RHCP vs LHCP Patch Antenna for GNSS: How to Choose

The RHCP vs LHCP patch antenna question is already answered by the published signal specifications: GPS, Galileo and BeiDou all require their satellites to transmit right-hand circular polarization, so a GNSS receive antenna is RHCP unless a system document tells you otherwise.

Short answer. For receiving GNSS — GPS, GLONASS, Galileo, BeiDou, RTK, timing, telematics, trackers — choose RHCP. Choose LHCP only when a system document, a test plan, or a dedicated diagnostic channel calls for it. And once RHCP is settled, judge candidates on axial ratio across the band and across elevation angles, not on peak gain: two antennas can both be labelled “RHCP” and still differ by more than 10 dB in how cleanly they reject the wrong-hand signal.

Quick Verdict: RHCP or LHCP?

The US GPS interface specification states it directly: “the transmitted signal shall be right-hand circularly polarized (RHCP)”. The same document defines the reference user antenna as a 0 dBi RHCP antenna, meaning 0 dB axial ratio (IS-GPS-200N, §3.3.1.9).

China’s BeiDou B1I document puts a number on the cost of getting polarization wrong. It specifies the minimum power on the ground, -163 dBW, measured at the output of a 0 dBi RHCP antenna or a 3 dBi linearly polarized antenna (BDS-SIS-ICD-B1I-3.0, §4.2.5). The standard itself budgets a 3 dB penalty for not being circularly polarized.

So the buying question is not “RHCP or LHCP?” It is: how much of that RHCP advantage survives once the antenna is mounted inside your product?

RHCP vs LHCP Comparison

Why GNSS Uses RHCP

Every major constellation transmits RHCP, and every one of them publishes it. What is less well known is that none of them claims perfect circular polarization. The specifications allow the satellite itself to be slightly elliptical, and they say by how much:

Sources: IS-GPS-200N, ESA Navipedia Galileo Signal Plan, BDS SIS ICD.

Two things follow from this table.

1. Matching the sense is mandatory, not a preference. It is written into the interface specifications, so an LHCP antenna pointed at these satellites is working against the signal definition.
2. Polarization purity is a budget, not a checkbox. The satellite already spends 1.8 to 2.9 dB of it. Your antenna, your ground plane and your enclosure spend the rest. That is why “it says RHCP on the datasheet” is not an answer.

For a tracker, telematics unit, asset tracker or RTK receiver, an RHCP ceramic patch is the starting point. Installed performance then depends on axial ratio, gain pattern, ground plane, phase centre behaviour, cable loss, filtering and receiver sensitivity. For available product options, compare GPS / RHCP patch antennas.

What Is Axial Ratio, and Why It Decides Everything

Axial ratio is the single number that tells you how cleanly an antenna is right-hand polarized. Picture the tip of the incoming electric field tracing a shape as it rotates. A perfect antenna traces a circle, which is 0 dB. A poor one traces a stretched ellipse. It still receives, but it no longer separates the wanted RHCP signal from the unwanted left-hand one.

Turning axial ratio into a number you can put in a specification

Most articles stop at “lower is better”. You can actually calculate the rejection. Cross-polarization discrimination (XPD) is how strongly the antenna suppresses the wrong-hand signal, and it has a fixed relationship with axial ratio:

XPD (dB) = 20 × log10 ( (r + 1) / (r − 1) ), where r is the axial ratio as a linear value, so r = 10\^(axial ratio in dB / 20).

This relationship is tabulated in ETSI TR 102 031-2. Running the formula gives numbers you can check yourself:

These are values derived from the formula, not measured test results. Treat them as an engineering estimate.

Now read the last two rows again. An antenna with 6 dB axial ratio gives you under 10 dB of wrong-hand rejection. One with 1 dB gives roughly 25 dB. That 15 dB gap is an order of magnitude more important than the 1 to 2 dBic of peak gain that datasheets usually compete on. It also explains a result that surprises many buyers: fit an antenna with higher peak gain and positioning in a reflective environment can get worse. Peak gain raises what you collect at zenith. Only axial ratio governs how well you reject reflections.

