Can someone design me an S-Band microstrip filter


Andy G4JNT
 

I don't have much in they way of microstrip design software, and the learning curve is too long to start playing  - especially at this time of year, so:

Is there anyone so au-fait with a microwave / microstrip design package that this spec for a comb line bandpass filter is plug-N-play?   I'm after a 1:1 PCB artwork in some common graphics format like PDF that can just be dropped onto acetate to etch.    Don't mind playing with scalpels and bits of copper foil to do the fine tuning on the fingers, but need to be pretty much there straightaway with finger spacing

Passband to cover 2290 - 2460MHz or even a bit wider, ripple  <0.5dB
Fourth or  higher - not concerned how high it has to go.
Rejection at 2306 >40dB (highest LO)    and > 70dB at 2162MHz (highest image)
Loss isn't terribly important as it'll be for interstage use.

PCB material 0.8mm  Er 2.50   copper thickness 35um
Think it's RT-Duroid, I do have a fair bit of that PCB material in the junk box and it's about time it was used for something useful. 
Measured the Er and it does come out close to 2.50
 
I reckon  you can guess the application.   It's the only uWave band I don't have a 144MHz drive transverter for, so might as well make it cover the full allocation in one go.

TIA 


 

Methinks you are specifying 40 dB rejection at a frequency that is within the specified passband. Does not compute.
I do not have the abilities you search, but at least I read the message!


Andy G4JNT
 

You're quite right, I wasn't thinking straight when I wrote that email.  
In fact thinking was very wobbly.
Trying to get 150MHz passband bandwidth is not compatible with a 144MHz IF anyway.   The spec needs more thought
A fifth order 2290 to 2460MHz with 0.5dB ripple would be a better spec, and just leave out rejection figures.   Suitable IF chosen as required

Actually, for this band with it's wide spread of user frequencies, a solution  by G3WDG quite a while ago would be a better bet.  To use a varactor tuned filter.    He breadboarded a simple two stripline filter with a few tens of MHz bandwidth that met the rejection specs for a 144MHz IF  
If the filter tuning is done via a D/A from the same controller that sets the synth for the LO, selecting the band portion could be completely transparent

Can anyone recall where the G3WDG idea was published?



On Thu, 10 Jun 2021 at 09:24, Ken G3YKI <kenneth@...> wrote:
Methinks you are specifying 40 dB rejection at a frequency that is within the specified passband. Does not compute.
I do not have the abilities you search, but at least I read the message!


Dave G6HEF
 

I’d really like to know more about this myself. It would be great to have an idiots guide to designing all sorts of PCB based stripline gubbins.

Perhaps someone could do a lecture
at the next RSGB convention, or an online video thingy if we still can’t do a real one this year?

Meanwhile I did find a series of videos
supported by Altium. I’ve not
watched them all but found what I did watch very good.

https://m.youtube.com/watch?v=bVdwu1IoX4k


Andy G4JNT
 

Since I realised my mistake yesterday (a 150MHz wide RF range in a single filter with  144MHz IF just isn't feasible), I'm looking at another solution.
It's easy for Rx only - just use a quadrature downconverter IC and get 30 - 40dB sideband rejection immediately.   Don't even need 144MHz then, a lower If will suffice and I do have a perfectly good Rx converter covering 800 - 2500MHz  using an AD8347 with 50MHz IF

But not for transmit

But more generally for filters and microstrip generally, several people have recommended Sonnet-Lite.   SO maybe worth a download and learning session
 



On Fri, 11 Jun 2021 at 07:52, Dave G6HEF <hardknottdave@...> wrote:

I’d really like to know more about this myself. It would be great to have an idiots guide to designing all sorts of PCB based stripline gubbins.

Perhaps someone could do a lecture
at the next RSGB convention, or an online video thingy if we still can’t do a real one this year?

Meanwhile I did find a series of videos
supported by Altium. I’ve not
watched them all but found what I did watch very good.

https://m.youtube.com/watch?v=bVdwu1IoX4k


g4cch_1
 

Did anyone find the link for the article with G3WDG's varactor tuned filter?

Howard, G4CCH 


Andy G4JNT
 

EME conf 2012 

On Fri, 11 Jun 2021 at 11:35, g4cch_1 <g4cch_1@...> wrote:
Did anyone find the link for the article with G3WDG's varactor tuned filter?

Howard, G4CCH 

--
Andy (out keeping fit)


g4cch_1
 

Thanks Andy, will have to find the cd...

Howard, G4CCH 


Andy G4JNT
 

Now I'm back home on the taplop...

Charlie's design is a two section filter with about 90MHz bandwidth designed for RX, and as such only needs 36dB or so rejection of the image.  He tunes over a 150MHz range with 0 - 8V on the varicaps
For transverting appreciably higher rejection is needed, so I will look at a three section filter using similar resonators .   I think his design is on glassfibre board, although the article doesn't say.   I'll be using Duroid.



On Fri, 11 Jun 2021 at 12:39, g4cch_1 <g4cch_1@...> wrote:
Thanks Andy, will have to find the cd...

Howard, G4CCH 


Greg - ZL3IX
 

Hi Andy,

I downloaded Sonnet-Lite about 6 months back. I took the trouble to go through the tutorial and it was well worth the effort. I've found that package works well.

Greg, ZL3IX (G3ZZI)