Unless you understand these 40 antenna knowledge, don’t say you know how to play Ham Radios.
Newcomers who have just started often pay special attention to the power of radio equipment and overlook the importance of antenna systems. Every time I check in at the relay network, I often find that the signal report of my own small station at 50W is not as good as that of someone else’s 5W small station. Apart from the distance and environmental conditions, the power of the radio station is not transmitted with low loss, which is wasted on the antenna system. Before solving this problem, the first step is to master the basic knowledge of the following 40 antennas.
An antenna is a transformer that transforms guided waves propagating on a transmission line into electromagnetic waves propagating in an unbounded medium (usually free space), or vice versa. A component used in radio equipment to transmit or receive electromagnetic waves.
Classic half wave oscillator antenna
The ratio of the total input power of the antenna is called the maximum gain coefficient of the antenna. It is a more comprehensive reflection of the effective utilization of the total RF power by the antenna than the directional coefficient of the antenna. And expressed in decibels. It can be mathematically deduced that the maximum gain coefficient of an antenna is equal to the product of the antenna directivity coefficient and the antenna efficiency.
The Invention of Antennas
The antenna was invented by Russian scientist Popov.
In 1888, at the age of 29, Popov learned of the discovery of electromagnetic waves by the famous German physicist Hertz. This young scientist, who had once aspired to promote electric lights, said to his friends, “I have devoted my entire life to installing electric lights. For the vast Russia, it only illuminates a small corner: if I could command magnetic waves, I could fly over the whole world
So he immersed himself in research and launched an attack towards a new goal.
In 1894, Popov made a radio receiver. The core part of this receiver uses an improved metal chip detector, and Popov uses an electric bell as the terminal display. The small hammer of the electric bell can loosen the metal chips in the detector. The electric bell is driven by an electromagnetic relay. When the metal chip detector detects electromagnetic waves, the relay is powered on and the electric bell rings.
Once, Popov discovered in an experiment that the distance at which the receiver detects radio waves suddenly increased significantly compared to usual.
What’s going on here? “Popov kept searching, but couldn’t find the reason.
One day, Popov accidentally discovered a wire attached to a metal chip detector. He removed the wire and the bell stopped ringing; He narrowed down the experimental distance to the original distance, and the bell rang again.
Popov was overjoyed and quickly connected the wire to one end of the metal chip detector and the other end of the detector. After further testing, the results showed that the signal transmission distance increased dramatically after using the antenna.
Radio antennas emerged from this.
Antenna classification:
- According to the nature of work, it can be divided into transmitting antennas and receiving antennas;
- According to their purposes, they can be divided into communication antennas, broadcasting antennas, television antennas, radar antennas, etc;
- According to directionality, it can be divided into omnidirectional antennas and directional antennas, etc;
- According to the working wavelength, it can be divided into ultra long wave antennas, long wave antennas, medium wave antennas, short wave antennas, ultra short wave antennas, microwave antennas, etc;
- According to their structural form and working principle, they can be divided into linear antennas and planar antennas. The characteristic parameters of an antenna include directional pattern, directional coefficient, gain, input impedance, radiation efficiency, polarization, and bandwidth;
- According to dimensionality, it can be divided into two types: one-dimensional antennas and two-dimensional antennas.
One dimensional antenna: composed of many wires, which are either straight lines like those used in mobile phones or some clever shapes, like the old rabbit ears used on televisions before the emergence of cables. Monopolar and bipolar antennas are the two most basic one-dimensional antennas.
Two dimensional antennas: varied, including sheet shaped (a square metal), array shaped (a bundle of organized two-dimensional patterns), horn shaped, and dish shaped.
- Antennas can be divided into three categories based on their usage scenarios: handheld station antennas, vehicle mounted antennas, and base antennas.
Handheld radio antenna: refers to the antenna used by individuals for handheld walkie talkies, commonly divided into two categories: rubber antenna and rod antenna.
Vehicle mounted antenna: refers to the communication antenna originally designed and installed on the vehicle, with the most common application being suction cup antenna. There are also shortened, quarter wavelength, mid sensing, five eighth wavelength, and double half wavelength types of antennas in the structure of car mounted antennas.
