Hypothesized Signal Leak

sallehzxc said:

Hi guys!

I am a student doing an experiment on a two-dipole(transverse and longitudinal) antenna. Currently the set-up(in a metal cylinder) has an exposed top and i was hypothesizing that it has to do with the longitudinal wave experiencing higher crosstalk than the transverse wave being due to fact that the signal is leaking out(or picking up some interference) from that opening.

Any idea where i should direct my enquiry to(in terms of papers) or if anybody has any advice i would love to hear it!

Thank you!!

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gophert said:

You may likely get internal reflections (losses) by adding a cap.

When a magnetic field passes through a conductor (or conductor passes through a magnetic field) a current flows in the conductor (Lens' law). Depending on how the antenna is tuned (dimentions and material), you can get internal reflections (signal losses). Adding a cap changes the length of the antenna and, therefore the tuning of the antennna. Also, the material you are adding may have different properties (electrical conductivity, permeability) that may convert the flowing. Current to heat (see "eddie currents") .

Also, depending on the frequency, different effects may be at work here. As you go higher, the signal may be flowing inside the tube (see "waveguide"). If you are looking at microwave antennas, an "absorber" is used at the end of the antenna to (1. Avoid reflections back into the antenna, and 2) to control where the signal is converted to heat instead of relying on random internal reflections which can lead to localized heating and unintended heating of some point on the antenna assembly.

In summary, any single experiment and associated correlation relationship you identify, may not be the simple cause and effect. Antennas are complicated.

If you try your cap experiment, you could try with steel, copper and an EMI absorber. Even the shape is important. Contact Thorndike for a "cone terminator" tuned for the diameter and frequency (if you are in microwave frequencies). **broken link removed**

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