Antenna Gain & Directivity Simulator

The core of wireless link calculation is the Friis Transmission Equation. It tells you the power received ($P_r$) based on transmitted power ($P_t$), the gains of the antennas ($G_t$, $G_r$), the wavelength ($\lambda$), and the distance between them ($r$).

$P_r, P_t$: Received and transmitted power (Watts).
$G_t, G_r$: Gain of transmit and receive antennas (linear ratio, not dB).
$\lambda$: Wavelength, calculated from frequency ($\lambda = c / f$).
$r$: Distance between antennas (meters).
The term $(\lambda / (4\pi r))^2$ is the free-space path loss, representing how the signal spreads out and weakens with distance.

Path loss is often expressed in decibels (dB) for convenience. The Free-Space Path Loss (FSPL) formula is derived directly from the Friis equation.

$f$: Frequency (Hz).
$c$: Speed of light (~$3 \times 10^8$ m/s).
This shows a critical insight: path loss increases with both distance and frequency. In the simulator, increase the "Frequency f" and watch the received power drop faster over the same distance.

Satellite TV Dishes: The large parabolic dish is a very high-gain antenna. It's precisely pointed at a geostationary satellite over 35,000 km away to focus on its weak signal and reject interference from the ground. The simulator shows why high gain is non-negotiable here—try achieving a positive link budget at that distance with a dipole!

Wi-Fi Router Placement: Most home routers use moderate-gain antennas with a broad radiation pattern to cover all rooms. If you replaced them with high-gain Yagis, you'd get amazing signal in one direction but dead zones everywhere else. This trade-off is easily explored by changing antenna types in the tool.

Long-Range Microwave Backhaul: Cell towers often connect to each other via focused microwave links. Engineers use the Friis equation to select antenna gain, frequency, and power to ensure a reliable link over tens of kilometers, often aligning antennas with sub-degree precision to maximize the gain benefit.

RFID and NFC Systems: These short-range systems operate with very low power. The reader antenna's gain and directivity are carefully designed to create a specific "bubble" of coverage. The path loss calculation is crucial to define the maximum read range, which you can simulate by setting a very short distance and low power.

There are a few key points you should be especially mindful of when starting to use this simulator. First is the misconception that higher gain is always better. It's true that with antennas like the Yagi-Uda, gains exceeding 10 dBi can extend communication range in a specific direction. However, the trade-off is that the beamwidth becomes narrower. For example, a device like a smartphone needs to receive signals from base stations in all directions, so an omnidirectional antenna is actually more suitable. For a directional antenna, "where you point it" is everything.

Next, don't forget that the simulation assumes "free space". The calculations here do not include any reflections from walls or the ground, scattering by trees, or effects of rain. In actual urban areas, it's not uncommon for received power to drop by 20 dB or more at the same distance when behind a building. Treat this tool's results as "theoretical values under ideal conditions," and it's a golden rule to include a sufficient margin (e.g., 10–20 dB) in your actual design.

Finally, a pitfall in parameter settings: frequency and wavelength have a trade-off relationship. Looking at Friis' transmission equation, you see that received power is proportional to the square of the wavelength λ, right? This means that for the same distance, lower frequency (longer wavelength) results in smaller propagation loss. For instance, comparing 2.4 GHz (Wi-Fi) and 28 GHz (5G mmWave), the frequency is about 11.7 times higher, so the loss difference is 20*log10(11.7) ≈ 21 dB. If you use a high-frequency band, you need to compensate for the loss with higher gain.