Base station antenna: plays a crucial role in the entire communication system, especially as a communication hub for communication stations. The commonly used base station antennas include fiberglass high gain antennas, four ring array antennas (eight ring array antennas), and directional antennas.
Common antenna indicators
Antenna efficiency
It refers to the ratio of the power radiated by the antenna (i.e. the power that effectively converts electromagnetic waves) to the active power input to the antenna. It is a value that is consistently less than 1.
Antenna polarized wave
When electromagnetic waves propagate in space, if the direction of the electric field vector remains fixed or rotates according to a certain rule, this electromagnetic wave is called polarized wave, also known as antenna polarized wave or polarized wave. It can usually be divided into planar polarization (including horizontal polarization and vertical polarization), circular polarization, and elliptical polarization.
Polarization direction
The direction of the electric field of polarized electromagnetic waves is called the polarization direction.
Polarization surface
The plane formed by the polarization direction and propagation direction of polarized electromagnetic waves is called the polarization plane.
Vertical polarization
The polarization of radio waves is often based on the earth as the standard plane. Any polarized wave that is parallel to the normal plane (perpendicular plane) of the earth is called a vertically polarized wave. Its electric field direction is perpendicular to the earth.
Horizontal polarization
Any polarized wave that is perpendicular to the normal plane of the earth is called a horizontal polarized wave. Its electric field direction is parallel to the earth.
Plane polarization
If the polarization direction of electromagnetic waves remains in a fixed direction, it is called planar polarization, also known as linear polarization. In the component of the electric field parallel to the earth (horizontal component) and perpendicular to the earth’s surface, the spatial amplitude has any relative magnitude, and plane polarization can be obtained. Vertical polarization and horizontal polarization are both special cases of planar polarization.
Circular polarization
When the angle between the polarization surface of radio waves and the normal plane of the earth varies periodically from 0 to 360 °, i.e. the electric field remains constant in magnitude and changes direction over time, and the trajectory of the electric field vector at the end is projected as a circle on a plane perpendicular to the propagation direction, it is called circular polarization. When the amplitude of the horizontal and vertical components of the electric field is equal and the phase difference is 90 ° or 270 °, circular polarization can be obtained. Circular polarization, if the polarization surface rotates with time and forms a right spiral relationship with the direction of electromagnetic wave propagation, is called right circular polarization; On the contrary, if it forms a left spiral relationship, it is called left circular polarization.
Elliptical polarization
If the angle between the polarization surface of radio waves and the normal plane of the earth changes periodically from 0 to 2 π, and the trajectory of the electric field vector at the end is projected as an ellipse on a plane perpendicular to the propagation direction, it is called elliptical polarization. When the amplitude and phase of the vertical and horizontal components of the electric field have arbitrary values (except when the two components are equal), elliptical polarization can be obtained.
Main antenna types
Long wave antenna, medium wave antenna
It is a general term for transmitting or receiving antennas that work in the long wave and medium wave bands. Long and medium waves propagate through ground waves and sky waves, while sky waves continuously reflect between the ionosphere and the earth. According to this propagation characteristic, long and medium wave antennas should be able to generate vertically polarized radio waves. Among long and medium wave antennas, vertical, inverted L-shaped, T-shaped, and umbrella shaped vertical grounding antennas are widely used. Long and medium wave antennas should have a good grounding network. There are many technical problems with long and medium wave antennas, such as low effective height, low radiation resistance, low efficiency, narrow passband, and small directional coefficient. To address these issues, antenna structures are often very complex and massive.
Shortwave antenna
Transmitting or receiving antennas operating in the shortwave band are collectively referred to as shortwave antennas. Shortwave is mainly propagated through the reflection of celestial waves from the ionosphere, and is one of the important means of modern long-distance radio communication. There are many forms of shortwave antennas, among which the most commonly used are symmetrical antennas, in-phase horizontal antennas, multiplier antennas, angular antennas, V-shaped antennas, diamond shaped antennas, fishbone shaped antennas, etc. Compared with long wave antennas, short wave antennas have a larger effective height, higher radiation resistance, higher efficiency, good directionality, higher gain, and wider bandwidth.
