2.1 Antenna Gain
The gain of an antenna stands for the amplification of its transmission energy. This gain is achieved by the transmission energy being focused by the antenna in horizontal and/or vertical direction. (see 2.2 opening angle).
A spherical emitter is a theoretical concept used for calculating antenna gain. It emitts the transmission energy uniformly in all directions, so it has no antenna gain (o dBi or 0 dBd). Omnidirectional antennas radiate transmission energy horizontally in a 360° radius, while less than 360° on a vertical axis. This results for example in case of the antenna with the article number 10926 in a gain of 2.5 dB.
2.2 Radiation Characteristics of an Antenna
The radiation characteristics of an antenna, also described as opening angle or beam width, can be displayed in a graphic that represents the directivity of an antenna. The opening angle refers to the area in which at least half of the maximum radiated power is available.
2.3 Omnidirectional Antennas
An omnidirectional antenna has an even radiation pattern horizontally in all directions. That means it has a horizontal opening angle of 360°. Therefore it is often used in rotating or mobile applications.
Tilt refers to the shifting of the vertical opening angle of an omnidirectional antenna in a specific direction, related to the horizontal level. The image below shows a vertical Opening angle of 40° with a tilt of 20°. This means the vertical opening angle has shifted 20° upwards.
2.4 Directional Antennas
A directional antenna focuses its radiation density in a specific direction. Due to its directivity, interfering transmitters placed outside of primary or secondary lobes are muted, and the antenna increases its reach in beam direction. Consequently the antenna radiates in one direction only, with an opening angle of e.g. 80°.
2.5 Fresnel Zone
The Fresnel zone is a 3-dimensional ellipse drawn between transmitter and receiver. The vertical radius of this zone is made up by transmission frequency and distance between the antennas. In an ideal setting there should not be any objects inside this zone. Objects inside the Fresnel zone have a negative influence on transmission range. Too many objects inside the Fresnel zone can block the connection entirely.
Example: At 2,4 GHz (DATAEAGLE with Bluetooth) and with a distance of 100m between antennas the Fresnel zone has a maximum radius of approx. 2m. At a frequency of 2,4 GHz, in order to ensure best possible operating conditions and longest reach, the antenna should be mounted at a height of 4 m.
Polarization indicates the directions of vibrations created by the electric field. It’s distinguished between horizontal and vertical linear polarization (VP), and right hand circular polarization (RHCP). The transmitting and the receiving antenna should have identical polarization. In case of unequally polarized antennas you can experience loss or no radio connection at all. We use antennas with vertical linear polarization (VP) or right hand circular polarization (RHCP). An RHCP antenna is suitable for directional radio communication with sight connection. For all other applications we recommend VP antennas.
2.7 Transmitting Power
Transmitting power, or EIRP (equivalent isotropically radiated power) indicates the actual output of the antenna. This value is a combination of the initial transmission power coming from the source (in this case the DATAEAGLE), minus attenuation loss coming from cable, adapter, lightning protector, plus antenna gain.
The equivalent transmitting power is regulated by law. The maximum values allowed vary depending on which frequency band is used, such as 100 mW / 20dBm on Bluetooth 2,4 GHz.
2.8 Link Budget
Link budget measures the difference between radiation power (EIRP) and receiver sensitivity. The link budget allows you to estimate the reach of the signal. To get a correct estimate you have to take a number of factors into account:
– Radiation power
– Antenna gain
– Receiver sensitivity
– Free space loss
– Cable attenuation
Reflections are disturbances that occur when radio signals meet obstacles on their way. Due to these reflections, the radio waves can overlap, thus causing interference.
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