Find out information on technology, deployment and applications for modern Digital Microwave Links
Microwave links are widely used for connectivity in modern digital IP networks. With capacities up to 6Gbps and beyond, a modern Microwave Link network can deliver bandwidth in a reliable, cost-effective and flexible manner – without need for disruption and delay caused by digging up streets and avoiding costly leased-line or leased fibre optic alternatives.
On this website you can find more information about radio link deployment and technology. Also we invite you to contact our experts with any questions by sending a message to us on our contact page.
Microwave links are used extensively in 4G & 5G LTE backhaul networks, 2G (GSM) and 3G (UMTS) mobile operators, wireless metropolitan area networks (Wi-MAN) and corporate networks where high performance, flexibility, speed of deployment and low operating costs are required. Key features of links include high spectral efficiency (256QAM, 1024QAM, 2048QAM and 4096QAM), Automatic Transmit Power Control (ATPC) and Adaptive Coding and Modulation (ACM).
Globally, MW radio links are used for around 60% of all mobile backhaul connections due to the compelling technical and commercial arguments in favour of MW radio compared to leased line and trenched fibre alternatives. Speed of deployment and flexibility – the ability to move sites or provision rapidly – are greatly in favour of MW radio over fibre and cabled alternatives.
A link typically features a radio unit and a parabolic antenna, which may vary in size from 30cm up to 4m diameter depending on required distance and capacity. The radio unit is generally either a “Full Outdoor”, “Split Mount” or “Full Indoor” design depending on operator preference, deployment, features and available indoor space for specific sites and installation.
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The contours of the map are for rain-rate (mm/h) exceeded for 0.01% of time. The map is positioned in relation to the UK according to the following co-ordinates:
The map of UK rain rates is constructed from British Atmospheric Data Centre and ITU data. A full explanation is given in (legacy) paper RSSP(05-01)/42, available from Ofcom on request.
UK Microwave Link Planning
Planning of Microwave Links requires understanding of Microwave Propagation. For frequencies above 10GHz, rain fade is significant and needs to be taken into account. Modern Microwave Planning tools can incorporate this data and calculations to achieve Availability Calculations for microwave links deployed in all regions worldwide.
Data is from regulator OFCOM document: “OfW 446: Technical Frequency Assignment Criteria for Fixed Point-to-Point Radio Services with Digital Modulation “
Two dependable and high performance microwave links available from reputable commercial microwave vendors are the CableFree FOR3 & HCR models.
CableFree Licensed Microwave Links offer long distance, high capacity and dedicated bandwidth.
The CableFree range of Microwave links include Full Outdoor (FOR3, Diamond), Full Indoor (LHR), Split Mount (HCR, LCR, MMR) and Broadcast (ASI) links to meet varied customer requirements for metro scale and national scale microwave networks. CableFree Microwave links are are available in licensed bands (4-42GHz) as well as unlicensed 5, 17, 24GHz.
CableFree High Performance Licensed Microwave Radios offer up to 440 Mbps and 880 Mbps Full Duplex payload (1.6Gbps aggregate capacity) and higher up to 3Gbps or more, with a software-selectable mix of SDH, PDH and IP/Ethernet traffic in 4-42GHz licensed frequency bands. Using suitable antennas and sites, ultra-long-distance links exceeding 100km can be achieved.
Introducing CableFree FOR3:
CableFree FOR3 is a Full Outdoor Microwave Link, comprising a fully outdoor radio unit, and just an indoor POE (power over ethernet) injector.
Introducing CableFree HCR:
HCR is a Split-Mount microwave, comprising an Indoor Unit (IDU) and Outdoor Unit (ODU).
Operators often choose Full Outdoor Radios for short links in cities, where rooftop space is limited and costs need to be reduced. Split Mount Radios are used for long-haul links where Space Diversity (SD), XPIC and other techniques are often required
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Long distance Microwave Links often use Space Diversity to ensure reliable communications between the two end points.
In certain geographic locations, such as over water and in deserts, multipath propagation poses an impediment to long-haul radio performance in the form of intolerable link outages. To compensate, a protection scheme must be applied. Space Diversity is one such widely implemented protection scheme that improves the performance of long-distance microwave radio links.
