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In this article, a dual-band sixth order double symmetric T-slot filter is proposed for the 5G communication systems. This filter contains two duplicate square resonators and a T-shape feedline on the Rogers RT duroid 5880 substrate. Operating at the 28 and 38.5 GHz frequencies from licensed 5G frequency bands and small size make this filter appropriate for different 5G applications. Furthermore, an LC equivalent circuit for the filter has been considered that helps us to have a better sight of this filter. Measurement results show good agreement with simulations. The attenuation on the passband is less than 1 dB. In order to evaluate the filter performance besides other millimeter waves components, a wideband antenna is combined with the filter to form a filtenna. The achieved results show the appropriate performance and well-matched with other 5G devices.

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.

This work reports on a novel design of a compact and tunable filter in substrate integrated waveguide technology. The proposed dual-band filter is based on resonators that exploit two resonating modes excited in a single SIW cavity. The structure is designed in such a way that the two bands of dual-band filter each having two poles can be tuned independently. This property of the proposed filter makes it a suitable choice for multistandard applications with fine tuning as envisaged for future generation wireless technologies. The measured results of the fabricated prototypes validate the proposed design concept.

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2016R1A2B2010170). Dr. Duk-Yong Choi acknowledges the financial support from the ARC Future Fellowship FT110100853.

This letter presents a whole UWB band suppressed ring resonator bandpass filter with small LUCs (Lowpass filter unit cells) [Lee W-K, Hwang H-Y. J Electromagn Eng Sci. 2014;14:387–392.] based on artificial transmission lines [Martin F. Artificial Transmission Lines for RF and Microwave Applications. 1st ed. New York: Wiley; 2015]. Two LUCs are used as building blocks for miniaturization and harmonic suppression of the ring resonator of the filter. Design equations for proper characteristic impedances of the ring and for proper stopband transmission zeros of the LUCs are newly presented. Fabricated filter shows insertion loss of 2.3 dB at center frequency of 2.55 GHz, fractional bandwidth of 2.5%, and good harmonic suppression about 20 dB in whole ultra-wide band, which agreed well with the simulation results. The ring area of the proposed bandpass filter has 36% of that of the conventional one.

This work presents a development of a filter and a waveguide using substrate integrated to work at millimeter frequencies with a demonstration method to correct the dimensions of a substrate integrated waveguides (SIWG). As a proof of concept, and using the method of dimensioning correction, another filter and a waveguide are created for working at frequencies up to 40 GHz, more precisely, at central frequency of 28 GHz to perform with 5G applications. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1333–1337, 2017

A compact and narrowband low temperature co-fired ceramic (LTCC) bandpass filter (BPF) is proposed using vertically stacked half-wavelength end-coupled resonators. The multilayered end-coupled stripline resonators are stacked and buried into LTCC substrate for vertical end-coupling and size reduction. The coupling strength between adjacent resonators is adjustable by offsetting the intermediate ground layer. A narrowband fractional bandwidth (FBW) of 1.9% and a significant size reduction of 80% are achieved. Measurements agree with the simulation results well. Performance and size reduction comparisons and discussions are also implemented. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:86–89, 2017

This letter proposes a high-linearity reconfigurable lower ultra-wideband (3.1–5.25 GHz) filter with independently controlled dual bandnotch at WiMAX 3.5 GHz band and satellite communication systems 4.2 GHz band. Reconfigurability has been achieved by the implementation of Graphene based switches (simulation only) and PIN diodes (measurements). The simulation and measurement results in OFF state show an entire bandpass response from 3.1 GHz to 5.25 GHz and with a very low insertion loss. In ON state, the results show that sharp rejections at 3.5 GHz and 4.2 GHz are achieved, with a low passband insertion loss. The two bandnotch operate independently of each other; thus allowing to control the behaviour of the required bandnotch. The third order intermodulation products were also measured in OFF and ON states and the linearity results have been presented. The filter is able to achieve a high performance with good linearity and no significant loss.

A novel reconfigurable dual-band bandstop filter (DBBSF) with tunable lower stopband is presented. This DBBSF is a double-layer structure composed of a pair of quarter wavelength (λ/4) open-end resonators on the top layer and a pair of novel slot-shaped structures occupying the bottom layer. Two varactors embedded in the λ/4 resonators are utilized to adjust the center frequency of the first stopband. Without increasing size, a fixed stopband located at 2.76 GHz is produced by the slot-shaped defected ground structure (DGS). Both stopbands are independent of each other thus great design flexibility can be obtained. For demonstration, a prototypical filter is implemented with tunable lower stopband of 1.47–1.84 GHz (22.4%) and a fixed upper stopband at 2.76 GHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2273–2276, 2016

