Good point. I’d envisioned 4 corner antennas being enough to cover 360 degrees but as you say, I may have to build 10 
Have anyone thought of/tested rotating a directional antenna?
Have it turn around at 6 RPM, just like any radar?
5.4 GHz Sectorized Omnidirectional Antenna Array
Quad-Antenna Array
https://s20.postimg.org/gg0k9uz7h/Sectorized_Omno_Array_1.png
https://s20.postimg.org/54xwlhscd/Sectorized_Omno_Array_2.png
Big problem with that is how will you feed the RF to the receiver?
Direct cable is useless as it will twist up in a bunch of knitting in no time.
Only option is with a slip ring, but anything of RF quality will set you back a pretty penny (or two)!
Slip rings (cheap ones) at RF levels are prone to ‘noise’ from the slip ring ‘mechanics’ itself - quality costs.
I have an antenna tracker for model aircraft and that has the Rx + antenna rotating on top of the slip rings and then just the decoded signals (at audio/video signal levels) are passed over the slip rings.
Nigel.
Been there, tried that (at 2.4GHz) - it was disappointing at best.
I had 4 patch antenna’s like you posted with a processor automatically switching to the antenna with the strongest RSSI signal.
See my post above ref model aircraft, the answer was a GPS on the aircraft with the Rx + antenna on the ‘rotator’, tracked/guided by the received GPS signal, working on both azimuth and elevation.
I think a decent vertical antenna for all round coverage or beam if interested in one direction only is the most viable (or combining multiple Rx’s + beam into one Rx).
Nigel.
Getting a bit surreal now but how about a spindle to rotate the antenna which travels through 360 degrees then returns to zero. A windscreen/windshield wiper type arrangement?
I’ve been busy building several quad antennas and, as has been mentioned many times before, at this frequency, “Accuracy is king!” I can’t build a repeatable quad antenna 
However, I found some interesting versions of the quad here
I found this Franklin type antenna called an AMOS antenna http://f5ann.pagesperso-orange.fr/antenneamos-51090mhz/index.html
Does anyone have a 4NEC2 file for it?
Original design by Dragoslav Dobričić
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Prepared 4NEC2 Model just now (without impedance matching coax), and uploaded the file to Dropbox.
Download link: AntenneAmos5.nec
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Hi abcd, Many thanks for modelling the AMOS and posting the file. I’ll take a longer look later today.
^ All the antennas on my block, when I was a kid, looked like this, but with 75 ohm cables. This was before the CATV and satellite time.
https://forum.adsb.in/f14/neizvestnyi-bort-delimsya-informatsiei-1744/index293.html#post50015
Вот этой антенной. Очень узконаправленная. Поворотом изменяется поляризация и можно ослабить сигнал дополнительно.
Обошел квартал - направление внутрь его. При случае заберусь на горку возле и и посмотрю на пеленг оттуда. Внешне никаких мачт там нет.
Обошел квартал - направление внутрь его. При случае заберусь на горку возле и и посмотрю на пеленг оттуда. Внешне никаких мачт там нет.
With this antenna. Very narrow focus. Turning to change the polarization and you can attenuate the signal additionally.
Walked around the block - the direction inside it. On occasion, I’ll climb the hill near and look at the bearing from there. Outwardly, there are no masts there.
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https://forum.adsb.in/f14/neizvestnyi-bort-delimsya-informatsiei-1744/index293.html#post50022
Размеры выдал калькулятор для ребристо-стержневой антенны для 1090МГц.
https://3g-aerial.biz/wi-fi-3g-4g-pushka-analiz-i-raschet
Не сохранились.
Dimensions given by the calculator for the ribbed-bar antenna for 1090MHz.
https://3g-aerial.biz/wi-fi-3g-4g-pushka-analiz-i-raschet
Have not survived.
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https://forum.adsb.in/f14/neizvestnyi-bort-delimsya-informatsiei-1744/index294.html#post50023
Нашел, рассчитал.
Found, calculated.
post moved to An antennes for ADSB 1090MHz
https://forum.adsb.in/f18/antenny-dlya-ads-b-cistem-1090-mgts-41/index48.html#post50030
I thing all this discussion about directional antennas is misguided. The ADS-B signal is not a faint SW radio station that needs huge amounts of gain.
Even with the 5.5dB gain you are limited by the natural obstacles, and Earth curvature, not by the antenna gain.
Directional antennas are potentially useful for a sectorized receiver (the benefit being that each sector sees fewer collisions / fruit - i.e. you’re not trying to improve signal strength in one direction, more trying to reduce it in the other directions)
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