Experiment on Triangular Copper-Strip as Impedance Matching for 2

Performance of a helical antenna designed for 2.4-GHz WLAN is experimentally investigated in terms of impedance matching. A section of the helical wire near the antenna feed point is replaced by a simple triangular copper strip. By deploying such technique, impedance matching can be achieved. Overall return loss is below −14 dB across entire WLAN frequency range. Moreover, overall return loss does not strongly depend on strip length around its optimum, allowing 15 mm of strip-length variation around the optimum of 50 mm. Adding the triangular impedance-matching strip causes the characteristic of the helical antenna to be similar to a parallel resonant RLC circuit, resulting in frequency dependence of return loss for a given length of triangular impedance-matching strip.