Radios consist of transmitters that send out signals, as well as receivers that take in these signals to recover information. An antenna plays an integral part in both devices.
An antenna uses metallic conductors to convert alternating electric currents into electromagnetic waves that carry signals over long distances.
Polarisation and impedance both play an integral part in an antenna’s effectiveness, so possessing some knowledge about antenna theory is valuable for its proper functioning.
Antennas and Accessories
Radio waves carry information encoded through electron oscillation within atoms, while two-way antennas receive these electromagnetic (EM) waves and convert them to electric current that can then be amplified to transmit data, audio or video signals – making these an indispensable communication method between public safety personnel, commercial companies, military forces and each other.
Electromagnetic waves typically travel along straight paths; when they encounter objects they may be reflected off in different directions depending on their shape or characteristics. This allows us to focus radio transmissions in particular directions and increase antenna range with ease. There is a wide variety of antennas designed specifically to tackle different applications; most fall into either transmitting or receiving categories but some even do both!
Antennas can be designed either omni-directionally, reflecting radio frequency (RF) energy evenly in all directions, or with specific radiation patterns that allow specific radio transmission patterns to penetrate buildings or structures that would otherwise block transmission of their signal. An omnidirectional antenna will reflect energy from all directions equally while an antenna with focused patterns may help extend a radio’s transmission range by penetrating buildings or structures that otherwise block its signal transmission.
Gain of an antenna is a measure of its power output in any given direction, and is related to both elements in its structure as well as effective aperture of its radiating surface. As more elements are removed and effective aperture increases, gain increases.
There are various kinds of antennas, each offering unique benefits and drawbacks just like different poker games do as mentioned over centiment.io. Popular examples of antennas include dipole, loop, parabolic and Yagi-Uda array.
Dipole antennas consist of two wires connected at one end by insulators and connected at the other to feedlines leading to transmitters or receivers, and resonating at half or quarter wavelength at whatever frequency is being applied; they’re easy to build. Because of its distinctive ‘rubber ducky’ appearance, these antennas are often known as rubber ducky antennas.
Reflectors can help redirect energy radiated from dipole antennas towards more desirable directions, while adding one behind a Yagi-Uda array (also referred to as Yagi antenna) will enhance and delay propagation respectively.
Frequency
Radio frequency (RF) of a signal refers to its oscillation rate, measured in hertz (Hz). This frequency corresponds to where radio waves travel for transmission of communications and broadcasting signals; additionally, different industries may use different RF bands as communication platforms.
An antenna’s ability to transmit or receive radio signals depends on several factors, including its frequency and directivity. These elements are expressed through its “gain” or “efficiency,” which takes into account signal strength and directionality of its antenna.
Radio antenna impedance is also of critical importance, determining how well its matching to transmission lines and transmitters. A poorly matched antenna will cause part of its output current to reflect into it, decreasing output power. Furthermore, operating far away from its design frequency causes performance losses in its radiation pattern area.
Radiation patterns of many antennas exhibit maxima or “peak radiation,” at varying angles, interspersed with nulls of zero radiation at other angles. An antenna’s ability to focus RF energy into one specific direction depends on how many maxima outweigh nulls; its directivity (its ability to point energy in a particular direction), is determined by this ratio; an antenna with high directivity allows easier targeting in an effortful fashion and typically covers wider area when receiving or transmitting signals.
Directivity of an antenna depends upon its size, shape and materials used to build it. Antennas with higher inherent directivity tend to be larger and slenderer while smaller antennas often feature omnidirectional patterns. Antennas with at least 1/10th the wavelength of their transmission wavelength should only be used for receiving while loop antennas or those equipped with Yagi configuration can help increase directivity further. Some antennas offer lightning protection features like inductivity between transmitter and antenna which limits voltage spikes should lightning strikes directly hits an antenna directly reducing voltage spikes when hit by lightning bolt.
Polarization
Polarization refers to the direction of electric field vector oscillation as radio waves propagate through mediums. While a plane wave radiates equally in all directions (known as isotropic), polarized waves have one direction that they transmit along. Most antennae are designed specifically to transmit along that particular polarization.
Linear polarization involves aligning the electric fields of radio signals perpendicularly. As seen from their direction of aim, these electric fields would form a flat plane when seen from this perspective, with horizontal polarization waves appearing as sideways-sloping lines and vertical polarization waves taking on a ribbon shape. To maximize energy transfer between transmitter and receiver antennae with linear polarization technology, both should ideally be facing in the same direction so their signals match perfectly and transfer as much of their respective energies as possible between them.
However, this may not always be feasible due to numerous factors, including mechanical positioning of antennas, user actions, channel distortion and multipath reflections resulting in cross-polarization leakage of 10-30dB that may significantly diminish signal strength.
There are many antennas that are capable of operating with multiple types of polarization. For instance, handheld mobile phone antennas that employ dipole elements folded together typically accommodate both horizontal and vertical polarization modes; this allows the antenna to be used with either horizontal or vertical receivers depending on personal preference and availability of suitable mounting locations.
Circular Polarization is another option available, which works by rotating the electrical field of signals in a circle around their propagation axis. This technique may be right- or left-handed circular polarization and allows an antenna to receive both horizontal and vertical signal directions simultaneously if required.
Elliptical polarization differs from circular in that its two axes can either align, as in circular polarization, or not align at all – giving this method of polarization more versatility than its counterparts.
Power
Radio signals are measured in watts, with higher powers meaning further travel and louder volumes. To increase power, one may increase antenna height or width or broaden their radiation pattern; other factors that can impact signal power include proximity to conducting objects and proximity of metal paneling/ductwork/water bodies that absorb some or all of its signal energy and reduce its strength.
Antennas can be designed to transmit and receive signals in all horizontal directions equally (omnidirectional antennas), or focus EM transmission and reception in one narrowly focused direction (directional or high-gain antennas). Many antennas incorporate components not connected with their transmitter that increase gain by reflecting electromagnetic waves back in specific directions.
Electrical conductors tend to exhibit negligible resistance in DC circuits, yet can pose significant impedance at higher frequencies. To maximize output from an RF amplifier, its design must match that of its antenna by employing an impedance matching network known as an antenna tuner or impedance matching network.
RF signals reflected off an antenna not tuned correctly to its design frequency will reflect back into the amplifier and reduce output power, leading to loss. An antenna tuned correctly will have very low feedpoint impedances.
Near-field effects occur when electromagnetic waves reflect off of objects near an antenna and induce currents in nearby conductive objects that create current flows that influence its performance, known as near-field effects. One source of near-field effects can be the interaction between electromagnetic wave reflections off of the ground and currents flowing through electrical cables that run close to or through it.
Sometimes this can create an undesirable feedback loop whereby electromagnetic wave reflection from the ground inducing currents in nearby conductors increases input impedance to an antenna and decreases efficiency.