Wideband microstrip quasi-elliptic function bandpass filter with high out-of-band rejection

Presented in this article is a novel and compact quasi-elliptic function bandpass filter based on microstrip technology that exhibits a high out-of-band rejection over a very wide frequency range. The design comprises stub-loaded halfwavelength resonators that are electromagnetically coupled to resonant structures that are interdigitally coupled to the input and output feed-lines. Perturbation introduced by the presence of the stub causes the resonators to act as a multimode device. In addition, the stub introduces two transmission zeros to significantly improve the filter’s passband selectivity and suppress harmonic and spurious modes. This configuration yields a wideband response with low insertion loss of 0.73 dB, high return-loss 40 dB across 2-4.5 GHz and 5.74-16 GHz. The planar filter structure can be easily manufactured using standard PCB technology

Quasi-elliptic ultra-wideband bandpass filter with super-wide stopband

This paper describes a low-loss and compact planar ultra-wideband (UWB) quasi-elliptical bandpass filter, which is based on a via-free multimode resonator (MMR) that requires no defected ground plane. The MMR structure essentially consists of a step impedance transmission-line resonator that is loaded centrally with a folded open-circuited stub. The MMR structure is also loaded with two pairs of short high impedance stubs with their ends folded towards the central stub. The proposed MMR structure excites several resonant modes comprising three even and two odd-modes within the filter’s passband. The resulting transmission response is highly selective with a low-loss (0.4 dB) passband across 3.60 GHz – 11.3 GHz when fabricated on a conventional dielectric substrate, which is otherwise only possible using high temperature superconductors. In addition, the structure generates transmission zeros to yield a filter that exhibits an extremely wide stopband extending up to 35.5 GHz for S21 ≥ 20 dB. The via-free planar filter structure makes its design and construction easy and economical for mass production. The filter’s performance was verified through measurements. The planar filter structure can be easily manufactured using standard PCB technology

Quasi-elliptic dual-band planar BPF with high-selectivity and high inter-band isolation for 5G communications systems

A novel dual-band planar bandpass filter structure is presented that exhibits the following characteristics: (i) a quasi-elliptic function response with high passband selectivity; (ii) high inter-band isolation; and (iii) a wide out-of-band rejection. The filter is suitable for highly demanding wireless communications systems where the channel capacity is at a premium. The via-free dual-band filter consists of open-loop resonators that are shunt loaded with a half-wavelength open-circuit stub. The resonators are coupled electromagnetically to the stepped impedance resonators, which are inter-digitally coupled to the input/output feed lines. Altering the dimensions of the two stubs allow modification of the resonant mode and transmission zero frequencies. Measured results validate the filter’s performance. The center frequencies of the two passband responses at 4.6 GHz and 5.4 GHz have 3-dB fractional bandwidth of 13.5% and 11.5%, respectively. Insertion-loss at the two passband center frequencies are 1.02 and 0.8 dB, and the return-loss is better than 20 dB. Skirt steepness of the filter is >290 dB/GHz, and isolation between the two closely positioned adjacent bands is better than 35 dB