I need to match the impedances of waveguide form microwave oven to the
resonant cavity which will be hollow cylinder. Do you know how to
calculate the dimensions of both to have best impedance matching?

Kind regards
Jakub

On Apr 9, 5:22?am, wrote:
I need to match the impedances of waveguide form microwave oven to the
resonant cavity which will be hollow cylinder. Do you know how to
calculate the dimensions of both to have best impedance matching?

Kind regards
Jakub

Yes, but the answer is VERY long and depends on the MODE of
excitation of the cavity resonator. Depending on the dimensions
of the cavity and the excitation point - and kind of coupling - there
could be 6 to 8 different EM field configurations. You will have to
consult a microwave components basic text to learn about the
various modes in a cavity...and the ways to couple RF energy
into the cavity to achieve each mode.

I am not being evasive here. The answer is NOT a simple one.
The 1 to 2 GHz frequency range is a sort of "transition" from
lumped constants (conventional resistors, capacitors, inductors)
to "distributed constants," where the Fields and Waves and their
excitation-pickoff dominate...on up to the top of microwaves.

It's been about 30 years since I was really active in microwaves
from 1 to 25 GHz and I'm a bit rusty on that...but the ways it
is handled remains the same and found in many textbooks,
old to new. My particular "bible" on microwave structures is
"Microwave Filters, Impedance-Matching Networks, And
Coupling Structures," by George Matthaei, Leo Young, and
E.M.T.Jones, McGraw-Hill 1964.

73, Len AF6AY

I did that long ago . I found you need

far more than just the ratio .

I discoverd i needed to have a more

intuitive feel for the whole circuit , than

merely the Ratio .

Now i have that intuitive feel for electronics

and microwave and antennas .

I can see obvious errors that will ruin the

hook-up .

The secret is to NOT use a critical piece

of gear , you desperatly want to work .

If you have a piece of gear you want/need

to work , you'll learn the hard way .

I have found , easy learning is to

start with someone elses success , then try

to gleen what you can . But if it gets tricky ,

put it aside and find an easier explanation .

I.E. MFJ 209 .

I spent time trying to master its use .

Then i stumbled on a Ham Radio article

about Dipper , using the 209 .

This simple ( resistor , CAP , air coil ) circuit

made me toss some of what i learned from MFJ's

tutorial !

It was a new approach . MFJ did not include

it , cause it would enhance 209 til it would obsolete

other MFJ boxes ! It was a political thing .

So , now i learn faster , by stopping my learning

when i see it may get too detailed to make a value

judgement .


Back to microwave . You should not learn

it on something you NEED .

You should not learn from texts nor

"new, improved , enhanced Special for Hams
this box does EVERYTHING ....

I struggled when i tried to learn from building
my own antennas , but learned very fast when
i listened to the crowd , tout J-poles , then
tried to find the fundamental error of the
J-POLE .
Be opportiunistic in your learning !
If you see the crowd touting something , then
it probably does not "work" , except as snake
oil to enhance their reputation as antenna experts.

Few talk microwave , but you can still learn
what does NOT work in MicroWave .

You posted about matching .

Losses skyrocket as you go above 200 MHZ .
No more long leads and everyting is an accidental
capacitance , that drops Q .
But once you learn how to avoid these
losses , then you can go to about 2 ghz .
rect' wave guides are lossy , we use round
for long runs , but its more complicated , for
really long runs , RF is far lower loss !
2 small dishes are far less cost than
200 feet of hardline !

I can cobble up a WiFi link with 12 " dishes
and amplify the rcv end to a kilowatt , cheaper
than you can transmit that kilowatt on hardline .

Must we use WG ?!

So you need to give us more details of
you "match" , so we can help the easiest
way , the lowest cost way .

I see big changes , things we thing we need
becoming extincnt .

Did you know , 30 years , no one will want
nor need to drive a car , and gas will be back
down to $1 / gallon !

By solving problems ( our govt sees as a windfall
to themsleves , job security ) ,

we will free ourselves from their technical "slavery" .
They will no longer be able to "license" us in any way .
We wont have any need for Nuke power plants.


KC7CC ..

Some of your stuff is very clear and
easy to follow . .


But i think it starts lower than 1 or 2 GHZ .


And the current text books are worthless .

I have HP by .....

somebody ADAMS ..

Still too much obtuse in this book , but it
does have a few simplifications .

What humans need to know , is the

gotchas . When to toss a method ,

and experiment .

There are some really exciting secrets ...

When i hear someone wants to TX some

real big power ( Magnetron) , i see a lower

cost way .




TX only a small power ( modulation ) , then

demodulate at destination ..


plug in a huge 115vac P.S. and recreate the power ,

at the target , lower frequency .

I know how to lightning protect my
440 Yeasu 8800 , so i put it on the pole .


an HT in a Golfers hands will not be damaged
by lightning if it has a

low Z circuit to all components in the HT .

The HT must have both
1) a way to generate an E fld , and
2) be a low Z conductor ...
to be damaged .


Copper box your TX and then allow the hookup
wires to create the E fld , and it blows up .
But short the input and output wires and its
impossible to generate the E fld ,
the Lighning will use to "find" a path .

Lighning rods create an attraction to lighning
If you could generate and sustain a sig'
opp polarity , youd force lightning away .

Say you pound a copper rod in the gnd , 200 '
away . You still have the very high amps , into
the rod to create a E fld !

So , the theory of first attracting
then diverting 2 million amps in your conductor .
becomes costly .

You cant make antenna non-conductive ,
so live with it . But you can short all wires
leading into the TX box . And add other low
Resistance paths , and more importantly
Hi capacitance paths around your TX box ....