OTA testing: what it measures and how a device passes 

OTA testing usually comes late in the schedule, when the board is laid out and the enclosure is tooled. A shortfall in the chamber at that stage costs a respin and weeks of re-test

Over-the-air (OTA) testing measures how well a fully assembled wireless device transmits and receives across a real radio link. It reports Total Radiated Power (TRP) on the transmit side and Total Isotropic Sensitivity (TIS) on the receive side. Carriers and the certification bodies CTIA and PTCRB require it before a device can go to market. 

A conducted measurement taps the antenna connector, so it only ever reports what the radio chip puts out. By the time that signal has crossed the antenna, the board, the enclosure and whatever sits near it, the number has changed, and OTA testing measures what is left. A module can be perfectly healthy at its pins and still radiate too little to clear a carrier threshold, because the antenna in that specific product is not efficient enough.

OTA measurement has to happen in free space, where nothing but the device influences the reading. An anechoic chamber gets there by lining every surface with radio-absorbing material, so there are no reflections and the device is measured as if floating in open air.

A compact antenna test range (CATR) uses a shaped reflector to form the same flat wavefront in a smaller room. CATR is the usual choice at higher frequencies, where a direct far-field range would have to be impractically long.

• Passive measurement characterises the antenna on its own through efficiency and return loss (S11, how much power reflects back instead of radiating).  

• Active measurement drives the whole assembled device end to end and reports TRP and TIS.  

Certification is decided on the active numbers, but the passive numbers predict them well enough to see a failure coming before the chamber does. 

TRP is the total power a device radiates, summed across every direction, expressed in decibel-milliwatts (dBm), a logarithmic power scale where every 3 dB is a doubling or halving. Think of it as how loudly the device can shout. It is set by the transmitter power the radio delivers minus everything lost on the way out, and antenna efficiency is the dominant loss. Drop antenna efficiency by 3 dB and roughly 3 dB comes straight off TRP. 

TIS is the faintest signal a device can still receive reliably, averaged over every direction, also in dBm. Lower (more negative) is better. Think of it as how quiet a whisper the device can still hear. The same antenna efficiency that drives TRP drives TIS, with the receiver’s own noise added on top. A device that shouts well usually hears well, because both depend on the same antenna. 

The radio module inside a device arrives pre-certified for its own chipset. The finished product does not inherit that pass. With its own board, antenna and enclosure around the module, the assembled device has to clear OTA testing on its own before it certifies. 

Wireless device certification for North American networks runs through PTCRB, a certification program the mobile operators set up and still steer. CTIA Certification administers it, and the measurement method is CTIA’s own “Test Plan for Wireless Device Over-The-Air Performance”, which every accredited lab follows. The pass numbers are the carrier’s, set in a requirement such as AT&T’s 13340 Radiated Performance Requirements v19.2. A device earns PTCRB certification by being measured the CTIA way and judged against those figures. 

FCC certification is a separate, regulatory step. It caps how much a device may emit, where carrier requirements set a minimum for how much it must radiate, so a device can hold FCC authorization and still fail OTA testing. 

Ignion is not an accredited certification lab, and the PTCRB submission happens elsewhere. Ignion supplies the antenna part, the RF support to place it on a real board, and a pre-certification chamber run that reports TRP and TIS while the layout can still change. 

The CTIA test plan specifies how the device is positioned, which orientations are averaged, how many points are sampled around the sphere and how TRP and TIS are computed from them. Because every accredited lab works from the same plan, a CTIA certification result from one chamber carries the same weight as one from another, and a carrier can accept it without re-testing. 

Carrier requirements decide which bands are in scope, and PTCRB certification is granted against them band by band. That AT&T document makes LTE Bands 2, 4 and 12 mandatory for IoT devices, the low and mid-band mix that underpins cellular IoT connectivity across the United States. Missing performance on any one of the three and approval stops there, leaving a real coverage gap in the field.

The same AT&T requirement sets these minimums for LTE Category 1+ devices measured in free space, keyed to the bands your region actually requires. Treat these as one carrier’s numbers rather than a universal spec, because thresholds vary by carrier, device class and region. 

A second receive antenna is mandatory for LTE Category 1+ devices, and its TIS has to land within 4 dB of the primary antenna’s, so a weak diversity branch fails the whole device. And a device under 107 mm on its longest side counts as a small form factor (SFF), which changes the applicable targets and makes low-band efficiency the hardest thing to hold. 

Narrowband IoT (NB-IoT), designed for deep indoor coverage, carries the strictest TIS targets of the common cellular IoT options. On Band 12 its free-space TIS target runs near −103 dBm, against roughly −93 dBm for LTE-M (LTE for Machines) on the same band. Ten decibels of extra sensitivity has to come from somewhere, and on a small board it comes from antenna efficiency. 

Every OTA number traces back to how well the antenna radiates once it sits inside the real product. The common failures are all versions of the same story, and each has a design answer. 

