868 MHz Antenna Selection: PCB-Mount Helical, Whip and Sub-GHz Antenna Design

Choosing an antenna for an 868 MHz wireless device involves more than matching the nominal operating frequency. Engineers must also consider the regional frequency plan, available ground plane, mounting method, enclosure materials, radiation pattern, and the RF performance required by the application. These factors are particularly important for LoRaWAN, LPWAN, remote monitoring, smart metering, and other Sub-GHz wireless systems.

This guide explains how to evaluate PCB-mounted antennas, helical monopoles, and external whip-style antennas for 868 MHz applications. It also introduces practical wavelength and ground-plane calculations, compares representative Kinghelm products with the TE Connectivity ANT-868-HETH, and outlines the RF validation steps needed before production.

1. Confirm the Operating Band and Application Requirements

Before choosing an antenna, confirm the actual frequency range used by the device and the regulations that apply in its target market. The terms 433 MHz, 470 MHz, 868 MHz, and 915 MHz describe commonly used Sub-GHz frequency categories, but they are not interchangeable. Regional allocations, permitted transmit power, duty-cycle restrictions, and channel plans vary.

An antenna designed around 868 MHz should not automatically be assumed to perform well across the 915 MHz band. Even when two products look similar, their resonant frequencies, matching networks, and radiation characteristics can differ significantly.

For a new design, document the following requirements before shortlisting antenna candidates:

• Operating frequency: Specify the actual frequency range rather than only the nominal center frequency.
• Radio technology: Identify whether the application uses LoRaWAN, another LPWAN protocol, telemetry, or a proprietary Sub-GHz link.
• Available space: Record the PCB dimensions, clearance area, enclosure dimensions, and permitted antenna height.
• Mounting method: Decide whether the design requires a PCB-mounted component, a through-hole antenna, or an external antenna.
• RF targets: Define acceptable impedance matching, efficiency, radiation coverage, and communication range.
• Environmental requirements: Consider temperature, moisture exposure, vibration, and the intended installation environment.

A compact antenna can simplify mechanical integration, but size alone does not determine system performance. The antenna must work with the complete device, including its ground plane, enclosure, battery, cables, and nearby electronic components.

2. Compare PCB-Mounted, Helical and External Antenna Configurations

Different antenna structures address different mechanical and RF constraints. A PCB-mounted ceramic antenna can help save space, while a helical monopole provides a compact implementation of a monopole radiator. An external whip or rubber antenna can move the radiating element away from some of the electronics and may offer more flexibility in positioning.

PCB-Mounted Antennas for Space-Constrained Devices

A PCB-mounted antenna can be a practical option when the product enclosure is small and an external radiating element is undesirable. However, the antenna's published gain or center frequency does not fully describe its performance after installation. The PCB layout, ground plane, matching components, and surrounding materials can shift resonance and affect radiation efficiency.

When evaluating a PCB-mounted antenna, follow the manufacturer's recommended layout and keep-out requirements. Avoid placing batteries, metal brackets, display frames, shields, or other conductive structures too close to the radiating element unless the design has been evaluated in that configuration.

For additional background on PCB antenna integration, see Patch vs. Chip vs. PCB Antenna for BLE Wearables. Although the article focuses on wearable-device integration, its layout and clearance principles are also useful when planning compact antenna designs.

Helical Monopoles for Compact Sub-GHz Designs

A helical monopole uses a conductive coil structure to provide a compact antenna implementation. Through-hole variants can be useful when the PCB and mechanical design accommodate the component's mounting style and clearance requirements.

Do not assume that every helical antenna is electrically or mechanically interchangeable with another. A through-hole version and a surface-mounted version may have different footprints, installation requirements, and performance in a particular device. Confirm the exact part number and its manufacturer drawing before modifying the PCB.

External Whip and Rubber Antennas

An external antenna can be useful when the enclosure allows an antenna to be positioned away from major sources of RF detuning. This arrangement may be suitable for gateways, monitoring equipment, and devices where a larger antenna profile is acceptable.

