Choosing the right antenna is not as simple as picking a random high gain 4G antenna and expecting it to work! There are several types of antennas and connectors. Even the cable type and length can make a difference.
Before considering an antenna, check out the article on choosing the right 3G/4G router. A proper mains-operated 4G router can do away with most indoor antennas.
Like TV antennas, there are a wide range of 3G and 4G antennas. These range from small portable antennas to large outdoor antennas. Portable antennas generally provide a significant signal boost for small data modems and portable hotspots. However, they may not provide any benefit over the internal higher gain antennas in larger mains-operated desktop routers.
Larger outdoor antennas can provide a vast signal improvement, particularly if mounted high up. They are available in a choice of single and MIMO, omni-directional and directional, wideband and band specific. Antenna suppliers may also offer a choice of cable connectors.
- Cell towers enforce a maximum range! – Seriously.
- Active signal boosters / mobile repeaters – Caution!
- Portable antennas – Avoid, except for portability.
- Single vs MIMO antennas – MIMO involves two antennas.
- Omni-Directional vs Directional – Indoor or outdoor?
- Antenna gain and radiation pattern – Directivity.
- 3G and 4G band coverage – Wide or narrow band?
- Cable connectors – SMA, FME, CRC9 and TS9.
- Cable and connector impedance matching – Avoid TV/sat coax!
- Coaxial cables – Choosing the right coax and length.
- DIY with UHF TV antennas and satellite dishes – On a budget?
Update 16th April 2018: I added the Antenna gain and radiation pattern section. If a directional antenna does not have a radiation pattern graph, consider avoiding it!
Cell towers enforce a maximum range!
Before purchasing any antenna, first check that 3G/4G reception is possible with a router. For example, try operating the router outdoors or outside an upstairs window facing the cell tower. If a router fails to connect in 3G or 4G mode, an antenna will very unlikely help.
Cell towers determine the distance based on the signal round trip time between it and the user’s equipment. Devices with round trip times over the configured threshold will be considered out of range, preventing a connection. This cannot be overcome even with clear line of sight and a powerful antenna. See this troubleshooting article for further information.
To make matters worse, there may be different range limits for phones and data devices. This is the case with the Three network in Ireland. A phone that picks up 4G does not necessarily mean that a router will also be able to operate on 4G. In 4G+ areas where cell towers operate simultaneously on bands 3 and 20, the cell tower may enforce different range limits for each band. See the band coverage section below.
Active signal boosters / mobile repeaters
Do not confuse antennas with signal boosters or repeaters! A signal booster, also known as a mobile repeater, amplifies the signal in each direction. These are typically placed inline in-between an indoor and outdoor antenna.
Most low cost non EU mobile boosters blindly amplify everything, including background noise and other sources of interference. Improper isolation of the indoor and outdoor antennas can result in signal oscillations, like a PA speaker whistling near its microphone. These unwanted transmissions can severely affect the mobile networks in the area, not just one network.
According to ComReg, mobile repeaters are the main source of interference in Ireland. Mobile repeaters and boosters that don’t meet ComReg’s strict criteria are prohibited for consumer use. It is also illegal to posses non-compliant signal boosters and they can be seized by customs.
Antennas, cables and connectors on the other hand are purely passive components. These carry the signal received over the airwaves or transmitted by the data device’s radio hardware. A purely passive antenna setup connects directly to the antenna ports of the data device.
ComReg has recently permitted the use of mobile repeaters that meet their strict technical conditions. However, even with a high quality mobile repeater, it will only improve the reception on one polarity. While this is great for calls, texts and data on mobile phones that lack antenna ports, 4G MIMO reception requires two repeaters running in opposite antenna polarities.
4G will work with a single repeater for the correct 4G band, but with its bandwidth cut in half. One workaround for 4G MIMO would be to use an indoor rabbit ear antenna on the router’s port #1. Then install an outdoor antenna with the opposite polarity and connect it to port #2.
Warning: Do not connect a repeater or signal booster directly to the antenna port of a modem or router! This will potentially damage the repeater or the modem/router, like connecting an speaker amplifier to a microphone input.
A quick search of “4G antenna” on eBay or Amazon will return countless sellers offering antennas like the image on the right. This type of antenna can be useful when travelling with a data dongle or hotspot. For example, the antenna can attach to a campervan window with its suction cup. Check that the antenna has the correct connector to fit the data dongle or hotspot. TS9 and CRC9 require different connectors despite looking similar.
This type of antenna will unlikely offer any improvement for desktop routers. These routers have much more sensitive antennas than the tiny antennas in dongles and hotspots. The exception would be to locate antenna in an area that the router cannot easily go.
The “rabbit ear” antennas that attach directly to the ports can also be hit & miss. With routers that have internal antennas, external antennas can avoid interference from circuitry within the router. The benefit is usually minimal, sometimes no better than repositioning the router, turning it or raising its height.
