Forgotten Electrical Engineer's Work Paved the Way for Radar Technology

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Sallie Pero Mead was first hired at AT&T in 1915 as a “computer”—a human calculator—shortly after completing her master’s degree in mathematics at Columbia University. Before long she started working on the company’s transmission engineering team as both a mathematician and an electrical engineer. She and her team developed and tested hollow metal tubes used as waveguides: structures that confine and direct electromagnetic waves. In 1933 they discovered a new way that hyperfrequency waves could propagate down these tubes, and this made radar technology possible—just in time for use in World War II.


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Lost Women of Science is produced for the ear. Where possible, we recommend listening to the audio for the most accurate representation of what was said.


Katie Hafner: I’m Katie Hafner, and this is Lost Women of Science: From Our Inbox, a series of mini-episodes featuring women in science who came to us from you, our listeners.

On today’s episode, we hear from electrical engineer Greg Coxson and mathematician William Haloupek, about Sallie Pero Mead, whose work at AT&T paved the way for early radar technology. Producer Erica Huang brings us her story.

Greg Coxson: I was talking, we were emailing, Bill and I were emailing this week, and I said Bill, I’ve, did you ever get to see the back of one of those spy radar, uh, antenna arrays? We, we used to work on the spy radar together in Morristown, New Jersey. And if you look at the back of these enormous radar arrays, it’s like a – a snake pit of waveguides just intertwined. 

Erica Huang: If you’ve never heard of a waveguide, I think this is a pretty good place to start.  By imagining a snake pit of twisting, interlocking, hollow metal tubes.

Greg Coxson: Somehow you have to work these metal tubes, somebody had to design this.  Because you have to get these, the lengths of these waveguides so precise.

Erica Huang: And the story of the waveguide is the story of an electrical engineer and mathematician named Sallie Pero Mead. It’s also the story of the birth of radar technology, the creation of the coaxial cable, and the miracle of conveying something important across an impossible distance. It’s also, in a way, the story of Greg Coxson and Bill Haloupek.

Greg Coxson: I’m Greg Coxson. I teach electrical engineering courses at the Naval Academy in Annapolis, Maryland.

William Haloupek: I’m William Haloupek. Friends call me Bill. And I’m a retired mathematician. Also, uh, worked in the radar engineering field for 10 years, but I’m, I’m really just a math guy. Greg is the–more of an engineer. But he knows enough math to be able to communicate with me, so.

Erica Huang: Greg the engineer, and Bill the mathematician, came across Sallie Mead’s story in 2022.

Greg Coxson: I was asked to do a class on radar history at the IEEE radar conference. And um, in doing my slides, I got to a point where, you know, here’s this woman who was part of the story that I wanted to tell. And I couldn’t, I couldn’t find her, uh, birth year, couldn’t find her death year. And I got a little bit frustrated. I couldn’t find it anywhere. So I contacted Bill. Actually, Bill was the perfect person to go to for this project.

William Haloupek: Basically, I’ve been working on my genealogy since I retired. So, my contribution is mainly looking up family information, finding newspaper articles, old census records, all kinds of stuff like that.

Erica Huang: Bill started digging through old New York census records, college yearbooks, and ancestry databases, and here’s some of what he found.

Sallie Mead was born Sallie Pero in 1893 in Manhattan. She was a bright student, skipped several grades, and started studying at Barnard, one month shy of her 16th birthday.  She played field hockey, basketball, and baseball. There’s a great photo of her in the 1914 Barnard yearbook, standing with the five other members of the varsity Basketball team, her hair in a braided crown and her hands in her pockets.

William Haloupek: Sallie went to Barnard College because Columbia wouldn’t admit women. Then when she went for her master’s, for some reason they allowed that. But that was 1914, I think.

Erica Huang: By the turn of the twentieth century, all of the graduate faculties at Columbia had opened their doors to women for degree study.

Sallie graduated from Columbia with her master’s degree in mathematics. And after a year of trying out the more common path of teaching, she decided to instead apply for a job at AT&T. She was hired first as a computer.

William Haloupek: Of course, they didn’t have electronic computers back then. So, uh, what they meant by a computer was someone who does calculations by hand.

