Patch antenna radiation pattern is the map of where an antenna really receives, and it is the fastest way to judge whether a GPS/GNSS antenna will still work once it is inside your product. Peak gain is a single number from a single direction. The pattern is the whole picture, and it is the judgement basis used throughout this article.
Short answer
- A patch antenna is strongest broadside, meaning straight out from the patch face. A GNSS patch typically covers about 160°, close to a hemisphere.
- Expect gain to fall 10 to 20 dB from zenith down to the horizon. That roll-off is deliberate: it helps reject reflected signals.
- Beamwidth alone is not a selection metric. Read it together with axial ratio, ground plane size, and installed test data.
- Ask for pattern plots measured on your ground plane and in your enclosure. A free-space fixture plot proves very little.
Quick Answer: What Is a Patch Antenna Radiation Pattern?
A patch antenna radiation pattern is a plot of gain, meaning how strongly the antenna sends or receives, in each direction around it. It shows four things:
- Main lobe – the direction where the antenna is strongest
- Side lobes – weaker lobes off to the sides
- Back radiation – what leaks out behind the antenna
- Coverage angles – how far off the main direction you can go before performance drops
For a typical patch, the main lobe points away from the patch face. GNSS receiver antennas are designed so this near-hemispherical pattern can see satellites from zenith down to the horizon in any azimuth direction, and they use right-hand circular polarization (RHCP) to match the satellite signal. ESA’s Navipedia puts the typical coverage of a GNSS patch pattern at around 160°.
When a supplier says “beam pattern”, they usually mean the same practical question: where does this antenna have useful coverage, and where does it fall off a cliff?
Pattern Terms in Plain Language
| Term | Meaning | Why it matters |
|---|---|---|
| Main lobe | Direction of strongest radiation or reception | Shows where the antenna works best |
| Beamwidth (HPBW) | Angular width of the main lobe where gain has dropped 3 dB from the peak | A first estimate of coverage angle |
| Axial ratio beamwidth | Angular width over which polarization stays close to circular (usually within 3 dB) | The angle that actually matters for GNSS |
| Side lobe | Smaller lobe away from the main direction | Can pick up interference or unwanted signals |
| Back lobe | Radiation behind the antenna | Drives ground plane and mounting decisions |
| Front-to-back ratio | Main direction compared with the rear direction | Useful measure of directional control |
| Polarization pattern | RHCP, LHCP, linear, co-polar and cross-polar response | Critical for GNSS accuracy and multipath rejection |
Why a Patch Antenna Is Directional
A patch antenna is a metal patch sitting over a ground plane with a dielectric layer in between. The radiation comes from the fringing fields at the open edges of the patch, which add up in phase, while the currents on the ground plane largely cancel each other. That is why a patch radiates but a plain microstrip line does not.
The ground plane then acts as a reflector and pushes the energy into the upper half-space. The result is a broadside pattern: useful when you know where the signal comes from, such as a sky-facing GNSS antenna.
The same directionality becomes a problem when device orientation is random. If the patch faces away from the sky or sits behind metal, the peak gain on the datasheet will not save you.
Patch Antenna Beamwidth
Patch antenna beamwidth is the angular width of the main lobe. It is usually given as half-power beamwidth (HPBW): the angle between the two directions where gain has dropped 3 dB, that is to half of the peak power.
Beamwidth can be widened or narrowed by patch size, ground plane, substrate, array layout, and nearby structure. But for commercial GPS/GNSS and embedded devices, the useful question is not “how wide is the beamwidth?” It is “does the installed pattern cover the angles my device needs, with clean polarization?”
The beamwidth trap: HPBW is not axial ratio beamwidth
This is where most datasheet comparisons go wrong. A wide 3 dB gain beamwidth tells you the antenna still has power off-axis. It does not tell you the signal is still circularly polarized off-axis, and GNSS receivers care about both.
Two published facts make the gap concrete:
- A single-feed 25 x 25 x 4 mm ceramic L1 patch is only truly circular at resonance, and delivers good circular polarization over roughly 16 MHz. Push toward the band edges and the axial ratio degrades to about 5 dB; further out the response becomes nearly linear, with poor cross-polarization rejection (GPS World).
