Band n257 (28 GHz)
Understanding Band n257
Band n257 occupies the 26.5 to 29.5 GHz range in the Ka-band portion of the electromagnetic spectrum. At these millimeter wave frequencies, the physics of propagation differ fundamentally from sub-6 GHz cellular bands. Free-space path loss is 22 dB higher than at 2 GHz, rain attenuation can reach 10 dB/km in heavy downpours, foliage causes 10 to 20 dB of additional loss, and modern low-emissivity glass windows attenuate the signal by 20 to 40 dB. These challenging propagation conditions necessitate high-gain beamforming antennas at both the base station and the user equipment.
The compensating advantage is bandwidth. The 3 GHz of spectrum in n257 is more than all sub-6 GHz cellular spectrum combined in most countries. A single 400 MHz NR carrier at 28 GHz carries the same data volume as twenty 20 MHz LTE carriers at 2 GHz. This extreme capacity makes mmWave ideal for dense urban hot spots, stadium coverage, fixed wireless home broadband, and industrial IoT applications where a small number of high-capacity base stations serve concentrated user populations.
Band n257 Link Budget
FSPL = 20 log(4πRf/c) = 32.4 + 20 log(fGHz) + 20 log(dkm)
At 100 m: FSPL = 32.4 + 28.9 + (−20) = 81.3 dB
At 300 m: FSPL = 32.4 + 28.9 + (−10.5) = 90.8 dB
Array Gain (64-element phased array):
Garray = 10 log(N) + Gelement = 18 + 5 = 23 dBi
Effective Link Budget Improvement:
MIMO Tx array (256 elements): ~29 dBi
UE Rx array (4 elements): ~11 dBi
Combined array gain: ~40 dB (compensates for FSPL increase)
Shannon Capacity (400 MHz BW):
C = 400 × log2(1 + SNR) Mbps
At SNR = 20 dB: C ≈ 2,660 Mbps per stream
5G NR mmWave Band Comparison
| Band | Range (GHz) | Total BW | Primary Markets | Overlap |
|---|---|---|---|---|
| n257 | 26.5 – 29.5 | 3 GHz | US, Japan, South Korea | Superset of n261 |
| n258 | 24.25 – 27.5 | 3.25 GHz | Europe, China, Japan | Partially overlaps n257 |
| n260 | 37.0 – 40.0 | 3 GHz | US | None |
| n261 | 27.5 – 28.35 | 850 MHz | US (FCC LMDS) | Subset of n257 |
| n262 | 47.2 – 48.2 | 1 GHz | US (FCC proposed) | None |
Frequently Asked Questions
What frequencies does Band n257 cover?
Band n257 spans 26.5 to 29.5 GHz (3 GHz total) in TDD mode. Maximum channel bandwidth is 400 MHz with up to 16 component carriers for aggregation. It overlaps with n261 (27.5 to 28.35 GHz), which is the US FCC LMDS allocation. The full 3 GHz of n257 is available in Japan and South Korea; US deployments typically use the n261 subset.
Why does 28 GHz 5G require beamforming?
At 28 GHz, free-space path loss is 22 dB greater than at 2 GHz. Additional losses from rain (up to 10 dB/km), foliage (10 to 20 dB), and building penetration (20 to 40 dB through modern glass) further reduce signal levels. Beamforming with 64 to 256 element phased arrays provides 15 to 25 dBi of array gain, compensating for the higher path loss. Without beamforming, the link budget at 28 GHz would be unworkable.
What data rates does Band n257 achieve in practice?
With 400 MHz bandwidth and 256-QAM, a single carrier delivers approximately 2.5 Gbps downlink with 4-layer MIMO. Carrier aggregation pushes peaks above 4 Gbps. Real-world user throughput ranges from 500 Mbps to 2 Gbps in line-of-sight conditions, dropping to 100 to 500 Mbps in NLOS environments. Fixed wireless access deployments achieve median speeds of 300 to 700 Mbps at distances up to 300 meters.