Substrate...urgent help !

hello guys well this is my first topic .. and am new here.. well i am need some help here i hope some urgent help will be there for me .. i am doing a project on patch antenna .. and for that reason am following an IEEE paper.. fortunately i founded a HFSS tutorial on a microstrip antenna .. and that is the solved example of that paper ... the PDF is attached with it

the problem or confusion am facing is that ... in patch antenna ..the ground and substrate length and width is taken almost 6 times the length of the patch(more than 5 times) .. here in this case the length is 12.45 mm and the width is 16 mm of the patch ... but the substrate length is 28.1 mm and the width is 32 mm(in the pdf file) which is almost 20 times ...

how is this length and width calculated ..is there any specific formula? HOW and WHY it comes out to be 28.1 and 32 mm

i hope you people will help me !

any one ? :S

hi there

well i dont know how come the dimensions of substrate becomes 5 times of the patch dimensions. may be my maths is too weak,

this is how i calculate:

substrate length=28.1
pathc length=12.45

substrate_ length/patch_length≈2.2


can you explain why you are saying its 5 times?

regarding formula for substrate length n width well i dont know of any such formula

however rule of thumb is to choose substrate/ground length close to λ.

i hope this helps

regards

hi Mr.shahid .. well thanks for the reply ... well about the confusion of 5 times the patch length ...all i meant was that .. i read and got advice from some people that .. when modeling a patch antenna the substrate length should be greater than 5 times the length of the patch .in the mean while i founded out this report as well in which the dimensions of the patch are calculated and when the substrate/ground plane is calculated following is written


The transmission line model is applicable to infinite ground planes only. However, for
practical considerations, it is essential to have a finite ground plane. It has been shown by [9] that
similar results for finite and infinite ground plane can be obtained if the size of the ground plane
is greater than the patch dimensions by approximately six times the substrate thickness all around
the periphery. Hence, for this design, the ground plane dimensions would be given as:

Lg = 6(h) + patch's length
Wg = 6(h) + patch's width

2)secondly ..the frequency with these dimension length 12.45 and width 16 mm comes out to be 7.8ghz on the microstrip calculator ..but theoratically it is comming out 7.5 Ghz...

3) as you said that the length should be equal to lamdah.if i follow v=f lambdah

v is 3*10^8 m/s
and f= like 7500 MHz ... then the lamdah is
0.004? what next :S ! i cant really get it :S

hi alee_alee

well as i said there is no definite formula for the substrate length and width , people have come up with approx formulas after lot of experimental observation.

the formula which u mention is also correct . and if u use this formula even than you get substrate dimension close to λ. as substrate height is normally in the range
0.02λ-0.04λ. so 6 times this dimension and patch dimenion is apprx λ.

well from your calculation λ=c÷f=.04 meter

so its 40mm and in the HFSS tutorial they have used 32mm. its not exactly equal but u can at least start with these initial values and see the affect in simulations

and than choose the optimized dimension if that is necessary


regards

well Mr.Shahid ..thanks alot for the information ..can you also guide me through a Definite procedure to determine the STARTING points X,Y,Z of the patch on the substrate.. ? should i take them as half the total values of the length and width(dx,dy) or is there any other way to determine it as well?
because if i take a frequency of my choice i find it difficult to model the patch in the middle of the substrate and thats due to the starting point..i usually take them as half of the Dx dy ..
thanks and regards

hello
i have calculated patch dimensions,i got width is 16.01,lenght is 12.8. and resonant frequency is 5.7GHz ..but how cum u got the resonant frequency of 7.5GHz for this dimensions...can u explain me how did u calculated the values and 'm also doing project on the patch with this dimensions...may i know what is substrate thickness and dielectric constant....can u attach ur pdf of project....

Added after 18 minutes:

can u say me how the feed position is adjusted in that paper,the feed position is along 12.45mm then what is distance from one edge of the patch alon 12.45

well 5.7 is i thing wrong .. because i confirmed it through the patch antenna calculator as well it comes out to be 7.8ghz but theoratically it is comming out 7.5 Ghz .. i am not sure i mite be doing it wrong ..i just placed the value of the width in the formula and calculated the frequency from there..the dielectric height is .794 and constant value is 2.2 (duroid)...

can u plz tell me how feed position is adjusted ...i have done for a dielectric const of 4.4...

for the feed in HFSS i think its hit and trial method... you have to adjust the feed so that you get the return loss >than -9.5 db

r u doing project on rectangular patch antenna? ya i know its trial and error but im asking u that at wat position it has been adjusted can u plz say me...

yah i am doing it on rectangular patch antenna ..hey give me your hotmail id .. !

Added after 2 hours 26 minutes:

if any one knows how to position the cordinates then please let me know !

hi to all..need some help here..my patch dimension is W=33.91mm and L=46.82mm.Then i calculate ground plane using formula

Lg=6h+L
Wg=6h+W

and my ground plane dimension is L=116.26mm and W=103.35mm.Next step is how to determined the dimension of the substrate?Ive tried simulate the dimension of the substrate equal to ground plane.Is this wrong?..hope someone will help..

hi lovhana ..this is rite ..the dimensions of the ground plane and substrate are the same ..the formula you are using is al rite .. ! it is for both the ground plane and substrate .ill attach a pdf it will give you a better idea

thanx replyin..it will be helpful if u can email me the pdf to my email..aaritter@hotmail.com ..thanx

you can contact Dr. Atabak rashidian : http://homepage.usask.ca/~atr997/resume/default.html , he is an expert in dielectric materials, especially dielectric resonator antennas, and willing to help interesting people.

PLEASE tell me what is the signification of h bescause when i calculate it with the values of this exemple (W=33.91mm and L=46.82mm) h=11.57?
please it's very urgent.
because i don't understand this method

Lg=6h+L
Wg=6h+W
thanks you.
my mail is basma.oueslati(at)gmail.com