Mahmood Alizade Pahlevani - Department of Electrical Engineering, Islamic Azad University, Ilam, Iran.
Ramin Sayadi - Department of Electrical Engineering, Islamic Azad University, Ilam, Iran.

In this paper, a novel design of microstrip lowpass filter has been proposed. T-shaped, modified T-shaped and elliptical resonators have been properly combined to achieve the final structure. The designed filter has a cut-off frequency at 1.643 GHz. The results indicate that the filter has a narrow transition band resulting is a remarkable roll-off rate of 128 dB/ GHz, which is considered as an outstanding achievement. Moreover, the structure benefits from a compact size, approximately 10.2 * 21.4 mm2, which equals to 0.091*0.1922 . It should be noted that is the guided wavelength at cut-offfrequency. Besides, the insertion loss and return loss in the pass band is better that 0.2 and 24 dB, respectively. Finally, the result show that the proposed filter can achieve a figure of merit (FOM) of 24550.

lowpass filter, T-shaped resonator, return loss, roll-off rate