Microwave links below and above 10GHz
At link frequencies above 10 GHz, the path length of the link is limited by fading due to the occurrence of precipitation, while at link frequencies below 10 GHz rain attenuation has a limited effect on the path length. For this reason, frequencies below 10 GHz are best suited for long-haul communication networks. However, even in these preferred long-haul frequencies, path length and link availability can be limited by another phenomenon—fading caused by multipath propagation.
The probability of fading due to multipath propagation is dependent upon geographic factors such as the locale, the terrain over which the radio waves propagate and the path inclination (angle). The path length itself also has an effect since the likelihood of multipath propagation increases as the path length increases. In general, multipath propagation is more likely to occur in tropical areas, desert areas and in links over large bodies of water
Multipath propagation occurs as a result of one or more waves that are sent out from the transmitting antenna being reflected or deflected back onto a path that leads to the receiving antenna. The reflected/deflected wave is received in addition to the direct path wave.
Why use Multiple Antennas?
Spatial diversity employs multiple antennas, usually with the same characteristics, that are physically separated from one another. Depending upon the expected incidence of the incoming signal, sometimes a space on the order of a wavelength is sufficient. Other times much larger distances are needed.
As the multipath transmission is typically caused by fluctual layers in the atmosphere or at ground level, the delay difference between the direct path and the reflected/deflected paths vary over time. Also, the reflection coefficient (strength of the reflection/deflection) varies over time resulting in erratic fading behavior. By putting a second receive antenna on the tower, with a vertical separation from the first antenna, we create a second set of delay combinations. This technique is called Space Diversity. As described below, selective fading will occur at different frequency notches in the two received signals (one at each antenna) due to different delays, resulting in a significantly higher probability of receiving an undistorted signal.
How to achieve Space Diversity
Space Diversity is usually achieved using two vertically spaced antennas (space diversity), multiple transmitter frequencies (frequency diversity), both space and frequency diversity (quad diversity), or reception using two different antenna patterns (angle diversity). Frequency diversity was the first diversity used by fixed point to point microwave systems. Combining dual‐channel space and frequency diversity produces a powerful diversity improvement receiver configuration. The chapter illustrates the receive signal levels for a quad‐diversity path. The purpose of angle diversity antennas is to mitigate the destructive effects of multipath propagation without using a vertically spaced diversity antenna on the microwave tower.
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RadioMobile: Popular software for Microwave Link planning
RadioMobile is a widely-available software package which can be used for Microwave Link planning, including path profiling and clearance criteria, power budgets, choosing antenna sizes and tower heights.
For website for RadioMobile, please see this the relevant website.
For Microwave Link Planning, the software package can be configured with the characteristics of your required radio links.
Link Budget & Fade Margins
The software enables quick and rapid calculation of link budget and fade margins for any frequency band.
The software uses the freely available SRTM terrain data which can download “on demand” for calculation of terrain heights. Combined with LandCover, this enables estimation of trees/forests also.
Line of Sight
The software uses the terrain database to allows quick establishment of available Line of Sight and “what if” adjustment of antenna/tower heights in a microwave radio network design
Radio Fresnel Zone
RadioMobile automatically calculates the Fresnel Zone for any required link, with graphical display enabling quick feasibility and identification of any obstacles to be noted.
Radio Parameters & Network Properties
Any new user to Radio Mobile will have to enter link parameters for the chosen equipment. This includes transmit power, receive sensitivity and antenna gains. Some vendors such as CableFree include this data as a planning service with their products
Radio Mobile: Free to Use
The Radio Mobile software is free to use including for commercial use. Radio Mobile software is a copyright of Roger Coudé. The author notes:
Although commercial use is not prohibited, the author cannot be held responsible for its usage. The outputs resulting from the program are under the entire responsibility of the user, and the user should conform to restrictions from external data sources.
