# Antennas and Propagation Aspects for Emerging Wireless Communication Technologies
###### Abstract  
The increasing demand for high data rate applications and the delivery of zero-latency multimedia content drives technological evolutions towards the design and implementation of next-generation broadband wireless networks. In this context, various novel technologies have been introduced, such as millimeter-wave (mmWave) transmission [1], massive multiple input multiple output (MIMO) systems [2], and non-orthogonal multiple access (NOMA) schemes [3] in order to support the vision of fifth generation (5G) wireless cellular networks. The introduction of these technologies, however, is inextricably connected with a holistic redesign of the current transceiver structures as well as the network architecture reconfiguration. To this end, ultra-dense network deployment along with distributed massive MIMO technologies and intermediate relay nodes have been proposed, among others, in order to ensure improved quality of services to all mobile users. In the same framework, the design and evaluation of novel antenna configurations able to support wideband applications is of utmost importance for the 5G context support. Furthermore, in order to design reliable 5G systems, the channel characterization in these frequencies and in the complex propagation environments cannot be ignored because it plays a significant role. In this Special Issue, fourteen papers are published, covering various aspects of novel antenna designs for broadband applications, propagation models at mmWave bands, the deployment of NOMA techniques, radio network planning for 5G networks, and multi-beam antenna technologies for 5G wireless communications. [PERSON] T et al. [4] have designed a novel cedar-shaped multiband frequency reconfigurable antenna for WLAN, WiMAX, and X-band satellite wireless communication systems. The broad tunability of operating bands is achieved by employing switches to alter the effective electrical length of the radiating element of the antenna. The proposed antenna design is evaluated for specific output metrics, such as reflection coefficient, antenna gain, and radiation pattern, through simulation as well as measurements. The authors highlight the efficient radiation of the proposed antenna structure in all desired bands. [PERSON] and [PERSON] [5] present a novel reconfigurable filter antenna for impulse radio-ultrawideband (IR-UWB) applications integrated with WLAN and WiMAX. According to the presented results, the proposed antenna design can integrate the WLAN and WiMAX narrowband with the IR-UWB operating band without changing the size and time domain performance compared with the original UWB antenna. These features enable the proposed filtering antenna to be widely used in IR-UWB systems integrated with WLAN/WiMAX. [PERSON] and [PERSON] [6] have conducted various high time resolution spectrum occupancy measurements and analysis for 2.4 GHz WLAN signals. To this end, it was found that distributions such as Gamma and lognormal can be used to model the idle state of a 2.4 GHz WLAN channel along with the generalized Pareto distribution. In addition, in this work, analysis is performed per channel, which shows that different concurrentlymeasured channels in radio technology may have different idle time window statistics and their idle states can be modelled using different distributions. [PERSON] et al. [7] have conducted an extensive review on different antenna designs for non-contact vital sign measurements. In this context, specific guidelines for proper antenna design are highlighted, that are related to frequency selection, polarization, directivity, gain, and size. [PERSON] et al. [8] propose an extension of the ray tracing simulation method for a typical outdoor-to-indoor (O2I) scenario, in which the incident radio waves penetrate indoors through building windows. The presented method consists of the Fresnel zone shielding loss calculation and the transmission loss calculation by equivalent dielectric plate.