Antenna Bandwidth Calculator
Calculate antenna bandwidth, center frequency, fractional bandwidth, bandwidth ratio, quality factor, and bandwidth classification.
2
Inputs
Live
Math
3
Related
Enter parameters and click Calculate to view results
Formula & Theory
BW = fH − fL, FBW = (BW ÷ fC) ×100, Q = fC ÷ BWThis formula is used to calculate antenna parameters for antenna bandwidth calculator.
Overview
The Antenna Bandwidth Calculator estimates critical frequency response parameters for RF antenna designs. Easily calculate absolute operating bandwidth, arithmetic center frequency, Fractional Bandwidth (FBW), bandwidth ratio, radiation Quality Factor (Q), and bandwidth classification (Narrowband vs. Ultra-Wideband) based on lower and upper cut-off frequencies.
Input Guide
Enter Lower Frequency, Upper Frequency exactly in the units shown by this antenna bandwidth. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Lower Frequency — use MHz.
- Upper Frequency — use MHz.
Output Guide
The results describe the calculated antenna bandwidth values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Antenna Bandwidth uses BW = fH − fL, FBW = (BW ÷ fC) ×100, Q = fC ÷ BW. Supply Lower Frequency (MHz), Upper Frequency (MHz) in the displayed units, then use the calculated values as the first engineering target for this basic antenna parameters design or analysis.
Design Notes
Antenna bandwidth is typically defined by impedance matching criteria, such as VSWR ≤ 2.0:1 or Return Loss (S11) ≤ -10 dB across the band. High-Q antennas (like electrically small loops or thin dipoles) offer narrow bandwidths, making them highly selective but sensitive to detuning. Conversely, low-Q designs (such as biconical, log-periodic, or planar UWB antennas) yield wider bandwidths at the cost of higher physical volume or lower peak directional gain.
Build and Tuning Notes
Measure actual operating bandwidth using a Vector Network Analyzer (VNA) or SWR meter. If the measured bandwidth is narrower than calculated, consider increasing conductor thickness/diameter, adding parasitic elements, utilizing thicker PCB substrates with lower dielectric constants, or inserting impedance matching networks. Always perform VNA calibrations at the antenna feedpoint plane to eliminate cable phase shift and loss errors.
Frequently Asked Questions
What is Fractional Bandwidth (FBW) in antenna design?
Fractional Bandwidth measures the relative bandwidth of an antenna expressed as a percentage of its center frequency: FBW = (Absolute Bandwidth ÷ Center Frequency) × 100. It helps classify antennas as Narrowband (< 10%), Wideband (25–50%), or Ultra-Wideband (UWB ≥ 50%).
How are Antenna Quality Factor (Q) and Bandwidth related?
Quality Factor (Q) is inversely proportional to Fractional Bandwidth (Q ≈ 1 / FBW). A high-Q antenna stores more reactive energy per cycle, resulting in sharp resonance, narrow operating bandwidth, and high tuning sensitivity. A low-Q antenna dissipates or radiates energy more rapidly, offering broader bandwidth.
What S11 or VSWR threshold defines lower and upper frequencies?
In commercial and amateur radio RF engineering, lower (fL) and upper (fH) frequencies are defined where antenna return loss drops below -10 dB (VSWR 2:1) or -3 dB (half-power bandwidth), depending on system requirements.
What is Bandwidth Ratio (fH / fL)?
Bandwidth ratio expresses the upper frequency limit relative to the lower limit (e.g., a 2:1 ratio antenna covers 100 MHz to 200 MHz). It is commonly used to describe frequency-independent and ultra-wideband (UWB) antennas like log-periodic arrays.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.