Erica Huang: Human computers date all the way back to the mid-18th century; the first cited instance involves French mathematicians trying to calculate the return of Halley’s comet. By the 19th century, computers were working across a vast array of scientific and technological fields; wherever calculations were needed. And by the twentieth century, computers were often women.

William Haloupek: There was an idea, prevalent idea, that women were suitable for that kind of work. Because… men were more daydreamers and big thinkers and had, they had come up with big ideas, but women could concentrate on the work and not be distracted by all that.

Erica Huang: It was also cheaper.

Greg Coxson: It’s interesting because they had a unit of computers and I’ve seen some references talking about that unit saying, oh, you know, these women were way overqualified for what they were doing, and everyone pretty much realized it.

Erica Huang: It seems like Sallie recognized this too. She wrote an article in the Vassar Quarterly in 1922, talking to the then entirely female student body about her early work at AT&T. She says: “With regard to advancement, it must be remembered that women have been in the technical field a comparatively short time. Advancement, however… is to be found in engineering.”

Sallie didn’t stay a computer for long.

Greg Coxson: For us, one of the mysterious things is how did Sallie Mead get to be such an applied mathematician, even an engineer. Because she studied pretty theoretical math at Barnard and Columbia, and then she goes to work for AT&T and, you know, by the 1920s, she’s like the expert on some pretty complicated mathematics and properties of these cables. You’ve been impressed with that, right, Bill?

William Haloupek: Yeah.

Erica Huang: It seems to come back to the fact that AT&T was an outlier.

Greg Coxson: They had this math research department, which was like no other company. And, uh, those people were meant, that was their job, was to be mathematicians who would be called in to, uh, support an engineer.

Erica Huang: Sallie Mead was tasked with doing mathematical analysis for one of these engineers. So this was how she crossed over the line from crunching numbers, into applied mathematics and electrical engineering, eventually joining AT&T’s Bell Telephone Laboratories.

Greg Coxson: She ended up in a unit called Transmission Engineering. She spent the 1920s basically doing one project after another involving cables and tubes for carrying signals, and they were usually circular cross-section tubes.

Erica Huang: Circular cross-section hollow metal tubes.  This is the most basic form of a waveguide. And waveguides do what they say on the tin. They guide waves. You can imagine the waves zigzagging down the inside like sound moving through a flute.

There are acoustic waveguides that direct sound and optical waveguides that direct light. And the waveguides that Sallie was working on were called hyper-frequency waveguides. They directed electromagnetic waves in the radio frequency, and even beyond.

Greg Coxson: I’ve been trying to explain this to Bill that they’re used mainly to take the, the waves from the – the exciter that generates the signal to the antenna, and then you disperse them out to the atmosphere.

Erica Huang: Sallie is working on these waveguides, calculating and running experiments alongside the rest of the Transmission Engineering team. And in 1933, they make a major discovery.

Greg Coxson: I think they were all pretty excited. It’s an unusual paper in that you can sense the excitement over their result, like, can you believe this, you know? And actually, uh, George Southworth, who they were supporting, uh, in 1962, he wrote a book and he’s still glowing. He’s like using poetic language, you know, and not just once he’s, he just can’t get over it. Even, um, 30, 25 years later.

Erica Huang (interview): What was it that they discovered about this particular type of waveguide and the way that the waves propagated that was like so different that they were so excited about?

Greg Coxson: Bill?

William Haloupek: You’re the engineer… 

Greg Coxson: (Laughs) I know Bill was studying up before this interview…

Erica Huang: It’s a little complicated.

Sallie and her team were used to sending waves down these tubes and seeing them behave in this predictable way. So, as frequency increased, attenuation also increased. In other words, as there were more and more waves per second, the waves lost power. But then, they discovered a certain way that a wave could propagate down one of these waveguides, which did the opposite thing.

So as the frequency increased, the attenuation decreased. This is really good news for super high-frequency waves.

Greg Coxson: They’re like, wow, this is gonna revolutionize, uh, communications. Which is what they were interested in. Um, it actually didn’t really revolutionize communication.

Erica Huang: But there was another use for waves in the radio frequency right around the corner.

Greg Coxson: This was, you know, 1936, 1937. We’re only four years before World War II.