A tunable multiwavelength erbium-doped ring cavity fiber laser based on a Fabry–Perot filter and Mach–Zenhder interferometer is proposed. A tunable single wavelength laser is realized from 1526.8 to 1558.6 nm, and the space interval and peak power shift are less than 2.6 nm and 0.8 dBm, respectively. A dual- and tunable triple-wavelength laser are achieved, and the power fluctuation of the dual- and triple-wavelength lasers is less than 0.153 and 1.28 dBm, respectively, at room temperature within a 20-min scan time. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1790–1794, 2016

This letter presented a novel compact continuously tunable low-pass filter (LPF) using varactor-loaded coupled rhombic stubs. The proposed LPF demonstrated excellent roll-off selectivity, wide stopband range as well as good cut-off frequency tunability. This LPF consisted of three varactor-tuned coupled rhombic stubs loaded on a section of high-impedance microstrip line symmetrically and two coupled line LPFs which could further improve the stopband performance. A detailed explanation of the tuning mechanism was illustrated by adopting lumped-element equivalent circuit model. The measured results showed not only a wide cut-off frequency tuning range of 56% from 350 to 800 MHz, but also an excellent steepness factor of less than 1.14. Additionally, a rejection level of greater than 20 dB up to 8 GHz (>10 fc) was observed in the stopband. The proposed ideas were verified by the measured results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1641–1644, 2016

In this letter, a miniaturized electrically tunable bandpass filter, based on liquid crystal (LC) technology, has been designed, manufactured and characterized through particular configuration schemes, which include low cost inverted-microstrip structures and a dual-mode inverted-microstrip square loop resonator with capacitively loaded open-loop arms. In the filter, its transitions between inverted-microstrip and microstrip are specifically designed at the I/O ports for the self-packaged, and its central frequency tenability is induced by applying low AC voltages for low power consumption. By measuring, the filter has a relative central frequency tuning range of 11.7% from 4.01 GHz to 4.51 GHz, and has a relative bandwidth of 13% ± 0.5% over the tuning range, a size of 28 mm × 28 mm, and an insertion loss of 1.9 and 4.5 dB at 4.01 and 4.51 GHz, respectively. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1686–1689, 2016

In this article, a novel very compact DGS lowpass filter (LPF) and reconfigurable bandpass filter are proposed. The designed filter consists of one T-DGS resonator, which is excited by 50 ohm microstrip line, placed on top layer between the input and output of the proposed structure. The selected filter topology has several advantageous compared with the other previous works such as the compactness and its simple design. The addition of compensated patch capacitor improves the low insertion loss and ultra-wide stopband with 15 dB attenuation from 2.2 to 3.6 GHz. The size of the proposed single T-DGS LPF-BPF is less as (0.023 λg × 0.044 λg) with λg = 0.263 m. The tunable bandpass filter (BPF) is extracted from LPF topology using variable Chip Monolithic Ceramic Capacitors and J-inverter technique. Finally, the measured, EM- and field simulation results are presented and discussed. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1142–1148, 2016

A novel compact bandpass filter based on linked hexagonal-omega resonators (LHORs) is presented. The proposed filter is realized by loading the LHORs to the microstrip line on the top of the substrate. The LHORs provides the possibility of designing bandpass filters with small size and simple structure. Two prototypes of filters were designed based on this structure. To validate the proposed prototypes, two-cascaded and three-cascaded bandpass filters using LHORs are simulated and fabricated. The proposed filters show a good pass-band performance and a high out-band suppression. The good agreement between the measured and the simulated results proves the excellent performance of the proposed filters. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1049–1052, 2016

This letter reports a new implementation of miniaturized wideband bandstop (WBBS) filter using a gallium-arsenide (GaAs)-based integrated passive device technology (IPD). The implementation of an air-bridge capacitor explores the possibility of frequency selectivity from 8.15 to 9.20 GHz. The WBBS filter generates a return loss of −0.50 dB with a rejection depth of −38.01 dB at the resonance frequency of 9.20 GHz. The size of the filter was drastically reduced by implementing a microfabrication (IPD) with folded meandered-line, featuring the length equal to 0.38 times the guided wavelength (λg) that occupies only 0.22 λg × 0.13 λg of the die area. The selectivity of the filter was reflected by the higher value of return loss with sufficient suppression of out-of-band signals close to the resonance frequency. Experimental verification of the filter response demonstrates its potential as a WBBS filter operating in the X-band frequency spectrum. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:980–985, 2016

A novel bandpass filter (BPF) with multiple transmission zeros (TZs) and wide stopband is proposed. The filter is realised using complementary open-ring resonators (CORRs) loaded half mode substrate integrated waveguide (HMSIW). Besides, a novel electric source-load electric cross-coupling configuration is introduced to generate extra attenuation poles at either side of the passband, which improves the passband selectivity and the stopband suppression level. Based on this structure, a BPF operating at 5.8 GHz with multiple transmission zeros is designed and fabricated. The Measurement and simulation results indicate that the proposed configuration is a good candidate for filter design. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:998–1001, 2016