868 MHz PCB Antenna Design: Complete Guide for LoRa & EU ISM Band

Designing an 868 MHz PCB antenna sits in a sweet spot between the challenging long wavelengths of 433 MHz and the compact dimensions of 2.4 GHz. When I first started working on LoRa sensor nodes, I assumed I could just scale up my 2.4 GHz antenna experience. That partially worked, but 868 MHz has its own quirks—the quarter wavelength is still 86mm, which means careful folding and layout planning. The good news is that these antennas are much more practical to integrate than their 433 MHz counterparts.

This guide covers practical 868 MHz PCB antenna design for European LoRa applications, smart metering, and ISM band devices. Whether you’re building an SX1276-based sensor node, a LoRaWAN gateway, or a wireless M-Bus meter reader, these dimensions and matching techniques will get your RF design working. I’ll focus on proven antenna structures—meander monopoles, inverted-F antennas (IFA), and inverted-L antennas (ILA)—that work on standard FR4 boards without exotic materials.

Understanding the 868 MHz EU ISM Band

The 868 MHz band is the European equivalent of the 915 MHz US ISM band. Understanding the regulatory framework helps you design antennas with appropriate bandwidth and efficiency.

868 MHz Band Allocations in Europe

The relatively narrow sub-bands (250–600 kHz typical) mean your 868 MHz PCB antenna doesn’t need extremely wideband performance. A well-tuned antenna with 10–20 MHz bandwidth centered on 868 MHz covers all relevant channels comfortably.

868 MHz Wavelength Calculations

Compared to 433 MHz where quarter-wave is 173mm, the 86mm at 868 MHz is much more manageable. Most IoT enclosures can accommodate this without extreme miniaturization.

868 MHz PCB Antenna Types Compared

Silicon Labs’ AN768 application note documents nine different antenna types for 868 MHz. Each has trade-offs between size, gain, and ease of integration.

Antenna Type Selection for 868 MHz

When to Use Each 868 MHz Antenna Type

For most 868 MHz PCB antenna applications in LoRa devices, the IFA or ILA along the board edge provides the best balance of performance and space efficiency.

Meander Antenna Design for 868 MHz

Meander antennas compress the required electrical length into a serpentine pattern. At 868 MHz, the dimensions are more practical than at 433 MHz, but you still need dedicated antenna space.

How 868 MHz Meander Antennas Work

The meander monopole folds a quarter-wave element back and forth. Total trace length must approximate the effective quarter wavelength (52–65mm on FR4), while the physical footprint can be 40–60% smaller.

Key design relationships:

• Total trace length ≈ 55–70 mm (depends on trace width, spacing, substrate)
• Physical footprint: 30–50 mm length typical
• Bandwidth: 15–30 MHz (adequate for all 868 MHz sub-bands)
• Efficiency: 70–90% (better than 433 MHz meanders)

Meander Antenna Dimension Tables for 868 MHz

Compact Meander (30 × 15 mm footprint):

Standard Meander (40 × 20 mm footprint):

Large Meander (50 × 25 mm footprint):

IFA and ILA Design for 868 MHz

Inverted-F antennas (IFA) and Inverted-L antennas (ILA) route along the PCB edge, making efficient use of board perimeter space. These are popular choices for 868 MHz PCB antenna designs in LoRa modules.

IFA vs ILA Comparison

IFA Dimensions for 868 MHz

ILA Dimensions for 868 MHz

The ILA is simpler but requires external matching. The IFA’s built-in shorting stub provides inherent impedance matching, often reducing the need for external components.

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Ground Plane Requirements for 868 MHz

The ground plane serves as the antenna’s counterpoise. At 868 MHz, requirements are more relaxed than at 433 MHz but still important.

Minimum Ground Plane Dimensions

Ground Plane Design Rules for 868 MHz

For 868 MHz PCB antenna designs, a ground plane of at least 30×50mm provides reasonable performance. Larger is always better, but diminishing returns set in beyond about 60×100mm.

