LOOKING FOR DIELECTRIC RESONATOR FROM 400 TO 900 MHz, PLEASE!!

[Marquesa]

Hi all,

I am a engineer working in an university. For one of our new projects with a company, we need to find a dielectric resonator in the band of 470 to 860 MHz, with a high Q (as high as possible), and a high temperature stability.

I think this is a bit unusual request, because dielectric resonators usually operate at much higher frequencies. The meterials companies I have contacted so far, don't fabricate any like this. The dielectric resonators they sell resonates as low as 800 MHz, but not lower than that.

Can someone help me? Do someone know if there exist these kind of resonator in the industry? Can someone tell me a company name which fabricates something like this? Can someone tell me if this kind of product is possible from a technicall point of view?

I'm just a bit hopeless!!! I have an interview with the client just in two days!!

Thank you very much!

 

[Comcokid]

I am not a expert on dielectic resonators but there are types that I have seen used at lower frequencies - they appear in the front end of some UHF radios I have opened-up.

Look at the MuRata K series. They have resonators down to 440 MHz.

http://www.murata.com/catalog/o95e9.pdf

At lower frequencies where a resonant structure is used you usually find saw filters, coaxial resonators, or helical resonators.

However, you have not indicated exactly what you are attempting. Is it an oscillator or filter? What do you mean by high temperature stability? - High stability over temperatuer or high temperature operation?

 

[Higgler]

Are you looking for an RF item or for MRI/NMR usage. Since you mention high temp stability, there is a similar thread thread239-143492 where Probewizzard is trying to locate possibly the same thing.

He's planning on a long term development and it seems you won't find what your looking for in a few days, or even a few months.


Here is a note on his application: Do you have the same application?

probewizzard (Electrical) 10 Jan 06 14:32
Higgler: The resonator is used not for imaging in bodies, instead for high field solids NMR. Penetration depth, at least due to parasitic e-field components, is the problem: Compared with a classical solenoid coil a DR in TE01d-mode has a reduced electrical field inside the sample volume and therefore even very salty (lossy) samples can be used (given of course, that an apropriate material is available).

 

[Marquesa]

Thank you very much both, Comcokid and Higgler.

First: I saw Murata catalog, and at those frequencies they seem to have ceramic (piezoelectric) resonators, not dielectric resonators. I talked with them directly, they think that perhaps they have something similar to that I'm looking for, but at the moment I'm not sure. I will see it tomorrow.

Second: I want to make a cavity filter, and it has to support high power. SAW filter is not appropriate. I know that resonant dielectric filter is nos appropriate for high power, but we can arrange it, I think it. Coaxial and others filters are OK, but the client wants resonant dielectric filter!!! It has to have stability in resonant frequency with respect to the temperature.

I saw the Probewizzard's post, but we are not looking for the same thing exactly. First, we need resonators at lower frequencies. There are companies which distribute dielectric resonator @ 600 MHz, the problem is to find them at 400 MHz... Probewizzard is looking for something at 700 MHz, I think that the frequency will not be an issue for him, but yes for me. Second, he needs something with a dielectric permitibity of 400.. I don't need such a big Er. Third, and most important, I need a very high quality factor, more than 2500, and he doesn't need such a big quality factor, Qu. We are not looking the same.

This project is for a long term too, but I have got a first interview with the client tomorrow and I would like to have something to say him... I wouldn't like to say "I don't know if the project is feasible at the moment".

 

[pstuckey]

A number of companies make cavity filters in your frequency range. For instance see

http://www.larkengineering.com

bandpass series 3C.

Would this work for you, or do you need something different?

Peter

 

[Marquesa]

Thank you, pstuckey.

Now I have at least one option: I can say to my client tomorrow: it's okey, don't worry, your problems are gone, go to Larken and buy your filter to them, they have exactly what you are looking for, goodbye, it was a pleasure making business with you, I don't need your money at all...

No, that's not the point. I know that there are combline and coaxial filters in these bands which work properly a lot time ago. The problem is my client wants a filter with dielectric resonators in these bands, and I haven't found the proper material at the moment. I wonder why he wants this, but my chief says that the client needs to do something "new"... Don't ask, I have to do it with dielectric resonators.

Thank you anyway!

 

[Higgler]

Sounds odd that a client would specify the makeup of a filter.
99.99% of the time, you'd get your RF spec. plus an environmental/mechanical spec. Maybe the dielectric resonators are needed to shrink the size. Or at altitude they won't arc with high power.

Did the customer say why they require dielectric resonators? Maybe it's a test to see if you're smart or to prove that they have heard of the words dielectric and resonator.

kch

 

[Marquesa]

jajajaja!!

Yes, you're right, one of the issues is to reduce the volume of the base stations of the digital terrestrial television. Another issue is that he has received an ammount of money for the goverment to do some investiment, to do something new in colaboration with an university (us). He wants to define, more or less, the makeup of the filter because he doesn't need only to meet an electrical requirements, but also making something new. I think doing something with dielectric resonators in these bands, and with high power, could be sufficiently new, and could help to reduce the volume of the transducers. An another issue is that I think he has not very clear the ideas in his mind so far... (sorry for my english). I will try to help him to clear the ideas, but at the moment I would like to clear my ideas first, and one of the points is to clear out if we can find dielectric resonators in these bands. That is one of the first points in the project.

I like the idea of doing something more or less new in these frequency bands, in which I have never worked before. And there are people working with dielectric resonator and high powers in the 800 MHz band... but not as low as 400 MHz. And that, again, is my problem. (I don't think that the client, who seems a very good person, wants to prove me or to prove his inteligence. I think nor he nor we want to loose the time)

Anyway, I think you seem to have a large experience with people, because of that "to prove that they have heard of the words dielectric and resonator". jajajaj!!

 

[nbucska]

There was an interesting resonator I played with in the
late sixties. High Q, relative small, easy to make.

How can I send you a sketch ?


Plesae read FAQ240-1032
<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS

 

[probewizzard]

Hi,

since I have been cited (thanks for the honour;-) I want to contribute to the discussion...

1.) If your project is still hot, check a small french company TEMEX. The people there are quite kind and they will listen to your questions and may give you some hints (as opposed to murata... but this you probably have found out already...)

2.) For a dielectric resonator resonating at 400MHz you will need a high eps_r-material (at least 80...150) to keep the dimensions in reasonable dimensions. The good news is that there is a material around which is temperature stable and has a eps_r=80. I cant tell you the name, but I have it off the shelf from another company called NTK spark plugs. The resonator is rather big for a fundamental TE01d-mode at 850MHz, but it provides a loaded Q of >3500. And if you would make it bigger...
I operated this resonator with long pulses up to 1kW and the temperatur drift was almost not observable (I cant find my notes, but it was in the <50ppm league...)

3.) during my quest for high eps_r materials I talked to quite a few ceramics people and the common opinion was that a good eps_r value for both, high eps_r and high temp stability would be around 150.

hope I could help you ...

cheers

probewizzard