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The design and analysis of two defected ground structures (DGS)‐based filters have been proposed in this article. The first is a multifrequency bandstop filter (BSF) which utilizes a semi‐H defect in the ground plane. This structure is then prototyped on a Rogers 4350B substrate of overall size 45 mm × 15 mm with an external SMD capacitors employed to control the resonance of the circuit for the stopband frequencies of 433, 700, and 915 MHz. An equivalent π‐circuit is modified to validate this multiband filter. The second filter is a combination of a BSF and bandpass filter in one structure. The filter operating with a controllable passband and stopband frequency is fabricated on Rogers 4350B lossy substrate. Two SMD capacitors are loaded in the filter structure to control the passband and stopband frequencies of the filter with a structure size of 20 mm x 20 mm. Finally, the equivalent circuit from the BSF is modified further to encompass the bandpass and bandstop frequency response of the proposed work. [ABSTRACT FROM AUTHOR]

Design procedure of a novel transmission line low‐pass filter is presented. The filter has a flexible rejection response for a prescribed cut‐off frequency and an in‐band ripple factor. It is compact by using a Z‐shaped coupled‐line section, which is loaded with open‐circuited stubs. All of the transmission line elements are identical in electrical length, and the impedances can be calculated by solving certain specific equations according to prescribed in‐band specifications. The simulated results show that the circuit can generate low‐pass responses with third‐, fifth‐, and seventh‐order filtering functions. The filter order depends on the number and position of the loading stubs. For verification, two sample filters with cut‐off frequency of 0.5/0.3 GHz are fabricated using a three‐/five‐layer PCB process, which generate seventh‐order low‐pass filtering responses with good selectivity. The experimental results agree well with the predictions. [ABSTRACT FROM AUTHOR]