Check the antenna's rated frequency, impedance, gain specification, polarization, mounting interface, and cable or feed arrangement where applicable. The final installation should also be evaluated for mechanical durability and RF performance in the intended operating environment.

3. Apply Wavelength and Ground-Plane Principles

Wavelength provides a useful starting point for understanding antenna dimensions. It does not, by itself, determine the final physical size of a practical antenna, because loading, coil geometry, dielectric materials, nearby conductors, and the matching network all influence the design.

Calculate the Wavelength at 868 MHz

For an initial estimate, use the following formula:

Wavelength (λ) in meters ≈ 300 ÷ Frequency (MHz)

At 868 MHz:

• Wavelength: λ ≈ 300 ÷ 868 ≈ 0.346 m, or approximately 346 mm.
• One-quarter wavelength: λ/4 ≈ 86.4 mm.

The quarter-wavelength result is a theoretical reference for a simple monopole in free space. A practical antenna may be physically shorter or otherwise configured through loading and tuning. Its effective electrical length and performance depend on the antenna structure and installation.

Why the Ground Plane Matters

A monopole antenna operates in conjunction with its ground structure. The PCB ground plane, mounting arrangement, and nearby conductive components influence the current distribution and radiation pattern. A ground plane that differs from the manufacturer's reference setup can change impedance matching and realized performance.

For example, the TE Connectivity ANT-868-HETH product information identifies a 38 × 84 mm ground-plane reference in its antenna documentation. This should be treated as a reference configuration for evaluation, not as a universal PCB-size requirement for every 868 MHz antenna.

When laying out the PCB, consider these practical steps:

1. Follow the antenna manufacturer's recommended land pattern, ground connection, and keep-out area.
2. Keep conductive objects and sensitive components away from the radiating section where required by the design guidance.
3. Place the antenna feed and matching network according to the recommended RF layout.
4. Allow space for tuning components if the design process requires impedance adjustment.
5. Measure the antenna in the assembled product, rather than relying only on calculations or a bare-PCB simulation.

For more detailed design considerations, see RF Antenna Design: A Practical Guide for Intermediate Engineers.

Matching and Measurement

A 50 Ω impedance specification is a useful interface reference, but it does not guarantee that the antenna will present a 50 Ω load when installed in the final product. The antenna and PCB together form the RF system.

Use a vector network analyzer (VNA) to evaluate the input match over the required operating band. S11 and VSWR measurements can help identify resonance shifts and matching problems. Where practical, also assess total radiated efficiency, radiation patterns, and over-the-air communication performance.

A good S11 result alone does not guarantee high radiation efficiency or the expected communication range. Conductive losses, dielectric losses, enclosure effects, antenna orientation, and the receiver environment all influence real-world results.

4. Compare Kinghelm 868 MHz Products with the TE ANT-868-HETH

When comparing products, distinguish between electrical specifications and mechanical compatibility. A compact PCB-mounted antenna, an external rubber antenna, and a through-hole helical monopole can all be considered for Sub-GHz designs, but they serve different integration requirements.

Representative Kinghelm Products

Important: The values above are manufacturer-listed product specifications, not a controlled, same-condition performance comparison. Gain figures should not be interpreted as directly equivalent unless the measurement definitions and test conditions are comparable. The final design must be evaluated in its intended PCB, enclosure, and installation environment.

How to Interpret the Comparison

The KH-10032-A83 is a compact PCB-mounted option with a published 868 MHz center frequency and 10 MHz bandwidth. It may be worth evaluating when the design prioritizes a small antenna footprint, subject to the required operating band and the manufacturer's layout guidance.

The KH-(868)-J505-JB is listed as a rubber antenna with a nominal frequency of 868 MHz, 50 Ω impedance, and 2.0 dBi gain. It represents a different integration approach from a PCB-mounted ceramic antenna and may be considered when the product's mechanical design accommodates an external or separately mounted antenna.

