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coaxial feeding printed antenna

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asondas

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hello;
im going to design a printed antenna withcoaxial feeding resonants at 3 and 5.5 GHz at the same time.
i modelled this antenna with cst and hfss respectively. simulation results are fitting. so i fabricate this antenna and get the measurement results. but there are differences between simulation and measurement. i dont know what is wrong?
can you help me
 

FvM

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Looks like a considerable difference in substrate Er or another parameter that influences the effective wavelength.
Also the impedance matching is apparently affected.
 

asondas

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sorry;
i atteched wrong result.
this is the true one
 

prafuldeo

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Hello,

results are close but higher frequency resonance is off by considerable margin. Howz the manufacturing quality of antenna?
 

asondas

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the manufacturing seems ok, but i dont know why are the results so different.
as you see, i modelled coax in simulation and get good results. in practical can i get these results by coax or must i use a balun structure? can you say anything about this?
thanks for the help
 

e_m_c

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Do you have photos of the manufactored sample? Especially detailed view of the feeding connections. This might be helpful to analyse what is going on here.
 

asondas

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here are the photos af the manufactures antenna
 

asondas

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the blue structure is supporting the substrate
its epsilon is nearly 1. it doesnt change the resonance frequency
 

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