- The radionavigation-satellite spectrum a multi-constellation antenna has to live in, 1559 to 1610 MHz, is 51 MHz wide (ITU allocation, via the NTIA band compendium).
So a small single-feed patch that looks fine for GPS L1 alone can be effectively linearly polarized at GLONASS or BeiDou frequencies, even though its gain pattern plot still looks wide and healthy. Dual-feed patches hold axial ratio to typically better than 2 dB, which is why precision products pay for them.
Practical rule: if a supplier gives you only HPBW, ask for the 3 dB axial ratio beamwidth at each band you intend to use. If they cannot provide it, treat the wide-beam claim as unproven.
Reference Numbers for a GNSS Patch Pattern
Use these as sanity checks when you read a plot, not as specifications of any particular product.
| What you are checking | Published reference value | Source |
|---|---|---|
| Coverage width of a GNSS patch pattern | About 160° | ESA Navipedia |
| Gain roll-off from zenith to horizon | 10 to 20 dB | ESA Navipedia |
| Axial ratio at 10° elevation, high-performance antenna | 3 to 6 dB | ESA Navipedia |
| Peak gain, 25 x 25 x 4 mm L1 patch on a 100 mm ground plane | Just under 5 dBic, falling to about 0 dBic at ±60° from zenith | GPS World |
| Same patch with no external ground plane | About 3 dBic peak; adding a ground plane recovers up to 2 dB | GPS World |
| Truly circular bandwidth, single-feed 25 mm patch | About 16 MHz | GPS World |
| Spectrum a multi-GNSS antenna must cover | 1559 to 1610 MHz | ITU / NTIA |
| GPS L1 minimum received power at 5° elevation | -158.5 dBW | ESA Navipedia, GPS SPS signal specification |
The last row explains why pattern shape is not a cosmetic detail. The signal arrives below the noise floor, so a few dB lost to a squashed pattern or poor polarization directly costs you satellites.
Reading a Radiation Pattern Datasheet
Work through this checklist before you compare two antennas:
- Frequency of the plot. One frequency does not prove performance across all bands.
- Test ground plane. Patches are normally characterised on a 70 mm or 100 mm square ground plane. Your PCB is probably not that.
- Plane cuts. Look for several cuts, not only the most flattering one.
- Polarization. For GNSS, ask for RHCP gain and LHCP rejection, plus axial ratio versus angle.
- Scale and normalization. A normalized plot shows shape only; it hides absolute gain.
- Installed data. A measurement in your enclosure beats any fixture plot.
GNSS: Why Gain Roll-Off Is a Feature, Not a Flaw
Many buyers ask for more gain at low elevation, assuming more satellites means better accuracy. For RTK, surveying, and tracking devices, that instinct can make results worse.
Here is the mechanism. When a GNSS signal reflects off the ground, a wall, or a vehicle roof, the reflection flips the polarization: a right-hand circular signal comes back mainly left-hand circular. Reflections mostly arrive from low elevation or from behind the antenna. So a pattern that rolls off toward the horizon and keeps back radiation low is filtering out exactly the signals that corrupt your position fix.
Navipedia formalises this as the multipath ratio: RHCP gain at the direct signal angle divided by the sum of RHCP and LHCP gain at the multipath angle. Two consequences follow:
- Roll-off helps, but roll-off alone is not enough. A poor axial ratio lets reflected energy in through the main lobe.
- Receivers usually apply an elevation mask around 10° to 15° anyway, because satellites below that are weak and reflection-prone. Buying gain below the mask buys you noise.
For RTK, surveying, tracking devices, and precision agriculture, review these pattern items: RHCP gain pattern, axial ratio over angle, phase centre behaviour, ground plane size, enclosure and radome effects, and cable and LNA details for active antennas. The deeper polarization discussion lives on the RHCP vs LHCP patch antenna page.
How Installation Changes the Pattern
The datasheet pattern is not guaranteed inside your product. These factors change it:
- Small or irregular ground plane
- Metal frame, battery, display, shield can, or mounting bracket
- Plastic enclosure thickness and dielectric loading
- Nearby cellular antennas and transmitters
- Coaxial cable routing near the patch
- Adhesive, radome, or weatherproof housing
The ground plane is not a “bigger is better” dial
This is the most common design surprise. The ground plane is part of the antenna, and its effect on the pattern is not linear.
