Polarization in Fixed Wireless Access:
H/V or ±45° X-pol?
Choosing FWA polarization: how horizontal/vertical (H/V) and cross-polarized (±45°) antennas between a 5G/4G FWA modem and the base station affect MIMO rank, branch balance, uplink and beamforming.
Two structures, the same physics
Both H/V and ±45° X-pol antennas provide two polarization branches perpendicular (orthogonal) to each other. The signals of the two branches are decorrelated, which allows two independent layers to be carried in MIMO.
The difference is the orientation of the branches relative to the ground and the environment. In H/V, one branch is parallel to the ground and the other is perpendicular. In ±45°, both branches are tilted 45° to the ground and each carries equal vertical and horizontal components (cos²45° = 0.5).
Rotating an X-pol antenna by 45° turns it into an H/V antenna. The FWA polarization choice is therefore not about the antenna's internal design but about how the channel affects the polarizations.
FWA polarization: H/V vs. ±45° X-pol at a glance
| Criterion | H/V (0° / 90°) | X-pol (±45°) |
|---|---|---|
| V/H component in each branch | Pure V or pure H | Equal V and H (50% / 50%) |
| Power balance between branches (NLOS) | Unbalanced, H branch usually weak | Balanced |
| Match with cellular base stations | Usable, risk of rank loss in NLOS | Natural match (gNB/eNB use ±45°) |
| Uplink 2 Tx and SRS | Weak H Tx branch, degraded SRS estimation | Two balanced Tx branches |
| LOS performance | Equivalent | Equivalent |
| XPD in rain (high frequency) | ≈15 dB better | Worse |
| Typical use | Point-to-point microwave backhaul (CCDP + XPIC), mmWave modules | Cellular FWA CPE, external 4G/5G MIMO antennas, Wi-Fi |
Ground reflection: why does the H branch stay weak?
- Horizontal polarization: At grazing angles the reflection coefficient is Γ ≈ −1. The reflected wave combines with the direct wave in opposite phase, and at low mounting heights the H component is partially cancelled.
- Vertical polarization: Around the Brewster angle the reflection weakens, so the V component is less affected by this fading.
- Urban NLOS: Scattering mixes the polarizations, but the channel stays V-dominant. The cross-polarization discrimination (XPD) is typically around 5–10 dB.
- Result: On an H/V CPE, the H port stays systematically weak. On a ±45° CPE, each port receives a mix of V and H, so both branches see the same losses.
CPE branch balance: LOS and NLOS
Relative signal levels seen at the CPE ports while the base station transmits at ±45°. As the difference between branches (Δ) grows, rank-2 SINR falls and the link drops to a lower MCS or to rank 1.
H/V CPE
±45° X-pol CPE
Does polarization mismatch reduce capacity?
Between a ±45° base station and an H/V CPE, the LOS channel is approximately equal to the matrix below. This matrix is orthogonal: rank and condition number are preserved. In other words, a 45° rotation alone does not reduce MIMO capacity.
±45° gNB ↔ ±45° CPE
Balanced branches in LOS and NLOS, rank 2 most often (rank 3–4 with 4×4), balanced uplink.
±45° gNB ↔ H/V CPE
No loss in LOS. In NLOS, as the H branch weakens, rank tends to drop and the uplink becomes unbalanced.
±45° gNB ↔ single polarization
PLF = −3 dB from each BTS port. MRC recovers the total power, but the multiplexing gain is lost: rank 1 only.
Comparison in 5G applications
The logic is the same as in LTE, but because 5G relies more on layer count and beamforming, the impact of the FWA polarization choice grows. In FR1, Massive MIMO AAUs (32T32R, 64T64R) are arrays of ±45° dual-polarized elements: the array shapes the beam, and polarization provides two independent layers per beam. The 3GPP channel model (TR 38.901) also models the base station antenna as ±45° slant.
| FR1 FWA CPE (n78 etc.) | ±45° X-pol | H/V |
|---|---|---|
| LOS / short range | Equal | Equal |
| NLOS (urban FWA) | Branch balance preserved, rank 3–4 more often | Weak H branches, rank tends to drop |
| 4×4 DL | Natural structure with 2 X-pol elements | Lower rank in NLOS |
| UL MIMO (2 Tx) | Two balanced Tx branches | Weak H Tx branch, UL rank 2 harder |
| TDD reciprocity (SRS beamforming) | Balanced SRS, accurate channel estimation | Low SRS SNR on the weak branch, lower beamforming quality |
The uplink also determines the downlink
In TDD 5G, the gNB estimates the downlink beam from the SRS sent by the CPE. The CPE's uplink branch balance therefore directly affects downlink throughput. This is an extra advantage for ±45° compared with LTE.
The standard structure for 4×4 FWA is two ±45° X-pol elements, which provides polarization and spatial diversity together.
FR2 (mmWave)
- Beam-based and mostly LOS; polarization provides 2 layers per beam.
- mmWave modules usually use H/V dual-polarized patch arrays.
- The difference is smaller than in FR1; beam alignment and blockage are the main factors.
Why H/V in backhaul?
Fixed, LOS and aligned microwave links have no imbalance problem. The two polarizations carry independent data on the same channel (CCDP), and with XPIC the capacity roughly doubles.
Rain depolarization: Flattened raindrops are aligned along the horizontal axis, so H and V polarizations are the drop's eigenpolarizations. With ±45° (and circular) polarization, differential attenuation and phase shift turn into cross-polarization.
The polarization tilt term in ITU-R P.618: Cτ = −10·log[1 − 0.484·(1 + cos4τ)]. For τ = 0° or 90° it is ≈ +15 dB, for τ = 45° it is 0 dB. This difference becomes decisive on links above 10 GHz.
FWA polarization: practical ranking for CPE
±45° X-pol, mounted vertically, pointed at the base station
Natural match with the cellular network; balanced branches in NLOS, the highest rank and a balanced uplink. Example: Poynting XPOL-1-5G+. Application example: antenna for Turkcell Superbox 5G.
H/V dual polarization
Equivalent in LOS; in NLOS the H branch weakens, so rank and uplink performance may drop.
Single polarization (vertical)
The MIMO multiplexing gain is lost; the link runs at rank 1 only.
Port-to-port isolation
Low coupling between the two polarization ports.
XPD
Check the drop at the sector edge (±60°) as well as the boresight value.
Branch gain matching
The patterns and gains of the two branches should be close to each other.
Cable length and loss
Cable imbalance spoils the branch balance the antenna provides.
Frequently asked questions
Which FWA polarization is more efficient for a modem?
Does an H/V antenna work with a ±45° base station?
Why is a single-polarized external antenna not recommended?
Why is H/V preferred on point-to-point links?
Which antenna should be used with 5G FWA modems such as the Superbox?
How should I mount an X-pol antenna?
Let's choose the right antenna for your FWA project together
Talk to the BağLAN technical team about X-pol antenna and cable selection based on your location, distance to the base station and modem model.