This letter proposes an asymmetrical low-radar cross section (RCS) frequency selective surface (FSS)-based low band (LB: 1.7-2.7 GHz) antenna for the application in tri-band shared-aperture array. In the array, high band 1 (HB1: 3.3-3.8 GHz) antennas and HB2 (4.8-5 GHz) antennas are distributed on the two sides of the asymmetric LB antenna with four FSS unit cells. The bandpass property of the FSS unit cell is formed after inserting a patch into the square loop, meanwhile, it can be controlled by cutting the patch into more pieces. To respectively suppress the blockage effect of the LB antenna on the two-side HB1 and HB2 antennas, a low-RCS FSS-based LB antenna is constructed asymmetrically by placing two kinds of low-RCS FSS unit cells with different patch pieces. Importantly, the low-RCS characteristic of the FSS unit cells on both bands and LB working performance can be independently controlled, so that good performance for both of them can be obtained, without timeconsuming optimization. Finally, the LB blockage effect on the entire HB1 and HB1 has been significantly reduced as expected and good agreement is achieved between the simulation and experiment.

This paper investigates the uplink energy efficiency (EE) of a wireless-powered cell-free massive multiple-input multiple-output (mMIMO) system with hardware impairments, considering Rician fading and maximum ratio processing, anchored in linear minimum mean-squared error (LMMSE) channel estimation. The transceivers of access points (APs) and user equipments (UEs) are non-ideal with hardware impairments. The closed-form expressions of the total uplink (UL) EE and the average harvested energy (HE) are derived by employing a non-linear energy harvesting model and coherent transmission schemes. An optimization problem is formulated to maximize the total uplink EE, in which power control coefficients for APs and UEs, and the large-scale fading decoding vectors are considered. An alternating algorithm based on successive convex approximation (SCA) is proposed to tackle the complexity issue of the non-convex optimization problem. The numerical results show that the proposed algorithm can significantly enhance the total uplink EE comparing with the equal power allocation strategies. Moreover, it is revealed that the hardware impairments on the UEs can be the primary limitation to the total uplink EE in comparison with those on the APs, however, the impact can be effectively mitigated by the proposed algorithm.

A novel wideband self-decoupling method for a closely spaced dielectric patch (DP) antenna (DPA) array is proposed in this paper. Based on the miraculous characteristics of the employed resonator modes, the HEM _11δ and TE ₁₂ modes can be excited and decoupled simultaneously. For the fundamental HEM _11δ mode, the attenuation constant outside the DP is crucial to address the high mutual isolation issue. Furthermore, the E -field and H -field of the higher TE ₁₂ mode are both null at two marginal regions, which are attractive features for decoupling design. Therefore, with the appropriate dielectric constant of DP, the attenuation constant of fundamental HEM _11δ mode not only can be controlled but also the weak field region of higher TE ₁₂ mode can be constrained better. Thus, the two modes can be decoupled at the same time without adding extra components. To validate the proposed decoupling method, a two-element DPA array is developed and demonstrated. Then, a four-element DPA array is fabricated and measured with 21.5 dB isolation in a bandwidth of 10.5%. The DPA array supports up to ±46° beam scanning in the E -plane.

The cell-free (CF) massive multiple-input multiple-output (mMIMO) is considered as a key technology for sixth-generation (6 G) wireless networks. However, the system performance is affected by low cost transceivers and the mobility of the user equipment (UE) which can lead to the hardware impairment and channel aging. In this paper, we investigate the downlink spectral efficiency (SE) of the hardware-impaired CF mMIMO networks over Rician fading channels. More specific, the impact of the oscillator phase noise and channel aging as well as the correlation between the two factors are studied. Two downlink transmission modes, i.e., the coherent and non-coherent transmission are considered. Closed-form expressions are derived and verified by the simulations. In addition to the theoretical analysis, two strategies are presented in order to improve the downlink SE, namely, statistical channel cooperation power control and rate-splitting (RS), which have been shown to be able to improve downlink SE significantly. This paper also reveals that channel aging is the major factor that impacts the system performance compared with the oscillator phase noise caused by the hardware impairment.

Integrated sensing and communication (ISAC) can improve the energy harvesting (EH) efficiency of simultaneous wireless information and power transfer (SWIPT)-assisted IoT networks by enabling precise energy harvest. However, the transmit power is increased in the hybrid system due to the fact that the sensing signals are required to be transferred in addition to the communication data. This paper aims to tackle this issue by formulating an optimization problem to minimize the transmit power of the base station (BS) under a nonlinear EH model, considering the coexistence of power-splitting users (PSUs) and time-switching users (TSUs), as well as the beamforming vector associated with PSUs and TSUs. A two-layer algorithm based on semi-definite relaxation is proposed to tackle the complexity issue of the non-convex optimization problem. The global optimality is theoretically analyzed, and the impact of each parameter on system performance is also discussed. Numerical results indicate that TSUs are more prone to saturation compared to PSUs under identical EH requirements. The minimal required transmit power under the nonlinear EH model is much lower than that under the linear EH model. Moreover, it is observed that the number of TSUs is the primary limiting factor for the minimization of transmit power, which can be effectively mitigated by the proposed algorithm.