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    Phase monopulse vs Doppler shift unambiguous angular position

    First some links:
    http://en.wikipedia.org/wiki/Phase-Comparison_Monopulse
    http://www.microwaves101.com/encyclo...seantennas.cfm
    And in book i am reading says: "-90...90 deg unambiguous angular position for antenna spacing λ/2".

    For example:
    1 - we have two antennas with spacing λ/2, book says this gives unambiguous angular position. It looks right, because if signal comes from -90 deg, then it arrives at first antena with phase Phi, and second antenna with phase Phi+180 (λ/2). When signal comes from +90 deg, second antenna would be Phi, and first antenna Phi+180. So relative phases would be -180 deg to +180 deg (Phi-Phi-180=-180 deg to Phi+180-Phi = 180 deg)

    2 - Real objects can move in two directions. It is well known, that for moving objects IQ mixer can be used, then we can sense direction (+/-90 deg shift for different directions).
    And here what i am curious about:

    Let's go back to monopulse receiver with 2 antennas. Assume signal comes from some point, that gives phase Phi on first antenna and Phi+90deg on the second antenna. But then i realized, that it is the same, that having IQ mixer "in air". The problem is, if object approaching, then that would be +90deg, and when the object goes away, that would be -90deg. There are no longer unambiguous angular position, because it will depend on movement direction of the object.

    There is nothing written about this phenomenon in my book or articles i found. I guess there must be not only phase monopulse receiver, but also an IQ receiver to detect direction of object, then fix somehow this phase "mirroring"? Is it necessary to have IQ receiver to make angle measurement unambiguous using phase monopulse?

    Thanks!

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    Re: Phase monopulse vs Doppler shift unambiguous angular position

    There are other issues such as Rican fading off tall buildings from GPS giving false position, so antenna directivity can be important to reject Rican fading noise.

    THe only azimuth Doppler track designs I have done used two separated quad helix antenna for 500 mile rocket range and azimuth tracking
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975


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  3. #3
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    Re: Phase monopulse vs Doppler shift unambiguous angular position

    I want to understand how that "mirroring" problem is solved in two-antenna monopulse receiver. Because if simply put mixer on each antenna, unambiguous angle can be only given for one direction of object movement. For objects at same angle but with different direction phase shift will differ because of doppler effect and all that trigonometric multiplication stuff in mixer for higher/lower frequencies. So it seems that each antenna must have IQ mixer, or there must be an additional antenna with IQ mixer to sense direction, and two antennas to measure phase angle. I want to read some article / patent / book that explains at least one good method. Because i am unsure about my guess. For example, i googled some phase monopulse modules photos for Car driver assistance. They usually have three antennas, i guess one is TX, two others are phase monopulse receiving antennas. There no additional antennas for IQ mixer. I want to know what is inside of those sensors, IQ mixer on each antenna and some additional schematic to solve angle "jumping" problem?



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