[UPDATED] iPhone XS and XS Max mostly fail to impress in lab tested RF power output

Following Apple's keynote presentation yesterday, authorization filings for many of its newly announced mobile devices started being made publicly available in the FCC OET database.  Among others, this included the US variant iPhone XS (model A1920, FCC ID BCG-E3218A) and iPhone XS Max (model A1921, FCC ID BCG-E3219A).  The US variant iPhone XR (model A1984, FCC ID BCG-E3220A) was not included.  Its authorization documents likely will be disclosed closer to its October release, thus may be the subject of a later update or a different blog post.

Before proceeding any further, RF power figures to come represent best averaged and rounded estimates of maximum uplink EIRP test results provided to the FCC OET in individual device authorization filings.  Or in the case of ERP low band test measurements submitted in the filings, that ERP has been converted manually to EIRP for level comparison purposes.  All EIRP figures are normed against a baseline of 200 mW (23 dBm), which corresponds to a standard conducted power target with unity antenna gain and generally represents good RF transmission performance.  Caveats about lab testing versus real world capability and uplink versus downlink always apply.

Now, let the EIRP graphs speak for themselves...

As the blog post title indicates, the lab tested radiated output from the two new iPhone XS models does not set the world on fire.  Nearly all bands on both handsets fall short of the 200 mW benchmark.  Only band 41 HPUE on iPhone XS looks pretty good on paper, and even that comes with a conducted power asterisk to be analyzed later.

But first to nip in the bud one potential conspiracy theory, Apple's decision to forgo Qualcomm this year and source all cellular modems from Intel is not responsible for the RF power output limitations in the new iPhone models.  The cellular baseband modem is separate from and well upstream of the amplifiers that generate the conducted power and antennas that generate the radiated power being measured in lab testing.

Furthermore, conducted power is not the issue.  The standard conducted power target of 200 mW (23 dBm) is +/- 2 dB.  And Apple is using the +2 dB margin to enhance its figures, pushing 250-320 mW (24-25 dBm) conducted power across many included bands.  This extends to band 41 HPUE, which has a standard conducted power target of 400 mW (26 dBm).  Again using the +2 dB margin, Apple has upped that ante to 500 mW (27 dBm).  That inflated conducted power is fine.  But bear in mind that it assists only in transmission, never in reception.  Plus, it also can be used to mask some antenna shortcomings.

Yes, with often greater than standard conducted power being generated -- rhetorical questions ahead -- where is all that power going?  Where is it being diminished?  The answer lies in antenna gain.

Indeed, deeper analysis of the FCC OET authorization filings shows the underwhelming EIRP figures to be almost entirely products of negative antenna gain.  For every 3 dB drop in antenna gain, 50 percent of conducted power is attenuated.

To illustrate visually, look at a graph of the iPhone XS Max antenna gain (Ant. 1) across its entire uplink low band, mid band, and high band frequency range.  Antenna gain inevitably reduces conducted power by about 5-7 dB.

Now, both iPhone XS and XS Max this year incorporate four antennas operational across many but not all bands.  That antenna diversity in and of itself is a good thing.  However, even with the four antennas -- and possibly because of the four antennas crammed inside -- antenna gain is universally negative.  And simultaneous transmission from multiple antennas is not possible due to a "break before make" switching mechanism among the antennas.

For a partial look at all four antennas, see a snapshot from the iPhone XS Max authorization filing:

Lastly, for an interesting comparison and stronger RF output, see lab tested EIRP figures from last year's iPhone X (model A1865, FCC ID BCG-E3161A) and iPhone 8 Plus (model A1864, FCC ID BCG-E3160A).

The takeaway is that iPhone EIRP in the lab has not always been so compromised as it appears to be this year.  Real world RF performance comparisons when some users switch from the iPhone X and 8 generation to the iPhone XS generation, no doubt, will be interesting.

Also, see follow up articles (1, 2).

Source: FCC OET