What is antenna bandwidth?
Bandwidth is the range of frequencies within which the performance of an antenna, with respect to some characteristic, conforms to a specified standard.[1] Most often it means impedance bandwidth (e.g., VSWR ≤ 2), but it can also be defined for gain, pattern, beamwidth, efficiency or axial ratio. It is stated as a fractional bandwidth (fH−fL)/fc for narrowband antennas or as a ratio fH:fL for broadband ones.[2]
How does Q relate to bandwidth?
For a single-resonance antenna tuned to resonance, Yaghjian and Best showed that the matched VSWR bandwidth is approximately FBW ≈ (s−1)/(Q√s), where s is the VSWR limit; for s = 2 this gives FBW ≈ 0.707/Q.[3] Q itself is bounded below by antenna size; see Q factor and the Chu limit.
What bandwidths are typical?
| Antenna | Typical bandwidth |
|---|---|
| Half-wave dipole | ≈ 5–15% (VSWR 2), wider for thick elements |
| Patch on thin substrate | ≈ 1–5% |
| PIFA | ≈ 5–10% |
| Discone | up to ≈ 10:1 |
| Log-periodic, spiral | 10:1 and more |
| Vivaldi, ridged horn | ≈ 10:1 or more |
Values summarized from Balanis and the Antenna Engineering Handbook.[2][4]
How can bandwidth be increased?
- Thicker conductors and fatter shapes (biconical, bow-tie, blade).
- Thicker, lower-permittivity substrates for patches; stacked or parasitic patches; aperture coupling.[5]
- Multiple resonances (multi-branch PIFAs, parasitic elements).
- Frequency-independent geometries defined by angles (spirals, log-periodics).[6]
- Broadband or tunable matching, within the Bode–Fano limit.[7]
- Resistive loading, at the cost of efficiency.
Frequently asked questions
What is fractional bandwidth?
The bandwidth divided by the center frequency, usually in percent.
What is ultra-wideband?
In FCC rules, a fractional bandwidth of at least 0.20 or at least 500 MHz of −10 dB bandwidth.
Can matching networks add unlimited bandwidth?
No; the Bode–Fano limit bounds the achievable match over a band.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “IEEE Standard for Definitions of Terms for Antennas (IEEE Std 145-2013)”. IEEE Antennas and Propagation Society. 2014.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “Impedance, Bandwidth, and Q of Antennas”. A. D. Yaghjian and S. R. Best, IEEE Transactions on Antennas and Propagation, vol. 53, no. 4, pp. 1298-1324. April 2005.
- “Antenna Engineering Handbook, 4th ed.”. J. L. Volakis (ed.), McGraw-Hill. 2007.
- “Microstrip Antennas”. D. M. Pozar, Proceedings of the IEEE, vol. 80, no. 1, pp. 79-91. January 1992.
- “Frequency Independent Antennas”. V. H. Rumsey, Academic Press. 1966.
- “Theoretical Limitations on the Broadband Matching of Arbitrary Impedances”. R. M. Fano, Journal of the Franklin Institute, vol. 249, pp. 57-83 and 139-154. 1950.