We used 100mm x 50mm rectangular hollow box section aluminium with 3mm thick walls. This gives us an internal size of 94mm x 44mm. We chose to build the antenna for 2.442GHz, or channel 7, as this is close to the center of the 13 channels available to us (US designs use channel 6 (2.437Ghz), as they have 11 channels). The internal width (the wide side), determines the operating frequency. The internal height (the narrow side) determines the impedance. We used Rob Clark's 5 wavelength design over Trevor Marshall's 4.75 wavelength design simply because we could cut the 5 wavelength design down to get the 4.75 wavelength one if our first try didn't work. Trevor's design also has wider slots and our slots could be made wider if we messed them up too much. We used Paul Wade's spreadsheet (Slotantenna.xls)to calculate the slot sizes and placement (The "Improved from Elliot" figures with a 2% reduction in slot length for square ends (see his text)). I have included a key lengths calculator in the form below.
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