U Slot Antenna
- The double modified U slots planar patch antenna is designed, simulated and fabricated to operate at 2.8 GHz (between 2.794 to 2.846 GHz), at 3.1 GHz (between 3.145 to 3.196 GHz), at 3.6 GHz.
- The U- slot patch antenna is designed for increasing the bandwidth and return loss but gain cannot increase. If array of the U- slot patch antenna is used then the gain can be im- proved. Therefore, the antenna will be better work in the Wi- MAX applications and wireless communication s system.
The first U-Slot antenna was introduced in 1995 by Huynh and Lee 9. Since then, the design has been extensively studied for different applications. U-Slot technique is known to improve the impedance bandwidth by introducing air substrate which increases the overall size of the antenna 10. AbstractA compact quad-band microstrip slot antenna applied to WLAN/WiMAX applications is proposed in this letter. This antenna has a simpler structure than other antennas designed for realizing quad -band characteristics. It is just composed of a microstrip feed line, a substrate, and a ground plane on which some simple slots are etched. Then, to prove the validation of the design, a.
Linearly Polarized Hmsiw U-slot Antenna
A slot antenna consists of a metal surface, usually a flat plate, with one or more holes or slots cut out. When the plate is driven as an antenna by an applied radio frequency current, the slot radiates electromagnetic waves in a way similar to a dipole antenna. The shape and size of the slot, as well as the driving frequency, determine the radiation pattern. Slot antennas are usually used at UHF and microwave frequencies at which wavelengths are small enough that the plate and slot are conveniently small. At these frequencies, the radio waves are often conducted by a waveguide, and the antenna consists of slots in the waveguide; this is called a slotted waveguide antenna. Multiple slots act as a directivearray antenna and can emit a narrow fan-shaped beam of microwaves. They are used in standard laboratory microwave sources used for research, UHF television transmitting antennas, antennas on missiles and aircraft, sector antennas for cellular base stations, and particularly marine radar antennas. A slot antenna's main advantages are its size, design simplicity, and convenient adaptation to mass production using either waveguide or PC board technology.
Structure[edit]
As shown by H. G. Booker in 1946, from Babinet's principle in optics a slot in a metal plate or waveguide has the same radiation pattern as a driven rod antenna whose rod is the same shape as the slot, with the exception that the electric field and magnetic field directions are interchanged; the antenna is a magnetic dipole instead of an electric dipole; the magnetic field is parallel to the long axis of the slot and the electric field is perpendicular. Thus the radiation pattern of a slot can be calculated by the same well-known equations used for rod element antennas like the dipole. The waves are linearly polarized perpendicular to the slot axis. Slots up to a wavelength long have a single main lobe with maximum radiation perpendicular to the surface.
Antennas consisting of multiple parallel slots in a waveguide are widely used array antennas. They have a radiation pattern similar to a corresponding linear array of dipole antennas, with the exception that the slot can only radiate into the space on one side of the waveguide surface, 180° of the surrounding space. There are two widely used types:
- Longitudinal slotted waveguide antenna - The slots' axis is parallel to the axis of the waveguide. This has a radiation pattern similar to a collinear dipole antenna, and is usually mounted vertically. The radiation pattern is almost omnidirectional in the horizontal plane perpendicular to the antenna over the 180° azimuth in front of the slot, but narrow in the vertical plane, with the vertical gain increasing approximately 3 dB with each doubling of the number of slots. The radiation is horizontally polarized. It is used for vertical omnidirectional transmitting antennas for UHF television stations. For broadcasting, a cylindrical or semicircular waveguide is sometimes used with several columns of slots cut in different sides to give an omnidirectional 360° radiation pattern.
- Transverse slotted waveguide antenna - The slots are almost perpendicular to the axis of the waveguide but skewed at a small angle, with alternate slots skewed at opposite angles. This radiates a dipole pattern in the plane perpendicular to the antenna, and a very sharp beam in the plane of the antenna. Its largest use is for microwave marine radar antennas. The antenna is mounted horizontally on a mechanical drive that rotates the antenna about a vertical axis, scanning the antenna's vertical fan-shaped beam 360° around the water surface surrounding the ship out to the horizon with each revolution. The wide vertical spread of the beam ensures that even in bad weather when the ship and the antenna axis is being rocked over a wide angle by waves the radar beam will not miss the surface.
