Reading an Antenna Pattern
- Boresight: the peak direction
- Main lobe: near the peak
- Sidelobes and nulls: other directions
- In this example the first sidelobes are about 13 dB below the peak, and later sidelobes fall off further (≈ −18, −21, −23 dB)
- A pattern gives the gain in each direction; whether that gain is enough is a link-budget question (usable coverage)
Beamwidth
- HPBW (half-power beamwidth) = full angle between the two half-power (−3 dB) points
Reflector Beamwidth Rule
- in GHz, in m
- Approximate; depends on illumination
1 m at 8.4 GHz
- Half-angle: about 1.25°
- Same antenna has (reflector gain)
- Gain and beamwidth move together: doubling or adds about 6 dB of gain and halves the HPBW (Homework 3 table)
- A narrower beam is harder to keep on target: pointing loss scales with