# Metamaterial Integrated Folded Dipole Antenna with Low SAR for 4G, 5G and NB-IoT Applications
## 1 Introduction  
The continuous escalation in the number of wireless users is estimated to be expanded ten-fold by the end of 2025. There will be a need for more efficient technology, enhanced data rates and better spectrum utilization techniques. The 5G (Fifth Generation) is the latest generation to roll out the extremely high data rate services, such as enhanced mobile broadband (eMBB), massive machine type communications (mMTC), ultra-reliable, and low-latency communications (URLLC), in addition to vehicle to everything (V2X) communications in the near future [1]. The 5G networks will significantly improve the performance over the current 4G (Fourth Generation) systems and will also offer seamless connectivity to numerous devices by integrating different technologies, intelligence and flexibility. By comparison, 4G technology provides high quality video and audio services only. The Long Term Evolution (LTE) standard for 4G uses DSP (Digital System Processor) in addition to the modulation techniques to increase the data rates, and is incompatible with the 2G (Second Generation) and 3G (Third Generation) network. Thus, a separateradio spectrum is required. Leading mobile operators, global vendors and developers are launching NB-IoT (Narrow Band-Internet of Things) and LTE-M (LTE for machines) networks as an integral part of their long-term 5G IoT strategies. The NB-IoT is an LPWA (Low Power Wide Area) standard operating in the licensed frequency bands. It is better in terms of latency, quality and reliability in comparison to Sig-Fox and LoRa, which works on license free bands [2]. Existing cellular networks are evolving to deliver service to billions of new devices providing complete IoT connectivity in the 5G era. The increasing data demand requires an emergent number of frequency bands to be used in 4G and 5G applications. The LTE standard supports frequency division duplexing (FDD) and time division duplexing (TDD). The paired FDD LTE band can simultaneously transmit on two frequencies--one for uplink and the other for downlink. Alternatively, TDD LTE bands are unpaired because they share the same frequency for uplink and downlink with the help of the time-multiplexing technique. Thus, a different frequency spectrum allocation is required for TDD and FDD LTE bands. Numbers are being allocated to differentiate the LTE bands. The FDD LTE bands are being allocated with numbers 1 to 32, whereas 33 to 43 are allocated to TDD LTE bands [3]. These bands are regularly updated for necessary additions in the regulatory meetings of ITU (International Telecommunication Union). Although some of the bands are overlapping, the distribution is feasible, because the possibility of transmission for TDD and FDD at the same time, and for the same LTE frequency band, is less likely to happen [4]. Currently, the LTE TDD unpaired frequency bands are preferred for mobile communications. 3 GPP (Third Generation Partnership Project) released the 5G NR (New Radio) bands. Two radio spectra have been defined for these--one for sub-6 GHz and the other for the millimeter wave band [5]. The low frequency sub-6 GHz band has low path loss and better coverage in contrast to high frequency millimeter wave bands [6]. Additionally, the sub-6 GHz band is being widely used in the current 4G LTE operations and will probably play a crucial role in the pre-5G operations. The 5G NR spectrum defined the frequency of 3.3 to 3.8 GHz as the n78 band. In 3 GPP Release 13, the NB-IoT specification was finalized and allocated with fourteen frequency bands. Four more (B11, B25, B31 and B70) bands were allocated to the service in release 14. Release 15 specified seven additional bands (B4, B14, B71, B72, B73, B74 and B85) [7]. These different bands' operations can be obtained by using a multiple-input multiple-output (MIMO) antenna system or frequency reconfiguration operations. In recent years, a number of MIMO and frequency reconfigurable antennas have been explored for different band coverages. MIMO antennas for band nos.