Circular or Linear Polarized Antenna For FPV

Antennas for FPV can be categorized by their polarization: linear and circular. In this article we will discuss the differences between linear and circular polarized antennas.

To learn more about FPV antenna basics and our recommendations. If you are new to FPV, you should read up on this guide for FPV system.

Types of Polarization

Polarization means the way radio signal travels in space. It’s often mentioned in discussion of FPV antennas. In this section we will discuss the differences, pro’s and con’s of Linear and Circular Polarization to FPV system performance.

Linear Polarization

Linear polarized signal oscillates horizontally or vertically in one plane while travelling.

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Linear Polarization is used in some of the most basic antennas, such as the stock dipole antennas that comes with your VTX and VRX, or even in your home WiFi.

 

Pros and Cons of Linear Polarization

Linear polarized antennas are widely used due to its structural simplicity, which can be as simple as a piece of wire. The antennas tend to be smaller, cheaper and easier to build and repair.

In general linear polarization is great for long range as all the energy is focused on a single plane. The range advantage is seldom realized due to multipath interference which we will discuss shortly.

In order to get the best reception, both transmitting and receiving linear polarized antennas have to be aligned to ensure maximum radiation overlap.

The most extreme case is when the transmitter and receiver antennas are 90 degrees to one another, resulting in the least amount of signal overlap. This results in 30dB loss in signal strength and it’s referred to as cross polarization.

Our multirotor is moving constantly in the sky, it’s simply impossible to keep the antennas aligned at all times and therefore resulting in unstable FPV signal.

To solve this problem, we normally use circular polarized antennas.

Circular Polarization

In circular polarization, signal are transmitted on both horizontal and vertical planes with 90 degree phase shift that looks like a spinning corkscrew.

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Here are some of the common circular polarized antennas for FPV.

Skew-Planar Wheel antenna is circularly polarized and has excellent multipath rejection capability. This antenna is used for general purpose flying where aerodynamic drag (e.g. wind) is not a critical factor. While generally regarded as a receiver antenna, it works well as a transmit antenna too.

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The Cloverleaf antenna is more commonly seen on a transmitter. It can be coupled with a Skew Planar wheel for better range and signal penetration.

Pros and Cons of Circular Polarization

Circular polarized signal always overlap no matter what orientation or angle your mini quad is flying at relative to your receiving antenna. For this reason circular polarized antennas have become the standard in FPV flying.

Another advantage of circular polarized antennas is their ability to reject multipath interference.

Multipath interference is the most common reason for bad video quality, in the form of random color change, static, scrambled image and drop-outs. It happens when the signal is reflected from object and gets distorted with phase delay, and it interferes with the main signal.

VideoCrypt-signal

Circular polarized antennas are either left-hand (LHCP) or right-hand (RHCP). Transmitter and receiver need to have matching antennas otherwise it could result in significant signal loss.

CP antennas can benefit from this property against multipathing. Every time a CP signal bounces off object it changes its polarization direction. And LHCP antenna rejects RHCP signal and vice versa (cross polarization).

When to use circular polarization

  • When flying close to large objects such as trees, buildings, or in enclosed environment such as car parks and stadiums
  • Acrobatic flying where the aircraft orientation and angle are constantly changing
  • Low altitude flying (proximity flying)

When to use linear polarization

  • Long distance flying in the open without any obstacles
  • Stable flying without too much roll or pitch
  • When antenna size, weight and durability are the most important consideration

Edit History

  • Oct 2013 – article created
  • May 2017 – article revised

17 thoughts on “Circular or Linear Polarized Antenna For FPV

  1. Yoann

    In my experiences (without scientist facts), I’ve better reception with linear (simple wire) than with circular, specially in indoors conditions. Not having any range consideration but only glitches consideration

    Reply
    1. Oscar Post author

      There are a lot of variables in this, such as the quality of the CP antenna you are comparing to, tuned frequency, the power of your VTX etc…

      Reply
  2. shazzner

    One question, I’ve been very curious about and maybe you could write a blog piece about is how to handle multiple transmitters on a single aircraft. I’m talking about a Video Transmitter (possibly even two), MavLink, perhaps Wi-Fi or Mobile. All I’ve seen so far is ‘keep them away as far as possible’ to prevent interference but this doesn’t seem the best guideline for something as relatively small as a drone. I’ve seen techniques such as beamforming, but I believe that only applies for signals all on the same frequency. Just curious on your thoughts!

    Reply
  3. Jim eastep

    Oscar:
    Your explanations and diagrams are the BEST!
    My question is regarding the facts, not hype on patch/planar antennas. I am seeing some providers claim they have patch antennas that are designed for circularly polarized signals, presumably from clover leaf or skew planar transmitter antennas.
    Could you discuss and explain how a patch antenna would/could be adapted to circularly polarized signals and confirm/refute my belief that patch antennas have historically worked best with linearly polarized signals?
    Thanks!
    Jim

    Reply
  4. Steven G

    Hi Oscar, I’m trying to improve the wifi link and rc link on my Q500 quad. The system I have is a Itelite DBS Phantom linear polarized antenna on my tx for both 2.4ghz and 5.8ghz, And on my quad I have externally mounted a RHCP cloverleaf for the 2.4ghz side and a skew planer RHCP for the 5.8ghz side. Is this setup totally wrong and if so what could I do to improve it ? I’m thinking that I have a mismatched antenna system. Thank you in advance. Steven

    Reply
  5. Kelvin

    Hi Oscar
    I am a physics graduate and I’d like to point out:
    A cloverleaf (or a skew antenna) DOES NOT transmit circularly polarized waves! It only transmits mixed polarity signals (ie Horizontally + vertically polarized). Just like radio waves from your local radio stations.
    it’s a common mistake. The term “circularly polarization” is often erroneously used to describe mixed polarity signals.

    (To transmit circularly-polarized radio waves, you’ll need something like a helical antenna or something else clever. )
    While a cloverleaf minimizes loss of signal, I doubt it maximizes range – as long as you are comparing it to a linear antenna with the same size.

    Reply
    1. Oscar Post author

      Hi Kelvin, thanks for the info, i will look into this in more detail and come back to this :)
      regards Oscar

      Reply
  6. Francis

    Can a skew planar antenna be used with a radio transmitter (Dx7, Taranis, etc.)? Will it increase the range of the radio link?

    Reply
    1. Oscar Post author

      i don’t see why not! but most people never have any problem with weak radio link so it’s not very common i guess :)

      Reply
  7. Keith

    Can’t find info I need on the net anywhere.
    Please can some one help.

    Fpv, circular polarised antennas.
    Do right circular transmitter polarised antennas work with right or left polarised receive antennas?

    That’s it. But hard to find the answer as I have found out.
    Thanks in advance for any help you can give me.
    Keith.

    Reply
  8. Alex

    Thanks for the article but I have a question. What happens if you mix circular cloverleaf antenna on the transmitter with linear polarized on the receiver?

    Reply

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