Inset characteristic of a microstrip patch antenna at 12.1 GHz on glass substrate

I have to design a microstrip inset fed patch antenna that resonates at 12.1GHz using a glass substrate of dielectric constant= 4.8 and effective dielectric constant=3.5, I found out my patch length= 6.5 mm and patch width= 8.26 mm, and inset length(inset distance from the edge toward the center of the patch)= 1.84 mm- does these sound right, as the measurements indicate that the antenna is going to be very small?? I am having problem with designing the inset, what should be the width of the 50 ohm transmission line feed and the inset gap length- is there any equation to find them?

Hello Humayra

i did a little bit of the calculations for the inset came out to be 1.976mm,width of the 50ohm transmission line also depends on the height of the substrate which i have assumed it to be 1.6mm(60mils) is 2.86mm which is quite comparitive to the size of the patch.

coming to the notch size,it also determines the resonant frequency of the patch the thicker the notch lesser the surface current distribution.

hope that helps

Best Regards
Sajid Mohammed.

Let's assume that the inset gap length used by the questioner means the width of the inset gap, which is the dimension along the same direction as the patch width. One antenna textbook says that the inset gap length commonly is 3 times of the feed-line width. However, if the feed-line width calculated by rotmanlens is used here, then the inset gap length will become 8.58 mm(=3*2.86), which is even larger than the patch width! Therefore, you may forget this rule of thumb (i.e. 3 times of the feed-line width) and take your actual problem into consideration. Anyway, the inset gap length influences the resonant frequency and input impedance by introducing parasitic capacitance.

PS: I have modified the statements for clarity.
To romanlens: I agree with u qualitatively on your comments on the feed-line width. I have no intention to evaluate your calculation results.

width of the line depends on the substrate and the height of the substrate for a given impedance and is independent of the frequency.what you said makes no sense.can you re iterate your words streamlet so we can get a good idea as to what you are saying

Regards
Sajid Mohammed.