Attenuation

What cannot be avoided in RF propagation is attenuation. Literally, attenuation is to reduce the strength of the RF signal. To be precise: when the signal propagates in the transmission medium, a part of the energy will be converted into heat energy or absorbed by the transmission medium, resulting in the continuous weakening of the signal strength. This phenomenon is called attenuation. The phenomenon that the signal of the UHF RFID reader decreases in amplitude after passing through the water medium is attenuation. The general attenuation is represented by L (Loss):

Attenuation in RF propagation exists in the following places:

• In the cable—The resistance between the cable and the connector converts RF into heat.
• The energy expansion caused by the path in the air is the biggest factor of failure, and dust, rain and fog in the air will cause failure.
• Passive components in the system heat up, causing the RF signal to fail.
• Artificially added to the system to reduce the sincerity (useful).

Gain

1) RF gain

Gain is the opposite of attenuation, resulting in increased RF signal strength. RF gain (not antenna gain) is generated by active devices. It can be understood that to amplify a signal, it must be given corresponding energy. Generally, gain is expressed as Gain:

Among them, P_o represents the output power, and P_i represents the input power. Gain's dB is negative for attenuation and P_o is less than P_i: Gain's dB is positive for gain and Po is greater than P_i. If a positive gain is achieved, external energy needs to be introduced and supplied to the amplifying device to achieve signal amplification.

Below Figure is a schematic diagram of attenuation and gain, where the signal is attenuated by passive devices to reduce amplitude and generate heat loss; the amplitude is enhanced by the energy gain provided by active devices. One thing to note is that the operating frequency of the signal remains the same regardless of gain or attenuation.

2) Antenna gain

When it comes to antenna gain, it needs to be distinguished from RF gain, which is completely different from RF transmission gain. The gain of an antenna is to increase the intensity of energy in a particular direction rather than to increase its total energy. Antennas are generally passive components and cannot provide additional energy to enhance the RF signal. Below Figure is a schematic diagram of the radiation of a pot-shaped microwave antenna. The transmission and reception of the antenna are sufficient to concentrate all the energy on the main lobe, and there is no new energy increase.