In this paper, a compact dual‐band bandpass filter (DB‐BPF) is implemented by using a pair of coupled stepped impedance resonators (SIRs) and a pair of λ/2 bended resonators for the modern wireless communication systems such as WiMAX and WLAN (3.4 and 5.4‐GHz). The physical layout is presented and explained the establishment of an LC equivalent circuit. Moreover, the second passband of the proposed dual‐band bandpass filter can be independently controlled by inserting the open‐circuited stubs at the end of the λ/2 bended resonators without increasing the circuit size. Simulation results show that the second passband can be ranged from 5.6 to 4.8‐GHz with the bandwidth of 400 ± 96‐MHz, whereas the first passband is fixed with the bandwidth of 280 ± 8.5‐MHz. The measured results exhibit the insertion losses (S21) lower than 1.2 and 1.4 dB, and the return losses (S11) of −23 and −32 dB at the first and second passbands, respectively, which show a good agreement with simulation results. The dual‐band microstrip filter is fabricated on RT/Rogers 4003 substrate with a compact size of 0.24λg × 0.25λg.

A compact narrowband band pass filter (NB BPF) with wide stop-band has been designed and fabricated. The presented filter based on modified slow wave resonator of microstrip is designed to achieve narrow bandwidth. The bandwidth of this filter capability of changing with the coupled lines is used in the middle of this structure filter. For the first time, by using transmission line theory and coupled line structure, the new design methodology of a narrowband BPF is employed and resonant frequency has been clearly explained. The filter has been designed for operating at center frequency 3.82 GHz, that suitable for WiMAX applications. The measured insertion loss (s21) and return loss (s11) are 20.38 dB and 233 dB, respectively at 3.82 GHz resonant frequencies. The proposed filter is designed, simulated and fabricated and the simulation results are in good agreement with measurement result.

In this article, a new compact, wide bandwidth dual-band bandpass filter (DB-BPF) with four transmission zeros (TZs) is proposed. A dual-path configuration is realized by cascading different dual-mode resonators. The novel dualmode resonators are based on stepped impedance resonators (SIRs) that generate the TZs owing to their intrinsic characteristics. The proposed DB-BPF can fulfill simultaneous independent control of the external and internal-resonator coupling. The design procedure based on the cascaded dual-mode resonators and frequency transformation is also introduced. The surface current distributions are simulated to verify the performance of the proposed filter. The measured results show 2.14/4.33 GHz DB-BPF with 3-dB fractional bandwidth (FBW) of 0.27/0.15, respectively, which is suitable for WLAN applications. The return and insertion losses of the passband are better than 15/15-dB and less than 0.8/1.3-dB, respectively. The overall physical size of the fabricated DB-BPF is 20.4 mm  20.4 mm, equivalent to 0.23λ g  0.23λ g , where λ g is the guided wavelength at 2.14 GHz.The simulation results are in good agreement with the measurement results.

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