- Antenna Theory Tutorial
Printed antenna becoming popular for its features like small size, low profile, light weight also wide bandwidth & reduced size is obtained by cutting slot at proper position on patch 1 2. To achieve wide band characteristic for slot antenna with coplanar waveguide (CPW) feed lines. Disadvantages as compared to other conventional antennas. The major disadvantages are. Bandwidth is narrow. Efficiency is low. Less Gain 4. MICROSTRIP PATCH ARRAY ANTENNA Antenna arrays are used to enhance various antenna parameters like bandwidth, directivity, gain, beam width and efficiency. There are a variety of methods to feed the. 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. The following are the advantages of Slot antenna −.
- Antenna Basic Terms
- Types of Antennas
- Antenna Arrays
- Wave Propagation
- Antenna Theory Useful Resources
- Selected Reading
A Collinear array consists of two or more half-wave dipoles, which are placed end to end. These antennas are placed on a common line or axis, being parallel or collinear.
The maximum radiation in these arrays is broad side and perpendicular to the line of array. These arrays are also called as broad cast or Omni-directional arrays.
Frequency range
The frequency range in which the collinear array antennas operate is around 30 MHz to 3GHz which belong to the VHF and UHF bands.
Construction of Array
These collinear arrays are uni-directional antennas having high gain. The main purpose of this array is to increase the power radiated and to provide high directional beam, by avoiding power loss in other directions.
The above images show the pictures of collinear arrays. In figure 1, it is seen that collinear array is formed using folded dipoles, while in figure 2, the collinear array is formed by normal dipoles. Both types are half-wave dipoles used commonly.
Radiation Pattern
The radiation pattern of these collinear arrays is similar to that of a single dipole, but the array pattern of increasing number of dipoles, makes the difference.
The radiation pattern of collinear array when made using two elements, three elements and four elements respectively are shown in the figure given above.
The broad side array also has the same pattern, in which the direction of maximum radiation is perpendicular to the line of antenna.
Advantages
The following are the advantages of collinear array antennas −
- Use of array reduces the broad ends and increases the directivity
- Minor lobes are minimised
- Wastage of power is reduced
Disadvantages
The following are the disadvantages of collinear array antennas −
- Displacement of these antennas is a difficult task
- Used only in outdoor areas
Applications
The following are the applications of collinear array antennas −
- Used for VHF and UHF bands
- Used in two-way communications
- Used also for broadcasting purposes
- Antenna Theory Tutorial
- Antenna Basic Terms
- Types of Antennas
- Antenna Arrays
- Wave Propagation
- Antenna Theory Useful Resources
- Selected Reading
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.
Advantages And Disadvantages Of Television
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
Advantages Disadvantages Of Credit
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.
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
Comments are closed.