Slot Antenna Applications Ppt

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Slot antenna A slot antenna is a radiator made by cutting a one-half wavelength slot in a conducting sheet of metal or into the side or top of a waveguide. – A free PowerPoint PPT presentation (displayed as a Flash slide show) on PowerShow.com - id: 48ea10-NjgzO. SLOT ANTENNAS Tapered slot antennas (TSAs) were first introduced in the late 1950s. It was then that Eberle et al9 produced a waveguide-fed, flared slot antenna for use in aircraft skins where conventional antennas could not be easily integrated. Gibson10 then developed the strip-line-fed, exponentially tapered slot antenna, which he called the. Antenna to that of the field of a dipole antenna. The polarization of a slot antenna is linear. The fields of the slot antenna are almost the same as the dipole antenna, but the field’s components are interchanged: a vertical slot has got an horizontal electric field; and the vertical dipole has got a vertical electrical field. Antenna Design Multi-band slot antenna consists of a rectangular slot with a size of L1×W1 = 48×18 sq.mm on one side of the substrate. The rectangular slot is loaded with an inverted T-shaped stub at the upper edge of the rectangular slot and two E-shaped stubs on the left-hand (LH) and right-hand (RH) sides of the slot 7.

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

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.

Slot Antenna: Radiation Pattern Project Charles Tumbaga San Jose State University Electrical Engineering 172 Microwave Engineering Final Project.

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.

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.

Impedance of the Slot Antenna

The relation between the terminal impedance of slot, Z_s and dipole Z_d is given as:

: η₀ denotes the intrinsic impedance of free space.

Since, η₀ = 376.7

Thus on substituting, we will get

Z_sZ_d = 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

Z_d = 73 + j (42.5) Ω

Then the terminal impedance of slot antenna will be:

On simplifying, we will have

Z_s = 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.

Slot Antenna

Figure 1: The length of a slot determines the resonant frequency, the width of the slit determines the broad bandwidth of the slot radiator.

Figure 1: The length of a slot determines the resonant frequency, the width of the slit determines the broad bandwidth of the slot radiator.

Slot Antenna

Slot radiators orslot antennas are antennas that are used in the frequency range from about 300 MHz to 25 GHz. They are often used in navigation radar usually as an array fed by a waveguide. But also older large phased array antennas used the principle because the slot radiators are a very inexpensive way for frequency scanning arrays. Slot antennas are an about λ/2 elongated slot, cut in a conductive plate (Consider an infinite conducting sheet), and excited in the center. This slot behaves according to Babinet's principle as resonant radiator. Jacques Babinet (1794 - 1872) was a French physicist and mathematician, formulated the theorem that similar diffraction patterns are produced by two complementary screens (Babinet's principle). This principle relates the radiated fields and impedance of an aperture or slot antenna to that of the field of a dipole antenna. The polarization of a slot antenna is linear. The fields of the slot antenna are almost the same as the dipole antenna, but the field’s components are interchanged: a vertical slot has got an horizontal electric field; and the vertical dipole has got a vertical electrical field.

The impedance of the slot antenna (Z_s) is related to the impedance of its complementary dipole antenna (Z_d) by the relation:

Slot Antenna Applications Ppt Presentation

It follows for Z_s = 485 Ω.

The band width of a narrow rectangular slot is equal to that of the related dipole, and is equal to half the bandwidth of a cylindrical dipole with a diameter equal to the slot width. Figure 2 shows slot antennas different from the rectangular shape that increasing the bandwidth of the slot antenna.

Figure 2: Various broadband slot antenna.

Although the theory requires an infinite spread conductive surface, the deviation from the theoretical value is small when the surface is greater than the square of the wavelength. The feeding of the slot antenna can be done with ordinary two-wire line. The impedance is dependent on the feeding point, as in a dipole. The value of 485 Ω applies only to a feeding point at the center. A shift of the feed point from the center to the edge steadily decreases the impedance.

