Antennas for Maritime ApplicationsOctober 2021
In this post, we will answer some of the most common questions regarding marine antennas.
What makes an antenna suitable for maritime applications?
Perhaps the most obvious answer is that the antenna has to be essentially waterproof. Any antenna that is put on a boat must be “marinized,” meaning that it must be optimized or modified for marine use. Any active or electronic elements such as PCBs, for example, must be insulated and protected against water and weather, as well as enclosed in a plastic or corrosion-resistant metal.
What kinds of antennas are most typically found on a boat?
Normally, the number of antennas on a single vessel would be proportional to its size. To put simply, the bigger the boat, the more receiving and transmitting devices it will need. Besides the basic AM/FM antenna radios and WiFi, it is important for modern boats of all sizes to have a GPS system. Additionally, VHF (very high frequency) antennas are necessary for the vessel to transmit and receive signals. Sometimes, especially in cases where it is crucial to avoid misinterpretation of data, boats have to transmit the data digitally using DSC.
DSC, or digital selective calling, is an integral part of a boat’s GMDSS (Global Maritime Distress Safety System) station. MF/HF/VHF transceivers use the DSC to transit a signal digitally. These signals can include identification data, such as coordinates and MMSI (Maritime Mobile Service Identity), a mandatory identifier for ships subject to the GMDSS system.
Multi-band antennas can also be used at sea to amplify the signals from handheld devices. Blade antennas can also be used as radar (Radio Detection and Raging) devices. Radar antennas are especially important in maritime applications because it allows the user to avoid collisions by mapping out the coastline, as well as detecting other vessels even in poor visibility.
What is an AIS Transponder?
AIS stands for Automatic Identification System. Its purpose is to primarily avoid collision by monitoring the position of other AIS-equipped boats in the surrounding area, as well as other information such as the boats’ speed, course, name, type, size, and MMSI. AIS transponders operate within VHF, with a range between 10 and 30 miles, typically. AIS transponders are categorized in two classes: A for ships and fishing vessels, and B for recreational vessels.
Are antennas with higher gain better for marine use?
Not necessarily. In a previous post, we described gain (dB rating) as a measurement that combines the antenna’s efficiency with its ability to receive energy better from a particular direction. Essentially, a higher dB results in a more focused signal. When a signal is more focused in one area, in other areas, the signal will be weaker. The signal strengths of the vessel’s antennas should account for how much the vessel will rock.
How high should the antenna be mounted for it to work effectively?
Generally, the rule of thumb is that the higher the antenna is mounted, the further it can transmit. The antenna’s line of sight needs to be taken into account in addition to it’s actual transmission range.
How can I determine the best antenna for my nautical application?
The best way to find the ideal solution for your application is to consult with experts. Not only does JEM Engineering’s team specialize in antenna development, our existing products are modifiable to our clients’ specification. Additionally, we offer antenna testing services, which can be performed on-site, as well as remotely. To learn more about our rapid testing capabilities, please refer to An Intro to RF Testing.
Dielectric (non-conductive) materials, such as foam and wood, for example, are ideal for test fixturing.
The polarization of an antenna is loosely defined as the direction of the electromagnetic fields produced by the antenna as energy radiates away from it.
Microstrip antennas were patented in 1955, although their origins trace back to 1953. They became more commonplace in the 1970s.