Microstrip antenna design problem..plzzzzzzz

im designing dual resonance microstrip patch antenna.im using HFSS.im using stacked method.im using foam as my substarte for upper layer(height is 60mm),for bottom layer im using air as substrate(height 15.2mm).my problem is the height for foam is large.when i reduce the high ,i cannot achieve dual resonance.my supervisor asking me to reduce the height.its there any thesis using foam for 60mm.if there any comment to improve design. .plz.tq


regards

alan

Hi Al,
I think you should try to change dielectric permittivities. I suggest to try to separate problems at first approximation. Design the lower patch separately for the desired frequency. Choose an higher dielectric constant material (with a relatively low dielectric loss tangent) respect the one you are using now, reducing the substrate height. Try to use standard values for thickness and permittivity (provided by vendors' datasheets). After that, cover the ustrip antenna with another substrate and try for different values of EpsR and thickness (always available values for each material) and reoptimize antenna dimensions to have the desired resonance. I guess you should try different configurations for several dielectric heights and EpsRs. Choose the best configurations (i.e. in term of bandwidth) and put the second antenna on the higher substrate. Reoptimize for both the first and the second resonances. A parametric sweep associated to an optimization would be very helpful to optimize the whole structure. I think it should be working. In the end you may have different working configurations, since there are many degrees of freedom in your design. The procedure is not immediate of course, but you may get good results after some steps. In the past I helped a friend in designing a broadband antenna having a similar structure. In that case, the two resonances had to be partially overlapping to obtain a wider bandwidth.

Hope this helps.

I.

thanks ivan .do u have any suggestion substrate material which can replace foam

I usually employ materials by Arlon or Rogers, but many other are substrate vendors (Neltec, etc.). One parameter you have to look at is the dielectric loss tangent. Look at this vendors' datasheets. They specify all characteristics such as permittivity and tan(delta) (loss)-->find out what's the best tradeoff between low losses and high permittivity. Use a relatively high permittivity to reduce substrate height, usually slightly less than lower substrate. Anyway, you should try with different characteristics of substrates, to have a view of what's the best, as I said in the last post. HFSS ,Designer and CST have a detailed material library whare u can find several vendors' materials.
Let me know.
Bye.

I.

Hi Alan,
Which is your working frequency?
You could use honeycomb.
Regards
Z

hi zorro..
im designing for frequency 1.8 to 2.2 ghz

regard
alan

Alan,

With wavelength in the order of 15 cm, a thickness of 60 mm (~0.4 lambda assuming low permittivity substrate) seems a lot. It should be possible to reduce it and obtain double resonance by adjusting the size of the parasitic patch.
A honeycomb as Hexcel (or Hexcell?) can be useful as substrate.
Regards

Z

tq zorro..
how to determine size for upper patch, it is smaller than lower patch or bigger lower patch.is there any method to find it?


regards
alan

any suggestion

Alan, I got ur pm. I think you'd better start with an Ansoft Designer analysis. I have a lot of work to do this days, but draw the designer model and I will try find some time to run some optimizations. After that, using the Designer circuit, it can be thought of improving model qualoty in HFSS. As first step in the Design process I suggest Designer 'cause we can get to a result faster than HFSS.
Bye

ok ..ivan ...tq very2 much for ur suggestion.i will try to find out..

regards
alan

Can i refer you to patent 5561435. Go to Google patents and download the claim. My understanding is multilayer Patch antennas are pretty old. You may also try suspended patch antenna in this design. It adds a bit of high dielectric layer between the first patch and the second one, changing the coupling characteristics.

Alan, I got ur message. Actually I have a lot of work to do this week. But I can try to find one hour to help u. Gain reduced? How much? What about resonances? Did u manage to get the desired resonances? What level of matching for each resonance? Typically, patches don't have high gain since they're not directive.

gain reduce 2db..manage to get dual resonance but beamwidth efficify is around 10%-13%.my crosss polarisation also high...

tq

regards
alan

Hey Al,
I can't say anything without seeing the file. Cross-pol? Sounds strange? Have you tried to plot currents on each patch? Post ur design. I will try to understand what's happening.

Bye

sorry for late reply ivan...i will post the result


regarsd

alan

Added after 16 minutes:

Well, I don't know what frequencies you want to be resonating exactly. Anyway, I see two resonaces (the second one is well-matched). Do they satisfy design requirements?
As for cross-pol, see one of my last posts in https://www.edaboard.com/viewtopic.php?p=989176#989176.

I.

hi ivan...
my frequcy range 1.8 to 2.2ghz(for UMTS)..im not able to satify the requirement...this is newest of design ...i upload the result....

tq very2 much

regards

alan

The 1st resonance is poorly matched, but the 2nd one is good. I see a -10dB bandwith quite satisfactory: 1.75 to 2.45GHz. Gain is stable around 9dB in the range of interest. What is exatly the point u think to be not so satisfactory?

gain variation must not exceed 0.5..and i need to reduce the height....