Brochures & General resources
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Direction Finding Antennas & Accuracy II
General
Alaris Cojot
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Direction Finding Antennas & Accuracy
General
Alaris Cojot
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An Introduction to Radio Direction Finding
General
Alaris Cojot
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Removable Dipole Radiator for Vehicle & Mast v1.0
General
Alaris Cojot
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Increasing Wideband Antenna Performance with Active Matching
General
Alaris Cojot
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Wideband Antennas - A Crucial Element in Todays RF Systems
General
Alaris Cojot
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Antennas in Unattended Ground Sensor UGS Systems
General
Alaris Cojot
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Switched Beam Antennas v1.0
General
Alaris Cojot
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Removeable Dipole Radiator for Vehicle and Mast Installations - A White Paper
General
Alaris Cojot
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Alaris COJOT - Expertise in antenna technology
General
Alaris Cojot
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COJOT White Paper: Increasing Tactical Wireless Network Performance with Switched Beam Antennas
General
Alaris Cojot
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Alaris COJOT Brochure
General
Alaris Cojot
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COJOT White Paper: Removable Dipole Radiator for Vehicle & Mast
General
Alaris Cojot
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COJOT White Paper: Wideband Antennas - A Crucial Element in today's RF systems
General
Alaris Cojot
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COJOT White Paper: Antennas in Unattended Ground Sensor UGS Systems
General
Alaris Cojot
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COJOT White Paper: Increasing Wideband Antenna Performance with Active Matching
General
Alaris Cojot
Frequently Asked Questions
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What to consider when using a monopole antenna?
A monopole antenna requires, in addition to the radiator, a ground plane as an essential antenna element. In order to work properly, typically an existing platform to which the antenna is attached to can be used as such (e.g. roof of a vehicle that is made of electrically conductive material like steel or aluminium). Monopole antennas will usually be smaller in height and slimmer in design than dipole antennas. This becomes especially important with antennas for lower frequencies as their size can be of the order of several meters.
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How to ensure proper capacitive (RF) grounding?
At radio frequencies the grounding can also be achieved by capacitive coupling even though there is no contact at DC. If you are using the rubber gasket which comes with the antenna (and which is in general non-conducting) and tighten the antenna well to the ground plane using the bolts that come with the antenna, then the capacitive grounding should be good enough for the antenna to perform as specified in the data sheet even though no DC path exists (assuming that the thickness of the layer of paint on the ground plane is of the order of tenths of millimetres). The use of any thicker non-conductive gaskets may, however, deteriorate the antenna performance starting at the lower frequencies.
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How to ensure proper DC grounding?
Proper grounding is achieved through a solid, short and non-inductive conductive path between the ground plane and the antenna base. COJOT antennas that require separate DC grounding have for that purpose a threaded bolt (M4) at the antenna base. A suitable grounding lead (length: 25cm) is supplied with the antenna. We recommend ensuring the DC grounding by connecting the grounding lead between the antenna base (through the 4 mm ring terminal at one end of the grounding lead) and the vehicle body (through the 5 mm fork terminal at the other end) to avoid the build-up of large static voltages and the resulting possibly harmful uncontrolled discharge of these.
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What to consider when using a dipole antenna?
Dipole antennas don't require a ground plane for proper operation. They are typically larger in height and bigger in design than monopole antennas, since they have the essential second conductive element already built-in.
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What is a rubber spring in COJOT manpack antennas?
Some COJOT manpack antennas feature a shock absorption spring made of rubber instead of steel. This new type of spring reduces the antenna's weight by up to 30% and better dampens oscillation. See the difference for yourself in this short video. https://youtu.be/WZWBeQwnJtM
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What to pay attention to when having to use a ground plane with the antenna?
The antenna ground plane must be made of electrically conductive materials like steel or aluminum (non-conductive materials such as fiberglass are not suitable). It’s important that the ground plane is large enough relative to the size of the antenna to ensure proper performance. Additionally, symmetrical ground planes are usually preferred, as an asymmetrical ground plane may alter the radiation pattern, causing the antenna to radiate more in some directions and less in others. When using monopole antennas, the installation location on the ground plane can significantly impact the antenna's radiation pattern. Optimal performance is generally achieved by installing the antenna at the center of the ground plane. While dipole antennas are less affected by ground planes, they can still experience some impact.
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What to consider when selecting the installation location for an antenna?
To achieve optimal radiation performance (coverage), it is essential to ensure proper antenna installation and carefully select its location. When installing one or multiple antennas, such as on a vehicle, several factors can negatively affect the antenna's radiation performance: Near Field Considerations: The area around the antenna (known as the near field) should be kept free of any objects, especially those that are electrically conductive. Objects in this area can severely impact the antenna’s functionality. The size of the near field depends on the frequency and antenna size. For example, a 2-meter antenna has a near field with a radius of approximately 0.8 meters at 30 MHz. Obstructions and Interference: Objects that block radio wave propagation can attenuate the signal or cause unwanted reflections and refractions, leading to degraded system performance. It is crucial to keep the desired transmission directions free from obstacles to avoid signal degradation. Ensuring these factors are considered during installation will significantly improve antenna performance and system reliability.
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Why to use the gasket that comes with the antenna?
We strongly recommend always using the gasket supplied with the COJOT antenna. Firstly, it helps prevent water ingress into your installation. Secondly, for some high-power COJOT antenna models, such as the WB10DXM, specific gaskets are required to achieve the maximum specified power rating. These special gaskets are made from highly heat-conductive material, enhancing heat dissipation from the antenna base by leveraging the mounting surface (ground plane) for improved thermal management. (When using the gasket, please also refer to the above question, ‘How to ensure proper capacitive grounding?’)
