Typical relative permittivity values

[sumit007]

For a microstrip patch antenna.. wat typical values of dielectric constant can we take for the substrate..

can someone suggest a few which are most common..
those which have low-k values
those which have normal range values
those that have high-k values

thanks

 

[masadi]

i think u should compromise to specification u want to achieve.

thing to consider, higher K means smaller physical size of antenna, then gain is lower and also antenna's lower in BW

regards

 

[nycheung]

FR406 is a sub-series from FR4 that has tighter tolerance at dielectric constant.

dielectric constant is around 4.1 to 4.3 @2.4GHz.

Our current 2.4GHz antenna is using it and is fine.

 

[sumit007]

Hi thanks for ur replies.

The antenna is to be used for experimental stuff.
The size of the antenna is a few millimeters with the substrate thickness less than 0.5mm. Besides, the antenna is to operate at about a frequency of 15Ghz.
So for this type of purpose, what dielectric constant values should i use?

If i keep the configuration of the antenna same and only change the dielectric constant to different values, what should i expect ?

 

[dch316]

hi all,
typically patch antennas have very bad efficiency (around 80% as maximum). The most important parameter for avoiding extra loss is the "loss tangent" (tand). For example I designed a CP patch antenna with RT Duroid6002 (rogers) because of its low tand = 0.0012., and epsilon =2.1. I couldn't made that antenna with Arlon1000 because although epsilon was around 10 and the dimensions then were much smaller, the loss tangent was 0.002 so the radiation efficiency droped drastically.
With high epsilon you will get lower dimensions and wider bandwith but probably the tand will increase. another parameter you should experiment on is the substrate thickness. Wider thicknesses have better (wider) bandwith but worse input impedance.
regards

 

[sumit007]

K= dielectric constant/epsilon
tand = loss tangent

Hi thanks.. i will play around with the substrate thickness also (by keeping K and tand constant)

Say the original design of the patch is
1. X (mm) in length and Y (mm) in width
2. K = some value = er
3. Operating Frequency = Fq
4. Substrate thickness = h

Now.. keeping this length and width constant..
Can i do like this ?
1. Keeping other parameters constant, Only change h and take simulations in Zeland's IE3D and see what happens ?

2. Keeping other parameters constant, only change K and hence tand ... and take simulations in IE3D and see what happens ?

Or .. if i change any of these parameters - either h or K .. i should change the patch length and width also in my simulations ? If so.. why ?

Added after 2 minutes:

Further..

If i want to keep my patch size constant.. what parameters can i play around?

 

[masadi]

what do u want to get by doing those two simulations? do u only want to prove the effect of K or h if they are changed?

the value of K is related to wavelength in substrate, so if u change K , u should chance the patch length, to keep it resonant at the desired frequency.

h has a less significant effect on wavelength than K.

 

[sumit007]

Hi.. Thanks for ur replies..
yeah basically i want to prove the effects of changing K/ h by keeping the dimensions of the antenna constant.. i'm not sure if this is a good idea or not.. but i wanna give a try and see what all happens..

like u said.. K has a greater effect on the resonating frequency..

I took out a few simulations and found this:
changing value of K (by keeping dimensions constant) => the resonating frequency shifts to another freq. point.. (which is exactly what one should be getting.. right)..

So what i'm trying to see is that if i design my antenna using a certain K value and then increase or decrease the K value.. where does the resonating frequency shift..and then try to find some kind of relationship between the two (or can this be logically shown/proven without taking out any simulations and just looking at the mathematical equations governing the patch antenna. i'm not sure , how i can find that... So thats why i'm trying to do all this) . And also.. i'm not sure why is this findings useful at all.. but still as a beginner i wanna try it...

Can someone give K values which are in range upto 4 with the loss tangent
Here are a few
K = 2.2 .. tand = 0.0009
K = 2.33 .. tand = 0.0012
K = 2.5 .. tand = 0.0025
K = 2.94 ... tand = 0.0012
K = 6.0 .. tand = 0.0019

Can someone give me more values of K and tand ?
mostly around ~ 2 and upto 3 or 4...