Axial ratio is a function of angle, not one number

Datasheets almost always quote axial ratio at zenith. Positioning problems do not happen at zenith. ESA Navipedia gives three figures worth writing down:

• Typical patch antenna radiation coverage is around 160°.
• Real GNSS antennas roll off 10 to 20 dB in gain from broadside (90° elevation) to the horizon (0° elevation).
• Axial ratio is near 0 dB at zenith but degrades as elevation drops, reaching only 3 to 6 dB at 10° elevation even for a high-performance antenna.

Combine that with the table above. An antenna at 1 dB on boresight, about 25 dB XPD, can fall to roughly 10 dB XPD at 10° elevation. That is exactly the angular region where low satellites are most contaminated by wall reflections.

So write the requirement as “axial ratio ≤ X dB across the full band at elevation ≥ 10°”, not just “axial ratio ≤ X dB”. A specification with one zenith number leaves the most critical angles unconstrained.

Does RHCP Help With Multipath?

RHCP does help with multipath. But the popular one-liner — “multipath is LHCP, so an RHCP antenna rejects it” — is only conditionally true, and the condition decides how much it helps in your installation.

Not all reflections flip the polarization sense

MITRE’s public work on GPS reference-station multipath separates the cases. For low-elevation satellites, a reflection off a structure arrives at close to normal incidence and does flip to LHCP, while a ground bounce can stay RHCP. ESA Navipedia is equally careful, saying only that depending on the material and the angle of incidence, an RHCP signal can be reflected as LHCP. Whether the sense reverses depends on the incidence angle relative to the Brewster angle, not on the mere fact that a reflection happened.

That splits multipath into two buckets:

• Polarization can help: near-normal reflections off building walls, masts, vehicle bodywork and machinery. Good axial ratio suppresses these.
• Polarization cannot help: grazing reflections off ground, water or a metal vehicle roof. Here you need gain roll-off toward the horizon, more antenna height, a larger ground plane or choke ring, and receiver-side multipath processing.

Navipedia quantifies the first bucket with the multipath ratio (MPR): RHCP gain at the satellite’s incident angle divided by the sum of the RHCP and LHCP gains at the multipath incident angle. It also states plainly that gain roll-off on its own is insufficient, so a good axial ratio is always required.

The practical version: an RTK antenna bolted to a metal vehicle roof will not have its ground reflections cancelled by polarization, even at 1 dB axial ratio. Choose RHCP, then treat placement, height and ground plane as separate problems.

For RTK, surveying, precision agriculture and tracking device positioning, combine RHCP selection with deliberate antenna placement and a stable mechanical design.

When Would You Use LHCP?

Most advice on this question comes from FPV video and RFID, where either sense works as long as both ends match. That answer does not transfer to GNSS. In GNSS there are only a few legitimate reasons to specify left-hand circular polarization:

• A custom RF link, telemetry channel or satellite service that is specified as LHCP.
• A controlled measurement or test setup where you deliberately observe the wrong-hand component.
• A polarization-diversity or interference-monitoring architecture where LHCP is a reference channel, not the positioning channel.

Do not choose LHCP for a standard GPS receiver because the datasheet gain figure looks higher.

The LHCP port is a diagnostic channel, not a receive channel

This is the part that rarely gets explained. A dual-feed patch driven through a 90° hybrid coupler produces two outputs at once, one RHCP and one LHCP. As Inside GNSS describes, in normal operation the LHCP port is terminated straight into a resistive load, because what arrives there is everything you do not want: leakage from the antenna’s own imperfection, atmospheric effects, and multipath components that reversed sense after a bounce. Even genuine high-elevation satellites deposit a small amount of energy there.

Bring that port out instead of loading it, and you have a wrong-hand reference channel. It is used for interference and spoofing research, and it is also the honest way to measure the installed polarization purity of your own product.

So the takeaway for a product team is a different purchase description. If your project involves interference monitoring, spoofing detection or multipath research, what you should request is not “an LHCP antenna” — it is a dual-feed antenna that exposes both the RHCP and the LHCP port.

If you are unsure which polarization your system requires, ask the receiver or module supplier. For the broader antenna selection path, use the patch antenna selection guide.

How to Choose the Best RHCP Patch Antenna

“Best RHCP patch antenna” depends on the device, not a universal ranking. The best RHCP patch antenna for one receiver may be wrong for another enclosure, ground plane, or cable path. Use this selection table:

What to Ask a Supplier Before You Approve an RHCP Antenna

Turn everything above into a short request list. If a supplier can answer all eight points, you can compare candidates properly instead of comparing peak gain numbers.

