How to Build a 1090 MHz ADS-B Antenna

[Pavel]

Short answer: A simple 1090 MHz quarter-wave vertical is an effective first ADS-B antenna: use a radiating element near 69 mm with several similar radials, mount it vertically and give it a clear view of the sky. Precise construction and low-loss feedline matter more than decorative complexity.

Before you start​

• Define the target frequency and polarization before choosing an antenna, LNA or filter. A wide tuning range on the SDR does not make one antenna efficient across that range.
• Sketch the RF path from antenna to receiver and include connector adapters, coax length, DC bias and every active component.

Step-by-step method​

1. Step 1: Use the quarter-wave estimate 75/f in metres: at 1090 MHz this is about 0.0688 m, or 68.8 mm. Cut the vertical and four radials slightly long so final trimming remains possible.
2. Step 2: Attach the vertical to the connector center and radials to ground. Bend four radials down roughly 30 to 45 degrees to provide mechanical separation and bring feed impedance closer to common coax.
3. Step 3: Weatherproof the connector without covering the radiating element in thick lossy material. Mount vertically, outside if safe and lawful, above nearby obstructions with the shortest practical low-loss coax.
4. Step 4: Establish a 24-hour decoder baseline, then compare another 24-hour period with identical receiver gain. Track unique aircraft, range distribution and messages per second rather than one farthest aircraft.

Concrete example​

For a compact ground-plane build, begin with one 69 mm vertical and four 69 mm radials. A millimetre or two will not decide the whole station; rooftop view, coax loss, overload and local traffic usually cause larger differences.

How to judge the result​

The antenna is useful when coverage becomes more even and valid message or aircraft counts improve over comparable periods. If nearby traffic rises but maximum range falls, test lower gain or a 1090 MHz filter for overload.

What to record​

• Compare the same signal at the same time, receiver gain and bandwidth; record signal level and noise floor separately.
• For a receive antenna, decoded message count or usable signal-to-noise ratio is usually more meaningful than waterfall brightness.
• An accessory helps only when the wanted signal improves more than interference, noise or overload products.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Testing the new antenna for five minutes against yesterday's busy-hour screenshot cannot separate antenna performance from changing air traffic.

Final check​

Return the RF chain to its original state and repeat the comparison. Keep the antenna or accessory change only when the wanted-signal result repeats without overload, unsafe DC or an unexplained noise increase.