Morgenstern antenna operating theory

yosimitesam · Feb 22, 2021

I'm trying to find information on how the Morgenstern ("Morning Star") antenna worked. I have a good understanding of lobing, phased array, and directors/reflectors (Yagi, Lichtenstein, etc.) but I cannot figure out how the Morgenstern gave "direction" indication. I appears to be two dipoles (with reflectors) at 90-degree angles. Are they energized alternately or are they coupled somehow? Are the different polarization planes used in any way? Any info would be useful as I cannot find anything useful on the web. Thanks.

MiTasol · Feb 23, 2021

Christopher Story at RadioNerds may be able to help you. He is a major collector (and FOC supplier of) airborne radio manuals and texts.
If you have any stray airborne radio manuals in pdf format he would love copies for his site. He also has a theory section that may help

rinkol · Feb 25, 2021

yosimitesam said:
I'm trying to find information on how the Morgenstern ("Morning Star") antenna worked. I have a good understanding of lobing, phased array, and directors/reflectors (Yagi, Lichtenstein, etc.) but I cannot figure out how the Morgenstern gave "direction" indication. I appears to be two dipoles (with reflectors) at 90-degree angles. Are they energized alternately or are they coupled somehow? Are the different polarization planes used in any way? Any info would be useful as I cannot find anything useful on the web. Thanks.

The Morgenstern antenna arrays were adapted to existing radar designs, primarily the SN-2 and Neptune. SN-2 operating frequencies were 72, 81 and 90 MHz (these frequencies seem version specific and not available on an individual radar). Neptune used rather higher frequencies up to about 180 MHz. It would seem that there must have been multiple versions of the antenna to accommodate the different frequencies. I'm not sure how scanning in angle was done. Possibly there are additional antenna elements on the wings or fuselage to allow some beam steering, but this isn't obvious in the photographs I've seen.

MIflyer · Feb 25, 2021

Possibly it worked similar to the Adcock Antenna? The attached is from the US Army Technical Manual on an antennas which has the intimidating appellation of TM 11-666.

yosimitesam · Feb 25, 2021

Thanks for the replies. It's still something of a mystery how left/right - up/down was detected using this antenna. It might have something to do with exploiting polarization but I cannot determine what. It seems that crossed Yagi's (assuming that is what Morgenstern is) are mostly used for circular polarization and, when receiving, they help with reflection noise since the polarization plane changes with reflection. If anyone can find any definitive information on how the Morgenstern determined direction, I will drink a toast to you on my next birthday. Here's some info on crossed Yagi's for circular polarization.

yosimitesam · Feb 25, 2021

yosimitesam said:
Thanks for the replies. It's still something of a mystery how left/right - up/down was detected using this antenna. It might have something to do with exploiting polarization but I cannot determine what. It seems that crossed Yagi's (assuming that is what Morgenstern is) are mostly used for circular polarization and, when receiving, they help with reflection noise since the polarization plane changes with reflection. If anyone can find any definitive information on how the Morgenstern determined direction, I will drink a toast to you on my next birthday. Here's some info on crossed Yagi's for circular polarization.

I've become convinced that the Morgenstern was mainly just the transmitter, sending out circular polarized pulses, and that SOMEWHERE on the aircraft receiving antennas (small) were placed (top/bottom of wings?) to give direction indication, similar to the AI Mk IV. Anyone ever seen these on the body or wing in a photo of an aircraft with a Morgenstern antenna? Do they exist on plastic model builds having Morgenstern antenna? Enquiring minds want to know. Thanks.

yosimitesam · Feb 25, 2021

I've become convinced that the Morgenstern was mainly just the transmitter, sending out circular polarized pulses, and that SOMEWHERE on the aircraft receiving antennas (small) were placed (top/bottom of wings?) to give direction indication, similar to the AI Mk IV. Anyone ever seen these on the body or wing in a photo of an aircraft with a Morgenstern antenna? Do they exist on plastic model builds having Morgenstern antenna? Enquiring minds want to know. Thanks.

11bwmech · Feb 26, 2021

yosimitesam said:
I've become convinced that the Morgenstern was mainly just the transmitter, sending out circular polarized pulses, and that SOMEWHERE on the aircraft receiving antennas (small) were placed (top/bottom of wings?) to give direction indication, similar to the AI Mk IV. Anyone ever seen these on the body or wing in a photo of an aircraft with a Morgenstern antenna? Do they exist on plastic model builds having Morgenstern antenna? Enquiring minds want to know. Thanks.

I don't know anything about this particular antenna, but loops work well for determining direction, especially when compared with the signal from a non-directional antenna, like a whip. I once maintained a system that used a single loop and a whip for determining source direction of a received signal. I have since forgotten how the 180 degree ambiguity of the loop was eliminated. 87 years will do that to you.

mikemike · Feb 28, 2021

yosimitesam said:
I've become convinced that the Morgenstern was mainly just the transmitter, sending out circular polarized pulses, and that SOMEWHERE on the aircraft receiving antennas (small) were placed (top/bottom of wings?) to give direction indication, similar to the AI Mk IV. Anyone ever seen these on the body or wing in a photo of an aircraft with a Morgenstern antenna? Do they exist on plastic model builds having Morgenstern antenna? Enquiring minds want to know. Thanks.

I do not have any detailed information, but I would guess that this was a receive/transmit antenna and that they used phase comparison between the four sets of dipoles for location. That was essentially how the "Hirschgeweih" antennas worked.

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