SX1276 and SX1262 LoRa Integration

The Semtech SX1276 and SX1262 are the dominant transceivers for 868 MHz LoRa applications. Understanding their RF interface is essential for antenna integration.

LoRa Transceiver RF Specifications

Both chips have single-ended 50Ω RF outputs, simplifying antenna connection compared to differential-output chips like the CC1101.

Typical LoRa Module to Antenna Path

SX1276/SX1262 RF_OUT → Pi Matching Network → 50Ω Trace → Antenna

Most LoRa modules (RFM95W, Ra-01, E32 series) include internal matching optimized for a 50Ω antenna. When designing custom boards with bare SX1276/SX1262, include Pi network footprints for tuning.

LoRa Module Antenna Recommendations

Matching Network Design for 868 MHz

Even with well-designed antennas, matching networks optimize performance and compensate for enclosure effects.

Pi (CLC) Matching Network Topology

LoRa Module ──[C1]──┬──[L1]──┬──[C2]── Antenna                    │        │                   GND      GND

Matching Component Starting Values for 868 MHz

For a typical PCB antenna (slightly inductive impedance):

Component Selection Guidelines

High-Q inductors are critical. Using cheap multilayer ceramic inductors in your matching network can waste 1–2 dB of precious link budget.

PCB Layout Guidelines for 868 MHz

Proper layout ensures your 868 MHz PCB antenna performs as designed. These guidelines apply regardless of antenna type.

Antenna Placement Rules

50Ω Microstrip Dimensions for 868 MHz

Layout Checklist for 868 MHz Antenna

868 MHz vs 915 MHz: Regional Considerations

If you’re designing for global markets, understanding the differences between 868 MHz (EU) and 915 MHz (US/AU) helps with antenna design decisions.

Regional Band Comparison

Designing Dual-Band 868/915 MHz Antennas

For most applications, designing a slightly wider-band antenna centered around 890 MHz provides acceptable performance across both EU and US bands. The 5% frequency difference results in only minor detuning.

Testing Your 868 MHz PCB Antenna

Proper testing validates your 868 MHz PCB antenna before production commits.

Test Equipment Options

S11 (Return Loss) Targets

LoRa Range Testing Benchmarks

Note: LoRa’s spread spectrum modulation allows communication at very low RSSI (-120 dBm or lower with SF12). Compare against a known-good reference antenna.

Common 868 MHz PCB Antenna Mistakes

Mistake 1: Forgetting Inner Layer Ground Clearance

Problem: Ground plane removed on top/bottom but present on inner layers. Effect: Severe capacitive loading, resonance shift down 50+ MHz. Solution: Check ALL layers in Gerber review before fabrication.

Mistake 2: Antenna Too Close to Ground

Problem: Insufficient clearance between antenna trace and ground pour. Effect: Reduced bandwidth, lower efficiency, detuning. Solution: Maintain ≥ 10mm clearance, preferably 12–15mm.

Mistake 3: Using Wrong Substrate Calculations

Problem: Calculating antenna length for air, not PCB substrate. Effect: Antenna resonates 20–30% too high in frequency. Solution: Use effective dielectric constant (εeff ≈ 3.0–3.5 for FR4 microstrip).

Mistake 4: Ignoring Enclosure Effects

Problem: Antenna tuned on bare PCB, then enclosed in plastic housing. Effect: Resonance shifts down 5–15 MHz, VSWR degrades. Solution: Final tuning with enclosure in place, include matching network.

Mistake 5: Poor RF Trace Routing

Problem: Long, meandering 50Ω trace from module to antenna. Effect: Added loss, potential radiation/pickup. Solution: Keep RF trace as short as possible, direct routing.

Mistake 6: Battery Under Antenna Area

Problem: Li-ion cell positioned beneath PCB antenna. Effect: Significant detuning, pattern distortion, reduced efficiency. Solution: Position battery away from antenna, add ground between them.

Useful Resources for 868 MHz Antenna Design

Application Notes and Design Guides

Design Tools

Commercial Reference Designs

Frequently Asked Questions

What’s the minimum PCB size for an 868 MHz antenna?