Erica Huang: And radar played a major role in World War II. Fun fact, RADAR is actually an acronym. It stands for Radio Detection and Ranging. Using waveguides, the army now had a way to transmit bursts of radio waves to detect objects at a distance, which is obviously useful in a war.

Greg Coxson: And by the time the war started, or even a little bit before the war started, the government was coming to AT&T and buying these waveguides as components of radar.

Erica Huang: Today, in addition to its military uses, radar is used in satellites and spacecraft; to detect weather conditions; to track the motions of planets and other celestial bodies; in air traffic control, and in ship navigation.

I asked Greg if we still use the kinds of waveguides that Sallie was developing in our modern radar technology.

Greg Coxson: Totally. We still use them. And you’ve got the big ones and you’ve got the little ones. You’ve got tiny little waveguides. I go to the Radar Conference every year. And there’s this company that comes and sells these things. And they’ve got this wonderful array of these cute little waveguides. And, and I’ve gone to their, their booth and I go, you know, I’m, I’m doing uh, research on this woman who was involved in waveguides. They have no clue. Like they’ve never heard of her before, but –

Erica Huang (interview): Wow, yeah.

Greg Coxson: Here they are selling these waveguides and it’s their whole business, and they’ve never heard of Sallie Mead!

Erica Huang: I find that when I work in a vacuum, I narrow my focus past the point of usefulness. I think that’s why I wanted to talk to Bill and Greg together, the mathematician and the engineer. This whole thing is people figuring out something together. It’s a story of cross sections. A woman crossing a Rubicon into engineering, and the people waiting on the other side to meet her.

Sallie Mead is, of course, not just her waveguides.

Greg Coxson: She, she bought nice clothes. She went to, um, the opera. She went to the theater in New York City. She loved Manhattan, I think.

William Haloupek: There was one mention of the fact that, uh, she and her second husband liked to take their boat out on Long Island Sound. So they were very, uh, much ocean-going people. They liked to get out on the, on the water.

Greg Coxson: She also went above the Arctic Circle. We have a certificate for that. She was on some cruise that went beyond the Arctic Circle. Always the sportsman. Or – sportswoman.

Erica Huang: I like to imagine her this way, out on her boat, having a fantastic adventure. And Greg and Bill are teaming up for another adventure too.

Greg Coxson: We’re currently working on one that’s a lot harder.

Erica Huang: Huh, really? Which one is that?

William Haloupek: (Laughs)

Greg Coxson: It’s this woman involved in the invention of the klystron. It’s almost impossible to find anything on her, but we’re trying. We’ll, we’ll, we’ll do it.

William Haloupek: Neither of us reads Russian.

Greg Coxson: Little by little.

Katie Hafner: Thanks to Greg Coxson and William Haloupek for writing to us about Sallie Pero Mead.

This episode of Lost Women of Science: From Our Inbox was produced and mixed by Erica Huang and sound designed by David Herman. Our executive producers are Amy Scharf and myself, Katie Hafner. Lizzy Younan composes our music. We get our funding from the Alfred P. Sloan Foundation and the Anne Wojcicki Foundation. PRX distributes us, and our publishing partner is Scientific American.

Here at Lost Women of Science, it’s our goal to rescue female scientists from the jaws of obscurity, but we need your help! If you know of a female scientist who’s been lost to history, let us know! You can go to our website to send us an email, we are lost women of science dot org. You’ll also find the phone number to our tip line. We love getting calls to the tip line.

Thanks for listening.

Episode Guests:

Greg Coxson

William Haloupek


Erica Huang


Erica Huang

Further reading:

Carson, John R., et al. “2. April 1936: Hyper-Frequency Wave Guides Mathematical Theory.” Internet Archive, 1 Apr. 1936.

Coxson, Greg, and William Haloupek. “Sallie P. Mead: An Industrial Mathematician in the Early 20th Century.” SIAM News

“Today We Celebrate the Invaluable Contributions of Women Technologists at Nokia Bell Labs.” Nokia Bell Labs, 8 Mar. 2021.

Haloupek, William. “Pero and Mead.” Gapinski Ancestry.

Pero, Sallie E. “Vassar Quarterly, Volume VII, Number 4, 1 July 1922 ‘Opportunities in Telephony.’” Vassar Quarterly 1 July 1922 – Vassar Newspaper & Magazine Archive, 1 July 1922.

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