In this article we will talk about the different specifications that are important when choosing an antenna and what makes an antenna compatible with your GNSS receiver, or better than another one.
We will use the Ellipse-N/D internal receiver as an example here. You can find below the specifications for it:
Connection:
Connector type:
There are different connector types available depending on the antennas and sometimes they are not the same as the connector type on the receiver side. This is easily fixed with an adapter. For example, the Ellipse-N/D uses SMA female connectors because they are smaller, but the Tallysman TW3972 uses TNC female connectors so most of the time a TNC cable male male will be used with it. An SMA male to TNC female adapter will allow you to connect the TNC cable to the antenna on one side and to the Ellipse on the other side.
This one is easy as 50 Ohm is an industry standard for coaxial cables and power amplifiers, so most coaxial cables, GNSS receivers and antennas will use 50 Ohm.
Power supply:
Active vs Passive:
Active antennas are passive antennas that also have an integrated Low-Noise Amplifier (LNA). Because of this, active antennas need a power supply that is usually fed through the coaxial RF cable by the GNSS receiver. SBG Systems embedded GNSS receivers require the use of active antennas.
Voltage:
The power supply that an antenna will accept is usually within a certain range. For example, the Tallysman TW3972 antenna will accept 2.5 to 16 VDC so it will be compatible with the Ellipse receiver that outputs 3V here, but also the Ekinox or Apogee receivers that output 5V.
Current draw:
Some antennas will draw more or less current compared to another antenna, and this current draw can depend also on the voltage used. The Tallysman TW3972 requires 24mA. So it is important to make sure the receiver can provide this much current. The Ellipse-N or D can output up to 30mA so it is compatible.
Signal:
Amplifier gain :
The antenna LNA gain is the ratio of input to output power.
The gain of the antenna should be within a range that is compatible with the GNSS receiver. For example the Tallysman TW3972 will have a gain of 37dB, and the Ellipse will be compatible as long as the gain is between 17 and 50 dB, so this antenna is compatible with the Ellipse.
Constellations :
A constellation is a set of satellites that work in the same network. GPS is the American constellation, Glonass is the Russian one, etc. A constellation is usually usable anywhere on earth, the GPS constellation is American but is available worldwide to everyone for example.
It is important to use an antenna that can use constellations compatible with the receiver. If the antenna is only compatible with GPS, then even if the receiver is compatible with GPS, Glonass, Beidou and Galileo, it will only use the GPS constellation which is limiting. And vice versa if the antenna is multi-constellation but the GNSS receiver is only compatible with GPS for example. The best choice would be an antenna that is compatible with the same constellations as the GNSS receiver.
Frequency band:
A same constellation will use different frequencies, also referred to as bands (L1, L2, L5 or L6). When using a dual antenna GNSS receiver for heading computation it is important to use L1/L2 antennas at the least because L2 is required for this. With an L1 only antenna the receiver won’t be able to compute a heading.