The TE ANT-868-HETH is a through-hole helical monopole with manufacturer-listed operation in the 862–870 MHz frequency category. Its mounting style and electrical characteristics should be assessed against the actual requirements of the target product.

These Kinghelm products should not be described as direct drop-in replacements for the TE ANT-868-HETH without verification. Differences in mounting, ground-plane interaction, matching, mechanical clearance, and RF performance may require PCB or enclosure changes. Confirm the exact dimensions, interface, and compliance documentation for the selected product before approving it for production.

5. Validate RF Performance in the Final Device

Even a correctly specified antenna can behave differently after integration. A metal enclosure, battery, display, cable, mounting bracket, or nearby circuit can alter the antenna's impedance and radiation characteristics. For this reason, antenna validation should be part of the product development process rather than a final sourcing check.

Recommended Validation Checklist

• Frequency coverage: Confirm that the antenna covers all required channels and the applicable regional band.
• Impedance matching: Measure S11 or VSWR over the operating range using an appropriate RF test setup.
• Radiation efficiency: Assess radiated performance in a representative assembled device whenever test resources allow.
• Orientation: Evaluate the intended antenna orientation and the expected position of the product during use.
• Ground-plane effects: Compare the final PCB layout with the manufacturer's recommended or reference configuration.
• Enclosure effects: Test with the final enclosure, battery, display, and major conductive parts installed.
• Communication performance: Test the actual radio link under representative operating conditions rather than relying on antenna gain alone.
• Environmental suitability: Verify temperature, moisture, vibration, and mechanical requirements against the product documentation.
• Regulatory compliance: Confirm that the finished device meets the relevant radio and product requirements in its target market.

Where the product is intended for LoRaWAN or another long-range wireless application, testing should reflect the real deployment environment. Installation height, antenna orientation, obstructions, interference, and the receiving antenna can all affect link performance.

For PCB-mounted designs, leave sufficient room for matching-network adjustments if the initial RF measurements show that tuning is required. Any component changes should be documented and verified on production-representative hardware.

6. Make an Informed Sub-GHz Design and Sourcing Decision

A practical Sub-GHz antenna decision starts with the target frequency band and continues through mechanical integration, RF validation, and sourcing review. The smallest antenna is not necessarily the best choice, and a higher published gain figure does not guarantee better performance in every product.

For a compact device, a PCB-mounted antenna such as the KH-10032-A83 may be a candidate for evaluation when its listed frequency range and layout requirements match the design. When a separately mounted antenna is more appropriate, the KH-(868)-J505-JB provides another form factor to assess. For designs requiring a through-hole helical monopole, the TE ANT-868-HETH provides a manufacturer-documented reference for evaluating that configuration.

Before finalizing a bill of materials, confirm the exact model, operating band, mechanical drawing, impedance, gain measurement conditions, mounting interface, and applicable compliance information. If replacing an existing antenna, test both the mechanical fit and the RF performance in the actual device rather than relying on nominal frequency alone.

Kinghelm's antenna portfolio includes products for different wireless integration requirements. Engineers and purchasing teams can review the published product specifications and confirm suitability for their intended application before selecting a part for production.

For further antenna integration guidance, read How to Choose a Bluetooth Antenna? From Patch to Ceramic. Although its focus is Bluetooth, the article provides additional context on matching antenna structure to the available product space and integration constraints.

References

1. TE Connectivity, ANT-868-HETH Product Page.
2. TE Connectivity, Antenna Catalogue.
3. Kinghelm, Antenna Product Listings.
4. Kinghelm, Rubber Antenna Product Listings.
5. Kinghelm, RF Antenna Design: A Practical Guide for Intermediate Engineers.
6. Kinghelm, Patch vs. Chip vs. PCB Antenna for BLE Wearables.
7. Kinghelm, How to Choose a Bluetooth Antenna? From Patch to Ceramic.