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In this paper, a multiband miniaturized crescent-shaped patch antenna with circular slots is presented for ultra-wideband applications. The proposed antenna is constructed on a Flame Retardant 4 (FR-4) dielectric substrate. Next-generation wireless communication systems, such as beyond 5G (B5G) and 6G mobile communication systems require a wider bandwidth and higher data rates. The overall size of the proposed antenna is 11×9×2.4 mm3 operating in the frequency range of 17.73 GHz to 26.04 GHz and 29.6 GHz to 31.02 GHz for satellite communications and radar systems, respectively, as well as 35.40 GHz to 38.65 GHz for future mmWave B5G mobile applications. These frequency ranges usually fall into the K-band and mmWave frequency spectrums. Simulation results demonstrate that the peak gain of the proposed antenna is 4.68 dB, which is obtained at 25 GHz.
Since frequency resources are limited, and power saving is also a vital issue, a more spectrum-efficient and power-saving communications system design is the most important research goal. In this paper, we propose an improved, spectrally efficient new discrete Fourier transform (DFT)-Spread Windowing and Restructuring (WR)-Orthogonal Frequency Division Multiplexing (DFT-Spread WR-OFDM) communications system, in thought of various strengths of high-power amplifier (HPA) nonlinearity for a reasonably allowable peak-to-average power ratio (PAPR) and out-of-band (OOB) power emission reduction. Compensation for HPA nonlinearity becomes a difficult task when properly designing efficient multicarrier schemes and fifth generation (5G)-beyond 5G candidate waveforms for cellular wireless communications systems. In practical communications systems, spectral efficiency and power are highly affected by HPA nonlinearity features, and bit error rate (BER) performance also deteriorates. We implemented a time domain window named Tukey (tapered cosine) and localized subcarrier mapping, and the impact of HPA nonlinearity on BER performance and spectral characteristics is comprehensively analyzed. Simulation results demonstrate that the proposed system reduces PAPR and OOB power emissions by 3.176 ㏈ and -81 ㏈, respectively. Additionally, compared to conventional systems, the communication quality of the proposed scheme clearly demonstrates better performance even inHPA nonlinear environments.