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Simulating Antenna(s) to Bits and Back in Wireless Communication and Radar Systems

Recently, I had the pleasure of attending a presentation by a company whose name requires no introduction, so I won’t introduce it (I’m joking—I’ll introduce it later). The topic of this talk was today’s “latest and greatest” tools and techniques for designing wireless communication and radar systems, with an emphasis on simulation.

Today’s simulation tools blow me away, but this got me wondering how analog and radio frequency (RF) engineers designed things deep in the mists of time before simulators entered the scene.

As I’ve mentioned in previous columns, I’m a digital logic design engineer by trade. I designed my first ASIC in 1980 at the gate-and-register level of abstraction using pencil and paper. My first experience of digital logic simulators was the HILO Logic Simulator. This was developed at Brunel University in the UK in the 1970s and later commercialized by Cirrus Computers in 1981.

I’m comfortable with no-nonsense digital 0s and 1s. I’m less enamored of the wibbly wobbly world of analog. A couple of analog simulators reared their heads in the 1960s—I’m thinking of GENIE (General Network Iterative Evaluator) and CANCER (Computer Analysis of Nonlinear Circuits, Excluding Radiation)—but the real game changer was SPICE (Simulation Program with Integrated Circuit Emphasis), which was developed at UC Berkeley in the early 1970s.

The fact is that I can see how it was possible to design digital logic systems prior to the introduction of digital logic simulators, using techniques such as Boolean algebra, DeMorgan transformations, Karnaugh maps, the Quine-McCluskey algorithm, and state diagrams and tables. However, I simply cannot wrap my brain around how analog engineers can design anything more complicated than a simple oscillator in the absence of simulation.

I presented this poser to my friend, Peter Traneus Anderson, who is a 10th dan black belt in the ancient and honorable art of analog design. Peter replied that there was a lot of “suck it and see” coupled with lots of knowledge and paper-based calculations.

I also had a conversation with Bill Schweber, who is an extraordinary figure in the world of analog, power, RF, and communications engineering. I don’t want to make him blush, but Bill is the quintessential analog engineer: deeply technical, widely knowledgeable, and generously committed to sharing that knowledge through writing, editing, teaching, and mentoring.

We started by reminding each other how things used to be in the old days when we were young. As Bill said, “Back in the day, I used a slide rule, which was both good and bad. The bad is that it only gave you an answer to three significant figures (if you were lucky). The good is that it forced you to think things through.”

I agree. To this day, before I start entering values into an electronic calculator, I first perform a quick approximation in my head or on the back of an envelope to obtain a guestimate value. If my subsequent calculated result significantly diverges from what I expect, I know that I’ve messed something up somewhere. By comparison, if the values are in the same ballpark, this gives me a reasonable level of confidence that I’m doing something right (but don’t tell my wife, because she’ll argue, LOL).

In the past, designers typically worked with a relatively small number of simple components, including resistors, capacitors, and inductors. These were coupled with more complex devices, including vacuum diodes and triodes (later replaced by semiconductor diodes and transistors). All these devices were characterized “into the ground” on the test bench, and designers were intimately familiar with the way components behaved individually and in conjunction with each other.

Bill noted that when working with something new, engineers would often set up an experiment to test things from one perspective, and then they would try to set up an independent experiment that was “orthogonal” (so to speak) to see if it would come out with the same answer to validate the first experiment. Data acquisition as we know it today was very crude and difficult, so “sanity checks” were a big part of the deal. He went on to say, “There are many examples of this. I just finished a book on…”, but we will return to Bill’s books in a moment. 

Bill told me something I didn’t know about the Smith chart, which was created by Phillip Hagar Smith in 1939. It appears that engineers in Smith’s day spent a considerable amount of time standing on benches or climbing ladders to physically probe coaxial or waveguide structures, measuring parameters such as impedance, standing waves, and reflection points. They were looking for nodes and antinodes to determine the standing wave ratio (SWR) or impedance mismatches. As you can imagine, this was tedious, error-prone, and physically awkward, especially when working on long or elevated transmission setups.

Smith, understandably frustrated with the time-consuming nature of these measurements, realized that much of this could be approached mathematically. He transformed the complex impedance transformation equations for transmission lines into a graphical tool—a nomogram (or nomograph)—that could instantly inform how impedance changes along a line, how to match it, and how reflections behave. And thus the Smith chart was born.

