Understanding Polarisation – Why It Matters for Your Antennas

When we talk about antennas, we often focus on things like frequency, length, height. But there’s another aspect that plays a critical role in how signals are transmitted and received: polarisation.

What Is Polarisation?

Polarisation describes the orientation of the electric field (E-field) in a radio wave. Most radio waves are linearly polarised, which means the E-field stays in a fixed orientation—either vertical or horizontal—as the wave moves through space.

But there’s also circular polarisation, where the E-field rotates in a corkscrew-like fashion, either clockwise (right-hand) or counterclockwise (left-hand). This type is mainly used at VHF, UHF, and higher frequencies—especially for satellite, space, and aviation communication, for both receive and transmit. In HF, circular polarisation is also being used for NVIS receive applications.

Linear vs Circular

  • Linear polarisation is simple and efficient for most HF (high-frequency) applications. A vertical dipole produces vertically polarised waves; a horizontal dipole radiates horizontally.
  • Circular polarisation is more complex but helps overcome orientation mismatches—useful when the antenna orientation isn’t fixed (e.g., satellites).

Why Does Polarisation Matter?

  • Matching: If your antenna is vertically polarised and the receiving antenna is horizontal, much of your signal will be lost—this is called polarisation mismatch. This matters most in line-of-sight (LOS) communication—like local VHF/UHF or groundwave HF—where the wave’s polarisation stays constant. But for skywave propagation in HF, the signal often gets rotated or distorted when passing through the ionosphere, especially due to Faraday rotation. That makes polarisation mismatch harder to predict—and usually less of a concern—particularly on the receiving end.
  • QSB (Fading): On HF, signals often take multiple paths to reach you—some get reflected, some refracted, and their polarisation may rotate. This causes fading and phase cancellation, a phenomenon known as QSB.
  • Diversity: Some high-end receivers use two antennas with different polarisations to reduce QSB and improve signal clarity. This is called polarisation diversity.
  • NVIS vs DX:
    • NVIS (Near Vertical Incidence Skywave) signals are reflected almost straight down from the ionosphere. They often benefit from horizontal polarisation, especially in the 80–40m range.
    • DX signals (long-distance) can rotate their polarisation as they travel, making the receive polarisation harder to predict.

TX vs RX – Should You Care?

For transmitting on HF, use a linearly polarised antenna (vertical or horizontal), matched to your intended purpose. You’ll lose less energy and achieve better coverage.

For receiving, it gets tricky:

  • In local line-of-sight, matching polarisation is still critical.
  • In long-range HF, signals may arrive with a different polarisation than they left. This is due to Faraday rotation, multipath, and mode changes in the ionosphere.

So for receive antennas, it sometimes pays to be flexible—or to use diversity reception. Some setups even employ circular polarisation for reception, particularly in NVIS systems, to cope with unpredictable rotation and maximise signal consistency across changing propagation conditions.

Still So Much to Discover

There’s a lot of research—both military and civilian—going into polarisation effects in NVIS communication. For other HF bands, there’s still plenty of room to explore how polarisation interacts with terrain, weather, and propagation modes.

We’ll cover more on that in upcoming articles on HF propagation.

Polarisation is the direction of the electric field in a radio wave. It affects how well antennas match and how signals behave during transmission and reception. On HF, it matters—but sometimes you can’t control it, especially on receive. So it’s good to understand, even if you can’t always predict it.

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.