Schematic view of the three parts forming the microwave billiards. A rectangular frame of the same size as the top and bottom plates was added and all three parts were screwed together through holes in order to improve the electrical contact. The sector frame had grooves along the inner rim of its top and bottom surfaces into which wire of solder was placed to ensure this in the whole frequency range.^[48] Seven antenna ports were fixed to the top plate of which four, marked by numbers, were used in the experiments.