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    A Novel Concept in Design of Microwave Planar Dual Band Filter having the Controllable Closed/Isolated Bands by Using the Simple Vias and the Slow Wave Effect for 5G/IoT Applications
    (IEEE, 2021) Karpuz, Ceyhun; Ozdemir, Pinar Ozturk; Senol, Huriye; Cengiz, Alperen; Balik, Hasan Huseyin; Gorur, Adnan
    A microstrip dual-mode dual-band bandpass filter with slow wave effect is presented in this paper. The slow wave effect is provided by interdigital unit cells. The interdigital unit cell located into microstrip resonator is investigated using full-wave electromagnetic simulations. It is shown that an extra surface area is not required to obtain the slow wave effect using these resonators. Using of metal vias on the resonator allows to be designing a dual-band bandpass filter configuration with out-of-band rejection characteristic. The proposed filter exhibits a wideband frequency response since the I/O ports are directly connected to the resonator. Both simulated and measured results are presented to demonstrate the proposed filter.
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    Channel Estimation in RIS-aided Multi-User OFDM Communication Systems
    (IEEE, 2024) Mutlu, Ural; Kabalci, Yasin; Cengiz, Alperen
    Reconfigurable Intelligent Surfaces (RIS) are planar arrays constructed of independently controllable passive reflecting elements that change the phase and the amplitude of the reflected signals between Base Station (BS) and User Equipment (UE). To facilitate the coherent combination of the reflected signals, the Channel State Information (CSI) of the channels should be known by the communication network. The main issue with CSI estimation in unstructured channels is the high number of channels and the long training time that is required to apply orthogonal training reflection patterns at the RIS. With multiple users, the required training period becomes even longer. Therefore, this study proposes allocating the users with orthogonal pilot sequences, which are transmitted over the orthogonal frequency division multiplexing (OFDM) frequency domain with the aim of separating the user signals in the frequency domain. In the study, the cascaded channels are separated in the time domain by a reflection pattern consisting of a DFT matrix and the users are separated in the frequency domain by the use of the Hadamard matrix. The algorithms are simulated over a 3GPP-defined Tapped Delay Line (TDL) channel model as well as a Rayleigh fading channel. The results show that due to the use of orthogonal sequences, channel estimation improves in flat fading channels, while the performance is also of acceptable level in frequency selective channels.
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    Compact Half-Mode Triple-Band Bandpass Filter by using Stepped Impedance Resonators with Grounding Via Holes
    (IEEE, 2023) Karpuz, Ceyhun; Ozdemir, Pinar Ozturk; Balik, Hasan Huseyin; Cengiz, Alperen; Gorur, Adnan
    This letter presents a half-mode triple-band bandpass filter based on folded stepped impedance resonator stub. Also, an interdigital structure with lumped capacitance is added to the circuit to obtain a compact-size filter while maintaining the filtering characteristics. The utilization of the lumped capacitor at the middle point of the interdigital structure contributes to the shift down of the higher modes. Thus, an extra passband generates at the operating frequency range. Also, more reduced size is achieved by using a half-mode circuit.
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    Compact Wilkinson Power Dividers Based on Narrow Slits Loaded Transmission Lines
    (IEEE Computer Society, 2023) Karpuz, Ceyhun; Gorur, Ali Kursad; Cakir, Mehmet; Cengiz, Alperen; Gorur, Adnan
    In this paper, a new approach based on the utilization of narrow slits to improve the return loss and isolation levels of the Wilkinson power dividers is proposed. 2-, 4- and 8-way power dividers are designed by using narrow slits on the quarter wavelength transmission lines. The proposed circuits are designed at the center frequencies of 2, 2.1 and 2.05 GHz. The fractional bandwidths (FBWs) for the return loss of better than 15 dB and isolation levels of better than 20 dB are 19.7%, 28%, 28.2 % for 2-, 4-, and 8-way power dividers, respectively. The proposed method can also reduce the circuit size about 25 % and more in the 2-way and 4-way (8-way) circuits, respectively. Three circuits have been fabricated and measured in a very good agreement with the simulated results. © 2023 IEEE.
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    The Next Generation in Communication Technology: Roadmap to 6G
    (IEEE, 2024) Cengiz, Alperen; Bilim, Mehmet; Kabalci, Yasin
    Since the last quarter of 2022, studies on fifth-generation (5G) communication systems have been conducted under the name of beyond 5G studies. With the standardization of 5G communication systems, researchers have intensified their work on communication technologies beyond the 5G. The rapid advancements in communication technology have prompted 5G studies to focus on mapping out the roadmap for sixth-generation (6G) communication, which will be the next communication technology. This includes determining the vision and requirements for this new technology. This study investigates the developments in mobile communications from the first generation (1G) to the 5G, the main technologies and challenges in the fifth generation, and the expectations for 6G. It is expected that 6G will be operational by 2030 according to many researchers, countries, and companies.