How to Choose an 868 MHz Antenna for Smart Water, Gas & Electricity Meters

For documented product options, compare LoRa antennas for smart metering.

868 MHz Antennas for Smart Water, Gas and Electricity Meters

Choosing an 868 MHz antenna for a smart water meter — or for a gas or electricity meter sharing the same band — is a mechanical and regulatory decision before it is an RF one. Four inputs settle it: the full band the radio must cover, the ground plane and keep-out area on the PCB, the material and geometry of the assembled housing, and whether the antenna can stay on the board or has to move away on a short coaxial lead.

Short answer: pick the mechanical format first (internal patch, short cabled antenna, or PCB/ceramic). Ask for the full operating band, because 863–870 MHz is a set of sub-bands with different power and duty-cycle rules. Compare efficiency on your ground plane instead of peak dBi. Then verify matching and radiation inside the finished meter, before certification.

RFTECH supplies three documented 868 MHz formats for metering: the GL-DY107 internal patch, the GLG4101 compact cabled antenna and the GL868S25 ceramic pin antenna. The sections below follow the review order we use with customers: format, band, integration, verification.

Which Installation Format Fits Your Meter?

Settle the mechanical format before comparing gain figures. An internal patch keeps the outside of the meter clean, a cabled antenna buys distance from noisy or metallic areas, and a ceramic pin antenna suits a board-level design. Each format changes what has to be checked during integration.

Internal adhesive or patch antenna

An adhesive or patch format fits against an internal plastic surface and keeps the outside of the meter clean. It still needs a defined antenna window and clearance from batteries, shields, displays and large metal parts. GL-DY107 is the adhesive option in the current set: 868 MHz, 2.5 dBi, UFL connector with RG174 or RG1.13 cable.

Compact cabled antenna

A short cable lets the hardware team move the antenna away from a noisy PCB area or an obstructing component. Cable loss and tight bends change the installed result, so cable type, connector and routing belong in the mechanical design, not in final assembly. GLG4101 covers this route: 868 MHz, 3 dBi, IPEX connector with RG178 or RF1.37 cable.

Ceramic or PCB-mounted antenna

A compact ceramic antenna supports a board-level design when the ground plane, keep-out area and matching network are planned around it. GL868S25 is the 868 ±3 MHz ceramic option in the current set. Fix its ground plane, keep-out area and matching network at schematic stage, before the layout and enclosure are frozen.

868 MHz Options for Smart Meters

All three target the same 868 MHz band and differ mainly in mechanical integration, which is why the format decision comes before the parameter comparison.

How to Read the Table Above

• Claim: these three formats are the 868 MHz starting points for a smart-meter design.
• Evidence: the published product record for each model, linked in the first column.
• Conditions: the values describe the antenna itself, measured before it is built into a meter with its battery, display, valve, shielding and cable route in place.
• Limitation: gain, efficiency and bandwidth shift after integration, so the installed values are the ones that decide the design, and they are measured on the assembled meter.

“868 MHz” Is a Label, Not a Band

Most selection mistakes start here. In Europe the sub-GHz short-range spectrum runs from 863 MHz to 870 MHz, and it is not one uniform band: the harmonised standard ETSI EN 300 220-2 splits it into sub-bands with different power ceilings and different rules on how often you may transmit. The CEPT recommendation ERC/REC 70-03 lists the same segmentation for national implementation.

One term first: e.r.p. (effective radiated power) is the power the antenna actually radiates in its strongest direction, referred to a half-wave dipole. It is a system limit, so antenna gain, cable loss and radio output all count towards it.

Sub-band limits from ETSI EN 300 220-2 V3.3.1 and CEPT ERC/REC 70-03. Mode frequencies from the wireless M-Bus standard EN 13757-4.

Why this decides your antenna: a part sold as “868 ±3 MHz” is specified across roughly 865–871 MHz, which covers the wireless M-Bus modes but says nothing about behaviour at 863 MHz or 869.65 MHz. If your radio hops across 863–870 MHz, or if the same hardware has to serve both a LoRaWAN uplink at 868.1 MHz and a wireless M-Bus reading at 868.95 MHz, ask for the S11 or VSWR curve across the whole 863–870 MHz range, not a single centre-frequency figure.