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For Microwave Links, the maximum transmission rate in a given bandwidth depends on system spectral efficiency, different equipment classes are here defined. They are based on typical modulation formats and limited by a “minimum Radio Interface Capacity density” (Mbit/s/MHz) shown in table 0. Radio Interface Capacity (RIC) is defined in EN 302 217-1
Radio Interface Capacity (RIC)
The minimum RIC density figures in table 0 are valid only for systems operating on the most common channel separation (CS) equal or higher than 1,75 MHz and taking into account that for channel separations “about” 14 MHz (i.e. from 13,75 MHz to 15,0 MHz), “about” 28 MHz (i.e. from 27,5 MHz to 30 MHz), “about” 56 MHz (i.e. from 55 MHz to 60 MHz) and “about” 112 MHz (i.e. 110 MHz or 112 MHz) the RIC density of actual systems is evaluated only over the “nominal” 14 MHz, 28 MHz, 56 MHz and 112 MHz channel width. Minimum RIC figures for some systems operating on 40 MHz channel separation, with RIC density lower than the minimum requirement in table 0, are defined only in annexes C and Ea. For the special cases of sub-STM-0 capacities (defined in ITU-T Recommendation G.708 [i.63] in annex D, alternative minimum RIC figures are not defined
CableFree FOR3 Microwave Links offer 881Mbps Full Duplex using 1024QAM, 112MHz Channels in 11GHz Microwave Band
The 11GHz version of CableFree FOR3 is ideal for Long Distance Backbone links for ISPs, Wireless ISPs (WISP), 4G/5G Operator for LTE Backhaul. In this demonstration you can see CableFree FOR3 Microwave Test Results for operation in the 11GHz Band. Our demonstration shows 881Mbps Full Duplex net throughput using 1024QAM modulation in 112MHz channels.This demonstration shows the clear advantages of a telecom carrier-grade FDD (Frequency Division Duplex) modem radio, which offers dedicated throughput and genuine Full Duplex capacity. Many operators use these links to upgrade from existing 5GHz MIMO radios when the capacity available on 5GHz is saturated, or interference levels too high for reliable operation.
Link Aggregation for Higher Capacity
CableFree Microwave Links can be aggregated for higher capacity: A 2+0 configuration of this radio in 11GHz would offer 1782Mbps Full Duplex net capacity.
The CableFree FOR3 radios were placed in a lab with suitable attenuator material between the waveguides to simulate long distance/range & attenuation. A pair of routers were placed either end of the link, to generate and receive test packet streams. These routers are capable of saturating a 1Gbps link therefore ideal for this test. Due to the nature of Telecom Microwave FDD modems, the same full capacity is available at range where suitable antennas are used. Longer range links require larger antennas to achieve high capacity.
Advantages of Licensed Spectrum
Licensed Spectrum ensures that links can operate without interference from other links within a region – the frequencies are allocated centrally by national government regulators. The 11GHz band is normally regulated by national governments for long distance links. Frequency allocations may be narrower than the 112MHz channels shown here. The FOR3 radio can be configured to operate within whatever channel assignments are offered,with channel widths and centre frequencies set under software control. Typical channel widths for lower frequency bands are 14MHz, 20MHz, 28Mhz, 30MHz, 40MHz, 56MHz.
About CableFree FOR3 Microwave
CableFree FOR3 Microwave platform is a high capacity, modern IP microwave radio link offering up to 891Mbps Full Duplex net throughput for diverse applications including 4G/LTE Backhaul, corporate networks, CCTV, Safe Cities and Wireless ISP backbones. Unique in the wireless industry, CableFree FOR3 is available in both Licensed (2 to 42GHz) and Unlicensed (5GHz, 17GHz and 24GHz) bands, allowing for lower Total-Cost-of-Ownership. Link to FOR3 Product Page
CableFree FOR3 is a Full Outdoor Radio for Zero-Footprint deployment, eliminating requirement for indoor locations or rack space. The radio is typically mounted on roof-top or tower location with antenna, with Power-over-Ethernet (PoE) connection to the radio using a single Cat5/e/6 cable. An optional SFP optical fibre interface is available for sites where long cable runs or electrical isolation to the radio is required.
Fully Shipping and Available
The CableFree FOR3 is fully shipping and available in all bands listed from 2 to 42GHz.
