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By exploiting bended microstrip lines and tapered resonators, a new microstrip dual‐band bandpass filter (DBBPF) with tunable center frequency and compact size is proposed, analyzed, and fabricated. The LC equivalent circuit of the basic resonator is introduced to present an analytical description. The proposed filter has two passbands at the center frequencies of 2.4 and 5.7 GHz. The measured data show <0.22 and 0.56 dB insertion losses in the first and second bands, respectively, which are considered as a marked advantage. Furthermore, without increasing the circuit size, the second band can be tuned between 3.85 and 7.5 GHz. Finally, an acceptable similarity is observed between the simulated and measured S‐parameters.

In this letter, a compact dual‐band bandpass filter (BPF) is designed, analyzed, and fabricated. A loop resonator loaded by two modified T‐shaped resonators, double T‐shaped resonators, and open bended stubs are applied to form the proposed configuration. The coupling spaces between the loop resonators and open bended stubs result in two passbands with the center frequencies of 2.4 GHz and 5.7 GHz. The LC equivalent circuit of the main resonator is introduced to present an analytical description. Without needing to increase the circuit size, the upper passband can be adjusted between 5.72 GHz and 6.93 GHz. The measured data indicates less than 0.64 dB and 0.76 dB insertion losses in the first and second passbands, respectively. Adjustable second center frequency, compact size, low insertion loss, good suppression level, and a symmetrical structure are the marked features of the proposed BPF. Finally, a good agreement between the simulated and measured results is observed.

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By exploiting butterfly and T-shaped resonators, a new design of microstrip lowpass filter (LPF) is proposed and analyzed. The LPF is investigated in four sections. Analyzing initial resonator and its equation in detail, providing a sharp skirt by using series configuration, suppressing in middle frequencies and suppressing in high frequencies are focused in each section, respectively. To present a theoretical design, LC equivalent circuit and transfer function are precisely calculated. The measured insertion loss of the LPF is less that 0.4 dB in frequency range from DC up to 1.25 GHz, and the return loss is better than 16 dB. A narrow transition band of 217 MHz and a roll-off rate of 170.5 dB /GHz are indicative of a sharp skirt. By utilizing T-shaped and modified T-shaped resonators in the third and fourth sections, respectively, a relative stopband bandwidth (RSB) of 166 % is obtained. Furthermore, the proposed LPF occupies a small circuit of

A symmetrical compact microstrip lowpass filter (LPF) with ultra‐wide rejection band and low voltage standing wave ratio (VSWR) using a novel structure of stepped impedance and butterfly‐shaped resonators is presented and fabricated. The LPF has a 3 dB cut‐off frequency at 1.513 GHz. The series structure of the butterfly‐shaped resonators result in a high roll‐off rate of 187.8 dB/GHz. By generating multiple transmission zeros, a wide stopband (with 35 dB rejection degree) is achieved. To reach a small circuit, the bended transmission line is properly utilised. Moreover, 171% relative stopband bandwidth and dimensions of 0.087λg × 0.157λg (λg is the guided wavelength at 1.513 GHz) are other specifications of this LPF. In addition, an acceptable match is obtained between the simulated and measured responses. In the end, the LPF achieves a high figure‐of‐merit of 82288.

In this letter, a microstrip lowpass filter (LPF) using bend configuration with several excellent features such as a compact size, great roll-off rate and high rejection in the stopband is presented. This structure is composed of a spiral transmission line loaded by several stepped impedance and T-shaped resonators. The cut-off frequency of the proposed filter is equal to 2.73 GHz and the transition band is from 2.73 up to 2.82 GHz with –3 and –20 dB attenuation point, respectively, which represents a very high sharpness in the transition band. To achieve a –40 dB rejection level in the stopband, multiple open stub and T-shaped patches are utilized. An acceptable agreement between EM-simulation and measurement results is observed.