Military SATCOM Antennas

Satellite communications antennas are available in several shapes and sizes. Meanwhile, active electronically scanned arrays are increasingly making their presence felt in the SATCOM domain.

Satellite Communications Antennas

Antenna design is a huge subject within the Radio Frequency (RF) community. Satellite Communications (SATCOM) antennas are used to send and receive radio traffic to and from communications satellites. These antennas equip teleports, also known as ground stations. Teleports are dedicated facilities handling radio traffic to and from satellites. SATCOM antennas also equip satellite communications terminals. These terminals can be used by individuals for SATCOM and are often easily transportable.

SATCOM terminals also equip vehicles, ships and aircraft, and are used at deployed headquarters or at fixed military installations.

Rain Fade

At a basic level a SATCOM terminal antenna must be able to handle the frequencies of the satellite communications link that terminal serves. Most SATCOM travels over eight distinct Radio Frequency (RF) wavebands stretching from 240 megahertz/MHz to 40 gigahertz/GHz. There are so many SATCOM bandwidths because there is no single, ideal frequency usable for all satellite communications.

Each SATCOM bandwidth has its own unique advantages and disadvantages. For example, RF transmissions travelling across some bandwidths are relatively unaffected by atmospheric contaminants like rain or snow. However, these transmissions may carry less data than other bandwidths.

Water particles in the atmosphere can affect radio frequencies above eleven gigahertz. Known as ‘rain fade’, this phenomenon can see precipitation absorbing some of the RF signal’s energy at these frequencies. Rain fade can degrade the power, and potentially the range, of SATCOM transmissions. This is because the size of the particles is comparable to the wavelengths of frequencies of eleven gigahertz and above. Other SATCOM frequencies, particularly those below eleven gigahertz, are unaffected by rain fade, but need large antennas.

Dish Design

A rule-of-thumb for SATCOM antenna dish design is that the larger the dish, the weaker the signals the dish receives. By virtue of being in space some satellites, particularly those in geostationary orbits, can be between 35,786 kilometres/km (22,236 miles) and 42,164km (26,199 miles) above Earth. Satellites are limited in how much power they can put behind a transmission. A satellite has a finite amount of space to accommodate powerplants and solar panels to generate electricity while still being reasonably economical to launch. This compromise means that SATCOM signals may be very weak by the time they reach Earth.

A SATCOM terminal antenna must receive weak signals despite the prevailing electromagnetic noise on Earth and in space. This imperative is akin to being able to hear someone whisper at a distance in a loud room.

SWAP Requirements for Portable Satcom Antennas

Another important consideration relates to where the terminal, and hence the antenna, will be used. If the SATCOM terminal is to be employed by dismounted troops it must be highly portable. Reducing Size, Weight and Power (SWAP) is vital and relates to antenna design as much as it does to the rest of the terminal.

Keeping power consumption within acceptable parameters is another important consideration. Soldiers may be limited in terms of the batteries, solar power systems or generators they can take with them when on foot.

SATCOM on the Move Antennas

SWAP reduction is also a consideration for vehicle, ship, and airborne satellite antennas. While warships, some military vehicles and aircraft may appear large, available space on any platform is at a premium, regardless of antenna size. Weight and power consumption must also be carefully considered. Once again, this will influence the design of a SATCOM terminal’s antenna alongside the performance criteria mentioned above.

Fixed sites may need to worry less about SATCOM antenna SWAP considerations. If terminals are permanent or semi-permanent installations, SWAP strictures may be less pressing. Nonetheless, SWAP will be a consideration for terminals at deployed facilities like field headquarters. SATCOM terminals may need to be moved in and out of theatre by truck, rail, ship or aircraft. For this reason, it may be imperative that the terminal and its antenna can be accommodated on a trailer or in a standard shipping container.

AESA for SATCOM

A trend is being observed within satellite communications with the adoption of Active Electronically Scanned Array (AESA) antennas to equip SATCOM terminals.

AESA antennas can be configured as flat panels that can easily adorn the surfaces of a ship, aircraft or vehicle. Such antennas also have all their backend electronics enclosed within a single unit helping to reduce size and weight demands.

Another benefit is that the antenna electronically points its transmission signal towards the satellite. This avoids the antenna having to be physically moved provided it is oriented towards the general direction of the satellite. Much as AESAs have done in the radar domain, these antennas could be increasingly used to support SATCOM in the future.