For Further Information
Out team has over 21 years experience with real-world deployment of wireless for mission-critical applications, with thousands of commercial deployments worldwide. For further information on Applications and Solutions for the range of CableFree wireless networking products please Contact Us
Many users consider upgrading existing Wireless Links such as Trango to add greater capacity, or network coverage. When considering a wireless vendor, factors generally include:
Vendor Track Record
Vendor Corporate Stability
Product Performance & Reliability
Product Support and Service
Attractive Vendor Roadmap
Product Pricing including all required options
Generally, Microwave links are required to operate unattended for many years in challenging outdoor environments, and therefore reliable and stable products and vendors are paramount in the selection process.
Turbulence in Wireless Vendor Market Space
Amongst many ongoing changes in the market for Microwave Backhaul and Microwave Transmission vendors, there is ongoing consolidation, M&A, and other activities. Recently, Microwave Vendor Trango Networks ceased trading and customers have reported that there is no longer supply of product, spares or support.
According to some former Trango customers in February 2019,
“Trango Systems has ceased trading trading and no longer or supporting existing installed links. We are therefore forced to find alternative suppliers”
Therefore many former Trango customers are looking for dependable alternative suppliers for Microwave and Radio links
Upgrade to Latest Microwave Technology for Higher Capacities
Some vendors are fully shipping products today with 1024QAM, XPIC, and upgrades to 2048QAM, XPIC, 10Gbps MMW (Millimeter Wave), which are features above and beyond those achieved by many in the market today. Customers can upgrade today and achieve higher capacity, longer range, reach and availability, at low Total Cost of Ownership compared to competing options.
Future Roadmap for Microwave Upgrades
In addition to today’s products, an impressive roadmap ensures access to higher speed links and features in future products also. Consideration is worthwhile into:
Vendor roadmaps to higher capacity links with microwave up to 4Gbps or more per link existing today.
Upgrading to E-Band MMW for shorter links especially in congested city environments
Using E-band Millimeter Wave for short links to free-up existing microwave spectrum, relief of spectral congestion and re-using valuable microwave spectrum for longer links where required
Several vendors and operators use this term: Find out what “Sub 6” means in practice.
What is Sub 6 ?
“Sub 6” means frequencies below 6GHz. Though frequencies from 1GHz up to 6GHz are still classified as microwave frequencies, they are often referred to “radio links”, “microwave links”, “microwave radio links” with these terms used interchangeably.
Why Consider Sub 6GHz?
Typically links below 6GHz are used for longer point-to-point links, or point-to-multipoint links for last-mile access to customers. Frequencies below 6GHz do not suffer significant rain fade. In addition, these lower frequencies can be used for Non-Line-of-Sight Links, in cases where there is no direct Line of Sight between the locations that require connection. The radio propagation characteristics of lower-frequency bands make them ideal for urban areas where radio signals may reflect from buildings and other man-made objects, and can – within limitations – penetrate walls, brickwork and concrete structures.
What does Unlicensed and Licensed mean?
The term Unlicensed in radio technology includes commonly used bands which can be used in many countries without need for a frequency license, such as 2.4GHz and 5.x GHz bands including 5.2GHz, 5.4GHz and 5.8GHz. Please note that in a few countries these frequencies still require licenses, or are not usable by private users.
Unlicensed frequencies have the benefit of not requiring a license to operate (typically, licenses have an annual fee, and are issued by a national regulator or state owned telecom operator). However, unlicensed links can be interfered with by other users, which can cause reduced throughput or complete link outage. Such interference is generally heavier in high density population areas and cities, where 100’s or 1000’s of radios may be competing for the same spectrum in a given region.
Conversely, licensed operation means that the equipment user has to obtain a frequency license before using the band. This can be available on a per-link basis, in which case the regulator allocates specific frequencies for a particular link, holding a central database of all links, or in the case of mobile operator networks, a country-wide license within which the operator self-coordinates the allocation of frequencies and coverage.
The lack of predictability in unlicensed bands is the main reason that operators prefer licensed bands for operation, despite the additional costs of licenses required to operate.
Single Carrier and OFDM Modulation
In the “Sub-6” bands 1-6GHz, a range of Single Carrier, OFDM and OFDM-A technology solutions are available. OFDM and OFDM-A use multiple subcarriers, and can use the properties of this modulation to overcome multipath fading and reflections from hard surfaces present in dense city areas. Conversely, Single Carrier radios use dense modulation with high symbol rates on a single radio carrier. This can give high spectral efficiency and data rates, but limited ability to cope with reflected signals, and hence worse performance in non-LOS situations.