A quick sanity check you can run yourself: wavelength is λ = c / f, so at 868 MHz λ ≈ 300 / 868 ≈ 0.345 m, and a quarter wave is about 8.6 cm. That single number explains most integration pain in a DN15 water meter — the meter is smaller than the quarter wave, so there is no position where the battery, the valve body and the display are all electrically “far away”. These are engineering estimates from free-space physics, not measured values for a specific part.

Duty Cycle, Not Gain, Sets Your Retry Budget

This is the calculation most selection guides skip. In the 868.0–868.6 MHz sub-band, a 1% duty cycle means the transmitter may be on for about 36 seconds per hour. In 868.7–869.2 MHz, 0.1% means about 3.6 seconds per hour. Those figures are simple arithmetic on the ETSI limits above, and they are a hard budget shared by every reading, every retry and every over-the-air configuration message.

Now connect that to the antenna. A poorly matched or badly positioned antenna does not usually produce a clean failure; it produces a lower success rate per transmission. Each lost frame is paid for out of the same 36 seconds per hour, and on a battery meter it is also paid for out of a battery that has to last the life of the meter. So an antenna with 1–2 dB less peak gain but higher installed efficiency and a stable match is often the better engineering choice than the higher-dBi part that only looks good in free space.

Practical consequence: when you compare two candidates, do not compare dBi. Compare frames delivered per transmission attempt on the assembled meter, at the position where it will actually be installed. That is the number that maps onto duty cycle, battery life and gateway density.

Why Datasheet dBi Figures Are Not Comparable Across Formats

Antenna datasheets are honest and still not comparable, because the measurement conditions differ:

• Peak gain vs average gain vs efficiency. Peak gain describes the best direction only. Average gain and total efficiency describe what the whole radiation sphere delivers, which is what matters for a meter that will be installed in whatever orientation the pipe dictates.
• The reference ground plane. Sub-GHz antennas are commonly characterised on a fixed reference board — a 100 × 100 mm plane is a typical choice. If your meter PCB is a fraction of that, the published figure was measured on a counterpoise you do not have.
• The matching network. Ceramic and PCB antennas are specified with a specific matching circuit. Change the layout and you change the tuning, not just the gain.
• The cable. A cabled antenna is usually specified with one cable type and length. A different cable, a tighter bend or a longer run moves the installed result.

So when you request a datasheet, also request three things: the reference ground plane used for the measurement, total efficiency across your full band, and the matching component values. If a supplier can only provide a peak dBi number, you cannot compare their part with anyone else’s.

The Meter Enclosure Is Part of the RF Design

Run these checks before choosing a sample:

• Operating band: provide the full radio band and deployment region, not only a centre-frequency label.
• Ground plane: share the PCB size, reference layout and the antenna feed/matching area.
• Keep-out area: show the distance from the battery, display, shields, valve body, wiring and other conductors.
• Enclosure: identify plastic type, coatings, metal fasteners and any metal cabinet, pit lid or surrounding structure.
• Cable route: confirm connector, cable type, required length, bend path and strain relief.
• Final verification: check matching, efficiency and radiation behaviour in the assembled meter, not only on a free-space antenna sample.

The enclosure item is not a formality. Where a meter sits inside a fully conductive housing, the enclosure acts as a shield around the radio — the Faraday cage effect described in UK government guidance on smart meter installations in new build premises, which identifies metallic enclosures and below-ground locations as recognised causes of poor smart-meter connectivity. No antenna choice fixes that; only a change of antenna position or lid material does.

Selection Notes by Meter Type

Smart water and ultrasonic water meters

Show where the radio, battery, valve and antenna sit relative to water, metal fittings and the meter cover, and state whether the meter is installed above ground, inside a cabinet or below a cover.

Underground installation is the hard case, and it is well documented: peer-reviewed work on the radio propagation characteristics of cast iron boxes for smart water meters reports that wireless stability is a recurring problem in field trials of pit-installed meters. Two conditions stack up in a pit — the depth itself and standing water, which absorbs strongly at 868 MHz. That is why the practical answer is often topological rather than electrical: move the radiating element to the lid, or change the lid material, instead of asking a higher-gain antenna to transmit through cast iron.

