Frequency Bandwidth Calculator

Frequency bandwidth is the difference between the upper and lower cutoff frequencies in a continuous band that a system can process. It is typically measured at the −3 dB points, where the signal power has dropped to half of its peak value. A wider bandwidth means the system passes a broader range of frequencies.

The formula is BW = f₀ / Q, where f₀ is the center (resonant) frequency and Q is the quality factor. For example, a center frequency of 1000 Hz with a Q of 10 gives a bandwidth of 100 Hz. The higher the Q factor, the narrower and more selective the bandwidth.

The lower cutoff frequency f1 and upper cutoff frequency f2 are the −3 dB points of a bandpass filter. They are calculated as f1 = f₀ × (√(1 + 1/(4Q²)) − 1/(2Q)) and f2 = f₀ × (√(1 + 1/(4Q²)) + 1/(2Q)). The difference f2 − f1 equals the bandwidth BW.

The quality factor Q is a dimensionless number that describes how selective or narrow a resonant system's frequency response is. A high Q means a narrow bandwidth and sharper filter response, while a low Q means a broad bandwidth. Q and bandwidth are inversely related: Q = f₀ / BW.

Bandwidth is directly proportional to center frequency for a given Q factor. If you double the center frequency while keeping Q constant, the bandwidth also doubles. This means higher-frequency systems inherently have wider absolute bandwidths for the same Q, even though their relative bandwidth (BW/f₀) stays the same.

5G operates across several frequency bands. Sub-6 GHz bands (600 MHz to 6 GHz) offer broad coverage, while millimeter wave (mmWave) bands typically range from 24 GHz to 100 GHz for very high data throughput over shorter distances. Each band has its own bandwidth allocation defined by regulatory bodies.

The quality factor depends on the bandwidth of the system, not just the center frequency. For the hydrogen line at 1420 MHz, a typical narrow-band receiver might have a Q of several thousand. Using Q = f₀ / BW, if the bandwidth is 1 MHz then Q = 1420 / 1 = 1420.

Radio frequency (RF) bandwidth refers to the range of frequencies a radio system can transmit or receive. AM radio uses bandwidths of around 10 kHz per channel, FM radio uses about 200 kHz, and cellular systems can use anywhere from 1.4 MHz to 100 MHz or more depending on the standard and band.