Waveguide standard transition 1

[bolci]

I look for explanation where to find construction tips ( maybe some cross section photos) for waveguide probe

http://www.alibaba.com/product-detail/Antenna-Probe_226659389.html

or similar or where to find some physical bacground for this probe,
I found also that it is standardised part , Which standard ?.

Regards

 

[VEBill]

Isn't that a microwave oven antenna?

 

[bolci]

Antenna is a part of Magnetron , Another part of probe is susceptance adjustment part that impedance at antenna plane could be transformed to 50 ohm.
This is my Idea how this works, but I need some more explanations. I am not so familliar with TE and TM and waveguides and I have no skills how to construct and aliggn (calibrate) this probe. It shall be fine that someone explain more or show where to find explicit knowladge about this probe.

Best regards

Andrej

 

[VEBill]

The image of it shows it has four screws that appear to be the usual waveguide VSWR tuner adjustments.

Is that your question? How to adjust the screws for lowest reflection?

 

[bolci]

Question is how to adjust, What is termination at waveguide side ,is it open end with 377 Ohm free space impedance or something else .I know that at magnetron reference plane the impedance have to be complex (from Rieke diagram) if we want that the magnetron properly works . Also I am interested in, some design hints. Could someone provide some photos how look this probe inside?.

 

[VEBill]

As can be seen in the image (I've embedded it by IMG reference below), the port at the bottom appears to be an N-connector and therefore must presumably present a nominal 50-ohm impedance (assuming the antenna is within its design environment and the tuner screws are adjusted correctly). The top is the "probe" (or antenna). Presumably it would be expecting to be within a microwave oven chamber along side a suitable load (food). Presumably it would be happy to be exposed to free space mounted on a ground plane, but be very careful if you're radiating 600 watts into free space and there are people nearby.

I wonder if the intermediate section (gold color section) is a waveguide or perhaps a section of transmission line. If it were waveguide, then it would need to contain launch and output probes inside at each end; and that seems very unlikely given the size. I wonder if it might be a section of coaxial transmission line.

The screws appear to be a tuner, and that can still be true with a section of transmission line. Adjusting procedure is usually "Adjust for best match" and I don't recall ever seeing any step-by-step. More a simple trial and error using suitable test equipment. I don't think it's difficult. There will be some interaction, but it's not overly difficult to tweak them in sequence until a good match is achieved.

 

[bolci]

Well, It is now much more clear how this looks like. At this moment is not exactly known what is inside. I expect two loops inside for launch and output . I think that this satisfy TE11 dominant mode in circular waveguide. Now only question is how properly calibrate this. Still do not know what are impedances on termination plane and what at probe antenna reference plane. I found something in

http://jmpee.org/jmpee-vol-14-issue-3/

.... - Magnetron Rieke Diagram Plotting and Application.
Any ideas.

So thank you

Best Regards

Andrej

 

[VEBill]

I don't think that there's enough length in the gold section for it to contain two launch probes. Therefore, I'd guess it's a coaxial transmission line.

Plus, I don't think that the gold section is big (wide) enough to contain 2.4 GHz waves (microwave oven frequency) as a waveguide. It would have to be about four times wider than X-band WR90, and it's clearly not.

The only procedure I've ever seen was as simple as "Adjust for best match".

 

[bolci]

Hi

I still think that between N connector and antenna is a waveguide, It is multiscrew tuner .... I will make an citation (Engineers Handbook of industrial Microwave heatin - R. Merdith)... "Each screw provides a variable, capacitive susceptance whose amplitude is a function of its insertion into waveguide and the diameter of the screw.If four such screws are considered, spaced apart by lambda/8, then , for small reflections, the screws can be seen to give, at a reference plane located at the first screw an admitance adjustment of -+ jb for screws 1 and 3 and conductance adjustment -+dr for screws 2 and 4. Within the adjustment range it is therefore possible to generate reflection of any amplitude and phase simply by setting the screws for minimum net reflected power from load/tuner combination"
Ok ... I also found how to calculate this part, It is an old NIST document ..., But about lounch and output probes or maybe loops I haven t find nothing on net .

About adjustment to best mach is still a question, I do not know the impedance I have to match, It is in some connection with Rieke diagram which represent magnetron characteristics where a mismatch ( forom 50 ohm) conditions are evident.


Funny. Magnetrons, measurements etc. are an old technology from WW2, There is a lot of informations ( MIT courses), But when I want to find an answer for this specific microwave part for measurements ( I found iti is standardised part in an Japan standard ??) there is "blind spot" about this on Web pages.

Have a nice weekend ..

Best regards

Andrej