INVESTIGATIONS ON AN H-FRACTAL WIDEBAND MICROSTRIP FILTER WITH MULTI-PASSBANDS AND A TUNED NOTCH BAND

This paper investigates an H-fractal wideband microstrip fllter with multi-passbands and a tuned notch band for wireless communication frequencies. The four difierent fllter conflgurations explored are: symmetric with zero ofiset, symmetric with nonzero ofiset, asymmetric with zero ofiset, and asymmetric with nonzero ofiset. The efiect of H-fractal iterations, fractal scaling parameters, and stub ofiset on the fllter's multi-passband response is presented. A comparison is made to a non-fractal straight stub fllter of equivalent length showing improved passband bandwidth while maintaining the same overall response. Then an asymmetry is introduced into the fractal geometry to produce a tuned notch band in the second passband. Two fractal scaling factors are shown to aid in the tuning of the fllter notch band. Finally, an asymmetric fllter is fabricated on FR-4 substrate and experimentally verifled, illustrating that the fllter has multi-passbands and can flnd applications in WiFi/WiMAX transponders. The fabricated fllter's flrst two passbands (with respect to S11 = i10dB) are from 2.09GHz to 3.18GHz (fractional bandwidth of 1.09GHz, 41.36%) and from 4.1GHz to 5.43GHz (factional bandwidth of 1.33GHz, 27.91%), both for WiFi applications along with a notch band (S21 = i3dB) from 3.3GHz to 3.94GHz (factional bandwidth of 0.64GHz, 17.67%) to suppress co-site WiMAX transmission. The measured data agrees reasonably well with the simulated fllter response.