Single vs MIMO antennas
All antennas with two cable connections are MIMO antennas. With 4G MIMO, one antenna is polarised at a 90-degree angle to the other. This effectively doubles the bandwidth by transmitting on opposite polarities simultaneously within the same band. With 3G, the second antenna handles receive diversity. The second antenna picks up signals that bounce from directions the main antenna misses and vice versa.
While 3G can operate with a single antenna, a second antenna can provide up to double the performance. If the data device lacks a second antenna connection, consider replacing it. Most 4G devices support diversity on 3G, with advantage of 4G support when it becomes available. See my router advice article for further information.
Wideband LOG antennas are typically available in a pair (right image), one coaxial cable per antenna. As the Irish networks operate on vertical and horizontal polarity, mount one antenna vertically and the second horizontally. The antennas can be up to several metres apart, however, both antennas must face the same cell tower.
From my own rural area testing, I find LOG antennas perform at their best a few metres apart. LOG antennas are also available that handle both polarities in one unit, as shown on the right. I suggest going for two separate LOG antennas over this type of antenna for fringe reception areas. Based on my testing, a dual polarity LOG antenna tends to perform no better than using just one LOG antenna.
Omni-Directional vs Directional
Portable antennas and larger indoor antennas are generally omni-directional. When the cellular signal penetrates the building, it will often bounce off various surfaces before reaching the antenna. While directional antennas have higher gain, it may not be possible to achieve a stronger signal than omni-directional antennas. An omni-directional antenna picks up the main signal as well as signals that bounce off objects from other directions.
Directional antennas generally perform better with clear line of sight of the cell tower. Unlike indoor reception, the signals coming from other directions are likely unwanted signals from other cell towers. A directional antenna will attenuate these unwanted signals that otherwise introduce interference. The higher gain facing the cell tower will also provide a stronger uplink signal at the cell tower receiving end.
The best place to install an omni-directional antenna outdoors is against a wall or gable. This will help attenuate unwanted signals coming from behind the antenna. See the ComReg SiteViewer to see the locations of the mobile operator masts, which will give an idea which side to install the antenna and the direction to aim it.
Antenna gain and radiation pattern
With antenna manufacturers trying to outdo each other on marketing, a lot of antennas have false gain ratings. If a wideband antenna gain rating is over 15dB, it very likely is a false rating. For example, the Wittenberg LAT-56 is one of the most sensitive wideband LTE antennas I’m aware of. Despite its 98cm length, its maximum gain rating is just 11.5dBi.
All omni-directional MIMO antennas have a maximum gain of 2.4dBi. These antennas basically contain a pair of dipoles, cross polarised. Even the popular “35dBi” portable antennas are typically 2dBi max.
When comparing directional antennas, look for the radiation pattern graph. If the antenna does not have a radiation pattern graph, I recommend avoiding that antenna for trying to isolate a mast. The exception would be for very long antennas (80cm+), which have a narrow acceptance angle. Note that omni-directional antennas generally do not provide a radiation pattern graph. The horizontal plane would be a circle and the vertical plane would be a figure 8 shape.
The following is an example from the Wittenberg LAT-56:
This graph shows the radiation patterns for three LTE bands – 2.6GHz (band 7), 1800MHz (band 3) and 800MHz (band 20). The ‘E’ plane (from the German data sheet) is for the vertical plane.
The top section of the graph shows the acceptance angle. Going by these graphs, the aim can be 30 degrees off to the left/right or up/down before losing about 3dB of signal.
The pattern around the rest of the graph shows the signal rejection. For example, if there is another mast anywhere between 60 degrees and 300 degrees to where the antenna points, this antenna will weaken the unwanted signal by over 18dB.
Panel and smaller LOG antennas typically have a larger acceptance angle and less rejection. Their smaller size make them easier to install, particularly in areas where the user has clear line of sight of the mast.
Band-specific antennas are much more sensitive for the equivalent wideband antenna size. For example, the Wittenberg LAT 22 offers 3dB higher gain than the above antenna for the 800MHz (band 20), has a narrower acceptance angle (more directional) and is 20cm shorter.
3G and 4G band coverage
Portable and omni-directional 4G antennas are generally wideband and cover the main 3G and 4G bands in Ireland. Directional antennas like group band TV antennas are available in both wideband and band specific. Band specific antennas provide higher gain and directivity than wideband for the same antenna size.
Single band coverage
All mobile operators in Ireland currently operate on 900MHz and 2100MHz for 3G and 800MHz and 1800MHz for 4G. The 800MHz 4G and 900MHz 3G bands have extensive coverage in rural areas due to the long signal propagation. The 2100MHz 3G and 1800MHz 4G bands mainly serve urban areas and larger towns due to the higher bandwidth.
For users over a kilometre from the nearest town, an 800-900MHz antenna will generally be adequate. An 800MHz panel antenna (right image) provides high gain, good directivity and is no larger than a typical grid TV antenna. It can easily mount on a typical TV antenna wall bracket.