The minimum practical PCB size for an 868 MHz PCB antenna is approximately 30mm × 50mm. This provides space for a compact meander antenna (30mm × 15mm) or an ILA along the board edge, plus the minimum ground plane (25mm × 40mm) needed for the antenna to radiate effectively. Smaller boards are possible using chip antennas or helical wire antennas, but PCB-integrated antennas need this minimum footprint. For LoRa applications requiring good range, target 40mm × 60mm or larger for best results.

How do I tune my 868 MHz antenna if it’s resonating at the wrong frequency?

First, measure the actual resonance with a VNA like the NanoVNA. If your antenna resonates too high (say 900 MHz), you need to electrically lengthen it—add a series inductor (start with 5–10 nH) in the matching network. If it resonates too low (say 820 MHz), you need to shorten it electrically—add a series capacitor (start with 2–5 pF). For fine tuning, adjust the shunt capacitors in the Pi network. If resonance is more than 50 MHz off, consider modifying the physical antenna length rather than relying purely on matching components, as extreme matching reduces efficiency.

Can I use the same antenna for both 868 MHz and 915 MHz?

Yes, with some compromise. The 5.4% frequency difference (868 vs 915 MHz) means an antenna optimized for one band will be slightly detuned at the other. Design for approximately 890 MHz center frequency with sufficient bandwidth (≥ 50 MHz for S11 < -10 dB) to cover both bands. Expect 0.5–1 dB efficiency reduction at the band edges compared to a single-band optimized design. For critical applications, use a tunable matching network or separate antennas. For most LoRa applications, a wideband compromise design works acceptably.

How much range can I expect from a PCB antenna vs external antenna?

A well-designed 868 MHz PCB antenna typically achieves 60–80% of the range of an external quarter-wave whip antenna. In practical terms, if a whip antenna gives you 5 km line-of-sight range, expect 3–4 km with a good PCB antenna. The PCB antenna might have -1 to -3 dBi gain versus +2 dBi for a whip, representing roughly 3–5 dB difference. In LoRa’s link budget, this translates to approximately 30–50% range reduction. For urban environments with obstructions, the difference is often less noticeable because multipath effects dominate.

Why is my LoRa range much shorter than expected after putting the board in an enclosure?

Enclosures—especially plastic ones with any metal content, or proximity to batteries—detune PCB antennas by lowering their resonant frequency. The plastic’s dielectric constant (typically εr = 2.5–4 for ABS/PC) loads the antenna capacitively. Solutions include: (1) Final antenna tuning with the enclosure in place, not on a bare board; (2) Including a Pi matching network and adjusting component values after enclosure; (3) Positioning the antenna section of the PCB away from enclosure walls if possible; (4) Using an enclosure window (thinner plastic) over the antenna area. Expect 5–15 MHz resonance shift from enclosure effects—this is normal and must be compensated.

Conclusion

Designing a working 868 MHz PCB antenna for LoRa and EU ISM band applications is achievable on standard FR4 boards with careful attention to dimensions and layout. The 86mm quarter wavelength is manageable—much easier than 433 MHz—and proven antenna structures like meander monopoles, IFAs, and ILAs provide good options for different board sizes.

For new 868 MHz designs, my recommendation is to start with an IFA along the board edge if you have 55–70mm of perimeter available. The built-in impedance matching from the shorting stub simplifies tuning. If space is tighter, a meander monopole in a dedicated 40×20mm area works well. Either way, include Pi matching network footprints even if you don’t expect to need them—enclosure effects almost always require some adjustment.

Test with a NanoVNA before production. Target S11 below -10 dB at 868 MHz with at least 20 MHz bandwidth. Compare LoRa RSSI readings against a known reference (like an RFM95W module with factory antenna) to validate real-world performance.

The 868 MHz band continues to grow for IoT applications. LoRaWAN, wireless M-Bus, and industrial sensors all rely on effective antenna design. With proper 868 MHz PCB antenna implementation, you can achieve multi-kilometer range with milliwatt power levels—exactly what low-power IoT demands.