RF and Microwaves - Do we use transmission line for the microwave transmissions..

[sindhuvel92]

hi guys..
I have a doubt..
Do we use transmission line for the microwave transmissions or only the wave guides.
If you say 'NO', Pl make me understand with the reasons...

 

[Positron89]

Hi,

Transmission lines are an important part in microwave frequency transmission. In terms of waveguides, it is itself a form of transmission line and functions at extremely high frequencies.

 

[jiripolivka]

For microwave transmission we have many types of transmission lines.
One is coaxial using TEM mode, you can use a symmetrical parallel wires, two or four, with the same mode.
Then there is a variety of "pipes", rectangular, circular, elliptical... each with specific mode of propagation. Pipes differ from the coaxial or strip lines in that they have a "critical" wavelength and waves longer than this cannot propagate through.

 

[Ow@i$]

Wave Guide is a Transmission line !!!!

 

[WimRFP]

Both (TEM) transmission lines and Wave Guides are used.

Over short runs and low power, cables, microstrips, striplines, etc are used. In case of long runs, and/or high power, Wave Guides are used because of lower loss and large power handling capability.

 

[SpaceDust]

Check this Link, U'L find it useful with ur doubt..

https://www.tpub.com/neets/book11/44a.htm

 

[DesignRF]

By this time you must have got the answer. Still curious to understand the cause of the confusion in the first place. Did you by any chance mean to ask coaxial or microstrip line instead of a transmission line? What was your understanding of transmission line?
Since you are asking to make you understand I thought I would ask a bit.

 

[Alan0354]

Transmission line is waveguide. A stripline, coax etc. are all waveguide where the EM wave travels in the dielectric. There is a big big miss conception that electrical signal travel as voltage and current. It is the EM wave that travel, voltage and current are just the consequence of the boundary condition of the EM wave. IF it is electron that is moving, you are going to wait a long time for signal to propagate.

 

[WimRFP]

Transmission line is waveguide. A stripline, coax etc. are all waveguide where the EM wave travels in the dielectric. There is a big big miss conception that electrical signal travel as voltage and current. It is the EM wave that travel, voltage and current are just the consequence of the boundary condition of the EM wave. IF it is electron that is moving, you are going to wait a long time for signal to propagate.

@Alan0354: You are fully correct! The energy is in the fields, not in the copper.

When discussing TEM transmission lines I let the students calculate the E- and H-field under a very wide well terminated parallel plate (strips) transmission line. As you sure know, such arrangement has near uniform E- and H-field between the strips. When they have the E- and H-field, I let them integrate the poynting vector (EcrossH) to show that the power (or energy) is in the fields. They can see that the two strips are only there to guide the fields towards the intended direction instead of propagating into free space.

 

[jiripolivka]

Another explanation of guided waves is that charges are moving in air and in conductors or dielectrics, alternately where the electric component alternates with the magnetic one. In conductors current does flow but it is concentrated in small areas, alternating with no current where voltage peaks. One can calculate currents and voltages in selected points but technically it is almost impossible to measure them. Current and voltage meters have their components large and by connecting them to microwave structures, fields are disturbed, so one cannot know what such devices indicate.
Many years ago people recognized the problem and developed the power technique which replaces voltages and currents and allow to precisely measure not only power but any impedance.

 

[sindhuvel92]

thanks i got a clear idea now..