Great Design, Bad Signal: The Physics That Degrades Antennas in the Real World
Antenna performance often fails if it is not your design, by overlooked physical parameters in the materials and surroundings.
Antenna performance often fails if it is not your design, by overlooked physical parameters in the materials and surroundings. You can simulate the perfect structure — but if you ignore dielectric behavior and ground plane implementation, the result will be disappointing in the field. And it happens more often than most engineers admit.
Why It Matters
Modern wireless systems rely on high-performing antennas. But even expertly designed antennas underperform—or outright fail—when material properties and environmental context are misunderstood. Every decision in antenna implementation, from substrate selection to housing materials and surrounding structures, alters signal efficiency, bandwidth, and tuning.
Dielectric properties and ground plane behavior are not secondary considerations—they are primary performance levers. Misunderstanding can cause detuning, power loss, and unpredictable behavior across frequency band.
By the Numbers
Dielectric Loss Tangent: This metric indicates how much RF energy is lost as heat in a dielectric material. A high-loss tangent reduces the signal that is radiated dissipating it as energy inside the material itself. A basic guideline is to use materials with a loss tangent below 0.01 at 1 GHz. Signal loss becomes unavoidable once that number creeps higher, particularly in wideband applications.
Takeaway: To maximize antenna efficiency, use dielectric materials with a loss tangent < 0.01.
- Dielectric Constant (εr): Dielectric constant measures how a material responds when an electric field is applied. Plastic housings typically fall between 2.5 and 3.5 at 1 GHz, while ceramics can reach values well above 20. Higher εr materials compress the wavelength, causing detuning of the antenna from its intended frequency. Even a thin plastic sheet added near the antenna can shift the antenna tuning and kill performance.
Takeaway: Always retune antennas when introducing materials with high dielectric constants. If you are using off-the-shelf antennas, check the datasheet for the environment where the given performance specifications have been measured.
- Ground Plane Size: The ground plane isn’t optional. It’s not just a supporting feature—it’s an active component of the radiating system. If your ground plane is too small, especially at lower frequencies, performance will suffer. The basic guideline: make the ground plane at least one-quarter of the wavelength of the lowest operating frequency. Consider this: at 700 MHz, the recommended ground plane is at least 11 cm. The larger the ground plane, the stable the impedance and hence better radiation patterns.
Takeaway: Design tip: ground planes should be at least ¼ wavelength of the lowest frequency to ensure stable performance.
- Distance to Metals: Nearby metallic objects can and will interfere with antenna performance. The good news: not all metal is bad. Electrically floating metal parts shorter than one-quarter wavelength of the highest operating frequency often resonate outside the band and may not severely impact performance. Metallic proximity can alter directivity, shift resonance, and even introduce phantom bands.
Takeaway: Think through on how to manage metal placement near antennas; test if proximity cannot be avoided.
Key Takeaways
- Aim for a loss tangent below 0.01 at operating frequencies by using low-loss dielectric materials
- Understanding the impact of dielectric constant on materials like plastics and ceramics.
- Understand that both these parameters can be verified against manufacturing specifications by measuring these parameters
- Ensure the ground plane size is at least ¼ wavelength at the lowest frequency.
- Manage metals near the antenna, to avoid un-wanted resonances or detuning.
The Bottom Line
Even a textbook antenna design can underperform in the real world if these physical factors are ignored. Dielectric losses, detuning due to εr, undersized ground planes, and poorly positioned metals are silent killers. They don’t show up in perfect lab simulations—but they dominate real-world signal behavior.
If your antenna design looks great but delivers poor performance, it’s time to stop blaming the layout—and start understanding the physics.
Ilkka Heikura, Senior Specialist
Ilkka Heikura is an experienced antenna design expert with 17 years of experience in developing high-performance antennas for mobile phones, laptops, smartwatches, and IoT devices.
His expertise spans cutting-edge wireless technologies, enabling seamless connectivity across various consumer and industrial applications.