Basics of the BDA Bidirectional Amplifier
There are many circumstances where it is critical to extend the range and/or reach of a wireless communication system, such as inside a large entertainment venue, enterprise office space, deep mine, etc. In these circumstances when bi directional communication is needed, even a very high power transmitter at either of the link may not be enough and a BDA Bidirectional Amplifier placed between the two connection points is necessary. A BDA is simply an active device that is able to amplify the signals it receives and transmit those signals at a higher power level than when received. Some types of BDAs do this using the same antenna or signal path (half-duplex), while others use separate antennas and frequencies for transmit and receive (full duplex).
In order for a BDA to transmit a clean signal based on the typically low power and noise receive signal, it is often also useful to include some signal conditioning components within a BDA. This could consider an antenna that is specifically designed for the spectrum of the designed wireless communications and filters that help to reduce noise and interference outside of the frequency bands of interest. A receive antenna for a BDA is often referred to as a donor antenna, where the antenna used for retransmission is typically called the transmit, main, or external antenna.
Typically, bandpass filters are used to condition and filter the incoming wireless signals from a BDA Bidirectional Amplifier. These signals are then amplified by the internal amplifier. In some cases, the incoming signals may be amplified and then filtered, or undergo two stages of filtering both before and after amplification depending on the BDA design and the desired dynamic range capability of the BDA. As an example, this L-/S-band Bi Directional Amplifier, covers the frequency range of 30 MHz to 2.7 GHz, which is commonly used for military L-band radio communications, unmanned aerial vehicle (UAV), unmanned ground vehicle (UGV), 4G cellular communications, commercial air traffic control, weather/earth observation, and satellite communications. This BDA is a half-duplex BDA and can only transmit or receive in a given time slot, though the switching system is extremely fast and is capable of manual Tx/RX switching in 1 microsecond, typically.
A BDA Bidirectional Amplifier can be used either wired directly to transmission lines or waveguides for in-line amplification, they can be used with free-space communications on both sides, or a combination of guided waves and free space.