- 2075 Bhadra · 3 marks
Antenna bandwidth
Short answer
Bandwidth is the frequency range where antenna performance (VSWR, gain, pattern) stays within specified limits, often VSWR ≤2. Narrowband BW% = (f_H - f_L)/f_c ×100; broadband ratio f_H:f_L. Example: 900 MHz centre, VSWR ≤2 from 860–940 MHz gives 8.89% BW.
Explain the bandwidth of an antenna.
Bandwidth of an antenna is the range of frequencies over which its performance (input impedance/VSWR, gain, pattern, beamwidth, polarization) stays within an acceptable limit of its value at the centre frequency.
Narrowband: BW% = (fH − fL)/fc × 100
Broadband: ratio = fH : fL (e.g. 10:1)
Resonant: BW ≈ fc / Q
Common criterion: VSWR ≤ 2 (return loss ≥ 10 dB).
Example: an antenna centred at 900 MHz with VSWR ≤ 2 from 860 to 940 MHz has BW = 80 MHz = 8.89 %.
Types: impedance bandwidth and pattern bandwidth. Thick conductors, travelling-wave and frequency-independent designs (log-periodic, spiral, biconical) give wide bandwidth; high-Q resonant antennas (thin dipole, small loop) are narrowband.
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