Like your humble narrator (I pride myself on my humility), Bill is interested in the history of technology—in understanding how and why we got to be where we are today. For example, the first televisions in the USA, circa the early 1940s, were monochrome (black and white), based on the NTSC standard (named after the National Television System Committee).

Later, in the early 1950s, the decision was made to add color, which led to NTSC being jokingly (and somewhat unfairly) dubbed “Never Twice the Same Color.”

The challenge was to embed the new color information within the existing monochrome signal in such a way that:

  • In addition to the new color sets, the signal would still display correctly on existing black-and-white sets.
  • Signals from legacy black-and-white transmitters would display correctly on new color sets.

In other words, the system had to support both forward and backward compatibility. The solution, which utilized a form of sideband modulation, was awesomely elegant. Even more impressive, it was conceived and implemented without the aid of modern simulation tools, because such tools didn’t yet exist.

Now, I know you are going to say that today’s systems—involving things like mmWave (30 GHz to 300 GHz) frequencies and beamforming using multiple antennas at both the transmitter and the receiver to precisely control multiple data streams—are unimaginably more complex than systems circa the middle of the twentieth century. That’s as may be, but I couldn’t even imagine designing an amplitude modulated (AM) radio transmitter and receiver by hand, let alone a frequency modulated (FM) system. The sort of wireless communication and radar systems people are creating today makes my eyes water just thinking about them.

All of which leads us back to the presentation I mentioned at the commencement of this column. This was provided by the folks at MathWorks, who are the proud purveyors of the MATLAB and Simulink product families.

The underlying theme of this presentation is that we now have the tools to simulate every portion of a wireless communication system or radar system, from the antenna(s) to digital bits and back again. This includes antenna design, beamforming, simulating in- and out-of-band interfering signals, ray tracing channel modeling to account for multiple paths in a channel (including reflections and refractions associated with buildings), and much more.

The folks from MathWorks talked about every aspect of this in excruciating exhilarating detail—so much so, in fact, that it made my head hurt. Happily, they would love to talk to you about it also, so feel free to reach out to them and tell them “Max says Hi.”

As a follow-up to our conversation, Bill kindly compiled a list of some of his favorite “Engineering / Science History” books that he thought I’d enjoy. Even better, he said it was OK for me to share these with you, which I now do so as follows:

  • Apollo: The Race to the Moon, by Charles Murray and Catherine Bly Cox, is the best book about the Apollo program I have read; it combines big–picture perspective with details, and insights into the people, technology, and challenges.
  • Digital Apollo: Human and Machine in Spaceflight, by David A. Mindell, focuses on the computers and programming of the various Apollo computers. After reading this, you will never complain about insufficient memory, CPU speed, or tools again. 
  • Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance, by Donald Mackenzie. This is a well-written book that combines history, technology, personalities, and political context to explore the development of guidance, from the earliest gyro systems to advanced missile units. Every other book I have read on guidance systems cites this one as a key reference.
  • Tube: The Invention of Television by David E. Fisher and Marshall Jon Fisher is a clear, readable history of this invention which changed our world in so many ways, the people who made it happen, the internal corporate and technical battles, and the challenges that had to be overcome in both prototype and mass production.

Eeek! I find that I’ve only read three of Bill’s suggestions, which means my Christmas wish list has just grown a whole lot longer. How about you? Do you have any engineering and/or science history book recommendations you’d care to share with the rest of us?

6 thoughts on “Simulating Antenna(s) to Bits and Back in Wireless Communication and Radar Systems”

  1. While I’d like to have read more on harmonics, I was impressed that an article this long on analog electronics could be written without once invoking chicken-blood and astrology! Kudos!

    …And nice selection of books. I would have included “Ignition!: An informal history of liquid rocket propellants”, by John D Clark, but there’s always more that can be added!

  2. Before simulations existed, we would build circuits on breadboards to test our designs and measure their performance using signal generators and voltmeters and oscilloscopes. This had the advantage of including stray capacitance and inductance often ignored in low-frequency simulations. Radio-frequency simulations include the strays.
    https://en.wikipedia.org/wiki/Point-to-point_construction gives an overview of how it was, and still is.

    A puzzle for analog designers: Take your favorite instrumentation amplifier chip, and connect an inductor and capacitor in series (instead of gain-setting resistor) across the gain-setting pins. How does the circuit behave?

      1. Allen B. Dumont introduced oscilloscopes mid 1930s. Radio development did not need oscilloscopes. Television development needed oscilloscopes. Signal generators existed from the beginning of radio. Galvanometers are even older.

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