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ISM Band of Frequencies and Allocation

ISM stands for Industrial Scientific and Medical and designates a portion of the radio frequency spectrum that was intended to be used for these purposes. It is defined and overseen by the International Telecommunications Union Radio Regulations, created in the 1980s by the Swiss-based ITU, an international body, derived from the UN, that regulates radio communications across the world. This is a band of radio and microwave frequencies clustered around 2.4GHz, reserved and designated for industrial, scientific and medical equipment that use RF. Industrial equipment like MRI machines, testing equipment, and some radio telescopes use this ISM band of frequencies. Smaller consumer devices such as microwave ovens, garage door system, cordless phone, wireless router and wireless mouse are also designed to run at frequencies around 2.4 GHz.

Most telecommunication devices operate at a much lower frequency than 2.4GHz. Having other devices operate at only a certain frequency range, in this case, ISM, reduces interference with the telecommunication frequencies. This means that using a wireless router and a cellular phone at the same time will have no interference with each other.

Allocation of ISM radio frequencies is stipulated by the International Telecommunication Union (ITU). ITU has documented a worldwide ISM allocation table which varies slightly depending on the region. ISM users must accept laid down terms and regulations to ensure safety and avoid interference. 

What is the ISM band?

2.4GHz is not the only ISM frequency. It is only the most common because there is no need for licensing devices to use it. Other ISM frequencies can be as high as 24.125GHz or even as low as 13.56MHz. Depending on the location and local acceptance, authorities can allocate ISM radio frequencies with some little flexibility. 

These parts of the radio spectrum which cover a range of frequencies between 6.765 kHz and 246 GHz, were initially intended to be harnessed for applications other than telecommunications and are reflected in their name. In particular, the ISM frequency band is used to generate heat, for example in microwaves, surgical diathermy, and industrial processes. However, over time, the use of the ISM band has expanded to include wireless communications, an unintended but so far successful application which we will explore below. The ISM bands are vulnerable to electromagnetic interference, but these problems have been largely overcome in the RF technologies that use these bands.

What are the ISM band frequencies?

ISM frequencies span low frequency to microwave frequencies. These are the key ISM frequency bands across the world.

  • 6 765-6 795 kHz
  • 13 553-13 567 kHz
  • 26 957-27 283 kHz
  • 40∙66 – 40∙70 MHz
  • 83·996-84·004 MHz
  • 167·992-168·008 MHz
  • 886-906 MHz
  • 433·05-434·79 MHz
  • 2 400-2 500 MHz (2.4 GHz)
  • 5 725-5 875 MHz
  • 24·0-24·25 GHz
  • 61·0-61·5 GHz
  • 122-123 GHz
  • 244-246 GHz

Are ISM bands legal bands?

The ISM band is also called the free band as it is license-free and not subject to regulatory protections and protocols as other radio communication frequencies are. They are not illegal frequencies or illegal channels, but activities using these frequencies may be subject to local laws.

In the US, the Federal Communications Commission (FCC) has designated 3 key ISM bands for unlicensed use. This was done in the 1980s and declassified the use of spread spectrum modulation, which previously had only been used for military applications. They are:

  • 900MHz
  • 2.4GHz
  • 5.8GHz

This means operators do not have to file with the FCC to use these frequencies.

Low power short-range wireless communications exploit a number of these frequency bands though use may be subject to interference and users have no legal or regulatory protections if their communications are compromised.

The 2.4 GHz band

The 2.4 GHz ISM band frequency is available worldwide and has been appropriated for a wide range of wireless communications as it is 100% free to use!

Unlicensed:  This makes the 2.4 GHz ISM band advantageous for the unlicensed wireless transmission that underpins a wide range of devices and solutions used in contemporary society. It is probably best known as the frequency at which local area wireless technology (WiFi) operates as specified in the proprietary protocol IEEE 802.11x.

Why is the 2.4 GHz frequency preferred?

It all comes down to how electromagnetic energy is transmitted at this particular frequency. At 900MHz signals have good penetration but a shorter range than can be achieved at 2.4 GHz. A 2.4 GHz antenna also does not have to be as large as those used for data transmission at lower frequencies.

