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In this paper, a lowpass filter with −3 dB cutoff frequency of 5.3 GHz using T-shaped and polygon resonators is presented. The applied resonators create a sharp transition band of 0.2 GHz from −3 dB to −40 dB. To obtain an ultra-wide stopband about 54 GHz (10.18f c) with a suppressing level of −21 dB, two different suppressing cells are employed. The overall circuit size is 59.16 mm 2 , which indicates a small occupied area. To clarify the performance of each resonator and describe the location of the transition zeros, exact equations based on the equivalent LC circuits have been calculated.

Abstract. In this paper, a branch-line coupler using closed-loop and open-loop resonators

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Abstract-In this paper, a microstrip lowpass filter with −3 dB cutoff frequency of 1.8 GHz composed of two resonators with different polygon patches and six symmetric suppressing cells is presented. To design the proposed filter, the impact of each microstrip transmission line on the scattering parameters of the employed resonators is separately determined by extracting the equations of the insertion loss (S 21 ) and return loss (S 11 ) on the basis of their equivalent LC circuit. The designed filter is fabricated and measured, and a good agreement between the results of simulation and measurement is obtained. In the whole stopband region, a return loss better than −0.35 dB and an acceptable suppression level of −22 dB from 1.87 to 19.75 GH are achieved. Furthermore, a flat insertion loss in the passband and an acceptable return loss (−19.32 dB) in this band can verify desired in-band performance. The designed lowpass filter has a high figure of merit about 36969.34.

Abstract-In this paper, a microstrip lowpass filter with −3 dB cutoff frequency of 3.8 GHz consisting of two cascaded resonators with flabelliform patches and two symmetric suppressing cells is proposed. To design the filter, the impact of each transmission line on the frequency response is determined by extracting the equations of the insertion loss (S 21 ) and return loss (S 11 ) on the basis of the equivalent LC circuit of the main resonance cell and the cascaded structure. The designed filter is constructed and tested, and a good agreement between the results of simulation and measurement is obtained. In the whole stopband region, a return loss close to zero and an acceptable suppression level of −30 dB from 4.47 to 25.17 GHz are achieved. Furthermore, a flat insertion loss in the passband and a low return loss (−23.02 dB) in this band can prove desired in-band and out-band frequency response.

In this article, a pair of T-shaped stepped-impedance-stubs plays a key role in the structure of a Wilkinson power divider. In the first step, to find a general relation between electrical lengths and characteristic impedances of the mentioned stubs and consequently how the operating frequency can be chosen, an equation based on a mathematical analysis is obtained. Then, by using this equation, several miniaturized Wilkinson power dividers with the same configurations at different operating frequencies and capable of suppressing spurious frequencies are designed. Moreover, in each of these circuits 2nd to 16th unwanted frequencies are suppressed. The simulation results of the designed dividers are in good agreement with the expected responses predicted by the obtained equation. To validate the proposed method, a Wilkinson power divider at 0.85 GHz as a sample is fabricated, and 77.83% size reduction is obtained. Furthermore, the fabricated divider suppresses 3rd to 21st harmonics better than −20 dB.