Physics help

[LT72884]

Any one have a physics math background or a background with microwave engineering. I need help with my homework. I have googled but im not finding what i am looking for.

I am trying to find the difference between TE11, TM01, TE01 and TM11 modes for cylindrical waveguides. I know for my waveguide(antenna)i made, had to use the math formulas for TE11 mode but i need to know why i HAD to use TE11 and NOT any of the other modes. There is a reason why i HAD to use TE11 and not any other mode but i cant seem to find it. This is where i need the help.

thanks guys.

 

[plumies]

Does it have anything to do with the cut-off frequencies of those modes? I'm just shooting in the dark here.

 

[LT72884]

Does it have anything to do with the cut-off frequencies of those modes? I'm just shooting in the dark here.

well, for me yes. because i have the formula for lower cut off but not upper.

for TE11 the formula is

Fc = 1.84(Ce) / 2(pi)b

Ce is velocity of light in a dielectric medium. 3*10^8 same as air.
b is the radius of my can in meters.

0.0389m

so i do this

Fc= 1.84*3(10^8) / 2*3.14159265*.0389

well that gives me

184000000 / .244415908 which = 752815156.3xxxxxx Hz

my professor ended up with 2253000000 Hz or 2.253Ghz

How the heck am i off so much

im not in a physics class, this is for my wireless communications class.

 

[seans_potato_business]

I'd suggest you try the Wikipedia Science Reference Desk.

 

[plumies]

for TE11 the formula is

Fc = 1.84(Ce) / 2(pi)b

Ce is velocity of light in a dielectric medium. 3*10^8 same as air.
b is the radius of my can in meters.

0.0389m

so i do this

Fc= 1.84*3(10^8) / 2*3.14159265*.0389

well that gives me

184000000 / .244415908 which = 752815156.3xxxxxx Hz

my professor ended up with 2253000000 Hz or 2.253Ghz

How the heck am i off so much

Okay, I see where you're off. In the first part of your equation, you forgot to multiply 1.84 by 3. You only applied 10^8.

When I ran the numbers, I ended up with 2258445469 Hz.

Fc = 552000000 / .244415908 = 2258445469

My number isn't the same as your prof's but it's a bit closer.

HTH

 

[LT72884]

OMG OMG OMG, i feel like a MORON. LOLOLOLHAHAHAHAHAHA. I dont know how i failed to do that. good thing im not going into math for my degree.

your number is fine. i have to round it to 2.25Ghz anyway. seriously i owe you one. the last math class i took was trig my junior year. after that i didnt continue on. I liek math but its been YEARS since i have done anything with it.

thanx.

I guess the difference between TM and TE modes are the different cut off frequencies they have. I bet TM mode wouldnt be able to capture 2.46Ghz at all.

 

[Jeekinz]

OMG Why did I venture in here?

 

[Chief Longwind Of The North]

Waveguides, mazers, RF antenna theory, and magnetrons. You bring back so many memories of Navy schools so many years back. I made it through the classes, but digital electronics is sooooo much easier. I'm glad I'm not the one in the physics and electronics classes any more. But keep on pushing through. You're doing just fine.

Seeeeeeeya; Goodweed of the North

 

[YT2095]

and I can warm up your dinner from across the room if you`re a slow eater with MW Cannon

effective range 160 feet Tested!

let it not be said that I`m a less than accomodating Host when it comes to meal times (or loud music played in the middle of the night across the road!).

 

[Chief Longwind Of The North]

and I can warm up your dinner from across the room if you`re a slow eater with MW Cannon

Are you using a parabolic antenna to focus that energy. I wouldn't want you going sterile from absorbing a bit too much RF.

Do you remember having to tune magnetron cavities with a set screw?

Seeeeeeya; Goodweed of the North

 

[LT72884]

and I can warm up your dinner from across the room if you`re a slow eater with MW Cannon

LOL, yeah i want to make one of those parabolic cookers. You can seriously slow cook with one of those.

http://solarcooking.org/images/scr/photor.jpg

 

[LT72884]

Waveguides, mazers, RF antenna theory, and magnetrons. You bring back so many memories of Navy schools so many years back. I made it through the classes, but digital electronics is sooooo much easier. I'm glad I'm not the one in the physics and electronics classes any more. But keep on pushing through. You're doing just fine.

Seeeeeeeya; Goodweed of the North

heck yeah. communications and technology ROCK. Just for a break i wouldnt mind taking a medical class. maybe i will do that this summer. So you deal with electronics then eh..