Bidirectional Amplifier Basics

Bidirectional Amplifier Basics

Bidirectional Amplifier Basics

By: Steve Bowman


Bidirectional Amplifier, or Bi-directional Amplifier (bda), is an active RF device that is widely used in a variety of telecommunication, radar, and other RF sensing applications. Though conceptually a Bidirectional Amplifier performs a relatively simple operation, the internal electronics can be somewhat complex. Moreover, many applications favor certain names and types of Bidirectional Amplifiers, which makes identifying a Bidirectional Amplifier in the wild somewhat difficult. The follow is a list of common names for Bidirectional Amplifiers:

Bidirectional Amplifier (bda) Common Names:
Antenna Amplifier
East-West Amplifier
Cable Amplifier
Range Extender
Cellular Repeater/Extender
WiFi Booster/Extender/Repeater/Amplifier
Signal Booster/Extender/Repeater/Amplifier

What does a Bidirectional Amplifier (bda) do?

The essential functions of a Bidirectional Amplifier are to amplify the signals transmitted by and received by the device. This means that signals generated by a telecommunication or sensing and intended to be transmitted will benefit from a higher output signal and the low power signals received by the antenna of the Bidirectional Amplifier will also experience some gain. The goal of a Bidirectional Amplifier is to gain the transmit and receive signals without adding significant noise or distortion. To do this, a Bidirectional Amplifier is typically placed either inline as a “booster” or “repeater” in a communication system. This can be done by installing a Bidirectional Amplifier on a tower with transmit/receive antenna or inline with a coaxial or waveguide transmission line to add gain to signals traveling between two distant points.

What is a Bidirectional Amplifier (bda)?

To gain both the transmit and receive signals a Bidirectional Amplifier requires both a Power Amplifier (PA) in the transmitter side signal chain and a Low-noise Amplifier (LNA) in the receive side signal chain. Moreover, a Bidirectional Amplifier consists of a means of separating the transit and receive signal chains from each other, so that the high power transmit signals aren’t fed into the LNA and the receive signal chain is optimized to reduce loss and minimize added noise to the received signals. There are a variety of methods to separate the transmit and receive signals, either with RF Switches, Duplexers, or Circulators. A Bidirectional Amplifier that uses Duplexers or Circulators and allows for simultaneously transit and receive functions is known as a Full-duplex Bidirectional Amplifier. The difference between a Duplexer-based Bidirectional Amplifier and a Circulator-based Bidirectional Amplifier, is that A Duplexer is a type of bandpass filter that separates signals from it’s input to the two outputs based on frequency, where a Circulator separates the signals at the input based on direction. A Bidirectional Amplifier that uses RF Switches to separate the transit and receive signal chains can only allow for transmission or reception at a given time and is known as a Half-duplex Bidirectional Amplifier. Typically a Bidirectional amplifier has either coaxial connector interconnect or waveguide interconnect depending on the type of system or application the device is used.

How does a Bidirectional Amplifier (bda) work?

A Bidirectional Amplifier works by separating the transmit and receive signals into separate signal chains. Once separated, the transmit and receive signals are then increased in signal strength using either a PA for the transmit signal or an LNA for the receive signal. A Bidirectional amplifier is installed in such a way that the receive signals to the radio or transmission line are increased in strength and isolated from the transmit signals and vice versa.

Courtesy of Pasternack

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