How does a base station sector antenna work?

A base station antenna uses a vertical array of cross-polarized radiating elements (typically patch antennas or folded dipoles) backed by a ground plane reflector. The vertical stacking of 8 to 12 elements produces a narrow elevation beamwidth of 6 to 8 degrees while maintaining a wide 65-degree azimuth beamwidth for sector coverage. Three sectors (3 antennas at 120-degree spacing) cover 360 degrees. The elements use slant 45-degree polarization (plus and minus 45 degrees) rather than vertical/horizontal, providing polarization diversity for MIMO that works regardless of the user's handset orientation. Electrical downtilt is controlled via remote electrical tilt (RET) using AISG protocol, adjusting the elevation beam direction from 0 to 10 degrees below horizontal to optimize coverage and minimize inter-cell interference.

What are the key specifications of a base station antenna?

Critical specifications include: azimuth beamwidth (65 degrees for 3-sector, 33 degrees for 6-sector, 90 degrees for 4-sector), elevation beamwidth (6 to 8 degrees for macro, 15 to 30 degrees for small cell), gain (15 to 18 dBi for macro panels), front-to-back ratio (greater than 30 dB), cross-polar discrimination (greater than 25 dB), VSWR (less than 1.5:1 across the operating band), intermodulation (less than minus 150 dBc PIM at 2 times 43 dBm carriers), port-to-port isolation (greater than 30 dB), and electrical downtilt range (0 to 10 degrees via RET). Frequency bands are increasingly wideband: 690 to 960 MHz for low band, 1695 to 2690 MHz for mid band, and 3300 to 3800 MHz for 5G n78. Multi-band antennas combine 2 to 4 band arrays in a single radome.

Cellular Infrastructure

Base Station Antenna

Q: What is a massive MIMO active antenna?

A 5G massive MIMO active antenna unit (AAU) integrates the antenna array, radio transceivers, power amplifiers, and beamforming processing into a single weatherproof enclosure. A typical configuration uses 64 transmit and 64 receive elements (64T64R) arranged in a 2D planar array, providing both azimuth and elevation beamforming capability. Each element has its own dedicated transceiver chain with 5 to 10 watts output power per element. The system forms user-specific beams in both planes, directing energy precisely to individual users or groups. This provides 15 to 25 dB of beamforming gain plus spatial multiplexing to serve multiple users simultaneously on the same time-frequency resources. Weight: 25 to 40 kg for sub-6 GHz AAUs, versus 15 to 20 kg for passive antennas.

/bayss stay-shun an-ten-uh/ — BSA

A directional panel antenna mounted on cell towers providing sector coverage for 4G/5G networks. Passive antennas use cross-polarized (±45°) patch or dipole arrays with 65° azimuth beamwidth, 6-8° elevation beamwidth, and 15-18 dBi gain. Three sectors at 120° spacing cover 360°. 5G massive MIMO active antenna units (AAUs) integrate 64T64R elements with per-element amplifiers for electronic beam steering, delivering 15-25 dB beamforming gain plus spatial multiplexing.

Gain: 15-18 dBi

Az BW: 65° (3-sector)

PIM: <-150 dBc

Understanding Base Station Antennas

The base station antenna is the interface between the cellular network and the air. Its pattern shape defines the coverage footprint of each sector, and its gain directly impacts the link budget. A well-designed antenna maximizes coverage within its intended sector while minimizing radiation into adjacent sectors (front-to-back ratio >30 dB) and toward the ground or sky (null fill and upper sidelobe suppression). The cross-polarized design with ±45° slant polarization provides two independent ports for 2x2 or 4x4 MIMO, using polarization diversity rather than spatial diversity to keep the antenna width manageable.

Modern multi-band antennas combine 2 to 4 frequency bands in a single radome. A typical tri-band antenna integrates low-band (694-960 MHz, 4 elements), mid-band (1695-2690 MHz, 8 elements), and CBRS (3550-3700 MHz, 8 elements) arrays in a single 1.3-meter tall enclosure. This reduces tower loading and lease costs compared to deploying separate antennas per band. The integration challenge is managing inter-band coupling and PIM while maintaining each band's radiation pattern integrity.

Antenna Pattern Equations

Array gain (vertical stack):
G = G_element + 10 log₁₀(N)
8 elements, 8 dBi each: G = 17 dBi

Elevation beamwidth:
θ_3dB ≈ 50.7° × λ / (N × d)
N=8, d=0.85λ: θ ≈ 7.5°

Electrical downtilt (RET):
θ_tilt = arcsin(Δφ / (k × d))
Δφ = progressive phase shift per element

PIM specification:
IM3 < -150 dBc @ 2×43 dBm
= -150 + 86 = -64 dBm absolute
Must be below receiver noise floor

Base Station Antenna Type Comparison

Type	Gain (dBi)	Weight (kg)	Bands	MIMO	Tilt
Passive panel	15-18	10-20	1-4	2x2/4x4	RET 0-10°
mMIMO 32T32R	23-25	25-30	1 (n78)	32-layer	Electronic
mMIMO 64T64R	25-27	30-40	1 (n78)	64-layer	Electronic
Small cell	6-12	2-5	1-2	2x2/4x4	Fixed
mmWave AAU	28-32	8-12	1 (n258)	Hybrid BF	Electronic

Common Questions

Frequently Asked Questions

How does a sector antenna work?

A vertical stack of 8-12 cross-polarized (±45°) elements backed by a reflector creates a 65° wide, 6-8° tall beam. Three sectors at 120° cover 360°. Polarization diversity provides 2x2/4x4 MIMO without spatial separation. Electrical downtilt via RET (AISG protocol) adjusts elevation 0-10° to optimize coverage and minimize inter-cell interference.

What is a massive MIMO active antenna?

A 5G AAU integrates 64T64R elements with per-element transceivers (5-10 W each) in a weatherproof enclosure. The 2D planar array steers beams in azimuth and elevation, forming user-specific beams with 15-25 dB gain plus spatial multiplexing of 16+ simultaneous users. Weight: 25-40 kg for sub-6 GHz. Replaces separate passive antenna plus remote radio unit (RRU) architecture.

What are the key BSA specifications?

Azimuth BW (65° for 3-sector), elevation BW (6-8°), gain (15-18 dBi), F/B ratio (>30 dB), cross-pol discrimination (>25 dB), VSWR (<1.5:1), PIM (<-150 dBc at 2×43 dBm), port isolation (>30 dB), and RET range (0-10°). Multi-band antennas cover 694-960 MHz + 1695-2690 MHz + 3300-3800 MHz in a single radome.

Related Terms

← Base-Loaded Monopole Base Station Compliance →