The 2.4 GHz frequency band has been settled upon internationally. 2.4 GHz vs 900mhz delivers:

  1. A broader channel selection
  2. Better range
  3. Effective penetration
  4. Cost-effectiveness
  5. Smaller 2.4 GHz wifi antenna

2.4 GHz Vs 5GHz

The 5 GHz was initially used for WiFi routers. 5 GHz delivers faster speeds but lacks the coverage that can be achieved in the 2.4 GHz frequency range. Due to these practical advantages, the IEEE protocol has secured 2.4 GHz as the standard, though some WiFi routers operate at both frequencies.

Key applications for the 2.4GHz frequency band

Despite the potential for interference amongst devices using this frequency, wireless 2.4GHz band users have minimized interference by using more powerful WiFi antennas like 2.4 GHz high gain antenna or developing sophisticated firmware for devices.

The range of devices that use the 2.4 GHz frequency range is diverse and span a variety of industries and sectors. Examples include:

Telecommunications

  • Cordless phones utilize the 2.4GHz frequency to transmit phone calls from the wired base station to the cordless handset. This is a major source of interference of WiFi and leaves open the potential for eavesdropping.

Audiovisual

  • Wireless baby monitors use this ISM frequency band to transmit audio and visual data from the crib to a proprietary monitor or smartphone.
  • Wireless CCTV operates in a similar manner and can transmit to a remote location using the 2.4GHz band.
  • Wireless speakers and microphones operate as reviewers and transmitters effectively and are reliant on 2.4 GHz WiFi antennas to operate.

Automotive

  • Car locking systems and immobilizers also harness this frequency.

Marine and Aviation

  • Some forms of radar utilize this ISM band frequency range.

Energy

  • Smart energy meters and novel wireless charging systems use the 2.4 GHz, frequency band.

In addition this unlicensed frequency band also is used for wireless printers, computer mice, remote control cars, drones, headphones, screens, and a range of 'smart' and Near Field Communication (NFC) consumer electronics and goods.

Wireless networking

A number of protocols have been developed that formalize and facilitate wireless local area networking between objects of all kinds. As mentioned above WiFi is the most well-known of these.

What is WiFi?

  1. WiFi is a trademarked technology developed by the WiFi Alliance to permit wireless local area networking according to specified standards. It uses the 2.4GHz ISM band. This has enabled not only standardized interoperability of devices using wireless communication, but also connection to the internet. This is achieved via designated wireless access points called hotspots which have a 2.4 GHz wireless range distance of up to 20m (65 feet). It works best in line of sight arrangements.

ZigBee operates at 2.4GHz

IEEE standard 802.15 specifies the operating standards for this wireless mesh network. Because ZigBee is low power and low cost it tends to serve battery-powered devices and uses specific channels within this ISM band to avoid interference.

Bluetooth also uses the 2.4 GHz ISM band

The Bluetooth protocol uses 2.4GHz frequency bands for low power, short-distance wireless communication, and the creation of personal area networks (PANs).

Data transmission on the 2.4GHz ISM frequency band

The WiFi standard outlines a number of modulation techniques of varying complexity that can be used to encode data to be transmitted at 2.4GHz.

Modulation techniques are important because ISM bands are unlicensed and therefore prone to interference from other wireless traffic at that frequency. They increase the likelihood of transmitted data being correctly received by the receiving antenna and reduce the need for repeated transmissions of the same information. Key techniques include:

  • Direct-Sequence Spread Spectrum (DSSS). This method involves the inclusion of spreading code within the transmitted signal to expand the bandwidth beyond what would normally be required. Encoded data are bits expanded into runs of smaller data fragments called 'chips'. This chip code data stream will be transmitted with a higher data rate than the data itself. These rates are specified by the FCC. Once received, the spread data is demodulated and condensed to recover the original data. DSSS tolerates a high data throughput and is scalable and robust, making it a key technique for securing WiFi data transmission.
  • Frequency-Hopping Spread Spectrum (FHSS) utilizes the various channels within a frequency band to transmit data by 'hopping' between channels at predetermined intervals during the transmission. The transmission spends no more than 400 milliseconds on any single channel and must utilize all the channels within the frequency band before returning to any channel a second time.
  • Orthogonal Frequency Division Multiplexing (OFDM) This signal modulation method involves using multiple carriers which each carry a small amount of data. OFDM has been found to be extremely resilient to interference and degradation and uses less of the available bandwidth.

What are the signs of WiFi interference?

