Slot Antenna Applications Ppt
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Should we find a new no deposit bonus, we will immediately put it on the Slot Antenna Applications Ppt list. (last update 6th May 2020). (last update 6th May 2020). + Read Slot Antenna Applications Ppt More. 3.0 – January 21 2010 Application note Document information Info Content Keywords UCODE EPC G2, G2XM, G2XL, Reference Design, Antenna Design, PCB Abstract This application note provides basic antenna knowledge, which is important for PCB antenna design. It contains as well a reference design based on a slot antenna. These slot antennas can be formed by simply making a cut on the surface, where they are mounted on. Frequency Range. The frequency range used for the application of Slot antenna is 300 MHz to 30 GHz. It works in UHF and SHF frequency ranges. Construction & Working of Slot Antennas. The use of slot antennas is well understood through its working.
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Slot Antenna is an example of Aperture antenna. A rectangular slot is made on the conducting sheet. These slot antennas can be formed by simply making a cut on the surface, where they are mounted on.
Frequency Range
The frequency range used for the application of Slot antenna is 300 MHz to 30 GHz. It works in UHF and SHF frequency ranges.
Construction & Working of Slot Antennas
The use of slot antennas is well understood through its working principle. Let us have a look at the structure of a slot antenna.
When an infinite conducting sheet is made a rectangular cut and the fields are excited in the aperture (which is called as a slot), it is termed as Slot antenna. This can be understood by observing the image of a slot antenna. The following image shows the model of a Slot antenna.
The working of Slot Antenna can be easily understood through Babinet’s principle of optics. This concept gives an introduction to the slot antennas.
Babinet’s Principle
Babinet’s principle states that- “When the field behind a screen with an opening is added to the field of a complementary structure, the sum is equal to the field when there is no screen”.
The above images clearly explain the principle. In all the regions, which are non-collinear with the beam, the above two screens, in figures 1 & 2, produce the same diffraction pattern.
Case 1 − Consider a light source and a conducting plane (field) with an aperture before a screen. The light does not pass through the opaque area, but passes through the aperture.
Case 2 − Consider the light source and a conducting plane of the size of the aperture in the previous case, being held against the screen. The light does not pass through the plane but through the remaining portion.
Case 3 − Combine these two conducting planes of both the cases and put before the light source. The screen is not placed to observe the resultant combination. The effect of screen gets nullified.
Working of Slot Antenna
This principle of optics is applied to electromagnetic waves for the wave to get radiated. It is true that when a HF field exists across a narrow slot in a conducting plane, the energy is radiated.
The image shows a slot antenna, which explains well about its working.
Consider an infinite plane conducting screen is taken and pierced with apertures of desired shape and size and this will be the screen of slot antenna. Another screen is considered interchanging the places of aperture and screen area which is the complementary screen.
These two screens are said to be complementary as they result in complete infinte metal screen. Now, this becomes the slot antenna. The terminal impedance is quite desirable for the radiation.
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Radiation Pattern
The radiation pattern of the Slot antenna is Omni-directional, just like a half-wave dipole antenna. Take a look at the following illustration. It shows the radiation pattern of Slot antenna drawn in Horizontal and Vertical planes respectively
Advantages
The following are the advantages of Slot antenna −
- It can be fabricated and concealed within metallic objects
- It can provide covert communications with a small transmitter
Disadvantages
The following are the disadvantages of Slot antenna −
- Higher cross-polarization levels
- Lower radiation efficiency
Applications
The following are the applications of Slot antenna −
- Usually for radar navigational purposes
- Used as an array fed by a wave guide
Definition: A type of antenna with an opening cut of certain dimensions in a metallic conductor which is excited using a two-wire transmission line or coaxial cable is known as a slot antenna. These antennas operate in the frequency ranging between 300 MHz to 30 GHz.
It is generally formed by making an elongated slot cut of about λ/2 length and width very less than λ/2 in a metallic conductive sheet. The excitation to the slot is provided at the centre or off the centre.
A horizontal slot antenna provides a vertically polarized signal. While a vertical slot antenna gives the horizontally polarized signal.
Operating principle
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Slot antennas operate on the principle that whenever a high-frequency field is present across the slot in a metallic sheet, then energy is radiated.
This is the reason when a slot is cut from the surface of the conductive plate then on energizing the slot, the electromagnetic wave is radiated thus acts as an antenna. Due to the presence of a slot, it is named as a slot antenna.
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Thus we can say a conductive surface with a slot of particular dimensions is referred as a slot antenna.
Working of Slot Antenna
Suppose we have a rectangular conductive sheet over which a horizontal slot is cut having length λ/2 and the breadth extremely less than λ/2, let it be ω.
This half wavelength slot resembles a half-wave dipole according to radiation and gain. However, the slot antenna and half-wave dipole antenna show variation according to the polarization.
The slot antenna follows Babinet’s principle.
Babinet proposed that two complementary screens generate a similar diffraction pattern. This is known as Babinet’s principle. According to this principle, the structure of the slot antenna and the half-wave dipole structure cut out from the conducting sheet are complementary to each other.
So, the region which is cut from the conducting sheet is the half-wave dipole that acts as the slot’s complementary antenna, known as a complementary dipole antenna.
This basically shows the relatability of the radiated field and impedance of the slot to the radiated field of the dipole.
The figure below represents the slot and complementary dipole antenna:
Here the external feed which is used as the excitation is provided at the center of the slot using the two-wire transmission line.
The impedance of the slot antenna relies on the feed point position. As impedance shows reduction with the shift of feed point towards the edge from the centre.
It is noteworthy here that the radiation pattern of the slot and the dipole are similar to each other. However, the electric field will be vertically polarized for the slot while horizontally polarized for the dipole.
Annular Slot Antenna
Till now we have discussed slot antenna having a rectangular slot. But it is not necessary to have a rectangular slot only, as the slot in the conducting sheet can be made in any convenient shape.
Annular slots are the slots of circular shapes that are present on the metallic sheet. The ease of construction and analysis highly facilitates making rectangular or circular slots.
A narrow beam of radiation is produced by the annular slot antenna.
Slotted Waveguide Antenna
In slotted waveguide antenna multiple slots are present in a waveguide forming a group of antennas.
The separation between each slot is such that there exists half guide wavelength distance between center of each adjacent slot. These slots are cut on the two sides of the waveguide which is separated by the central line.
It is noteworthy here that the guide wavelength is greater than the free-space wavelength.
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Impedance of the Slot Antenna
The relation between the terminal impedance of slot, Zs and dipole Zd is given as:
: η0 denotes the intrinsic impedance of free space.
Since, η0 = 376.7
Thus on substituting, we will get
ZsZd = 35475.7225
Hence,
Therefore, we can determine the properties of the complementary slot antenna if the properties of the dipole antenna are known.
For a half-wave dipole antenna
Zd = 73 + j (42.5) Ω
Then the terminal impedance of slot antenna will be:
On simplifying, we will have
Zs = 363 – j (211) Ω
Applications of Slot Antenna
Arrays of slot antenna find applications in aircraft. As the metallic surface of the aircraft allows the formation of the slot directly on it. These are also used in mobile radar systems.