# Yagi antenna radiating with respect to original signal

• SleepDeprived
In summary, the Yagi antenna radiates the original signal with less interference than other antennas.
SleepDeprived
I have a question regarding how a Yagi type antenna radiating its energy with respect to faithfully replicating the original signal. So let's say you have a FM modulating signal, F(x(t)) whereas x(t) is the data, and F(t) is the carrier, so basically x(t) would FM modulate the carrier F(x). The Yagi antenna (or any type antenna) needs to faithfully radiate the original signal F(x(t)) as much as possible. I include a pic of a Yagi below for reference.
The reason I have a question on the Yagi because it has a rather unique way of radiating. As you can see in the pic, the signal is fed to the 2nd element, the main element (where the wire is connected), whereas the first element is used to reflect the main signal which will combine with the main element to form an incident wave front. How the signal reflected by the first element depends on how far way it is from the main element in term of the carrier wave length. The rest of the elements are used further to direct the radiating pattern depends on the application.
Since the signal that is radiated by the main element (2nd element) is interfered by the reflected element (1st element), the final radiated signal is not the same as the original intended signal. For example, if you have the reflected element a quarter wave from the main element, if you send in a pure sinewave to the main element, the final signal would be the original sinewave plus the quarter wave delay of itself. So if the original signal is : F(x(t)), then the final radiating signal would be the summation: F(x(t)) + F(x(t) - q) where q is the quarter wave delay.
My guess is since the carrier frequency is much higher than the baseband data frequency, this won't be an issue in term of demodulate the signal to obtain the baseband data.

SleepDeprived said:
I have a question regarding how a Yagi type antenna radiating its energy with respect to faithfully replicating the original signal. So let's say you have a FM modulating signal, F(x(t)) whereas x(t) is the data, and F(t) is the carrier, so basically x(t) would FM modulate the carrier F(x). The Yagi antenna (or any type antenna) needs to faithfully radiate the original signal F(x(t)) as much as possible. I include a pic of a Yagi below for reference.
The reason I have a question on the Yagi because it has a rather unique way of radiating. As you can see in the pic, the signal is fed to the 2nd element, the main element (where the wire is connected), whereas the first element is used to reflect the main signal which will combine with the main element to form an incident wave front. How the signal reflected by the first element depends on how far way it is from the main element in term of the carrier wave length. The rest of the elements are used further to direct the radiating pattern depends on the application.
Since the signal that is radiated by the main element (2nd element) is interfered by the reflected element (1st element), the final radiated signal is not the same as the original intended signal. For example, if you have the reflected element a quarter wave from the main element, if you send in a pure sinewave to the main element, the final signal would be the original sinewave plus the quarter wave delay of itself. So if the original signal is : F(x(t)), then the final radiating signal would be the summation: F(x(t)) + F(x(t) - q) where q is the quarter wave delay.
My guess is since the carrier frequency is much higher than the baseband data frequency, this won't be an issue in term of demodulate the signal to obtain the baseband data.

Yes I agree with your conclusion. In addition, you will notice that the Yagi cannot operate over wide bandwidths because of the need to retain correct spacing/phasing between elements. In addition, the antenna relies on de-tuning elements to obtain currents in the elements having the desired phase, and these phase shifts change rapidly with frequency. As the antenna cannot operate over wide bandwidths, the base band width is naturally limited.

SleepDeprived said:
My guess is since the carrier frequency is much higher than the baseband data frequency, this won't be an issue in term of demodulate the signal to obtain the baseband data.
That is correct.

For an unmodulated carrier the radiated signal remains a sinewave. That is because the “Fourier shift theorem” takes care of the summation of all the phase shifted diverse paths.

An FM modulated signal can have a very wide bandwidth with a great number of sidebands.
See; https://en.wikipedia.org/wiki/Frequency_modulation#Bessel_functions

A limited bandwidth transmitter output stage, or the antenna tuning, will remove many outer sidebands, which luckily contained only duplicated information. The lost sidebands do not represent a loss of information as the information is still contained in the zero crossings of the band limited signal. Carson's bandwidth rule is used to determine the bandwidth needed to maximise energy transfer.
See; https://en.wikipedia.org/wiki/Carson_bandwidth_rule

davenn and nsaspook
I think there is a general principle that this effect will happen with any antenna that is not of zero size. There will be a difference in the phases of all frequency components of the signal when you look from any random direction at a physically large antenna system. Even for a broadside array of cophased dipoles, the phase difference of the signals from all elements will only be zero in the far field (@∞). Every antenna's bandwidth can be limited by this effect amongst several others. At least, with a Yagi, the re radiated signals from the forward parasitics are almost in phase with the net signal that's traveling in the main beam direction. (which is what makes it directive in the first place.)
For a large antenna, this dispersive effect can be very relevant and for multipath propagation, in which the local gasworks behaves as part of the antenna, the frequency response of the received signals can be seriously bad - and that's for delays less than those needed to form ghost images. (Only familiar to those of us who have watched significant analogue TV )

## 1. What is a Yagi antenna?

A Yagi antenna is a type of directional antenna commonly used in radio communication and broadcasting. It is a highly efficient antenna that consists of a driven element (a dipole) and several parasitic elements (usually metal rods) arranged in a specific pattern to create a directional beam of radio waves.

## 2. How does a Yagi antenna radiate with respect to the original signal?

The Yagi antenna radiates by producing a stronger signal in a specific direction, while minimizing radiation in other directions. This is achieved by the parasitic elements interacting with the electromagnetic field generated by the driven element. The result is a higher gain (signal strength) in one direction and a lower gain in other directions.

## 3. What are the advantages of using a Yagi antenna?

One of the main advantages of a Yagi antenna is its high gain and directionality, which allows for long-distance communication. It also has a narrow bandwidth, which reduces interference from other signals. Additionally, Yagi antennas are relatively easy to construct and can be made with inexpensive materials.

## 4. Are there any limitations to using a Yagi antenna?

While Yagi antennas have many advantages, they also have some limitations. They are highly directional, which means they must be pointed towards the desired signal source for optimal performance. They also have a narrow bandwidth, which makes them less suitable for wide frequency ranges or changing signal sources.

## 5. What factors should be considered when choosing a Yagi antenna?

When choosing a Yagi antenna, it is important to consider the frequency range you need, the gain and directionality required, and the physical size and construction of the antenna. Other factors to consider include the environment in which the antenna will be used, such as potential obstructions or interference, and the cost and availability of the antenna.

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