Your plot suggests your antenna is acting an omni, and not directional.
He gets the back-side planes via reflections of something in front of his window (a high-rise building?).
Possibly, but being close to a south window would also explain the greater number of planes to the south.
Itād take a well designed reflector to give such good performance!
Correct.
RF at 1 GHz tends to quite reflective (even more so at higher frequencies) so getting it to ābounceā off
a surface is actually easier than one might think.
Building materials that offer little or no attenuation to HF or VHF RF energy start to behave differently above
~400 MHz. At 1 GHz, metallic window screen looks more like a solid sheet of metal than it does a
surface with many small openings in it. (e.g. the āscreenā in a microwave oven door)
Other building materials, i.e sheetrock (drywall) lumber, concrete, et al, have higher attenuation
characteristics at 1 GHz than they do at lower frequencies.
A building can act like a Faraday cage (RF shield), a reflective (or directive) element of an antenna,
resonant cavity, attenuator or a combination of any of these characteristics.
With such a short overall (wave)guide length, the main lobe beam width will be quite wide.
As was pointed out at the top of the thread, it seems to be a common misconception that a waveguide length of 3/4Ī» is sufficient. The ARRL antenna book suggests that a waveguide of 2 or 3 guide lengths would offer much better performance. The larger the waveguide diameter, the more pronounced the effect.
Iāve been experimenting with building a waveguide antenna, and while itās been a fun project, itās also been frustrating. It seems that some of the popular online calculators are intended for only wifi frequencies around 2.4mhz, and even though they accept the input of frequencies in other bands, some of the resulting output appears to be incorrect. In fairness, the calculators are presented in the context of building a wifi antenna and donāt claim to be suitable for other frequencies, however Iām fairly certain that Iām not the only one to incorrectly assume that they could be used for other, non-wifi, frequencies.
The problem appears to be with the calculation of the guide wavelength, which ultimately affects the distance of the probe from the enclosed end of the tube.
Based on available materials, I decided to build a ācanā 196mm in diameter and 447mm in length. Anticipating that my metalworking āprecisionā might necessitate some provision for adjustment, I built a movable probe and started testing.
Using the calculator at Online Calculator .:. Cantenna, and entering the frequency (1090 mhz) and diameter (196mm) the distance from the closed end to the probe was given as 33.0725mm, and the guide wavelength was given as 132.29mm.
On the first attempt, I built a probe adjustment range of 20-90mm from the enclosed end. While the antenna DID recieve signals using those dimensions, the results were far less sensitive and much less directional than I expected.
Reading on other sites (linked below) convinced me that guide wavelength is always longer than freespace wavelength, and since freespace wavelength at 1090mhz is around 275mm, the 132mm guide wavelength and 33mm probe position must have been incorrect. Later testing of the calculator showed that regardless of the frequency entered, for any given can-diameter the guide wavelength remained the same.
After building a second can with a 40-170mm adjustment range, and using an N1201SA impedance analyser (calibrated open, short, load) to check the S11 return loss and vswr, the best results were with the probe at about 122mm from the enclosed end of the can. With the addition of a couple of tuning screws, vswr was 1.024 and s11 was -38.28, both of which seemed reasonable.
Recently, I mustered up the courage to work through the intimidating-looking formula to determine the guide wavelength and eventually, where the probe SHOULD be located. Using the formula from Microwaves 101, for a 196mm can, the guide wavelength is 483.46mm and distance from the probe to the closed end of the can is 120.87mm, pretty close to my 122mm.
The results to date have been more directional, but still with a lot of side and back reception. Now that I have reasonable measurements, next up is to roll a new can and properly attach the enclosed end, and fine tune further.
This calculator appears to handle more than just wifi frequencies. http://www.wikarekare.org/Antenna/WaveguideCan.html
References to guide wavelength.
https://www.microwaves101.com/encyclopedias/waveguide-mathematics
www.w1ghz.org/QEX/circular_wg.pdf
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Some are regional like Cal Poly in Cal is like RIT in NY
In post #1 at the top of the thread:
Sounds like this has a significant effect on performance:
Contrary to popular belief on the Internet, a can length of 3/4 the waveguide wavelength is not optimal. The ARRL Antenna book recommends 2-3 waveguide wavelengths instead. Iāve found that adding more cans indeed increases the gain. A 4-can one is the longest I tried; I didnāt write down the gain testing results, but it was considerably better than the 1-can antenna.
I donāt quite follow what youāre saying. Is there a word missing from your sentence?
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Missing punctuation.
This is like the third edit. I realized that people in NYC have no idea that Rochester NY even exists. So Rochester Institute of Technology is unknown to them. 
Take out the āmayā. Sorry
Some are regional like Cal Poly is in Cal. As is RIT is in NY.
I donāt live in NYC and I had no idea what you are talking about.
(I have an RIT on my HF XCVR - another bunch of acronyms thatāll mean nothing to most people)
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Ah yes, Receiver Incremental Tuning.
Well almost no one else. 
73 OM,
KR6K
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I already told you what it was and thank you for proving my point the people in NYC wouldnāt even know about one of the finest technical institutes in NY State. Just as most folks donāt know what a Cal Poly is.
My point was that it was regional name not a nationally recognized name.
(Not taking anything away from Cal Poly)
You did, but I was just pointing out that itās not only residents of NYC that didnāt understand.
I did nothing of the sort.
What I and others were trying point out, is that with a very few words, you could have made your post understandable.
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I accept your criticism in the manner it was offered. Thank you.
Nice work, and thanks for sharing your findings!
Thank you for the compliment, mikkyo.
Hopefully this work will save time for some folks and maybe even save them some frustration.