###### Abstract  
In this paper, an ultra-wideband (UWB) bandpass filter (BPF) with dual notched bands using a T-shaped resonator and L-shaped defected microstrip structure (DMS) is proposed and fabricated. First, the principle of generating notched bands by using a T-shaped resonator and L-shaped defected microstrip structure to determine the size parameters of the structure is analyzed. High frequency structure simulator (HFSS) software is used to analyze the performance of the filter, and advanced design system (ADS) is used to extract the equivalent circuit model parameters. The two simulation results are consistent, which further verifies the correctness of the circuit model. Finally, the filter is fabricated and measured. The measured results are in good agreement with simulated results, demonstrating good insertion loss and return loss. The proposed filter has dual independently controllable notched bands which are implemented by coupling the T-shaped resonator to the transmission line and by etching the L-shaped defected microstrip structure respectively. The proposed filter can suppress dispensable bands at 3.5 GHz and 7.5 GHz in WiMAX band and X-band to improve the performance of the ultra-wideband communication system. By adjusting the parameters of the T-shaped resonator and L-shaped defected microstrip structure, the UWB bandpass filter with dual notched bands working at WiMAX band and X-band can be designed and applied to the wireless communication system. microstrip filters; defected microstrip structure; microstrip circuits; bandpass filter +
Footnote †: journal:  
0000-0001-5000-6999-2280][PERSON] 0000-0001-5002  
A number of techniques to design ultra-wideband bandpass filters with notched bands have been studied [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. The notch bands are generated by introducing a resonance unit, such as a stepped impedance resonator (SIR) [2; 3] and multi-mode resonator (MMR) [4; 5; 6; 7; 8; 9]. The disadvantage of adopting stepped impedance resonator or multi-mode resonator is that the size of the notch filter is too large and the transmission zero cannot be flexibly adjusted. The stop-band function is achieved by introducing defect ground structure (DGS) [10; 11] and defect microstrip structure (DMS) [12; 13]. Defect ground structure can effectively reduce the size of the filter, but it is difficult to obtain good broadband and sharp skirt selectivity. In addition, there is leakage of the floor. The microstrip filter based on defect microstrip structure can solve the floor leakage problem. The coplanar waveguide (CPW) [14; 15; 16] is used to achieve notch characteristics. The coupling between the microstrip line and the coplanar waveguide is strong and the filter structure is compact, but the stop band characteristic is generally not good. Novel dual-band bandpass filters are implemented for 3.5 GHz and 5.8 GHz in [17], and the pass band of the proposed filter covers 2.4 GHz, 2.5 GHz, and 3.5 GHz in [18]. In order to remove interference from WiMAX and satellite communication bands, a dual notched ultra-wideband bandpass filter is proposed in this paper. A dual notched ultra-wideband bandpass filter using a T-shaped resonator and L-shaped defect microstrip structure is proposed and fabricated. The first and second notched band functions are respectively implemented by coupling the T-Shaped resonator to the transmission line and etching the L-shaped defect microstrip structure on the bandpass filter. In the second section, we will discuss the design of the ultra-wideband filter with dual notched bands and study the frequency rejection function based on a T-shaped resonator and L-shaped defect microstrip structure. In the third section, a dual bandpass filter with notched bands is fabricated and measured, with the measured results in good agreement with simulated results, demonstrating good insertion loss and return loss.