Detuning. Metal, the battery, the enclosure wall and even a user’s hand shift the antenna’s resonant frequency away from the band it was tuned for. A genuinely clear clearance zone fixes most of it, together with a matching network re-tuned for the final enclosure instead of the bare board.

A small ground plane. At low bands the antenna radiates by exciting currents on the board itself, so board length, not antenna size, sets low-band efficiency.

Small form factor. Under 107 mm the targets tighten at exactly the point where low-band efficiency is hardest to sustain, which is why compact cellular products fail on the low bands first. 

The mandatory second antenna. Because LTE Category 1+ needs a diversity antenna within 4 dB of the primary, a good main antenna paired with a poorly placed second one still fails the device on TIS. 

Connection placement on multi-board designs. On a two-board layout like a smart meter, the point where the communications board joins the main board can swing efficiency by as much as 15 dB depending on where it sits relative to the antenna. For a walk-through of these mechanisms end to end, our IoT antenna design guide, from layout to certification covers each one with layout detail.

NB-IoT carries the strictest TIS targets of the mainstream cellular IoT technologies, and the products that use it, such as meters and fixed sensors, are usually the smallest. The strictest receive target lands on the boards with the least antenna real estate, which is why small NB-IoT designs miss on antenna efficiency more than on anything else.

The design answer is to cover the required bands with a single booster rather than a custom-cut antenna per model, so one qualified design carries across an SKU family. Where the choice between the two technologies is still open, our LTE-M vs NB-IoT comparison lays out the coverage and sensitivity trade-off. 

A chamber failure is expensive in a way that has nothing to do with the chamber fee. It usually means a board respin and weeks of re-test, and a multi-band device multiplies the risk because every band is a separate way to miss.

Pre-certification moves that discovery earlier, off the lab schedule and onto the bench. You estimate and validate the antenna’s radiated performance against the target thresholds before booking the formal chamber run, so a shortfall shows up as a number you can fix at the design stage rather than a failed certification slot.

Oxion is the software step for it, estimating and validating antenna placement and performance on your actual board layout before you commit to hardware. Oxion is a platform for that analysis, not a test lab, and it does not stand in for the chamber run itself; it tells you what the chamber is likely to report while you can still change the board. 

The ST87M01 design, an NB-IoT and GNSS module paired with Virtual Antenna® boosters, was measured against the GSMA (the GSM Association) TS.51 v2.1 benchmark of +18 dBm TRP and −103 dBm TIS. It cleared both with margin, measuring +19.8 to +21.7 dBm TRP and −110 to −113 dBm TIS across bands 1, 3, 5, 8, 20 and 28. Those are European GSMA figures, a different framework from the United States AT&T table above, and the two should be read separately rather than compared cell for cell.

What they share is the pattern that matters, in that a design validated ahead of the chamber clears the bar it was checked against. 

Pre-certification applies the same TRP and TIS thinking on your own bench, band by band, with margin built in on purpose. It is not a lighter version of the official test. Aiming for a few decibels of headroom over each target absorbs the variation that real enclosures, batteries and production tolerances add, so the device that finally reaches the accredited chamber is one you already expect to pass. 

Over-the-air testing measures how a fully assembled device radiates and receives across a real wireless link, rather than at the chip’s pins. It reports total radiated power on transmit and total isotropic sensitivity on receive, and carriers require it before a device can certify. 

Total radiated power (TRP) is how much power a device transmits across all directions, so it measures how loudly the device shouts. Total isotropic sensitivity (TIS) is the faintest signal it can still receive, so it measures how well the device hears. Both are in dBm and both hinge on antenna efficiency.

OTA testing is a measurement; certification is the approval that measurement feeds. A device passes OTA testing in an accredited chamber, then that result is submitted through PTCRB against a carrier’s requirements to certify the device. The test is the evidence, not the certificate itself.

CTIA is the wireless industry association that publishes the OTA performance test plan every accredited lab follows. Its plan defines how TRP and TIS are measured so results are consistent across chambers. Carriers and PTCRB use CTIA-method results to decide whether a device meets their radiated-performance requirements.

An anechoic chamber is a room lined with radio-absorbing material that removes reflections, so a device is measured as if in open space. Without that free-space condition, TRP and TIS stop being repeatable. Some labs use a compact antenna test range to create the same condition in a smaller room. 

Most failures trace to antenna efficiency in the real product. Detuning from metal, the battery or a hand, a short ground plane on a small board, a weak mandatory second antenna, or a poor multi-board connection point all cut radiated performance. The device is healthy at the chip and still misses the radiated threshold. 

A first-pass result is realistic when antenna performance is validated before the chamber run. Estimating TRP and TIS against the target thresholds at the design stage, with a few decibels of margin, moves failures onto the bench where they are cheap to fix. Measured reference designs clear carrier and GSMA targets this way. 

Ignion’s RF engineers review your layout, tune the match for your actual enclosure, and run a pre-certification measurement that reports TRP and TIS while the board can still change.

Get that review before you book the chamber slot.