Multiple wireless domestic devices like CCTV, garage door openers, and baby monitors, that use the license free 2.4 GHz frequency can cause wireless interference. Key signs include:

  • Poor connectivity of the device
  • The connection does not hold
  • Slow connection
  • Low signal strength
  • Audio buzzing, skipping, or interruption

Interference on the 2.4 GHz band can be identified using spectrum analyzers that can be used with a 2.4 GHz directional antenna to search for the source of the interference.

WiFi network interference can be alleviated by increasing the number of base stations in the affected network or increasing the number of 2.4GHz antennas or a 2.4 GHz booster to reduce the number of poor links and increase signal strength.

Antennas key to developing 2.4GHz solutions

Devices and networking that use ISM bands are reliant on suitable antennas to facilitate wireless communication at this frequency. Antennas do the work of transmitting and receiving electromagnetic energy at the required frequency. They perform the work of transducers, which convert electrical energy into a radio frequency signal to be transmitted to a receiving antenna which converts the electromagnetic energy into electrical current. Antennas are incredibly diverse meaning that optimal antenna design and functioning can be found for the desired application.

ISM antennas

ISM band and short-range device antennas are specifically designed and configured to operate as part of a wireless Local Area Network (LAN) at the specified ISM frequencies. They provide the signal coverage necessary to implement the network in a range of environments.

ISM antennas will be used as part of LAN systems that include critical components like:

  1. Antennas
  2. Hardware for antenna housing and mounting
  3. Cables and adapters
  4. Connect

Federal regulation of ISM antennas

Though ISM bands are unlicensed, the FCC has stringent rules for radio frequency equipment including antennas that operate for wireless communication in these bands. These regulations are specified in Part 15 of the FCC rules. In particular, operators and installers of equipment that use ISM band channels carry the responsibility to ensure that their equipment remains within the limits denoted in these rules. Here are some of the key points:

  • A transmitting antenna should have a maximum transmitter output power of 1 Watt (30dBm).
  • The maximum Effective Isotropic Radiated Power (EIRP) of the antenna should be at 4 Watts (36dBM). EIRP measures the amount of power an antenna radiates in a given direction and can be calculated easily by adding the transmitter output power to the antenna gain.
  • For a 2.4 GHz antenna high gain can lead to the 36 dBm limit being lawfully exceeded if the transmitted power is reduced by 1 dBm for every 3dBm of gain.

This shows how important it is to work with a knowledgeable and reputable supplier of compliant and FCC certified 2.4GHz, WiFi, Bluetooth, ISM antennas for personal or commercial use. Globally, the Restriction of Hazardous Substances Directive (RoHS), a piece of EU legislation, is also an important certification that provides assurance that these electronic devices have not been fabricated with certain toxic materials. Using compliant antennas in a proposed RF module or network will save time and sometimes certification costs of a completed project as any certifications can be carried over into the finished setup without the need and expense of additional testing.

Why antenna selection is the priority for your ISM wireless set up.

Ideally your choice of antenna should form the basis of arranging your network setup as fixed positions and housings arranged ahead of antenna selection antenna may lead to a less than satisfactory final performance. Making an ISM antenna selection at the start of your project will ensure it delivers adequate range and has optimal mechanics and engineering for the space available.

How to select the best ISM antenna

Given the importance of antenna selection, a structured or methodical approach will help pinpoint the best performing 2.4 GHz radio frequency antenna for your application.

When considering an antenna the following factors should be addressed:

  1. Type of ISM antenna
  2. Size of the antenna
  3. Range of the antenna
  4. Performance and safety profile of the antenna
  1. Types of 2.4 GHz       ISM antennas available

The type of 2.4 antenna chosen for your application will determine the coverage you can achieve. With 2.4 GHz antenna high gain will affect the coverage area. For 2.4 GHz antenna long-range transmission due to increased gain is usually only achieved in a single direction unless an omnidirectional antenna is chosen. Here are the main 2.4 antennas you need to know.

[A] 2.4 GHz omnidirectional antenna

A 2.4 GHz omni antenna is easily recognizable by its circular radiation pattern which is also called a 'rubber-duck' pattern. They are q popular selection where a 2.4 GHz wifi antenna is needed to cover a large area with a WiFi signal. Depending on gain these antennas can achieve 2.4 GHz wireless range distance of tens of meters, as these antennas will radiate electromagnetic energy in all directions equally. The radio power of these antennas will be emitted perpendicular to its longitudinal axis.

