Why Your RF Performance Might Be Underwhelming:
1️⃣ Improper Placement and Ground Plane Design
Ground Plane Design: The ground plane is part of the radiating system for monopole antennas. The length of the ground plane should ideally be a quarter wavelength.
Cutouts: Antennas require ground cutouts in specific areas to radiate optimally.
Placement: Positioning matters! Avoid placing antennas beneath the battery unless you’ve accounted for detuning effects in your matching network.
2️⃣ Impedance Matching Issues
RF Trace Impedance:
Maintain 50 Ohms impedance across RF traces. Coplanar waveguide or microstrip models are often sufficient but depend heavily on PCB stackup and dielectric constants.
Tip: Dielectric constants vary across materials. Always document your layer stack up thoroughly, including copper weights, dielectric thicknesses, and material constants.
Pad-Trace Transition: Pads wider than traces create impedance mismatches. Use teardrop transitions and ensure the trace width closely matches pad dimensions for minimal mismatch.
3️⃣ Poor Routing
Angle Considerations: Avoid steep (90°) routing angles; opt for curved traces or mitered bends to minimize impedance disruptions.
Vias: Vias can introduce significant insertion loss at high frequencies. Use stitching vias where necessary to mitigate these effects.
Power Plane Interference: Never route RF signals over or near power planes, as parasitic coupling can degrade signal quality and introduce unwanted noise.
4️⃣ No or Poor RF Matching
Onboard Antennas: Most off-the-shelf antennas are not inherently 50 Ohms in your design. Ensure matching is done considering the enclosure, batteries and cables.
Unclean Soldering Joints: Soldering irregularities can disrupt your carefully tuned RF matching.
5️⃣ Component Tolerances
High Q and Tight Tolerances: Invest in high-Q components with tight tolerances (e.g., ±0.1 pF for capacitors in the GHz range) to minimize losses and maintain consistent performance.
RF-Specific Sample Kits: Many component vendors offer matched RF kits optimized for specific designs, ensuring the use of suitable components.
6️⃣ Improper Testing
Sub-GHz and Resilient Modulations: At low frequencies, such as the Sub-GHz range, and with robust modulations like hashtagLoRa, devices may still communicate under suboptimal conditions, such as without an antenna attached.
Complete Testing Setup: Perform RSSI testing for TX and RX paths using function generators, spectrum analyzers, or golden sample ping-pong setups.
Shielded Environment: RF tests in noisy environments can be deceptive. Always test in a shielded RF box to isolate the device under test from external interference.
🔧 Key Takeaway: Master the details or contact the experts at rfi@miromico.ch.
Have you struggled yourself or want to share your valuable experiences?
Think IoT – Think Miromico!