5G 4G 5G systems Beyond 5G Chebyshev Computer communication networks Computer science D2D Communications Decentralized Systems Doherty power amplifier (DPA) FR-4 GaN– HEMT Key Management LPF LTE Mobile Small Cells Multimedia systems Network Coding PIFA Quasi-Yagi antenna Security Small Cells Wireless Ad Hoc Networks band-pass cellular communications compact computer simulation technology differentially-fed antenna dual-polarizatio end-fire radiation beam filter-antenna impedance bandwidth long-term evolution (LTE) massive MIMO microstrip microstrip antennas microstrip filtering antenna mm-Wave applications multi-mode operation output power capacity phased array smartphone applications three-stage DPA