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Telecom Business Review | Thursday, July 03, 2025
FREMONT, CA: Antennas are the methods for coupling the transmitter to the medium, if so, free space.
An antenna is an electromagnetic radiator; it produces an electromagnetic field that proceeds from the transmitting antenna to the receiver’s antenna, which converts the electromagnetic wave into electrical signals applied to the receiver’s input stages.
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There are numerous antennas in three broad categories: Omni-directional, directional, and semi-directional.
– Omni-directional antennas broadcast in all directions.
– Semi-directional antennas distribute in a constricted fashion, characterized by a precise angle.
– Directional antennas have a contract “beam” that enables highly directional propagation; familiar types are the parabolic and Yagi. Each has special characteristics and applications.
Passive gain amplifies the signal: All antennas show a passive gain, which serves to amplify the signal. The quantity dBi measures passive gain, the gain mentioned in a theoretical isotropic antenna; an isotropic antenna sends energy equally in all directions and does not exist in nature. For example, the gain of an ideal half-wave dipole antenna is 2.15 dBi. It should also be considered that as directionality increases, so does gain.
EIRP, or equivalent (or efficient) isotropic radiated power, measures the maximum power a theoretical isotropic antenna would discharge in the direction of the greatest antenna gain. In addition to incorporating actual antenna gains, EIRP accounts for transmission line and connector losses. EIRP allows the calculation of real power output and field strength values if actual antenna gain and transmitter output power are known.
Dipole antennas, rubber ducky: Dipole antennas are the most general type of antenna used and are Omnidirectional, radiating RF energy 360 degrees horizontally. These devices are built to be deep at a half or quarter wavelength of the frequency applied. This antenna can be as plain as two pieces of wire cut to the proper length or can be encapsulated, as displayed in the illustration; this configuration is generally referred to as a “rubber ducky” antenna. The dipole is used in many enterprises, small, and home office (SOHO) Wi-Fi deployments.
An antenna exhibits a typical impedance, matching the antenna to the transmitter for utmost power transfer. If the antenna and transmitter are mismatched, reflections on the transmission line will degrade the signal or even damage the transmitter.
These reflections are explained by the term standing wave ratio (SWR) and suggest the efficiency of the transmission line. For example, an SWR of 1:1 would indicate that no power is reflected and lost; 5:1 would suggest a reflection and loss of 44%. SWR is often used as a voltage ratio and is referred to as VSWR.
Directional antenna: Directional and semi-directional antennas concentrate radiated power into narrow beams, adding significant gain in the process. Antenna properties are also reciprocal. The characteristics of a transmitting antenna, like impedance and gain, are also relevant to a receiving antenna. Therefore the same antenna can be used for sending and receiving. The gain of a greatly directional parabolic antenna serves to magnify a weak signal; this is a cause this type of antenna is regularly used for long-distance links.
Patch antenna, microstrip antenna: A patch antenna is a semi-directional radiator utilizing a flat metal strip climbed above a ground plane. Radiation from the backside of the antenna is efficiently cut off by the ground plane, enhancing forward directionality. This type of antenna is also called a microstrip antenna. It is generally rectangular and enclosed in a plastic enclosure. Standard printed circuit board methods manufacture this type of antenna. Patch antennas are broadly used semi-directionals; a patch antenna can have a beamwidth of between 30 to 180 degrees and a regular gain of 9 dB.
Sector antenna: Sector antennas are also a type of semi-directional antenna. Sector antennas give a pie-shaped (sector) radiation pattern and are usually installed in a sectorized array. Sector antenna Beamwidth can be between 60 to 180 degrees, with 120 degrees normal. In a sectorized array, antennas are fitted back-to-back to give full 360-degree coverage. Sector antennas are employed extensively for cellular communication.
Yagi antenna: A Yagi antenna utilizes several elements to form a directional array. A single-driven element, usually a dipole, propagates RF energy; elements located immediately in front of and behind the motivating element re-radiate RF energy in and out of phase, enhancing and retarding the signal. The elements are termed parasitic elements; the element behind the driven element has named the reflector, while the elements in front of the impelled element are called directors. Yagi antennas have 30 to 80 degrees beam widths and can provide more than ten dBi passive gain.
Parabolic or dish antenna: Parabolic, or dish, antennas are the most common type of directional antenna. Parabola is a symmetrical curve; a parabolic reflector is a surface that explains the curve throughout a 360-degree rotation—a dish or, to utilize the technical term, a paraboloid. A parabolic reflector has a great degree of directivity and can focus RF energy into a beam, much like a flashlight.
Parabolic antennas have a very narrow beamwidth, generally not exceeding 25 degrees. The gain depends on diameter and frequency; at 2.4 GHz, a 1-meter dish will provide about 26 dBi gain, while a 10-meter antenna will provide 46 dBi gain at the same frequency. The antenna is “fed” by either a half-wave dipole antenna or a feed horn. Parabolic antennas are used for long-distance links between buildings or large geographic areas. Very large parabolic antennas are utilized for radio astronomy and can provide a gain of 10 million or about 70 dBi.
Grid antenna: A difference in the dish is the grid antenna. Since a parabolic reflector will present a huge solid surface to the wind, high or moderate wind conditions will reason the dish to move out of alignment or deform. To avoid this, the reflector is perforated into a grid. The spacing of the grid elements is frequency-dependent; it is inversely proportional to the frequency. As a result, gain and beamwidth are likely for the parabolic antenna.
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