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Questions about microstrip array antenna

promach

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1. Why is 100 ohm transmission line used in this microstrip array antenna ?

2. Why A quarter-wavelength transformer of 70 ohm is used to match the impedance line of 100 ohm to the impedance line of 50 ohm. ?

3. Would a butler matrix be better than these simple impedance transformers in terms of reducing MIMO diversity issue ?

4. Is this stacked array antenna difficult to realize ?

microstrip_array_antenna.png

microstrip_stacked_array_antenna.png
 

Georgy.Moshkin

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1. It is arbitrary chosen value, constrained by manufacturing process and lines placement. Probably via in the center is forming t-junction from 50 Ohm line on the other side of substrate.
2. They can't continue divide 100 Ohm line with t-junctions, because it will result in 200 Ohm lines, which may be too thin to manufacture. So before each new T-junction they lower impedance from 100 Ohm to 50 Ohm with Sqrt(50*100)≈70 Ohm. Point after 70 Ohm line is 50 Ohm virtual impedance point, which is immediately divided to two 100 Ohm lines
3. I do not know, but butler matrix is too big and requires more RF hardware
4. Not difficult, especially with help of computer simulation.
 

vfone

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