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This is part 39 of the LoRa/LoRaWAN tutorial.

In this video series different topics will be explained which will help you to understand LoRa/LoRaWAN.
It is recommended to watch each video sequentially as I may refer to certain LoRa/LoRaWAN topics explained earlier.

In this tutorial I will:
- again explain the difference between dBi and dBd,
- what an antenna E-plane and H-plane is,
- what the effect is of ground to an antenna,
- what the difference is between main, back and side lobes,
- what antenna gain is,
- what negative antenna gain is,
- what the relationship is between ERP, antenna gain and tx power,
- how to calculate loss using an example,
- what unity gain is,
- what an antenna beam width is,
- what a take of angle is,
- and what a front-to-back ratio is.

An isotropic antenna is a hypothetic (not physically realisable) point source antenna, that radiates its power uniformly in all directions.
An isotropic antenna is considered a lossless antenna which means it has an antenna efficiency of 0 dB (or 100%).

A special tuned ½λ dipole antenna is used as a reference antenna for test purposes.
A reference ½λ dipole antenna has an isotropic gain of 2.15 dBi.

dBi refers to the antenna gain with respect to an isotropic antenna.
If antenna A has a gain of 3 dBi it means antenna A has twice (2x) the power relative to an isotropic antenna in the peak direction.
dBd refers to the antenna gain with respect to a reference ½λ dipole antenna.
If antenna B has a gain of 3 dBd it means antenna B has twice (2x) the power relative to a reference ½λ dipole antenna in the peak direction.
If an antenna manufacturer specifies its antenna gain, it must use the reference i in dBi or d in dBd otherwise you do not know the antenna’s actual gain.

The relationship between dBd and dBi is:
dBi = dBd + 2.15

For a vertical polarised antenna the E-plane coincides with the vertical plane.
For a horizontal polarised antenna the E-plane coincides with the horizontal plane.
The E-plane and H-plane (H refers to the magnetic fields) are 90 degrees apart.
In the E-plane the radiation pattern of a ½λ dipole antenna looks like the number 8 with the maxima perpendicular on the dipole axis.
The radiation pattern is circular in the H-plane for a ½λ dipole antenna.

Please be aware an antenna normally does not operate in free space, unless its actually in deep space.
An antenna has always some ground effect, how much this effect is, depends on the antenna distance to the ground and the ground conductivity.

Main lobe is the lobe containing the highest power.
Opposite of the main lobe is the back lobe.
The other lobes are called the side lobes.

The antenna gain (G) is defined as the maximum radiated power produced by the antenna (Pantenna) main lobe compared to a reference isotropic antenna (Pisotropic) or reference dipole antenna (Pdipole) supplied with the same input power.

An antenna can have a negative gain.
For example an antenna has a gain of -3 dBd or -1.15 dBi

A negative gain means that the antenna radiates less than the reference antenna and a positive number means that the antenna radiates more than the reference antenna.
The reference antenna can be an isotropic or dipole antenna.

The relationship between EIRP and ERP is:
EIRP (dBm) = ERP (dBm) + 2.15
or
EIRP(mW) = 1.64 x ERP (mW)

The maximum ERP = 25 mW for uplink and downlink (slot 1)
The maximum ERP = 500 mW for downlink (slot 2)

Unity gain is the power radiated by the antenna with the equivalent of 1x whatever the input power is.
In other words radiated power equals the input power.
Unity gain means a power gain of 1.

The antenna beam width, also known as half power beam width, is the angle between the half power (-3 dB) points of the main lobe.
The antenna beam width is the area where most of the power is radiated.
The antenna beam width for a reference ½λ dipole antenna is approx. 78°.

The take off angle is the angle where the gain of the elevation plot peaks.

The objective of a directional antenna is to transmit most of its radiated power in the forward direction and minimise its radiated power in the rearward direction.
The Front-to-Back Ratio (FBR) is expressed in dB (e.g. dBi or dBd) and is the forward gain minus the rearward gain.
The higher the FBR, the more directionally efficient the antenna is.

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