

No need to lay cables
The main advantage: there's no need to run fiber or copper cables through difficult terrain, private property, or forests. It's enough to install two stations with line of sight.
Fast deployment
Microwave links can be set up in hours or days-crucial for emergency communications, temporary sites, construction projects, expeditions, military tasks, and backup channels.
High throughput
Modern systems deliver tens or even hundreds of megabits, and up to 5-10 Gbps in millimeter bands-comparable to fiber for many needs.
Reliability and autonomy
The air between stations eliminates cable damage, corrosion, or power issues. Equipment on towers is robust and long-lived thanks to sealed enclosures and redundancy.
Ideal for remote areas
In mountains, forests, deserts, or sites where cable isn't feasible, microwave relay provides the only practical high-speed channel.
Ability to create chains hundreds of kilometers long
With repeaters, long routes can be built to bypass terrain and connect distant regions.
Low maintenance costs
Unlike buried or aerial fiber, microwave links require little ongoing repair and are less affected by environmental wear.

These advantages make microwave relay a reliable and efficient data transport technology, especially where cable is impractical or uneconomical.

Drawbacks of Microwave Relay Systems

While microwave relay systems offer significant benefits, they are not universal and cannot replace fiber optics in all scenarios. Their limitations stem from radio wave physics and equipment characteristics.

Dependence on line of sight
The main drawback is the need for clear line of sight between stations. Any obstacle-mountains, hills, tall buildings, trees, metal structures-can block the connection. Unlike mobile networks, microwave links can't "work around" obstructions.
Limited distance between stations
Range depends on frequency: low bands cover tens of kilometers, high bands only 1-5 km. Long routes require repeaters, increasing cost and complexity.
Weather impact
Rain, wet snow, fog, and high humidity especially affect millimeter bands (23-80 GHz). During severe weather, speeds may drop or brief outages can occur.
Need for precise antenna alignment
Antennas must be aligned to fractions of a degree. Any shift from wind, vibration, or icing impairs signal quality and requires adjustment.
Limited spectrum width
Microwave frequencies are state-regulated and spectrum is limited. This caps maximum capacity and may require permits.
Mutual interference
In densely populated areas with many microwave links, poor planning can lead to interference between systems.

Despite these drawbacks, microwave relay remains indispensable where cable infrastructure is impossible or too expensive, and where reliability and flexibility are top priorities.

Microwave vs Fiber Optics: Key Differences and Best Use Cases

Microwave relay lines and fiber optic networks are often compared since both are used for backbone and transport connectivity. They differ in architecture, cost, and application. Fiber is the gold standard for data transmission, but microwave links remain essential in many situations.

Throughput
Fiber delivers the highest speeds-tens or hundreds of gigabits per second, and even terabits with DWDM. Microwave links offer more modest speeds: 100-500 Mbps in mid-bands, up to 5-10 Gbps in millimeter-wave. If massive bandwidth is required, fiber is unmatched.
Latency and stability
Both technologies offer low latency, but fiber is more stable in all weather. Microwave is more sensitive to precipitation, fog, and humidity, especially at 23-80 GHz.
Infrastructure requirements
Fiber requires routing, cable ducts or aerial paths, property permissions, and complex construction. Microwave only needs line of sight and two mounting points, making it ideal for connecting mountain, forest, steppe, remote, or temporary sites.
Reliability and resilience
Fiber is extremely reliable, but vulnerable to physical damage: breaks, excavators, pole accidents. Microwave is immune to such breaks since the "cable" is air, not glass. This is why microwave is often used as a backup for fiber.
Cost
Building fiber can cost many times more and take months. Microwave can be deployed in days, avoiding bureaucracy, making it cheaper and faster to implement.
Scalability
Fiber scales almost infinitely by adding equipment. Microwave has physical limits: available spectrum, weather effects, and beam length.

Summary:

For cities, backbones, and high speeds-fiber is best.
For mountainous areas, remote sites, and backup channels-microwave relay prevails.
For mobile operators-a hybrid: fiber plus microwave to cover challenging terrain and ensure redundancy.

Where Microwave Relay Systems Are Used Today

Despite the expansion of fiber networks, microwave relay lines remain irreplaceable for certain tasks requiring reliable, long-range, and relatively affordable connectivity. They are widely used by both civil and governmental organizations as well as private companies.

Cellular operators
Microwave is widely used for connecting base stations, especially in hard-to-reach regions or where fiber is impractical. It provides traffic transport from base stations to the backbone, fiber backup, and rapid deployment of new sites. Many LTE and 5G towers are still connected via microwave links.
Mountainous and remote areas
In mountains, forests, tundra, and deserts, laying cable is extremely expensive or physically impossible. Microwave chains connect settlements, meteorological stations, geological bases, and industrial sites.
Energy and industry
Power plants, pipelines, oil fields, and substations use microwave channels for telemetry, SCADA data, and security systems-where reliability and autonomy are critical.
Military and government
Thanks to their resilience and long range, microwave links are still used for secure, including mobile and field, communications.
Emergency and temporary communications
Microwave is ideal for temporary construction sites, expeditions, emergency services, and post-disaster recovery. It can be deployed quickly without complex infrastructure.
Internet for remote sites
Tourist bases, mountain shelters, mining camps, lighthouses, and ports rely on microwave-often the only viable long-distance, cable-free technology.

Thanks to their autonomy and flexibility, microwave relay lines remain relevant even where the main infrastructure has shifted to all-fiber.

Why Microwave Relay Systems Are Still Used

Despite the explosive growth of fiber optic networks, microwave relay systems are far from obsolete. On the contrary, they are actively used today because they offer unique advantages that no other technology can fully replicate.

First, microwave links are the fastest way to deploy backbone or transport channels where no infrastructure exists. No kilometers of cable, route permits, pole construction, or earthworks are needed-just two points with line of sight. This makes them irreplaceable in mountains, forests, deserts, tundra, and on temporary sites.

Second, microwave links are used as a backup for fiber. While fiber offers huge capacity, it is vulnerable to mechanical damage-road accidents, construction, fires, falling trees. A parallel microwave link provides instant failover, which is vital for telecom operators, banks, industrial facilities, and security systems.

Third, modern microwave equipment delivers high data rates-up to 10 Gbps in millimeter bands. This is sufficient for most transport needs, especially for 4G/5G base stations and corporate backbones.

Another key advantage is low operational cost. With no cable to maintain or repair, and tower equipment lasting for years with minimal intervention, microwave is cost-effective over long distances and in sparsely populated regions.

Technologies have also continued to evolve: improved modulation, greater interference resistance, smart management, and weather adaptation systems. Microwave hardware is now more compact, energy-efficient, and reliable.

All these factors keep microwave relay systems relevant in today's telecom market-both as a standalone solution and as a crucial supplement to fiber optic infrastructure.

Conclusion

Microwave radio relay systems remain a key part of modern telecommunications thanks to their reliability, mobility, and ability to operate where other technologies fall short. They provide stable connections for mobile operators, industrial sites, remote settlements, and emergency services.

Despite advances in fiber optics, microwave relay maintains unique strengths: rapid deployment, minimal infrastructure requirements, resistance to physical damage, and the ability to build backbones through challenging terrain. Modern systems offer high capacity and continue to evolve, ensuring the technology's future demand.

Microwave links don't compete directly with fiber-they complement it, creating hybrid networks resilient to external conditions and failures. This is why microwave relay remains in demand for decades and will continue to be used for many years to come.

Microwave Radio Relay Systems: How They Work and Why They're Still Essential