[SOLVED] microstrip impedance matching

[Belugo]

Hi, i'm designing some microstrip antennas and i have some questions...First, i'm using an inset-fed retangular patch ready for 50ohm and i need to match it to a 100ohm microstrip line.
Using the tool Microstrip Patch Antenna Calculator on emtalk.com i found that for the 100ohm line the width calculated is so low, 0.65mm. Is that correct?

materials: er = 4.4 (glass-epoxy) ; h = 1.53 mm ; f=1.8GHz

There's an way to increase these widths? they're all so short...
Thanks!

 

[sandesh564_123]

If you have ADS tool, it comes with dimension calculator..using that you can find accurate dimensions

 

[jayce3390]

Something like that, I found 0.57 mm but depends on you conductor thickness and Tan delta. To increase this, you have to change the susbtrate by selecting one with smaller Er. Also, another way consists in increasing the susbtrate thickness.

Example : Er = 2.2 makes the line width = 1.36 mm

 

[sandesh564_123]

Using the following parameters
Er=4.4 , h= 1.53 mm, f=1.8GHz , t= 1 um
line width = 0.66943359375 mm

Check in this site **broken link removed**

I am not sure about the dimensions you get using ADS tool

 

[Belugo]

Sandesh, i checked this, is ok! Thank you so much Jayce, i'll try this!
But i have a segond question too: in this project, i'm building a matching impedance circuit for 2 different inset-fed patches(1.2Ghz and 1.8GHz) using the same feed line structure, e.g., each patch is connected to a Zo line and after that, to a 100ohm line. To finish it, the two 100ohm parallel lines result in one 50ohm line. What frequency i'll must use to calculate the 50 ohm line parameters (1.2 or 1.8?)? Can you understand what i'm talking?...

 

[sandesh564_123]

I am not sure about which frequency to use..but in ADS u can get output simulated for the range of frequencies( say from 1.2G to 1.8G)..try out the dimensions obtained for both the frequencies..and also try for some inbetween frequencies also..just use the dimension for which u get better output...this is a kind of trial and error method...

Just let me know for which u got better output..

 

[Belugo]

Sandesh, unfortunately, none of my tries gave me good results...In HFSS always when i try to match circuits with microstrip lines, the s11 parameter goes wrong (-8dB, maximum -15dB). Only when i use inset fed patches directly to the waveport provides me something useful..
Thank you so much for your help...