The application of slot antennas can be versatile. They can replace dipoles e.g. if it is required a polarization perpendicular to the longitudinal extension of the radiator. If a dipole is used for feeding of a parabolic antenna to generate a vertically orientated but horizontally polarized fan beam, then this dipole must be orientated horizontally. This would mean that the edge surfaces of the parabolic reflector will not be sufficiently illuminated, but a lot of energy above and below the reflector would be lost. In addition, the length of the dipole is extended in a plane, in which is demanding a point like source of radiation for the focus of the parabolic reflector. If this dipole is replaced by a slot antenna, in this case don't appear these disadvantages.

Slots in waveguides

Figure 3: Various slot arrangements in a waveguide.

Figure 3: Various slot arrangements in a waveguide.

Slot antennas in waveguides provide an economical way of the design of antenna arrays. The position, shape and orientation of the slots will determine how (or if) they radiate. Figure 3 shows a rectangular waveguide with a drawn with red lines snapshot of the schematic current distribution in the waveguide walls. If slots are cut into the walls, so the current flow is affected more or less depending on the location of the slot. If the slots are sufficiently narrow so the slots B and C (Fig. 3) have little influence on the current distribution. These two slots radiate not (or very little). The slots A and D represent barriers to the current flow. Thus, this current flow acts as an excitation system for the slot, this one acts as radiator. Since the wave in the waveguide moves forward, these drawn lines migrate in the direction of propagation. The slot gets one always alternating voltage potential at its slot edges (depending on the frequency in the waveguide). The power that the slot radiates can be altered by moving the slots closer or farther from the edge. The slots A and D (as drawn in Figure 3) have the strongest coupling to the RF energy transported in the waveguide. In order to reduce this coupling, for example the slot A could be moved closer to one of the shorter waveguide walls. Rotating of the slots would have a the same effect (an angle between the orientations of A and B or C and D). The coupling of this rotated slot ist a factor of about sin² of the rotating angle θ.

Slotted Waveguide Antennas

Slot Antenna Applications Ppt Presentations

Figure 4: Basic geometry of a slotted waveguide antenna (The slot radiators are on the wider wall of the rectangular waveguide.)

Slot Antenna Applications Ppt Software

Figure 4: Basic geometry of a slotted waveguide antenna (The slot radiators are on the wider wall of the rectangular waveguide.)

Several slot radiators in a waveguide form a group antenna. The waveguide is used as the transmission line to feed the elements. In order for radiate in the correct phase, all single slots must be cutted in the distance of the wavelength, that is valid for the interior of the waveguide. This wavelength differs from the wavelength in free space and is a function of the wider side a of a rectangular waveguide. Usually this wavelength is calculated for the TE₁₀ mode by:

a = length of the wider side of the rectangular waveguides
λ_h = “guided” wavelength (within the waveguide)
λ = wavelength in free space(2)

Figure 5: Basic geometry of a slotted waveguide antenna with rotated slot antennas on the narrower wall.

Slot Antenna Applications Ppt Templates

Figure 5: Basic geometry of a slotted waveguide antenna with rotated slot antennas on the narrower wall.

The wavelength within the waveguide is longer than in free space. The distance of the slot radiators in the group is set at this wavelength to a value that is slightly larger than the wavelength λ in the free space. The number and the size of the sidelobes is affected so unfavorably. The slots are often attached to the left and right eccentrically (with reduced coupling). If mounted on the narrow side of the waveguide, it may happen that the length for the resonant slot radiator is shorter than the wall. In this case, the slot can be also guided around the corners, it then lies also slightly on the A-side of the waveguide. In practice, these slots are all covered with a thin insulating material (for the protection of the interior) of the waveguide. This material may not be hygroscopic and must be protected from weather conditions.

A single narrow slot radiator can also work on frequencies ±5 … ±10% besides its resonance frequency. For array antennas, this is not possible so easily. Such a group antenna is fixed strongly to a single frequency, which is determined by the spacing of exactly λ_h, and for which the antenna has been optimized. If the frequency is changed, then these distances not correct, the performance of the antenna decreases. The phase difference arising between the antenna elements are added to the whole length of the antenna to values ​​that can no longer be tolerated. This antenna begins to “squint”, that is, the antenna pattern points in a different direction from the optical center axis. This effect can also be exploited to achieve an electronic pivoting of the antenna beam as a function of change of the transmission frequency.