7 Factors to Consider When Selecting a Military Antenna
Selecting a military antenna comes with many complex considerations to ensure it fits the application requirements. Here are seven key things to consider when choosing yours.
1. Frequency
The frequency range or bandwidth of an antenna indicates the range of frequencies over which the antenna has been designed to have an optimal VSWR and beam pattern for the antennas use case. If a wide bandwidth isn’t necessary, a narrow band should be chosen, suited to the specific application the antenna is intended for, as this will allow for a better matched VSWR, and improved gain and beam pattern.
2. Power Rating
The power rating defines the maximum RF power that can be applied to the antenna without resulting in damage. Receiving (Rx) antennas generally receive low RF power so the power rating is almost exclusively only relevant for transmitting (Tx) antennas, where high powers are applied to ensure that an observable signal is received by a receiving antenna after traversing a large distance. Applying more power than the antenna is rated for could potentially cause irreversible damage.
3. Beam Pattern
Whilst an antenna may appear to perform well with a low VSWR over the frequency range of interest, the antenna may be focusing its power in the wrong direction. Depending on the application, a user may require an antenna with an omnidirectional beam pattern where the antenna is equally good in all directions, or they may require a directional antenna where all of the antenna’s performance is focused in one direction. The beam pattern of an antenna is also frequency dependent so careful consideration needs to be made when choosing an antenna to ensure it is operating at all frequencies as expected.
4. Polarisation
The polarisation of an antenna describes the direction of the electrical field vector of the electromagnetic waves being transmitted. The most used polarisations are:
- Vertical Polarisation – where the electric field is in the vertical plane
- Horizontal Polarisation – where the electric field is in the horizontal plane
- Right Hand Circular Polarisation (RHCP) – where the electric field vector rotates in the clockwise direction relative to the direction of wave propagation
- Left Hand Circular Polarisation (LHCP) – where the electric field vector rotates in the clockwise direction relative to the direction of wave propagation.
As an example, a vertically polarised antenna will not receive a horizontally polarised signal, and it will only receive the vertical component of a circularly polarised signal which will result in a received signal reduction of 3dB. Therefore the polarisation should be chosen to match the signals and antennas used in the system to prevent potential signal loss.
5. VSWR
Voltage Standing Wave Ratio (VSWR) is a measure of how well matched an antenna is to a load or source. It is equivalent to return loss which describes how much of the power put into an antenna is reflected back, and thus the amount of power that is successfully transferred into the antenna. A VSWR of 1 indicates that all of the power applied to an antenna is successfully transferred into the antenna. Reflected power is unwanted as it means a reduced radiation power, and it may interfere with components within a system’s RF frontend which could cause oscillations, in band ripple and even irreversible damage.
6. Size
Antenna sizes are heavily driven by the frequency/wavelength that they are designed to work at, with higher frequency antennas being smaller. Different antenna technologies will be different shapes and sizes. Transmit antennas that are required to deal with much higher input powers than their receive counterparts will be physically larger. The dimensions, weight and portability of the antenna are important to consider as they affect where the antenna can be used and how easily.
7. Environment
Antennas are used in a wide variety of environments, some of which can potentially expose the antenna to harsh and hostile environments, such as large temperature swings, harsh sunlight/high levels of UV rays, high humidity, salty air or chemical exposure. There are also certain applications in which the radar cross-section and infrared emissivity are of concern. All of these factors determine the material construction, IP rating, or other environmental specifications that are required to be met. Careful consideration must be made to ensure that the antenna you choose is sufficiently rugged for your application.
The above considerations are just the key factors for selecting antennas to meet specific requirements in a complex system. You can contact PPM Systems to discuss your requirements further and find a range of antennas for Military Communications here.