Reverse Engineering A Phased Array System Reveals Surprising Details

The term “phased array” has been around for a long time, but in recent years we’ve heard more and more about the beam shaping that’s possible with phased array antennae. In the video below the break, [The Signal Path] breaks down a Qualcomm 60GHz WiGig unit, and does a deep dive, even looking at the bare silicon and an x-ray of an antenna.

An X-Ray of the antenna shows the intricate design

Some fascinating highlights include how not only the data signal is sent to the antennae through a standard coaxial cable, but so are control signals and a base clock frequency. [The Signal Path] explains how the manufacturer chose to use what’s called a SuperHeterodyne (aka “superhet”) architecture, which is not all that different from those used in traditional amateur radio transceivers. In theory, anyway.

Another element that is discussed is how the PCB’s themselves are used as waveguides, inductors, and transmission line matches, among other countless little hacks to fit a rather complex system into a truly diminutive space.

If you’re not familiar the concept behind phased arrays, check out this article we published in 2019 that shows how phased arrays can steer a beam without any moving parts. It’s quite fascinating!

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A Patch Antenna Is Just A Rectangle, It Should Be Easy To Design, Right?

If a grizzled RF engineer who bears the soldering-iron scars of a thousand projects could offer any advice, it would be that microwave antennas are not a field to be entered into lightly. Much heartache is to be saved by using an off-the-shelf design, and only the foolhardy venture willingly down the stripline into the underworld of complex microwave resonances.

But every would-be microwave designer has to start somewhere, and for [Adam Gulyas] that start came with a 2.4 GHz patch antenna. His write-up is a fascinating tale of the challenges and pitfalls of creating something which is deceptively simple at first sight but which becomes significantly more complex as he characterizes his design made real as a PCB.

The process started with a set of calculations to derive the patch dimensions and a bit of PCB work adding a stripline feed. This was produced on a PCB, a normal 1.6mm thick FR4 fiberglass board. When hooked up to a VNA its impedance was all wrong. Further, it had a resonance at the required frequency but also unexpected ones at 3.7 and 4.6 GHz. Simulation of the design also yielded a different resonance from the one calculated, and discussing it with others yielded the conclusion that the feed might be at fault. He ended up using an inset feed, with a co-axial cable emerging away from the edge of the patch, and was able to achieve a far better result.

We can all learn something from [Adam]’s write-up, and we salute him for staying the course to get the design to a usable point. It would be interesting to see the same antenna produced from a more consistent dielectric material than generic FR4. Meanwhile, if you are interested in microwave RF design, take a look at Michael Ossmann’s primer on the subject.