Smart gas meters

Provide the enclosure materials, permitted antenna zone and any separation or compliance constraints imposed by the complete product. Compliance is established on the finished meter, so the antenna position is fixed together with those constraints rather than after them. Note also that the wireless M-Bus modes usually chosen for gas meters (T1 or C1 at 868.95 MHz) sit in a 0.1% duty-cycle sub-band, which leaves very little room for retries.

Smart electricity meters

Show the antenna’s distance from conductive bus structures, shields, displays and the mounting cabinet. Electricity meters are mains-powered, so battery life is not the constraint — but the metal cabinet and the switchgear environment usually are. If the antenna has to move away from the main PCB, include the required cable and connector in the review.

Common Mistakes in Smart-Meter Antenna Selection

• Ranking candidates by dBi alone. A figure measured on a bare sample and a large reference ground plane does not survive a plastic housing, a small ground plane or a metal pit lid unchanged.
• Treating same-band parts as interchangeable. A patch, a cabled and a ceramic antenna at 868 MHz need different ground planes, keep-out areas and matching work.
• Ignoring the duty-cycle budget. If retries are not counted, an antenna that “works” in the lab can quietly exhaust 36 seconds per hour in the field.
• Verifying only in free space. A sample that looks correct on a test fixture can be badly detuned once the battery, display and valve body are assembled.
• Leaving the connector and cable to the end. Connector type, cable type, length and bend path change the installed result and sometimes the mechanical design.
• Assuming one deployment covers all. A wall-mounted meter, a cabinet installation and a below-ground pit are different RF environments for the same meter.
• Quoting a centre frequency instead of a band. Regional plans and sub-band rules differ; the full operating band and target region are needed before any model is proposed.

What to Send for Antenna Review or Quotation

Send one compact project brief with:

1. target country or regional band;
2. radio/module model and antenna-port requirements;
3. PCB dimensions, ground plane and matching area;
4. enclosure drawing or internal photos with the proposed antenna zone;
5. internal, adhesive, cabled or ceramic preference;
6. connector, cable type and required cable length;
7. installation environment and required ingress-protection target;
8. expected quantity and the documents needed for review.

RFTECH then matches the brief to the documented options and defines the checks to run on the sample. Quantities, documentation and sample terms are confirmed against your project brief.

For the broader product family, review LoRa and LoRaWAN antennas. For host-device design constraints, see embedded antenna integration guidance.

FAQ

Does a higher dBi rating mean longer range in a meter?

Not on its own. Peak gain describes one direction, measured on a reference ground plane that is usually larger than a meter PCB. Installed efficiency, enclosure material, cable loss and mounting position normally dominate, and they can only be judged on the assembled meter.

Can an 868 MHz antenna be used on a 915 MHz network?

No. The two band plans sit far enough apart that an antenna tuned for 868 MHz is mismatched at 915 MHz, and the regulatory limits differ as well. Select by deployment region and the full operating band of the radio, not by a centre-frequency label.

Internal or cabled antenna for a pit-installed water meter?

A cabled antenna is the stronger starting point whenever the pit lid or surrounding structure is metal, because it lets the radiating element move to or through the lid. An internal patch stays viable when the housing and cover are plastic and a clear antenna window is available.

How much transmit time does the 868 MHz band actually allow?

In 868.0–868.6 MHz the limit is 25 mW e.r.p. with a 1% duty cycle, roughly 36 seconds of transmission per hour. In 868.7–869.2 MHz, where wireless M-Bus T1/C1 sits, the 0.1% limit is roughly 3.6 seconds per hour. Reading interval, payload size and retries all have to fit inside that.

What is the minimum information needed for a recommendation?

Band and region, radio or module model, PCB and ground-plane dimensions, enclosure details with the proposed antenna zone, and the connector and cable length required.

Ask an RF Engineer

Send the band, radio, enclosure, antenna zone, connector and cable requirements with your RFQ. We will match them to the documented 868 MHz options and define the sample checks to run before production.