1. Axial ratio across the full band, as a curve, not one figure at centre frequency.
2. Axial ratio versus elevation angle, with a stated value at 10° elevation.
3. RHCP gain pattern over the sky angles your device actually uses.
4. The ground plane used for the measurement, plus the recommended PCB size for your design.
5. Phase centre behaviour, if the system is RTK, surveying or timing.
6. For active designs: LNA gain, noise figure, supply voltage and current, out-of-band rejection.
7. Whether a dual-feed version exists, in case you later need an LHCP reference port.
8. What the test fixture was, so you know how far the published numbers sit from your real enclosure.

Common Mistakes

1. Choosing LHCP for a normal GPS receiver. For direct GNSS reception, RHCP is normally required.
2. Checking only peak RHCP gain. Axial ratio and pattern coverage can be more important than a single gain number.
3. Ignoring the ground plane. A good RHCP patch can perform badly when placed on the wrong PCB or near metal.
4. Treating active antenna gain as antenna polarization quality. LNA gain does not fix poor axial ratio or weak antenna placement.
5. Accepting a single zenith axial ratio figure. Ask for the curve across the band and across elevation angles.
6. Expecting polarization to cancel ground reflections. Sense reversal mainly applies to near-normal reflections, so grazing ground bounces still need height, ground plane and receiver processing.

For the full topic hub, product paths, and application map, see the Patch Antennas guide.

FAQ

What is the difference between RHCP and LHCP patch antenna?

RHCP rotates in the right-hand circular direction, while LHCP rotates in the left-hand circular direction. GNSS receivers normally use RHCP to match satellite signals.

Which polarization do I need for GPS?

For standard GPS and GNSS reception, use RHCP unless your receiver or system documentation specifies another polarization.

Does an RHCP patch antenna reduce multipath?

It reduces reflected components whose polarization sense has flipped, which mainly happens on near-normal reflections from walls and structures. Grazing reflections off the ground can stay RHCP, so polarization alone cannot remove them. Placement, antenna height, ground plane, environment and receiver processing still matter.

What is axial ratio in an RHCP patch antenna?

Axial ratio measures the quality of circular polarization. A lower value means the antenna is closer to ideal circular polarization.

Can a patch antenna support multiband RHCP?

Yes. Multiband RHCP patch antennas can support combinations such as L1/L2/L5, but they require a purpose-built design and measured data for each band.

How much signal do you actually lose with the wrong polarization?

There are two separate penalties. Using a linearly polarized antenna instead of a circular one costs roughly 3 dB — the BeiDou B1I specification treats a 0 dBi RHCP antenna and a 3 dBi linear antenna as equivalent. Choosing the wrong circular sense is far worse, and the size of that loss is set by the antenna’s axial ratio.

Is a higher-gain RHCP antenna always better?

No. Peak gain and polarization purity are different properties. In reflective environments, an antenna with a lower axial ratio often outperforms one carrying 1 to 2 dBic more peak gain.

Conclusion

For GNSS reception, RHCP is required rather than preferred: the GPS, Galileo and BeiDou specifications say so in writing. LHCP belongs in specified links, test setups and diagnostic channels. Once RHCP is settled, the decision that actually changes your positioning performance is axial ratio across the band and across elevation, supported by the RHCP gain pattern, ground plane conditions, phase centre stability and installed measurements.

View RHCP patch antenna options or contact our engineering team if you need help selecting an RHCP GNSS antenna for RTK, tracking device, timing, or industrial positioning.

References

• IS-GPS-200N, Interface Specification, §3.3.1.9 Signal Polarization — US Coast Guard Navigation Center
• BDS-SIS-ICD Open Service Signal B1I (Version 3.0) — China Satellite Navigation Office
• BeiDou Signal In Space ICD (Version 1.0), signal polarization ellipticity
• ESA Navipedia: Galileo Signal Plan
• ETSI TR 102 031-2: Use of circular polarization, axial ratio and cross-polar discrimination
• MITRE: Multipath Mitigation Performance of Planar GPS Adaptive Antenna Arrays
• Inside GNSS: Single Antenna, Dual Use
• u-blox GNSS Antennas Application Note
• ESA Navipedia: Antennas