We’ve talked about RF signals and the components that generate and measure them. Now, it’s time to focus on antennas—the unsung heroes of wireless—and understand how RF signals behave once they leave the antenna. This knowledge is essential for designing networks with optimal coverage and performance.

What is an Antenna?

An antenna is a device that converts electrical signals into electromagnetic waves and vice versa. It’s the interface between wired electronics and the wireless airwaves.

Antennas don’t create RF energy, but they radiate or receive it, acting as both launchpads and catchers of RF signals.

Types of Antennas

There’s no one-size-fits-all in antenna design. Different types serve different purposes:

Omnidirectional Antennas

• Radiate equally in all horizontal directions
• Great for covering open areas like warehouses or outdoor spaces

Directional Antennas

• Focus energy in a specific direction
• Ideal for long-distance point-to-point links or targeted coverage areas

Examples:

• Yagi: Focused beam, long range
• Patch/Panel: Flat and rectangular, used for indoor coverage
• Parabolic Dish: Extreme range, high gain

Sector Antennas

• Combine elements of both omni and directional
• Common in cellular towers to cover pie-shaped areas

Antenna Characteristics

Gain

• Measured in dBi or dBd, gain represents how well an antenna focuses energy.
• Higher gain = longer range but narrower beam

Beamwidth

• The width of the antenna’s main lobe of radiation, typically measured in degrees.

Polarization

• Refers to the orientation of the electric field (vertical, horizontal, or circular).
• Must match between transmitter and receiver for best performance.

RF Signal Behavior

Once a signal is radiated, it interacts with the environment in complex ways:

Reflection

• Bounces off surfaces like metal or glass
• Can cause multipath interference when signals arrive at slightly different times

Refraction

• Bends when it passes through materials of different densities (e.g., air to glass)

Diffraction

• Bends around obstacles, allowing coverage beyond line-of-sight

Scattering

• Occurs when signals hit small objects or rough surfaces, dispersing the wave

These behaviors affect signal strength, quality, and coverage area.

The Fresnel Zone

The Fresnel Zone is an elliptical area around the line-of-sight path between transmitter and receiver. Obstacles in this zone can interfere with the signal even if there’s no direct obstruction.

Clearing at least 60% of the Fresnel Zone ensures good signal quality.

Antenna Placement Best Practices

• Height matters: Higher placement reduces obstacles and improves line-of-sight
• Avoid metal objects: These can reflect or absorb RF energy
• Mind the Fresnel Zone: Ensure it’s clear to reduce interference
• Use appropriate polarization: Match antenna orientation

Real-World Tip

When planning coverage in a building with multiple floors, consider the antenna’s vertical radiation pattern. Most omnidirectional antennas focus energy horizontally—so floors above or below may get weaker signals.

Summary

Antennas are vital to getting your RF signals into and out of the air, and understanding how signals behave after transmission can make or break a wireless deployment. Knowing the difference between antenna types, how to interpret gain and beamwidth, and managing signal behaviors like reflection and diffraction helps you design more reliable and efficient networks.

In the next blog, we’ll dig into the IEEE 802.11 standards—the protocols that define how wireless LANs communicate. Get ready to learn the language of Wi-Fi!