It radiates circularly polarized radio waves. These are used for satellite communication. Axial mode operation was discovered by physicist John D.
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Kraus . If the circumference of the helix is significantly less than a wavelength and its pitch axial distance between successive turns is significantly less than a quarter wavelength, the antenna is called a normal-mode helix. The antenna acts similar to a monopole antenna , with an omnidirectional radiation pattern , radiating equal power in all directions perpendicular to the antenna's axis. However, because of the inductance added by the helical shape, the antenna acts like a inductively loaded monopole; at its resonant frequency it is shorter than a quarter-wavelength long.
Therefore, normal-mode helices can be used as electrically short monopoles, an alternative to center- or base-loaded whip antennas , in applications where a full sized quarter-wave monopole would be too big. As with other electrically short antennas, the gain, and thus the communication range, of the helix will be less than that of a full sized antenna. The loading provided by the helix allows the antenna to be physically shorter than its electrical length of a quarter-wavelength. The reduced size of a helical provides the same radiation pattern in a much more compact physical size with only a slight reduction in signal performance.
Another example of the type as used in mobile communications is "spaced constant turn" in which one or more different linear windings are wound on a single former and spaced so as to provide an efficient balance between capacitance and inductance for the radiating element at a particular resonant frequency. Recently these antennas have been superseded by electronicly tuned antenna matching devices. Most examples were wound with copper wire using a fiberglass rod as a former. The usually flexible or ridged radiator is then covered with a PVC or polyolefin heat-shrink tubing which provides a resilient and rugged waterproof covering for the finished mobile antenna.
This mounting provided a ground plane or reflector provided by the vehicle for an effective vertical radiation pattern. When the helix circumference is near the wavelength of operation, the antenna operates in axial mode.
End-fire Array Vs Broad Side Array
This is a nonresonant traveling wave mode, in which instead of standing waves , the waves of current and voltage travel in one direction, up the helix. Instead of radiating linearly polarized waves normal to the antenna's axis, it radiates a beam of radio waves with circular polarisation along the axis, off the ends of the antenna.
The main lobes of the radiation pattern are along the axis of the helix, off both ends. Since in a directional antenna only radiation in one direction is wanted, the other end of the helix is terminated in a flat metal sheet or screen reflector to reflect the waves forward. In radio transmission , circular polarisation is often used where the relative orientation of the transmitting and receiving antennas cannot be easily controlled, such as in animal tracking and spacecraft communications , or where the polarisation of the signal may change, so end-fire helical antennas are frequently used for these applications.
Since large helices are difficult to build and unwieldy to steer and aim, the design is commonly employed only at higher frequencies, ranging from VHF up to microwave. The helix of the antenna can twist in two possible directions: right-handed or left-handed, the former having the same form as that of a common corkscrew. The 4-helix array in the first illustration uses left-handed helices, while all other illustrations show right-handed helices. WOA1 en. BRB1 pt. BRA pt.
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DEA1 de. CNB zh. GBD0 en. USDS1 en. Combined antenna apertures allowing simultaneous multiple antenna functionality. JPB2 ja. Wireless charging and communications systems with dual-frequency patch antennas.
Extraordinary electromagnetic transmission by antenna arrays and frequency selective surfaces having compound unit cells with dissimilar elements. USA en. Perfeccionamientos introducidos en un aparato de antena paraun receptor de television o similar. GBA en. JPSU ja. JPSA en.
Antenna Theory - End-fire Array
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Orthogonally polarized dual-band printed circuit antenna employing radiating elements capacitively coupled to feedlines. Implementation of multiple apertures through antenna interleaving and splitting. Method and system for measuring the polarized potential of a cathodically protected structures substantially IR drop free.
JPHA ja. Procede de fabrication d'un objet fractal par stereolithographie et objet fractal obtenu par un tel procede. FRB1 fr. Frequency selective surface with repeating pattern of concentric closed conductor paths, and antenna having the surface. Dividable transmit antenna array for a cellular base station and associated method. Polarization diversity phased array cellular base station and associated methods.
ESB1 es. Multiband, phased-array antenna with interleaved tapered-element and waveguide radiators. AUB2 en.
Learn about phased array antennas
Fractal antenna ground counterpoise, ground planes, and loading elements and microstrip patch antennas with fractal structure. USB1 en. SEC2 sv. Method and apparatus for transmitting communication signals using transmission space diversity and frequency diversity. EPA3 en.
DEC2 de. Funkantennen-Anordnung und Patchantenne auf der Fensterscheibe eines Kraftfahrzeuges. KRA ko. FIB fi.
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DET2 de. GBB en. CAA1 en. Multiple parasitic coupling to an outer antenna patch element from inner path elements. Combination cellular telephone radio receiver and recorder mechanism for vehicles. AUA en. EPB1 de. FRA1 fr.
Related CB MOBILE BEAM ANTENNA - End Fired Phased Array Antenna
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