waveguide speed of light
[align=justify:70974a0d4e]Is velocity in waveguide greater than the velocity in free space if yes than which material is used in the assembly of waveguide having a dielectric constant less than 1(free space dielectric constant is 1). In one of the antenna books, I study that the velocity in waveguide is always less than free space velocity. Where as in one of the antenna research papers the velocity in waveguide is shown greater than the free space velocity. Please help me out this confusion. Thanks[/align:70974a0d4e]
Regards.
the phase velocity(V_ph=omega/beta) in waveguide ist bigger and the groupe Velocity (V_gr=d omega/d beta) ist samller than free space.
Hi, I've never understood this about the group velocity and phase velocity.
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It must mean that if I just send one frequency, not a group of many, I can propagate my sinusoid faster than the speed of light ?
Why are people saying that nothing travels faster than the speed of light ?
/StoppTidigare
Phase velocity is a mathematical abstraction. It is like ocean waves going to a beach at an angle. What looks like the peaks of the waves moves across the water-land surface at a much higher velocity than the water molecules move towards the beach.
The wavelengh at the phase velocity is what you measure when you do slotted line measurements.
Dear Fellows,
[align=justify:4cd908d3d8]Thanks for the replies, but still i am confused regarding the velocity in waveguide. Is it greater or less than the speed of light. Can you guide me some websites where i can study this phenomenon. and one more thing, to achieve a beamwidth of 20 to 30 degrees using a horn antenna is it feasible or necessary to use a reflector(parabolic dish) having a minimum of 15dB gain. Reply as early as possible.[/align:4cd908d3d8]
Thanks.
The answer to your first question is that the product of phase and group velocity is the speed of light. So phase is more and group is less. As you approach the low frequency cutoff they go to infinity and zero respectively. This gave me an idea for a science fiction story of a microwave transmission from the past being caught in a waveguide and coming out years later.
As far as gain goes, it is the frontal area in square wavelengths that set the gain of the horn. There is a second factor of the phase front being spherical and you correct for this with a longer taper and if you are really precise an artificial dielectric lens at the end.
You can go to extremes on this. In 1948 the US Army Signal Corps bounced a microwave signal off the moon with a horn antenna tens of meters across in both dimensions at the mouth.
in one of the antenna research papers the phase velocity of TE11 in coaxial cable waveguide is shown slower than TEM. Please help me out this confusion
Could you upload the paper ?
Can you provide any more details? There are all kinds of funky effects that occur in metamaterials and photonic crystals, for instance, with both phase and group velocity. Provide some more information and someone may be able to help more.