showing compact size and superior radiation characteristics.
Based on this slot size, the center frequency of the resonant
mode of the reference slot antenna on a FR-4 substrate, is
designed at 4400 MHz with the following structural and
material parameters: h = 0.8 mm, εr = 4.4, and loss tangent =
0.02. Consequently, by using a pair of embedded spiral-shaped
strips with the width = 1 mm, it makes the electric current path
can be extended for dual-band operation and circuit
miniaturization. The dimensions of spiral-shaped strip are s =
0.5 mm, x1 = 7.6 mm, x2 = 6 mm, y1 = 4 mm, y2 = 3 mm. After
this pair of embedded spiral-shaped strips inserted into the slot,
two resonant bands are excited. However, the design with a
pair of embedded spiral-shaped strips could not cover the
desired WLAN 5.2/5.8 GHz operating bands. To improve the
impedance matching of these two bands, the technique of Tshaped
tuning stub was used. T-shaped tuning stub with
dimensions of length ( " ) and width (w) is connected to 50-Ω
CPW feed-line (Wf = 4.2 mm, g = 0.3 mm). As shown in Fig. 2,
by combining the two techniques, the proposed antenna
exhibits dual-band operation, operating from 2354 to 2536
MHz and from 4552 to 6416 MHz, respectively. The effects of
w and " of T-shaped tuning stub will be investigated in section
III.
I