What Are Active Antennas?

Active antennas are antenna systems in which the radiating elements and active electronic components, including power amplifiers, low-noise amplifiers, and transceiver circuits, are physically integrated into a single unit rather than connected by cables from a separate radio head. In a conventional passive antenna system, the radio equipment is housed remotely and feeds the antenna through coaxial transmission lines that introduce signal loss and limit flexibility. Active antenna systems eliminate most of this cable path by placing signal generation, amplification, and conditioning circuitry at or adjacent to each antenna element. This co-location reduces feed-line losses, enables per-element phase and amplitude control, and allows the antenna's radiation pattern to be shaped electronically in real time. Active antennas have been central to the development of massive multiple-input multiple-output (MIMO) radio systems and are a defining feature of modern cellular base stations.

The technology traces its commercial deployment to the introduction of active antenna units in fourth-generation LTE networks, where integrating RF components into the antenna housing reduced installation complexity and improved coverage in dense deployments. In fifth-generation (5G) NR specifications, active antenna systems are the standard architecture for base stations operating in both sub-6 GHz frequency bands and millimeter-wave frequency range 2 (FR2), where losses from long cable runs would be prohibitive.

Integration of Active Components

The defining characteristic of an active antenna is the tight integration of each antenna element with its own transceiver chain. As described in the telecom training overview of active antenna system evolution, an active antenna system merges antenna array elements with power amplifiers, low-noise amplifiers, and transceivers into one hardware unit connected to the baseband processing unit by fiber rather than coaxial cable. The power amplifier at each element boosts the outgoing signal without the losses that would accumulate over a coaxial run, while the low-noise amplifier on the receive path maintains sensitivity. Digital-to-analog and analog-to-digital converters at each element enable baseband processing to apply complex beamforming weights independently at every point in the array.

Beamforming and Smart Antenna Techniques

The per-element signal control enabled by active architecture is what makes large-scale beamforming practical. By varying the phase and amplitude applied to each element's signal, the antenna's beam can be steered electronically toward a target user without any mechanical movement. In a 5G FR2 system, this capability is essential: at 28 GHz the wavelength is approximately 10 millimeters, so antenna arrays with many elements can fit in a compact form factor, but beam steering must compensate for the narrow beams those arrays produce. Research published in PMC on a 5G NR FR2 beamforming system with integrated transceiver modules demonstrated an 8-by-7 phased array at 28 GHz capable of scanning a horizontal beam range of plus or minus 50 degrees in 10-degree increments, with a half-power beam width of 13 degrees and a conversion gain of approximately 20 dB. Massive MIMO configurations extend this principle to arrays with 32, 64, or more active elements, simultaneously serving multiple users through spatial multiplexing.

The MDPI Sensors journal published a companion study on the same 5G NR FR2 beamforming architecture, which confirmed real-time video transmission at 15-meter range and highlighted the architecture's suitability for beyond-5G deployments requiring simultaneous transmit and receive operation.

Applications

Active antennas have applications in a wide range of wireless and electromagnetic systems, including:

• 5G NR base stations, where active antenna units provide massive MIMO and beamforming capability for both sub-6 GHz and millimeter-wave bands
• Satellite ground terminals and phased-array earth stations requiring electronically steerable beams
• Radar systems, including automotive and airborne radar that demand rapid beam scanning without mechanical rotation
• Military and defense communications, where adaptive nulling through active apertures suppresses interference
• Point-to-point microwave backhaul links, where active antennas improve link margin in dense urban deployments