A Guide to Linear Antennas
I had touched on linear antennas slightly in another section of the blog which was on circular polarized antennas. In that section I was comparing the two.
I’m now going to explore linear antennas in more detail as they do still have a place in the FPV hobby. Linear antennas are normally supplied with your usual transmitters and receivers so I’m going to take you through a few different types of antenna and shed a little bit of light on the science behind them…
Known as a rubber duck or whip antenna collectively, are all omni antennas. These are the main antenna types you get with transmitters/receivers.
The omni antenna has a great circular pattern which means you can still get a good signal. However, you won’t be able to stray too far off course due to its shorter range.
Below is a diagram showing the omni pattern of the antenna measured at 3 dbi –
Below is a diagram showing the omni pattern of the antenna measured at 7 dbi –
You will now get what is called a flat disk pattern which means that when you fly higher you will leave the pattern range and no longer receive the intended picture.
An everyday TV antenna.
Yagi are directional antennas with their energy being more focused from them both horizontally and vertically. Because they are neither horizontally or vertically polarized, the polarization actually depends on how they are set up.
With this specific type of antenna they tend to possess a higher gain than say your omni or patch.
Below is a diagram showing the pattern of the antenna measured at 12 dbi –
This antenna has a much narrower field of view, so really must be pointed towards the plane when flying. A quick tip is that you can actually fly to the sides and behind this antenna if you do so wish. Don’t say I don’t tell you anything!
A panel style antenna.
Patch antennas vary dramatically in size yet they are a lot more compact than a Yagi antenna for instance. They come horizontally polarized but if mounted at 90 degrees they then become circular and vertically polarized.
Below is a diagram showing the pattern of the antenna measured at 8 dbi –
The patch is fairly similar to the yagi pattern, both directional but possessing a wider field of view. If you were to point in the general direction of the plane, a decent signal will be received making this great for long distance flying and also an excellent addition for diversity systems. I have a dedicated section on diversity and diversity modules so please take a look.
The Pattern Of Reception:
If you look at the vertical diagram, what it shows you is the pattern of reception if you were to be stood on the floor looking directly at your ground station. You can see the antenna in the middle receives a signal from the front and the back with a good amount of height to its pattern.
Combining the two forces the signal to spread in a doughnut shaped pattern thus leaving gaps above and below its centre.
Gain is not a measure of range and this is often a misconception. The possible reason for this misunderstanding is when the gain value of the antenna increases, so does its working range.
If you get confused with how gain works, this video does explain it in a manner that’s easier to understand:
SWR is used when we install and turn transmitting antennas. When you connect a receiver to an antenna the impeding antenna and feed line would have to match to get the best reception. SWR value can vary due to resonance, received frequency and height above ground.
This depicts how you mount an antenna to match waveforms from transmitter to receiver. Omni sends a linear polarized waveform which transmits the waveforms vertically. This means that the receivers polarization must match to receive a polarized signal.
SMA is the name of the connector which is used to accompany the receiver to the antenna. There are both a male and female SMA found on the antenna itself.
Thanks for reading!