Not so simple (?) : Te10 mode in Horn waveguide antenna.

[littlindian]

field component of te10-mode

Hi,

The TE10 mode in a rectangular waveguide has longitudinal components of magnetic field
It means that the port excitation sets the E-field component which is perpendicular to the larger side of the guide.

What happens if the guide is excited following the smallest side of the guide ?

For example, a WR62 has the following dimension a=0.622 b=0.311
What happens if this guide is the probe is centred in the middle of the b-side of the guide ?


The lower cut-frequency will be higher in frequency but
> what about the field distribution on the guide ?
> and does this mode on the horn will be a propagating mode or not ?

Thanks for your help.
Littlindian

 

[hamidmoghaddas]

polarized antenna + te10

i suppose that the modeTE01 will propagate.

 

[littlindian]

microwave mode te10

I can add that I have tried to simulate it
but ... CST Microwave Studio does not allow to set the direction of the excitation field... It automatically sets the E-field following the larger dimension of the guide.

Littlindian...

 

[sergio mariotti]

te10 mode waveguide

In my opinion a rectangular waveguide exited by it's TE10 mode, can propagate RF energy.
But:
1) "b" size is related to characteristic impedence, as b is large as Zo is large.
2) for the common geometry b=0.5a , the TE10 is the only one mode permitted, if b>=a other modes are possible but only perturbations may exite them.

WG with oversized "b" side are sometime (rarely) used. Many years ago, I've seen a short piece on an particle accelerator

 

[littlindian]

te10 magnetic field distribution

You'r right, thank you for answering me

But the trick is to know if it is really a TE10 mode when the E-field is polarized
as plotted in the following picture (simulation HFSS).

It seems to be correct but what is the consequence of such a design of waveguide on the antenna efficiency for example ?

 

[kecbackbencher]

Plz use coax to waveguide adapter at horn input correspoinding to the horn size.
It work definately

Regards

 

[jiripolivka]

The waveguide horn antenna has two components:
- the rectangular waveguide section- this can include a transition to coaxial line; in this section, TE-10 mode propagates.
- the flared pyramidal section- this part transforms the waveguide impedance ~ 400 Ohms into free space, 377 Ohms. There are certain recommendations on flare angle and length, I believe those are empirical. I have not seen a theory describing in detail the field distribution in the flared section.

I was curious, so I measured the field distribution in a "standard-gain horn" including polarization. Those who are interested, please see "Polivka, J,: Noise Can Be Good, Too, Microwave Journal, March 2004"

It is quite difficult to run such measurement with a CW signal, so I used microwave noise. The results are interesting; maybe someone knows a paper in which the field distribution was derived from a theory.
I can recommend using microwave noise fields for such interesting experiments.

 

[biff44]

Almost nothing would come out of the waveguide, and you would have nearly total reflection at the coax input pin. By derfinition, a TE10 waveguide can not propagate a wave in the TE01 mode, so the coaxial field probe would see a purely reactive (ρ=1) load.

You can make a square cross-sectional waveguide, and propagate only one mode of your choice: TE01 or TE10, depending on which way you orient the probe. But such a waveguide might not maitain the single mode as you get furter away and you meet some perturbations, like bends, etc. In fact, some dual polarization transducers use this fact on antennas to receive horizontal polarization on one connector, and vertical polarization on the other connector. They use some magic to go from circular guide with both modes into a guide where there are two probes, spaced 90 degrees apart, to receive one or the other.