History[edit]
The slot antenna was invented in 1938 by Alan Blumlein, while working for EMI. He invented it in order to produce a practical type of antenna for VHF television broadcasting that would have horizontal polarization, an omnidirectional horizontal radiation pattern and a narrow vertical radiation pattern.[1][2]
Prior to its use in surface search radar, such systems used a parabolic segment reflector, or 'cheese antenna'. The slotted waveguide antenna was the result of collaborative radar research carried on by McGill University and the National Research Council of Canada during World War II.[3] The co-inventors, W.H. Watson and E.W. Guptill of McGill, were granted a United States patent for the device, described as a 'directive antenna for microwaves', in 1951.[4]
U Slot Patch Antenna
Other uses[edit]
In a related application, so-called leaky waveguides are also used in the determination of railcar positions in certain rapid transit applications. They are used primarily to determine the precise position of the train when it is being brought to a halt at a station, so that the doorway positions will align correctly with queuing points on the platform or with a second set of safety doors should such be provided.
See also[edit]
- Microwave Radiometer (Juno) (has a slot array antenna)
- RIMFAX (radar for Mars rover has slot antenna design)
References[edit]
- ^Blumlein, Alan (1938-03-07), 'Improvements in or relating to high frequency electrical conductors or radiators', British patent no. 515684
- ^Burns, Russell (2000). The life and times of A.D. Blumlein. Institution of Engineering and Technology. ISBN0-85296-773-X.
- ^Covington, Arthur E. (1991). 'Some recollections of the radio and electrical engineering division of the National Research Council of Canada, 1946-1977'. Scientia Canadensis: Canadian Journal of the HIstory of Science, Technology and Medicine. 15 (2): 155–175. doi:10.7202/800334ar.
- ^Watson, William Heriot; Guptill, Ernest Wilmot (6 November 1951), Directive Antenna for Microwaves, retrieved 20 December 2016
External links[edit]
U Slot Antenna
- 'Slot Antennas'. Antenna Theory.
- Slotted Waveguide Antennas Antenna-Theory.com
U Slot Patch Antenna Bandwidth
U Slot Antenna Tuner
U Shaped Slot Antenna
| Slot antennas are used typically at frequencies between 300 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. Figure 1. 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. G. Booker in 1946).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: 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. The dual antenna is similar to a dipole antenna. The voltage source is applied at the center of the dipole, so that the voltage source is rotated. Babinet's principle relates these two antennas. The first result states that the impedance of the slot antenna() is related to the impedance of its dual antenna () by the relation: In the above, is the intrinsic impedanceof free space. The second major result of Babinet's/Booker's principle is that the fields of the dual antenna are almost the same as the slot antenna (the fields components are interchanged, and called 'duals'). That is, the fields of the slot antenna (given with a subscript S) are related to the fields of it's complement (given with a subscript C) by: Hence, if we know the fields from one antenna we know the fields of the other antenna. Hence, since it is easy to visualize the fields from a dipole antenna, the fields and impedance from a slot antenna can become intuitive if Babinet's principle is understood. Note that the polarization of the two antennas are reversed. That is, since the dipole antenna on the right in Figure 2 is vertically polarized, the slot antenna on the left will be horizontally polarized. Duality ExampleAs an example, consider a dipole similar to the one shown on the right in Figure 2. Suppose the length of the dipole is 14.4 centimeters and the width is 2 centimeters, and that the impedance at 1 GHz is 65+j15 Ohms. The fields from the dipole antenna are given by:What are the fields from a slot at 1 GHz, with the same dimensions as the dipole? Using Babinet's principle, the impedance can be easily found:The impedance of the slot for this case is much larger, and while the dipole's impedance is inductive (positive imaginary part), the slot's impedance is capacitive (negative imaginary part). The E-fields for the slot can be easily found: We see that the E-fields only contain a phi (azimuth) component; the slot antenna is therefore horizontally polarized. Video: Analysis of the Slot AntennaTo see this material presented another way, here is a video on the analysis of the slot antenna. Some of the information below will be complimentary to the above analysis. Hence, if you enjoy short lectures this video may be of interest to you. |