Within the town limits and urban areas, I strongly recommend checking what bands are available. Many Samsung, iPhone, Android 7+ phones and rooted Android phones can display the bands in use. On Samsung phones, dial *#0011#. For iPhone, dial *3001#12345#*. With other phones, install the CellMapper app. It can read frequency information on many Android 7+ and rooted phones and look up the LTE band on others. For phones that cannot read band information, go into the CellMapper’s Settings menu and turn on “Estimate Frequency Bands”. It will look-up the LTE band # from its server, which requires an Internet/data connection. If the phone shows ‘4G+’ on the network, then both 4G bands are in use.
LTE Advanced / 4G+ carrier aggregation
4G+ cell towers in Ireland operate on 800MHz and 1800MHz simultaneously to provide higher bandwidth. LTE cat 6 and higher devices connect to two bands simultaneously in 4G+ mode, also known as carrier aggregation.
For regular 4G devices (LTE cat 4 and lower), the cell tower may determine the band the device can use depending on the physical distance from the router. Some cell towers restrict devices within a certain range to the higher band only, while devices far away can operate on 800MHz only. As a result, I recommend choosing a wideband antenna if 4G+ is available in the area.
The most common band specific patch, panel and Yagi antennas are as follows:
- 800MHz – 4G bands 8 & 20 and 3G band 900MHz.
- 1800MHz – 4G band 3, some also extend to cover 3G band 2100MHz
- 2600MHz – 4G bands 7 & 38, not yet in use in Ireland
- 1710-2700MHz – Upper 4G bands, including 4G band 3, 7 & 38. These may cover 3G band 2100MHz.
LOG antennas are wideband only and generally cover all the 3G and 4G bands between 700MHz and 2700MHz.
Beware – So called “4G Ready” and “LTE Ready” antennas do not work with 4G! These are UHF TV antennas with circuitry added to filter out the 800MHz 4G band, formerly used by UHF channels 61-69.
Most desktop routers include either SMA or FME connectors. Huawei routers generally have two SMA connectors behind a removable panel on the back of the router. Portable 4G hotspots and data dongles typically have two small CRC9 or TS9 antenna connectors. The cable connectors must match to connect.
Adapters are available to connect from SMA to CRC9 or TS9 or from FME to CRC9 or TS9. Most of these adapters typically include two screw-on ends to fit either CRC9 or TS9.
Cable and connector impedance matching
People often ask me if they can reuse their satellite coaxial leads, such as from an old Sky dish. Unfortunately, satellite and TV cables are unsuitable for cellular antennas due to an impedance mismatch. TV antennas and satellite dishes use 75 Ohm cable. 3G and 4G antennas and data devices require 50 Ohm cable.
The two types of cable and connectors may look very similar. However, both have different characteristics such as inner/outer radii and the dielectric insulation in-between. While 75 Ohm cable can carry the signals, a small portion of the signal reflects when it meets the 50 Ohm impedance mismatch at each end of the cable.
Besides signal loss, the reflected signals are particularly troublesome with 2-way transmissions such as a video call. Each time the radio hardware transmits a signal, the reflections may obliterate the incoming transmissions. This can severely affect the performance or cause frequent drop-outs.
See this article for in-depth detail covering the differences between 50 Ohm and 75 Ohm cable and connectors.
Most antennas are typically available as complete kits, which include one or two antennas, 5 to 10 metres of RG-58 coaxial cable and the connectors. Some kits also include a wall mount bracket.
Try to keep the cable run as short as possible, preferably within 10 metres. With short cable runs, the signal to noise ratio remains mostly consistent all the way to the radio hardware. With long cable runs, some otherwise discernible signals will fall below the noise floor of the radio hardware. Similarly, unwanted signals that penetrate the cable shielding will interfere with the weakened signal towards the device end.
50 Ohm cable also requires a suitable 50 Ohm SMA, FME or ‘N’ connector at each end. Complete antenna kits typically include the proper matching connectors prefitted. While twist-on ‘F’ connectors and adapters may be tempting for a DIY cable build, they are 75 Ohm rated. As with using unsuitable cable, 75 Ohm connectors will introduce signal loss and reflections.
DIY with UHF TV antennas and satellite dishes
Older UHF antennas that handle UHF channels 61-69 can be modified to pick up LTE band 20 (800MHz). This typically involves replacing the 75 Ohm balun/cable connector and dipole assembly with a small cellular dipole antenna.
See the following video on YouTube where someone modified a TV antenna to function as a high gain LTE antenna.
Satellite dishes are a popular way of receiving the higher LTE bands 7, 38 (both 2600MHz) and 3 (1800MHz). This typically involves replacing the LNB with a small LTE antenna or a USB data dongle with water proofing.
The image on the right shows a purpose built MIMO antenna installed in the “LNB” holder. This type of setup generally does not work with the lower 800/900MHz bands. Unfortunately, with Irish operators enforcing strict distance limits from newer and upgraded cell towers, the satellite dish method will unlikely work more than a few kilometres of the cell tower either.