WiFi 6 PCB Design Guide and 802.11 Standards

WiFi is arguably the most successful wireless networking technology the world has seen to date, and WiFi 6 is like a brand new world for your networked devices. As I’ve slowly accumulated connected products for my home, everything from my garage door opener to my thermostat can be connected to my LAN and accessed through an app on my phone. As the wireless landscape in homes and offices becomes more cluttered, wireless products need to move to new frequency ranges, change bandwidth, and change other parameters to prevent further cluttering of allocated radio bands.

The 802.11 standards define important performance metrics for different WiFi generations, and PCB designers should familiarize themselves with these standards before creating layouts. If you’re designing new products with wireless capabilities, you’ll likely need to think about including WiFi 6 in your board. Here are some things to consider when designing a WiFi 6 PCB layout.

WiFi 6 and the 802.11 Standards

Just like earlier upgrades to the WiFi standards, WiFi 6 continues improving by providing higher data rates through greater modulation. It still operates at standard frequencies (2.4 GHz and 5 GHz) as earlier generations. The table below shows the relevant specifications for WiFi 6 compared to two earlier generations (WiFi 4 and WiFi 5 Wave 2). Thankfully, WiFi 6 is backwards compatible, so your customers won’t need to replace their devices when they buy a WiFi 6 compatible product.

Thankfully, this makes things somewhat easy in terms of routing for PCB designers. Designing transmission lines for WiFi 6 PCB layouts follows the same rules as for earlier WiFi generations. The main difference lies in the signal bandwidth as the frequency content in a 1024-QAM signal will be different from that in a 64-QAM signal. However, bandwidths do not become so large between WiFi 5 and WiFi 6 that existing techniques need to change.

Note that the data rates shown above are aggregated across multiple streams with 2x2 or 4x4 MIMO. Data rates also depend on the channel bandwidth. Note, however, that WiFi has taken the same strategy as Ethernet; higher data rates are provided through deeper QAM modulation, rather than increasing the frequency.

WiFi 6 vs. WiFi 6E

Just as everyone is getting acquainted with WiFi 6, the WiFi alliance released WiFi 6E. This technology extends WiFi 6 into the 6 GHz band and basically allows devices with 3 different frequency bands (2.4 GHz, 5-6 Ghz, and 6-7 GHz). The release of Wi-Fi 6E products is still pending regulatory approval of the opening up of the 6 GHz band. The decision frees up an extra 1200 MHz of spectrum to expand WiFi networks out to higher frequencies.

In my opinion, analog boards are somewhat easier to design than high speed digital boards because bandwidths do not extend out to higher frequencies. In terms of WiFi 6/6E PCB layout, you’re only worried about maintaining controlled impedance and signal integrity out to a maximum of 7.125 GHz (you should apply a +/- 25% safety factor here to account for rolloff). Both WiFi 6 and 6E need to have the digital section designed with strong power integrity to prevent data degradation as the modulation frequency in QAM is higher, so digital components will need flat PDN impedance out to higher bandwidths.

Beyond 802.11ax: White-Fi, WiGig, and 3.6 GHz

There are four other less-known WiFi bands that designers might consider using for different purposes. Among these, the most difficult to work with is WiGig, which operates in the 57 to 64 GHz ISM band. Commercially, WiGig is dead in the water for practical WiFi routers; it has negligible transmission through walls, and omnidirectional broadcasting has extremely low range (~10x lower than WiFi 5). Beamforming needs to be used to provide line-of-sight communication, and higher directionality could be provided with phased arrays and a radome. This might be fine for applications like chirped radar, but it’s impractical for WiFi.

The other three less-used WiFi protocols are White-Fi (802.11af, 470 to 710 MHz), 3.6 GHz WiFi (802.11y, US only), and WiFi HaLow (802.11ah, operates in sub-1 GHz unlicensed bands). These frequency ranges are much easier to work with in terms of routing and signal integrity compared to WiGig. Rather than WLAN products, these protocols are better options for specialized wireless applications, such as sensor networks or non-consumer IoT products.

Some application notes you’ll read for routing WiFi traces recommend, at minimum, placing guard vias along the transmission line leading to the antenna and placing the antenna section in its own region of the board. This is about where the application note recommendations should end, and you should carefully consider best practices for mixed signal boards. You might consider grounded coplanar waveguide or stripline routing in a dedicated layer, especially when working with multiple antennas. Isolation between digital and analog blocks is key, both in the ground plane and in terms of isolation on the surface layer.

I’ll likely dig into something more detailed on sub-1 GHz WiFi in a later article, but most products will decidedly include WiFi 6 for wireless communication. Whether you need to design new products with WiFi 6 or other high frequency wireless protocol, you can find all the design tools you need in Altium Designer®.

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