- A classic IEEE study of a circular patch on a finite ground plane found that pattern, directive gain, and input impedance all vary widely with ground plane size, because currents and edge diffraction change with it (IEEE Transactions on Antennas and Propagation, 1990).
- Growing the ground plane helps at first and then flattens out or oscillates, since edge diffraction matters less once the plane is already electrically large.
- Going too small fails hard rather than gracefully. In an RTK field study, a patch antenna that needed an added ground plane produced no usable GNSS reception at all with ground planes under 12 cm diameter, while larger planes reduced position scatter (Advances in Radio Science, 2023).
So the useful question is not “how big can I make it?” It is “is my ground plane big enough and symmetric enough that the pattern I measured is the pattern I ship?” An off-centre patch on a corner of the PCB will tilt the beam, and no receiver setting fixes a tilted beam.
If the device is used in changing orientations, test more than one position. A single upright lab result can hide real field problems. For ground-plane and enclosure validation steps, use the patch antenna design guide.
Common Mistakes
| Mistake | Why it is risky | Better approach |
|---|---|---|
| Choosing by peak gain only | Ignores coverage angle and pattern shape | Compare the full pattern and useful average coverage |
| Treating HPBW as the coverage spec | Wide gain beamwidth can hide poor polarization off-axis | Ask for 3 dB axial ratio beamwidth per band |
| Asking for more low-elevation gain | Adds multipath and noise below the elevation mask | Optimise RHCP coverage above about 10° to 15° |
| Assuming a bigger ground plane always helps | Gain gains flatten out; asymmetry tilts the beam | Size and centre the plane, then verify by measurement |
| Using the datasheet pattern as final proof | Your enclosure changes the pattern | Test in the final assembly |
For the full topic hub, product paths, and application map, see the Patch Antennas guide.
FAQ
What is the radiation pattern of a patch antenna?
It is a plot of gain in each direction. A patch usually has a broadside main lobe, so reception is strongest perpendicular to the patch surface, with coverage of roughly 160° for a GNSS patch.
What is patch antenna beamwidth?
The angular width of the main lobe, most often quoted as the half-power (3 dB) beamwidth: the angle between the two points where gain has dropped to half the peak power.
What is the difference between beamwidth and axial ratio beamwidth?
Beamwidth measures where you still have power. Axial ratio beamwidth measures where the polarization is still close to circular. GNSS needs both, and the second one is usually the limiting number.
Why does the ground plane affect the radiation pattern?
The ground plane is part of the antenna. Its size, shape, and symmetry change current distribution and edge diffraction, which in turn change back radiation, gain, and pattern stability.
Is a wider beamwidth always better?
No. A wider beam can improve coverage angle, but it may reduce peak gain and weaken rejection of reflected signals arriving from low angles. It depends on the application.
What radiation pattern should a GPS patch antenna have?
Useful RHCP coverage toward the sky with acceptable gain and axial ratio above the receiver’s elevation mask, controlled back radiation, and verified behaviour in the installed device rather than on a test fixture.
Conclusion
Radiation pattern is the most decision-relevant item on a patch antenna datasheet because it shows where the antenna actually works. Beamwidth is useful, but only inside the full pattern story, and for GNSS the axial ratio beamwidth usually decides the outcome. Check the installed pattern, not the lab fixture plot.
View GPS / RHCP patch antenna options or contact our engineering team if you need radiation pattern data for your device layout.
References
- ESA Navipedia: GNSS Antennas
- GPS World: Patch Antennas for the New GNSS
- NTIA spectrum compendium: 1559-1610 MHz (ITU RNSS allocation)
- GPS Standard Positioning Service signal specification (gps.gov)
- IEEE TAP: Effects of finite ground plane on the radiation characteristics of a circular patch antenna
- Advances in Radio Science: Impact of additional antenna groundplanes on RTK-GNSS accuracy
- Penn State GEOG 862: GNSS multipath
- Antenna Theory: Microstrip (patch) antennas
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