The slotted cylinder antenna, Alford Slot, was first introduced by Andrew Alford in 1946. Its an omnidirectional horizontally polarized antenna. Performance of this antenna have been measured with some simple homemade equipment and a PC. All measurements done at 1296.8 MHz using a VCO (locked to a 13 MHz reference), a logarithmic detector from Analog devices AD8313 connected to an A/D converter. The A/D converter is connected to the PC parallel port, the antenna rotator is also controlled by the parallel port.
A conducting sheet (metal) with a slot is equivalent to empty space with a wire. Excite the slot with radio frequency electricity, and it acts like a dipole, except the polarization is opposite of that of a solid antenna.