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    A high isolation quad-channel microstrip diplexer based on codirectional split ring resonators
    (Wiley, 2022) Gorur, Ali K.; Turkeli, Alper; Buyuktuna, Mert; Dogan, Engin; Karpuz, Ceyhun; Gorur, Adnan
    In this study, a novel microstrip diplexer with four channels is designed by using codirectional split ring resonators (CDSRRs). Since CDSRRs provide dual resonance behavior, dual-band bandpass filter with two poles at each passband can be created by coupling identical CDSRRs to input/output ports. Based on this approach, quad-channel diplexer can be designed by coupling two more CDSRRs in different electrical length to another output. Both filters are fed by similar feeding lines. High isolation can be observed between the output ports by means of CDSRRs. The designed quad-channel microstrip diplexer was also fabricated and tested for experimental verifications. The measured results are in a good agreement with the simulated results. Center frequencies of the channels were measured at 2.12, 2.45, 3.90, and 4.48 GHz with the minimum insertion losses of 2.27, 2.88, 2.00, and 2.71 dB, respectively. Isolation was observed as better than 44 dB from DC to 6 GHz.
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    A Novel Compact Microstrip Diplexer with Closely Spaced Channels
    (IEEE, 2020) Gorur, Ali Kursad; Turkeli, Alper; Dogan, Engin; Karpuz, Ceyhun; Gorur, Adnan
    A novel microstrip diplexer with closely spaced channels is introduced by using stub loaded dual-mode square loop resonators (DMSLRs). The proposed resonator is constructed by locating open-circuited stubs with narrow slits to the midpoints of a conventional DMSLR to achieve size reduction. By changing the number of narrow slits, resonant frequencies of the proposed resonator can be controlled. In order to design a diplexer with low channel frequency ratio, two stub loaded DMSLRs having different number of narrow slits are coupled to input and output ports by thin film capacitors. The designed diplexer was also fabricated and measured with a channel frequency ratio of 1.10. The channels were measured at 1.78 GHz and 1.96 GHz with the fractional bandwidths (FBW) of 5.4% and 5.3%, respectively. The measured insertion losses of the channels are 1.99 dB and 1.78 dB. Isolation between the output ports was obtained as better than 28 dB.
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    A Novel Dual-Wideband Four-Port MIMO Filtenna for Sub-6 GHz 5G Communication Systems
    (IEEE, 2023) Turkeli, Alper; Gorur, Ali Kursad; Altuncu, Yasemin
    In this study, a new dual-wideband four-port multi-input multi-output (MIMO) filtenna structure is presented for sub-6 GHz 5G communication systems. Each filtenna element on the MIMO structure is constructed by coupling a dual-wideband filter to the feeding line of a conventional broadband monopole antenna. Four identical filtenna elements are arranged perpendicular to each other for the sake of high isolation and polarization diversity. Furthermore, a new isolation performance improvement approach is introduced by locating a patch decoupling element on the ground plane. The designed four-port MIMO filtenna was fabricated and measured in a very good agreement. The frequency bands were measured at the center frequencies of 3.3 and 5.75 GHz with the fractional bandwidths of 42.4 and 22.6 %, respectively.
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    Design of a compact microstrip quadruplexer with closely spaced switchable and tunable channels based on asymmetrical dual-mode loop resonators
    (Elsevier Gmbh, 2020) Gorur, Ali Kursad; Turkeli, Alper; Karpuz, Ceyhun; Gorur, Adnan
    In this letter, a switchable microstrip quadruplexer based on asymmetrical dual-mode loop resonators (ADMLRs) is presented. Four ADMLRs at different electrical lengths for creating four channels are coupled to input/output (I/O) ports by means of thin film capacitors. Each resonator has two patch elements behaving as reference capacitors that are needed for switching process. In order to achieve the switching ability, varactor diodes are employed to provide variable capacitances at each resonator. Thus, all channels can be independently switched on/off by changing the capacitances of the varactor diodes. Moreover, all channels have fine bandwidth tuning mechanism depending on the capacitance changes. The designed quadruplexer was fabricated and the measurements were observed in a good agreement with the predicted results. Center frequencies of the proposed quadruplexer are adjusted to 1.8, 2.1, 2.4, and 2.7 GHz with the frequency ratios between the adjacent channels of 1.17, 1.14, and 1.13. Isolations between the outputs have been observed as better than 28 dB.
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    Design of a Novel Dual-Wideband Filtenna
    (IEEE, 2022) Turkeli, Alper; Gorur, Ali Kursad; Altuncu, Yasemin
    In this paper, a novel microstrip-fed filter-antenna (filtenna) exhibiting dual-wideband response is introduced. In this direction, a dual-wideband bandpass filter is designed first and then it is integrated into the feed line of a wideband monopole microstrip antenna. The dual-wideband bandpass filter is constructed by stub loaded multi-mode resonators. Two types of stub-loaded multi-mode resonators are coupled to the feeding lines from the filter's input and output ports. The proposed topology allows controlling both bandwidths independently. The designed filtenna was fabricated for the experimental verification. Measurements of the fabricated filtenna show a good agreement with the simulated results. Center frequencies of the proposed filtenna are 3.23 and 5.65 GHz with the fractional bandwidths (FBWs) of 46 % and 21.6 %.