Line of Sight, Non-Line-of-Sight, Near-Line-of-Sight and Radio Propagation
OFDM modulation is generally used in Sub-6 radios and is more suitable to rapidly fading and reflected signals, hence for mobility and non-line-of-sight (non-LOS, NLOS, Near-LOS, nLOS) applications. Generally, the lower the frequency band, the better non-LOS characteristics it has, improving range and in-building coverage and penetration through windows, walls, brickwork and stone.
4G & 5G Mobile and Fixed Networks
Both 4G and 5G technologies defined by the 3GPP use OFDM and OFDM-A technology in the sub-6GHz bands to deliver high speed fixed and mobile data services. These classify as “sub 6” but are rarely referred to as such. MIMO (Multiple Input, Multiple Output) technology is added on top of OFDM to increase throughput still higher. More recently, 5G includes “millimeter wave” bands above 20GHz to add still higher speed services and overcome congestion in lower frequency bands. It is envisaged that users could roam seamlessly between regions with “Sub 6” and “millimeter wave” coverage with suitable handsets or terminal devices.
Managing the Finite Spectrum Available in 1-6GHz
An obvious downside of Sub-6GHz is the limited spectrum available. There is just 5GHz of spectrum available between 1-6GHz which has to be allocated between multiple applications for Telecom Operators, Government and Private networks, utilising signals that can travel 10-50km or more and therefore potentially interfering with each other if inadequately managed. Though most applications are terrestrial, the bands include space for ground-satellite services which again have to avoid interference. Increasingly, frequency regulation is a global issue with international roaming, and huge spectrum demands and pressure on spectrum from Mobile Network Operators who face ever increasing demands for mobile data users worldwide. To meet this demand, spectrum is continually re-farmed and re-allocated between older 2G and 3G services to 4G and 5G services which are capable of delivering higher capacity services. Legacy frequency allocations to Government and Military applications are often released for lease to such operators also.
A Split Mount Microwave Radio consisted of Indoor plus Outdoor components – specifically Indoor Unit (IDU) and Outdoor Unit (ODU)
Split Mount Microwave Radios offer up to 500 Mbps and 1Gbps Full Duplex payload and higher up to 6Gbps or more, in 4-42GHz licensed frequency bands.
Indoor Unit (IDU)
A Typical Split Mount Radio consists of a 19″ Rack Mount Indoor Unit which is mounted in a rack, cabinet, comms room, or even roof-mount shelter as possible locations.
Outdoor Unit (ODU)
The Outdoor Unit (ODU) is typically mounted directly to the Microwave Antenna on a rooftop or tower location, which enables clear Line of Sight (LOS) between both ends of the Microwave link.
For most bands above 6GHz the ODU has a waveguide interface which enables efficient, low-loss connection directly to the antenna. For lower bands below 6GHz, commonly a coaxial cable is used between the ODU and the antenna.
In certain cases, the ODU can be remote mounted from the antenna, and a waveguide used to connect between them
Comparison with Full Outdoor Radios
A split mount radio is considered a “traditional” design and older radios always feature this. The Indoor Unit has all the network interfaces and processing in the easy-access indoor location at the foot the tower or building. Full Outdoor Radios by contrast have all the active items including the modem and user network interfaces inside the rooftop radio element. This saves on space, materials, installation time and cost. A downside is that in the event of any failure, a tower climb is almost always needed to rectify any fault, which may be impossible in rough weather, or require permits or have access limitations to reach
Distances and Range Capability of Split Mount Radios
Using suitable antennas and sites, ultra-long-distance links exceeding 100km can be achieved. Distances depend on:
Required throughput (Mbps)
Desired Availability (%)
Antenna size (gain)
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A waveguide flange is a connector for joining sections of waveguide, and is essentially the same as a pipe flange—a waveguide, in the context of this article, being a hollow metal conduit for microwave energy. The connecting face of the flange is either square, circular or (particularly for large or reduced-height rectangular waveguides), rectangular. The connection between a pair of flanges is usually made with four or more bolts, though alternative mechanisms, such as a threaded collar, may be used where there is a need for rapid assembly and disassembly. Dowel pins are sometimes used in addition to bolts, to ensure accurate alignment, particularly for very small waveguides where higher accuracy is required for higher frequencies.
