Wiki slot antenna
The slot antenna is studied. The basic principles of slot antennas are presented, along with design parameters. The slotted waveguide antenna was the result of collaborative radar research carried on A slotted waveguide has no reflector but emits directly through the slots. A slot antenna is a slot in a flat piece of metal or other conductor. It can be thought of as sort of the complementary version of a dipole.
Another extreme case of impedance matching occurs when using a small loop antenna usually, but not always, for receiving at a relatively low frequency where it appears almost as a pure inductor. When the irregularities of the surface are much smaller than the wavelength, the dominant regime is that of specular reflection , and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. Whether the number of Ohms of resistance at the feedpoint is a good match for the ratio of voltage to current delivered by the feedline is a different, but related issue. But as the antenna height is increased, the reduced power of the reflected wave due to the inverse square law allows the antenna to approach its asymptotic feedpoint impedance given by theory. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio SWR. Therefore, the above relationship between gain and effective area still holds.
Slot antennas are used typically at frequencies between MHz and 24 GHz. The slot antenna is popular because they can be cut out of whatever surface they are to be mounted on, and have radiation patterns that are roughly omnidirectional similar to a linear wire antenna, as we'll see. The polarization of the slot antenna is linear. The slot size, shape and what is behind it the cavity offer design variables that can be used to tune performance. Consider an infinite conducting sheet, with a rectangular slot cut out of dimensions a and b , as shown in Figure 1.
If we can excite some reasonable fields in the slot often called the aperture , we have a slot antenna. Rectangular Slot antenna with dimensions a and b. To gain an intuition about slot antennas, first we'll learn Babinet's principle put into antenna terms by H. This principle relates the radiated fields and impedance of an aperture or slot antenna to that of the field of its dual antenna. The dual of a slot antenna would be if the conductive material and air were interchanged - that is, the slot antenna became a metal slab in space.
An example of dual antennas is shown in Figure 2: Dual antennas - left the slot antenna, right the dipole antenna. Note that a voltage source is applied across the short end of the slot antenna.
This induces an E-field distribution within the slot, and currents that travel around the slot perimeter, both contributed to radiation.
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In radio , an antenna is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.
In reception , an antenna intercepts some of the power of an electromagnetic wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment, and are used in radio broadcasting , broadcast television , two-way radio , communications receivers , radar , cell phones , satellite communications and other devices.
An antenna is an array of conductors elements , electrically connected to the receiver or transmitter. During transmission, the oscillating current applied to the antenna by a transmitter creates an oscillating electric field and magnetic field around the antenna elements.
These time-varying fields radiate energy away from the antenna into space as a moving transverse electromagnetic field wave. Conversely, during reception, the oscillating electric and magnetic fields of an incoming radio wave exert force on the electrons in the antenna elements, causing them to move back and forth, creating oscillating currents in the antenna.
Antennas can be designed to transmit and receive radio waves in all horizontal directions equally omnidirectional antennas , or preferentially in a particular direction directional or high gain antennas. An antenna may include parasitic elements , parabolic reflectors or horns , which serve to direct the radio waves into a beam or other desired radiation pattern. The first antennas were built in by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell.
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