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RF circuits to go beyond 100GHz

Posted: 23 Feb 2015 ?? ?Print Version ?Bookmark and Share

Keywords:100GHz? RF circuits? connector? Wi-Fi? ISM?

Contrary to earlier outlooks, connectors can now cope at frequencies above 1GHz and even 10GHz, observed Bill Schweber, an electronics engineer and author who has written for EE Times. Engineers, then, must at least try to surpass this record and go even higher.

It wasn't that long ago that most RF circuits operating even slightly above 1GHz were mostly the domain of experimental, scientific or one-off projects, with just a few specialised exceptions such as costly radar systems. The required components were scarce, if available at all, and hard to use; the designs were complex and limited in performance. Equally frustrating, the tools needed to model and design, and the instrumentation needed for test and evaluation, were also costly, awkward or not up to the job (pick on or more). Mass-production consumer products operating in that part of the spectrum were rare and expensive.

Bill Schweber


Times have changed, a lot. The development of cell phones, Wi-Fi and the similarly situated licence-free ISM (instrumentation, scientific, medical) 2.4GHz band has driven availability of all the pieces needed to live and prosper in this >1GHz region. Now systems are moving higher, with activity in the 5GHz Wi-Fi band as well, due to crowding and interference issues at 2.4GHz. Ironically, this at least is partially due to the success of the cellular, Wi-Fi ad ISM initiatives at 2.4GHz.

No single technical development is the enabling factor for this move to higher frequencies; instead, it's the back-and-forth interplay between demand and resources. Demand drives the need for active analogue and passive components as well as associated modelling and manufacturing tools, while advances in the components and tools enable the demand to be realised, and then the virtuous cycle begins again.

Of course, 5GHz or even 10GHz is not the end of the RF spectrum. There's significant component and end-product work being done at 60GHz supporting data transfer rates up to 7Gbit/s, with standards promoted by Wireless Gigabit Alliance via IEEE 802.11ad. Moving up the spectrum, we're seeing automotive radar operating at 77MHz which will drive design, production and cost initiatives.

Still, it's a tough battle with many obstacles. While Maxwell's four equations, Figure 1, govern the electromagnetic reality regardless of wavelength, the interplay between the EM fields and materials is a complex function of frequency, and often non-intuitive. For example, his equations do not directly indicate that 2.4GHz would be the resonant frequency of water molecules, and so the critical frequency for microwave-oven magnetrons due to energy absorption. They do not show that a 60GHz signal can barely penetrate walls but can propagate via reflections from walls, ceilings and floors.

 Maxwell's equations

Figure 1: Maxwell's equations, reduced to this well-known set by Oliver Heaviside, are the foundation for all EM theory and practice.

(Side note: while we call them "Maxwell's equations", they should really be called "the Maxwell-Heaviside equations" as it was really Oliver Heaviside who reduced Maxwell's numerous and extremely complicated expressions to the classic quartet we use today, see Oliver Heaviside: A first-rate oddity from Physics Today.)

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