Key features of a waveguide join are; whether or not it is air-tight, allowing the waveguide to be pressurized, and whether it is a contact or a choke connection. This leads to three sorts of flange for each size of rectangular waveguide.
For rectangular waveguides there exist a number of competing standard flanges which are not entirely mutually compatible. Standard flange designs also exist for double-ridge, reduced-height, square and circular waveguides.
Unpressurised and Pressurised Waveguide Flanges
The atmosphere within waveguide assemblies is often pressurized, either to prevent the ingress of moisture, or to raise the breakdown voltage in the guide and hence increase the power that it can carry. Pressurization requires that all joints in the waveguide be airtight. This is usually achieved by means of a rubber O-ring seated in a groove in the face of at least one of flanges forming each join. Gasket, gasket/cover or pressurizable flanges (such as that on the right of figure 2), are identifiable by the single circular groove which accommodates the O-ring. It is only necessary for one of the flanges in each pressurizable connection to be of this type; the other may have a plain flat face (like that in figure 1). This ungrooved type is known as a cover, plain or unpressurizable flange.
It is also possible to form air-tight seal between a pair of otherwise unpressurizable flanges using a flat gasket made out of a special electrically conductive elastomer. Two plain cover flanges may be mated without such a gasket, but the connection is then not pressurizable.
Electric current flows on the inside surface of the waveguides, and must cross the join between them if microwave power is to pass through the connection without reflection or loss.
Microwave Flange Standards
International Electrotechnical Commission (IEC) standard IEC 60154 describes flanges for square and circular waveguides, as well as for what it refers to as flat, medium-flat, and ordinary rectangular guides. IEC flanges are identified by an alphanumeric code consisting of; the letter U, P or C for Unpressurizable (plain cover), Pressurizable (with a gasket groove) and Choke (with both choke gasket grooves); a second letter, indicating the shape and other details of the flange and finally the IEC identifier for the waveguide. For standard rectangular waveguide the second letter is A to E, where A and C are round flanges, B is square and D and E are rectangular. So for example UBR220 is a square plain cover flange for R220 waveguide (that is, for WG20, WR42), PDR84 is a rectangular gasket flange for R84 waveguide (WG15, WR112) and CAR70 is a round choke flange for R70 waveguide (WG14, WR137).
MIL-DTL-3922 is a United States Military Standard giving detailed descriptions of choke, gasket/cover and cover flanges for rectangular waveguide. MIL_DTL-39000/3 describes flanges for double-ridge waveguide, and formerly also for single-ridge guide. MIL-Spec flanges have designations of the form UG-xxxx/U where the x’s represent a variable-length catalogue number, not in itself containing any information about the flange.
The Electronic Industries Alliance (EIA) is the body that defined the WR designations for standard rectangular waveguides. EIA flanges are designated CMR (for Connector, Miniature, Rectangular waveguide) or CPR (Connector, Pressurizable, Rectangular waveguide) followed by the EIA number (WR number) for the relevant waveguide. So for example, CPR112 is a gasket flange for waveguide WR112 (WG15).
The Radio Components Standardization Committee (RCSC) is the body that originated the WG designations for standard rectangular waveguides. It also defined standard choke and cover flanges with identifiers of the form 5985-99-xxx-xxxx where the x’s represent a catalogue number, not in itself containing any information about the flange.
What is a Waveguide?
A waveguide is an electromagnetic feed line that is used for high frequency signals. Waveguides conduct microwave energy at lower loss than coaxial cables and are used in microwave communications, radars and other high frequency applications.
The waveguide must have a certain minimum cross section, relative to the wavelength of the signal to function properly. If wavelength of the signal is too long (Frequency is too low) when compared to the cross section of the waveguide, the electromagnetic fields cannot propagate. The lowest frequency range at which a waveguide will operate is where the cross section is large enough to fit one complete wavelength of the signal.
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