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log periodic dipolle or loop antenna

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long88

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Hi everyone, i am going to design a log periodic dipole or loop antenna.
Frequency range is from 800-1000 Mhz for UHF RFID applications. Currently, i am facing some problem. I am using CST to simulate the antenna
1) I am quite confuse on calculate the impedance of the loop or dipole array? Anyone can advise or share me with some useful documents?
2) There are two type feeding for log periodic array.either crisscross or parallel straight wire feed. How to calculate the characteristic impedance of the feeder line?
3) I wanna to design a planar log periodic dipole and loop on FR-4PCB. Can anyone tell me what is the effect of the substrate on the length of antennas?
I attach the 3d structure of my design at bottom.

THank you

 

The effect of substrate on length of antennas:
The dipole length will be reduced by a factor of square root of (effective dielectric constant).

Effective dielectric constant depends on the frequency of operation and the width of the dipole. You find the formula for calculating the effective dielectric constant in any microwave engineering book. D. Pozar's book and R. Collins book discuss this.

-sv
 
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    long88

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thank sv1437.
i will go check it first.
Do u know how to calculate the impedance of loop array or dipole array? and the feed line impedance for loop and dipole ?
For normal dipole array, what will be the impedance variation within a frequency range? I need to add a balun and impedance transformer to tune it to 50 ohm.
I can simulate the result but without proper impedance matching, the vswr performance is not well.
 

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