The use of millimeter-wave spectrum for 5G has some interesting ramifications for antenna design and placement in 5G smartphones...
The 5G era is well underway, though the rollout is still relatively new, and with only a few handsets capable of all the available spectrum, there are still questions that consume column space.
The upper portion of the spectrum offers opportunities to investigate since the mmWave band at 28 GHz currently available is new to the consumer market. Higher frequencies are coming later. Extra high frequency, or EHF, is the moniker for 30 to 300 GHz which may provide a clue as to why there are people who want to understand potential health impacts before they embrace this new technology.
Although the upper reaches of the 5G spectrum offer both higher potential bandwidths and open frequency allocations now given to cellular service, this range of frequencies suffers from very high atmospheric attenuation. That raises the potential for higher power outputs required at antennas in order to reliably connect a user to a base station cell.
But the open air attenuation is just part of the issue. The use of mmWave frequencies is new, but another issue is not. The flesh and blood and bone of the user will also absorb the RF energy. I will not address the potential biological reaction to the mmWave energy. Whether or not the user will experience physical effects, the hand or head (or any body part) will definitely reduce if not outright eliminate RF signal propagation for 5G (at least you hope the output power is in the range that makes this true).
When first considering 5G antenna module placement in phones, I pondered the designs and if they took into account the right handedness of the majority and placement against the head for voice calls. But I am from an older generation that thinks of phones as something you put up to your mouth and ear in order to carry out a conversation. It is much more likely that handset design for 5G antenna placement (at least good design) will optimize for the ubiquitous screen in hand, head down posture for surfing and social media. That could be for 99% of use cases, but the handset still needs to be able to connect on those rare occasions when it is up against your head. It should be able to react to changing circumstances.
We know that MIMO and beamforming techniques are used on both ends (base station and user equipment or UE) of the connection. The cell tower and handset will work together to make sure that their respective antenna arrays are concentrating the RF energy to maximize the signal received on both ends. However, there is another mechanism that can be employed for signal impeding objects near a handset. This was highlighted in a recent System Plus teardown analysis of the iPhone 12.
One relatively small detail in the iPhone 12 highlights the information value that can obtained through the simple task of opening and investigating products in the marketplace. The SystemPlus teardown also highlights the need for competent and experienced technologists to extract the most from the exercise. Although just a teaser for their full report, the SystemPlus teardown offers us valuable tidbits:
“With the Apple iPhone 12 series, we have a discovered a 5G mmWave system like we have never seen before. The system is built for high-speed communication with human safety consideration all controlled by only one chipset.”
The other other 5G antenna in the iPhone 12, the USI fully integrated module with antenna-in-package (AiP) was covered recently in this column. Although very similar to the Qualcomm second generation QTM525 5G mmWave antenna module, there were noteworthy differences. But there is also something more interesting in the second iPhone antenna array.
The SystemPlus teardown noted that a single RF front-end module is used to drive the USI AiP module as well as a second passive phased array antenna under the logic board. This second antenna differentiates the iPhone 12 from other handset designs. It’s unlikely to find any meaningful comparison of cellular connection performance between the 5G iPhone and its competitors, but it would be interesting to know more about this Apple-only (so far) design choice.
Beyond the passive antenna, there is the “human safety consideration” described by SystemPlus. The third component controlled by the Qualcomm SDX55M modem and SMR526 intermediate frequency chipset is a mmWave radar. The function of this radar is to detect “any human body in order to limit the radiation from the 5G mmWave communication system when a body is present.”
Is Apple concerned with health impacts enough to add a costly extra component to limit human exposure to mmWave energy? That is one possibility. The other is to detect proximate absorbers and funnel RF energy to another array, if for no other reason than not to waste energy. Power consumption is on everyone’s mind with mobile devices, and this is especially true for the 5G era. Apple definitely wants to maximize battery performance. Presumably, they also want to limit or eliminate exposure to their loyal users from concentrated mmWave RF energy.
Being deeply involved with every aspect of the 5G rollout, particularly the RF design, Qualcomm will continue to address the control of RF power for antennas with unintended absorbers nearby. A quick search of patents revealed a very recently published application entitled, “Radar for Detecting Human Body Part.” This very recently published application discloses the approach the SystemPlus teardown suggests — radar to detect the proximity to a human body part to allow the equipment to determine whether it is safe to transmit an RF signal.
It’s safe to say that SystemPlus was on target with its analysis of the iPhone 12 mmWave radar and its function. Just like the AiP module, though, we are left with questions about exactly where the Qualcomm RF design ends and Apple’s begins. Lucky. There’s always more column space to fill.