[B] 2.4 GHz directional antenna

Also known as beam antennas, these antennas radiate and receive radio power most strongly in a specific direction. This is beneficial as it increases antenna performance and minimizes interference, making them a good choice where radio waves need to be transmitted in a single direction. A 2.4 GHz high gain antenna is most often a directional antenna.

[C] 2.4 GHz yagi antenna

These directional ISM antennas have a familiar design that consists of multiple parallel antenna elements arranged in a line. The parallel paired rods feed off a single element that connects to the antennas transmission line. This distinctive antenna is eponymously named and was developed in Japan in the 1920s. These antennas are often selected as a 2.4 GHz outdoor antenna choice and can be used to receive signal accurately, as a point-to-point link, or to serve a specific area with the signal. They may be exposed or covered with cylindrical housing.

[D] 2.4 GHz dipole antenna

Dipole antennas are one of the simplest types of antenna. A basic dipole antenna is made from 2 conducting elements on an end to end orientation, with the transmission line connected between them. It may be used alone or as an element within a more complex antenna. These resonant antennas are widely used as they have a balanced performance and deliver good coverage.

[E] 2.4 GHz parabolic antenna

Known and recognized as 'dish' antennas these antennas use the curved surface of a solid or grid parabolic reflector to optimally direct radio waves. These high gain antennas are advantageous for WiFi setups where they are able to concentrate and direct signal to where needed. As parabolic antennas tend to be long-range and the coverage angle of these ISM antennas is very narrow, typically a few degrees, they are an ideal choice for point to point links and other configurations that require a high degree of accuracy.

[F] 2.4 GHz panel antenna

Flat-panel antennas are highly directional and consist of a dipole antenna with a flat panel reflector. They are typically used outdoors as an easily mounted and discreet 2.4ghz directional antenna alternative.

  1. Size of antenna

The size of the antenna selected will be determined by the availability of space in your planned setup, solution, or product. Clearly, a wearable or handheld device requires a smaller antenna than a 2.4 GHz omnidirectional outdoor antenna solution. There are many small ISM and 2.4 antennas can be secreted within devices for wireless communication including:

  • Wire antennas
  • PCB antennas
  • Chip antennas
  • Stamped metal antennas
  • Ceramic patch antennas
  • Dome antennas

Smaller size often limits the performance of the antenna, though UHF antennas like 2.4 antennas tend to be smaller than their HF and LF counterparts.

  1. Antenna range

A good ISM antenna will deliver excellent connectivity over a good range. A 2.4 GHz long-range antenna will have higher gain which can be calculated for a particular antenna by subtracting efficiency losses from the antenna's directional gain.

  1. Antenna performance

Evaluation of the performance of the 2.4 antenna you choose will be based on its key intrinsic properties. Always note:

  • Gain as discussed above, is the increase in power of the antenna and is measured in decibels.
  • Directivity is discerned by the shape of the antenna's radiation pattern.
  • Polarization regards the way in which the electromagnetic energy is transmitted or received by a particular antenna. It may be linear, circular, or elliptical.

These three factors will determine how you will optimally position and set up an antenna system as they each have to be addressed for the proper functioning of the antennas that participate in a wireless network.

Antenna matching also improves performance by optimizing impedance of the antenna input for maximum power transfer and reduction of any reflective losses.

Typically less complex and lower risk antenna designs are preferred as the consistency of service is assured. Complex antenna designs and configurations can easily become error-prone and accidentally detuned.

The positioning of your antenna will be critical to its performance. Free space around the antenna and line of sight will help to increase its visibility and functioning especially if the outer tip of the antenna, the most sensitive point, is kept clear. Proximity to the ground or materials like metal or plastic can alter the antenna performance or detune the antenna.

In conclusion

ISM frequency bands have provided the opportunity for significant advancement in the application of wireless communication. The 2.4ghz frequency band in particular has had a global impact due to its adoption as the carrier frequency for WiFi by the WiFi Alliance and it's harnessing by Bluetooth. Selection and proper deployment of ISM antennas, 2.4ghz antennas, and WiFi antennas are therefore keys to the optimal performance of the diverse range of applications that use this frequency band.

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