WiFi Antennas

Antennas are critical components that convert electrical signals to radio waves and vice versa
Performance directly impacts coverage area, signal strength, and interference mitigation
Antenna selection must match frequency band (2.4 GHz, 5 GHz, 6 GHz for WiFi 6E)
Measured in decibels (dBi) for isotropic gain - higher dBi = more directional focus

Di-Pole/Omnidirectional: Radiates signal 360° horizontally, limited vertical coverage
- Used for general coverage in offices, homes, and public areas
- Typical gain: 2-9 dBi
- Example: Standard access point “rubber duck” antennas
Directional: Focuses signal in specific direction for longer range
- Yagi antennas: High gain (10-20 dBi), narrow beam width
- Patch antennas: Medium gain (6-12 dBi), wider coverage than Yagi
- Used for point-to-point links, covering specific areas, or reducing interference
Sector: Covers specific angular segment (typically 60°, 90°, or 120°)
- Used in outdoor deployments and large venue coverage
- Allows multiple antennas to cover 360° with better control than omnidirectional

Multiple Input Multiple Output (MIMO): Uses multiple antennas for spatial diversity
Requires separate antenna elements - cannot use single antenna with splitter
Spatial streams increase throughput by transmitting different data simultaneously
802.11n supports up to 4x4 MIMO, 802.11ac up to 8x8 MIMO
Beamforming uses antenna arrays to focus signal toward specific clients

Antenna Type	Gain (dBi)	Coverage Pattern	Best Use Case
Di-Pole/Omnidirectional	2-9	360° horizontal	General office coverage
Yagi	10-20	Narrow directional	Point-to-point links
Patch/Flat Panel	6-12	Medium directional	Hallways, specific zones
Sector	8-15	60°-120° segment	Outdoor/large venues

Polarization: Orientation of radio wave’s electric field
Vertical polarization: Most common for indoor WiFi deployments
Horizontal polarization: Sometimes used to reduce interference
Transmit and receive antennas must match polarization for optimal performance
Diversity antennas: Multiple antennas combat multipath fading by selecting best signal

Line of Sight (LOS): Direct path between antennas improves performance
Fresnel zone: Elliptical area around LOS that should be 60% clear of obstacles
Antenna height matters - higher placement reduces obstacles and interference
Cable loss: Coaxial cable introduces signal loss (typically 3-6 dB per 100 feet)
Use lowest loss cable possible and minimize cable runs

Effective Isotropic Radiated Power (EIRP): Combined transmitter power + antenna gain
FCC limits: 2.4 GHz = 36 dBm EIRP, 5 GHz = 30 dBm EIRP (varies by band)
Higher gain antenna requires lower transmitter power to stay within limits
Some high-gain antennas may actually reduce legal transmission power

Vocabulary

dBi: Decibels relative to isotropic radiator (theoretical perfect omnidirectional antenna)
Beamwidth: Angular width of antenna’s main radiation pattern (measured at -3dB points)
Front-to-back ratio: Difference between forward gain and reverse gain (reduces interference)
VSWR: Voltage Standing Wave Ratio - measures antenna impedance matching (lower is better)
Multipath: Signal reflections creating multiple signal paths and potential interference

Never exceed regulatory EIRP limits - can result in FCC violations and interference
Consider antenna diversity for mobile environments where clients move frequently
Polarization mismatch can cause 20+ dB signal loss - verify antenna orientation
Use spectrum analyzer to identify interference before selecting antenna locations
Remember that higher gain antennas have narrower coverage patterns - may create dead zones
For outdoor installations, consider weather resistance ratings (IP65/67)
Cable connectors must match antenna type (N-type, SMA, RP-SMA are common)
Test coverage patterns after installation - theoretical and actual performance often differ