In Radio Systems
For a line-of-sight radio system, the primary source of loss is the decrease of the signal power due to uniform propagation, proportional to the inverse square of the distance.
- Transmitting antennas are for the most part not isotropic aka omnidirectional.
- Completely omnidirectional antennas are rare in telecommunication systems, so almost every link budget equation must consider antenna gain.
- Transmitting antennas typically concentrate the signal power in a favoured direction, normally that in which the receiving antenna is placed.
- Transmitter power is effectively increased (in the direction of highest antenna gain). This systemic gain is expressed by including the antenna gain in the link budget.
- The receiving antenna is also typically directional, and when properly oriented collects more power than an isotropic antenna would; as a consequence, the receiving antenna gain (in decibels from isotropic, dBi) adds to the received power.
- The antenna gains (transmitting or receiving) are scaled by the wavelength of the radiation in question. This step may not be required if adequate systemic link budgets are achieved.
Read more about this topic: Link Budget
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