FBW (fractional bandwidth)

Fractional bandwidth (FBW) is a term used in communication engineering to describe the bandwidth of a signal relative to its center frequency. It is a measure of the range of frequencies that a signal occupies in relation to its center frequency. FBW is an important parameter for a variety of applications in communication systems, including signal processing, antenna design, and radio frequency (RF) engineering.

In simple terms, FBW is the ratio of the difference between the upper and lower frequencies of a signal to its center frequency. It is expressed as a percentage or a decimal. A signal with a wide bandwidth has a high fractional bandwidth, while a signal with a narrow bandwidth has a low fractional bandwidth.

The formula for calculating fractional bandwidth is as follows:

FBW = (f2 - f1) / fc

where:

f2 = upper frequency of the signal f1 = lower frequency of the signal fc = center frequency of the signal

For example, consider a signal with a center frequency of 1 GHz and an upper frequency of 1.5 GHz and a lower frequency of 0.5 GHz. Using the formula above, we can calculate the FBW as follows:

FBW = (1.5 GHz - 0.5 GHz) / 1 GHz = 1

Therefore, the FBW of the signal is 100% or 1.

In communication systems, the FBW of a signal is an important parameter that affects the performance of the system. A signal with a high FBW requires a larger bandwidth, which may limit the number of channels that can be transmitted simultaneously. On the other hand, a signal with a low FBW can be transmitted over a smaller bandwidth, allowing more channels to be transmitted.

The choice of FBW also depends on the application. For example, in wireless communication systems, signals with high FBW are used to transmit large amounts of data, while signals with low FBW are used for voice communication. In radar systems, signals with high FBW are used to detect targets with high resolution, while signals with low FBW are used to detect targets with low resolution.

Antenna designers also use FBW to design antennas that can operate over a range of frequencies. The bandwidth of an antenna is often specified as its fractional bandwidth, which is the ratio of its operating frequency range to its center frequency.

In addition to communication systems and antenna design, FBW is also used in RF engineering to specify the bandwidth of RF components such as filters and amplifiers. For example, a bandpass filter may be designed with a certain FBW to allow only a specific range of frequencies to pass through while rejecting all others.

One of the challenges in communication engineering is to design systems that can operate over a wide range of frequencies. This requires a thorough understanding of FBW and its effects on system performance. Engineers must carefully choose the FBW of a signal based on the requirements of the application, the available bandwidth, and the performance trade-offs.

In conclusion, FBW is an important parameter in communication engineering that describes the range of frequencies that a signal occupies in relation to its center frequency. It is used to specify the bandwidth of signals, antennas, and RF components, and affects the performance of communication systems. The choice of FBW depends on the application, and engineers must carefully consider the FBW of a signal to ensure optimal system performance.