help needed patch antenna !

hi guys .. i hope every one is doing fine .. well am attaching a HFSS v9 file .. i am doing a project on probe feed patch antenna ... before this probe feed patch antenna i made a micro strip antenna and that worked perfectly fine ..its return loss graph was alrite

now ive started to work on this probe feed ..but the radiation pattern comes out to be like of a dipole to my surprise .. am fairly new in hfss .. kindly can any one help me out with the problem which i am not getting.

file description.

operatiing frequency 1800 Mhz.
length of patch 39mm
width of patch 50mm

width of ground plane 60 ( 6*h +width of patch)
length of ground plane 49.3 ( 6*h +length of patch)


the radiation boundary has been made so that the entire patch is inside it .. i made the first boundary that was only above the patch but errors came there ..

kindly let me know where am i going wrong ..thank you !

? any one ?

you have two mistakes in your design:

1. your coaxial feed does not have any outer conductor. Please draw the cylindrical conductor around the coaxial substrate.

2. the ground plane is not defined as finite conductor or so.

regards,
shameem

hi thanks for the reply .. i got dissapointed really that no one is there to help ..but thanks alot ..

i dont really understant how to make that outer conductivity ? in a tutorial it made the coax with a vaccum as material ? i am really confused ..can u kindly correct and then attach it :S ?

and about the ground plane? is it neccesory to give it finite conductivity ? do ill have to give it to patch as well ?

are we take it as an infinite ground plane here ? coz we already made its length and width 6 times the original dimensions ?

looking for urgent help
thanks

In this case just select the outer face of your coaxial and defined it as perfect-E boundary.

it is correct, however, you always need outer metal for a coaxial cable. as far as I remember, in the hfss tutorial, they didn't use any radiation boundary (since it was not a design of antenna). if you don't use any boundary, it is considered that the design is surrounded by pec. therefore, you don't need to define outer conductor since the coaxial vacuum is already surrounded by pec.

I'm using hfss 11.1. you can't open it in previous versions.

you defined your ground plane as sheet however, you didn't assign it to anything. it should be assigned as perfect-E or finite conductivity.

since patch is made of copper, it has finite conductivity already.

I don't understand your question. In the design, it doesn't seems like a infinite ground plane.

One more thing: your boundary is not well defined. it should be around λ/4 away (at designed frequency) from each substrate boundary except for the -z direction. in -z direction, it should be starting from where the waveport is defined. in this case it is starting from -2.

And please define the waveport using integration line starting from the outer surface of the inner conductor and ending at the outer surface of the coaxial substrate.

oh thanks alot ..ill inform after doing every thing i told you.can i have you email address so that i can contact u there?

hello mr shamim kabir ..ive tried to do what you said ..i placed the outer conductor of coax as perfect E and also the ground plane one as well..but the result is again not correct :( am attaching this new edited file ..kindly help me out ..am running out of time :(

Please do the following:

1. You made a mistake while defining the outer coaxial surface as perfect-E. First delete the boundary perfectE. select the outer surface of the coaxial (I guess you selected the whole coaxial). Go to edit -> select -> by name. select object name: coax and face 162. then define it as perfect E.

2. change material assignment of probe from copper to pec (not very important)

3. from excitation delete the waveport1 and defined it once again using integration line.

Then start the simulation. Everything will be fine.

leme do it .. rite now ill let u know .. ! thanks a lot ..please do visit again.. ill let you know .. thanks a ton

One more thing: your coaxial does not have 50 ohm impedance. Since your outer radius is 0.7 mm, the inner conductor should be 0.3 mm in radius (probe and pin)

yes ive corrected it :) ! ill let you know the result ive done just what u said .. lets see ..i hope it works now :S

Added after 49 minutes:

hi mr.shamim kabir :( sir ive tried every thing from what you said to changing the models but the return loss line still comes straight .. :( i dont understand whats the problem ..i made the microstrip antenna in an hour ..but this probe feed is not getting rite ..sir am again attaching this new file ..with what you said ... kindly sir help me out again .. thanks :(

Added after 38 seconds:

hi mr.shamim kabir :( sir ive tried every thing from what you said to changing the models but the return loss line still comes straight .. :( i dont understand whats the problem ..i made the microstrip antenna in an hour ..but this probe feed is not getting rite ..sir am again attaching this new file ..with what you said ... kindly sir help me out again .. thanks :(

I checked your second attachment.
I did not find any ground plane.
I think the block was named ground plane but material was not assigned to it. I may be wrong please check.
Do you know if you remove ground plane of a patch antenna it will behave like dipole!

Do you think this may be the problem?
:)

yah it mite be a problem ..coz when i click on the infinite ground plane an error comes as the selection must touch the background..other wise it is assigning simple perfect E or finite coductivity.. kindly check the latest attachment .. if any can help ill me great full ..thanks a ton

everything is fine. you simulated your design only for two points 0.9 GHz and 5 GHz; therefore, you got a straight line.

Just increase the "maximum number of passes" to 20 in analysis setup and in sweep setup, use linear step: start 1 GHz, stop 5 GHz and step size 50 MHz. Better to use sweep type "Fast" for faster simulation (may not be accurate).

regards,
shameem

hello mr shamim kabir ..your sweep values worked ... ! thanks alot ...the return loss graph came exactly how it should be ... but to my surprise ..the radiation pattern is comming of a dipole antenna .. :S ..how is this possible ..i am attaching the pics of the results .. kindly can you let me know ..where is the problem.. i think it is in the ground plane ..am unable to assign it as infinite ground plane ..the error comes as the selection must touch the back ground ... ! is it some thing really with the ground plane ?

2) i want to know about the ideal feed location on patch.. ! how can i confirm this that this is the ideal point .. do i have to shift the position of the coax and check for the minimum return loss ?

thanks for all the help..much appreciated
bless you !

May be little bit bigger ground plane would be better for this patch. Just increse the size of the ground plane, substrate, airbox around 10 mm each side (not in z-direction). However, this is not the problem for which you are getting wrong radiation pattern. This is due to the feed location!

In any patch antenna book you can find the calculation where to put your feed (same as inset feed). for reference: take a look at antenna theory by Balanis. In your case put your coaxial feed around x = 0, y = -10 (that means probe, pin, coaxial, ground cut) and simulate the structure. Now take a look at the pattern at 1.8 GHz. You'll definitely see what you want to see :D. However, please change the position of the feed to get better matching.

okay ill do so .. and let you know ! thanks alot ! do visit again ill ..confirm you about the results ! thanks a ton

hiii! mr.shamim kabir ..i hope you are doing good ... well ive tried almost all the positions but neither am i getting a radiation pattern... the return loss graph comes out to be good ..the max return loss i got was around -25db at 1.79 ghz .. ! i think its fair enough but i cant understand why there is no radiation pattern...the radiation pattern is like many colours of lines joined together on one..side ..typically shown when there is an error .. :S
thanks

I don't know why you didn't get the radiation pattern. I simulted your structure earlier and the patterns look like this.

OMG ! i am getting errors here :S ... ! ill make a new one and simulate it again :O this is so strange :S !

Added after 6 minutes:

i am getting this 3D image ..but not the radiation pattern 2d one..this is what i get ..on phi and Theeta cordinates ..