Helical Waveguides With Higher Symmetries

Sammanfattning: Helical waveguides are widely used today as slow wave structures and as normal or axial mode antennas. By introducing higher symmetries in the structure the dispersive properties of the waveguide can be manipulated and the helices can be made to radiate energy as leaky wave antennas. In this project the properties of a smooth helix and a helix with periodically added protrusions are studied. The waveguides are simulated and then constructed so that they can be used as study material for upcoming courses at KTH. The helices are constructed around neon filled glass tubes between two ground planes so that a resulting standing wave pattern can be observed as excitation in the neon. The results show that the helical structure shortens the wavelength of the propagating wave inside the waveguides to lengths small enough to be measured by visual observation. The addition of higher symmetries to the helix were shown to change the dispersion of the propagating waves and to lower the cut-off frequency at where the waveguide starts to behave as an leaky wave antenna.