With the emergence of higher 4G LTE versions (3GPP version 13 and version 14) and the latest 5G standard (3GPP version 15), antennas for wireless communication have begun to undergo substantial changes. In addition to adding frequencies below 6 GHz for 5G, there are other 5G use case technologies under development. With these technologies, current and future antennas will have huge changes. Early standards for 4G LTE allowed multiple input multiple output (MIMO) antenna structures to take advantage of spatial multiplexing and increase the throughput and capacity of cellular installations. The newly released multiple input multiple output (MIMO) technology transforms the antenna from a traditional passive design to an active device that is highly integrated with radio frequency front-end (RFFE) hardware and configurable digital hardware, which can adapt to the latest complex multiple input multiple output ( MIMO) and network requirements.

In the past few years, antennas with multiple input multiple output (MIMO) and carrier aggregation (CA) functions have been put into use, the most common being 2×2 MIMO. This requires two antenna units at the base station for transmission, two antenna units for reception, and two antenna pairs on the user equipment. Using spatial multiplexing, users can transmit data through two spatial streams, thereby increasing throughput. In this case, these 2×2 MIMO antennas usually only involve antennas and multiple coaxial feeds to the base transceiver station (BTS), or later to the base transceiver station (BTS) digital version, digital unit (DU) and A remote radio head (RRH). Normally, this type of antenna uses cross-polarized elements. For the subsequent 4×4 MIMO installation, the digital unit (DU) is usually connected to two remote radio heads (RRH) to feed two 2×2 MIMO antenna systems.

To continue this trend, 32 remote radio heads (RRH) and complex interconnections are required to feed each remote radio head (RRH) and 2×2 MIMO antennas, with 64× established in 3GPP Release 15. 64 MIMO function. Therefore, a new antenna and multiple-input multiple-output (MIMO) method are already in development, and some early versions are used for preliminary and mainly experimental 5G deployments. The result is the integration of the antenna system with radio and other active components, including digital control and signal processing technology. These so-called active antenna systems (AAS) have been considered the most economically feasible method of producing high-end multiple-input multiple-output (MIMO) antennas, and are within the actual installation constraints of already crowded antenna towers and platforms. In the latest generation of cellular antennas for infrastructure, digital processing for multiple input multiple output (MIMO), modulation and demodulation, as well as signal distribution and radio frequency front-end (RFFE) hardware have been integrated into the antenna system. These components usually include power combiners/distributors, mixers/upconverters/downconverters, analog-to-digital converters/digital-to-analog converters (ADC/DAC), switches, filters, power amplifiers (PA), low Noise amplifiers (LNA), circulators/isolators, attenuators, tuning components, and a large number of RF and digital interconnects. These Active Antenna Systems (AAS) also include high-density antenna elements, which can accommodate up to 128 if separate antenna elements are used for transmission and reception. However, some modern active antenna systems (AAS) divide the elements into sub-arrays and only need a transmit/receive module (TRM) for each sub-array, not each transmit/receive pair. In order to achieve a complete 64×64 MIMO, some of the active antenna systems (AAS) can be split into several modular subsystems, such as 8×8, 16×16 or 32×32, which can be assembled into Complete 64×64 MIMO system. 

The next generation of multiple input multiple output (MIMO) may be the so-called massive multiple input multiple output (MIMO). This can lead to extremely complex and dense active antenna systems (AAS). It may be necessary to integrate a large multiple input multiple output (MIMO) system into a single complete module, which has all the necessary radio frequency, signal processing, and even built-in network hardware. Since such systems may be suitable for densely populated cities and suburbs, they may also need to be much more compact than the typical active antenna systems (AAS) used today, so that they can be installed on metropolitan infrastructure such as Street lights, traffic light poles, etc.

High-density active antenna systems (AAS) require radio/microwave hardware that is more compact and more energy efficient than previous cellular technologies. Part of the requirement is due to the need to maintain a relatively similar active antenna system (AAS) cell tower footprint. Testing such systems is also a new challenge in the industry, and future systems may solve this problem. These systems include extensive self-diagnosis and other built-in self-test (BIST) functions.