Ultra short wave antenna
The transmitting and receiving antennas working in the ultra short wave band are called ultra short wave antennas. Ultra short waves mainly propagate through space waves. There are many forms of this antenna, among which the most commonly used are Yagi antenna, dish cone antenna, double cone antenna, “batwing” TV transmitting antenna, etc.
Microwave antenna
The transmitting or receiving antennas working in the millimeter wave, decimeter wave, centimeter wave, millimeter wave and other frequency bands are collectively referred to as microwave antennas. Microwaves mainly propagate through space waves, and to increase communication distance, antennas are installed higher. In microwave antennas, widely used ones include parabolic antennas, horn parabolic antennas, horn antennas, lens antennas, slotted antennas, dielectric antennas, periscope antennas, etc.
directional antenna
A directional antenna refers to an antenna that emits and receives strong electromagnetic waves in one or several specific directions, while emitting and receiving electromagnetic waves in other directions is zero or extremely small. The purpose of using directional transmitting antennas is to increase the effective utilization of radiated power and enhance confidentiality; The main purpose of using directional receiving antennas is to increase anti-interference capability.
Non directional antenna
An antenna that uniformly radiates or receives electromagnetic waves in all directions is called a non directional antenna, such as the whip antenna used in small communication devices.
Wideband antenna
An antenna whose directionality, impedance, and polarization characteristics remain almost unchanged over a wide frequency band is called a wideband antenna. Early broadband antennas included diamond shaped antennas, V-shaped antennas, doubling wave antennas, and cone-shaped antennas, while new broadband antennas included logarithmic periodic antennas.
Tuned antenna
An antenna that only has a predetermined directionality within a very narrow frequency band is called a tuned antenna or tuned directional antenna. Usually, the directionality of a tuned antenna remains unchanged only within 5% of its tuning frequency band, while at other frequencies, the directional changes are very significant, causing communication to be disrupted. Tunable antennas are not suitable for shortwave communication with variable frequencies. Coherent horizontal antennas, folded antennas, twisted antennas, etc. all belong to tuned antennas.
Vertical antenna
Vertical antenna refers to an antenna placed perpendicular to the ground. It has two forms: symmetrical and asymmetrical, with the latter being more widely used. Symmetric vertical antennas are often center fed. Asymmetric vertical antennas feed between the bottom of the antenna and the ground, and their maximum radiation direction is concentrated in the ground direction when the height is less than 1/2 wavelength, making them suitable for broadcasting. Asymmetric vertical antenna, also known as vertical grounded antenna.
Inverted L antenna
An antenna composed of connecting a vertical down conductor at one end of a single horizontal wire. Due to its shape resembling the English letter L reversed, it is called an inverted L-shaped antenna. The letter gamma in Russian is exactly the reverse of the letter L in English. Therefore, the Gamma type antenna is more convenient. It is a form of vertical grounded antenna. In order to improve the efficiency of the antenna, its horizontal part can be composed of several wires arranged on the same horizontal plane. The radiation generated in this part can be ignored, and the radiation is generated in the vertical part. Inverted L antennas are generally used for long wave communication. Its advantages are simple structure and easy installation; The disadvantages are large footprint and poor durability.
T-shaped antenna
At the center of the horizontal wire, a vertical down conductor is connected, shaped like the English letter T, hence the name T-shaped antenna. It is the most common type of vertically grounded antenna. Its horizontal radiation can be ignored, and the radiation is generated by the vertical part. To improve efficiency, the horizontal part can also be composed of multiple wires. The characteristics of a T-shaped antenna are the same as those of an inverted L-shaped antenna. It is generally used for long wave and medium wave communication.
Umbrella antenna
At the top of a single vertical wire, several inclined conductors are drawn in various directions, forming an antenna shape resembling an open umbrella, hence the name umbrella antenna. It is also a form of vertical grounded antenna. Its characteristics and uses are the same as those of inverted L-shaped and T-shaped antennas.
Whip antenna
A whip antenna is a flexible vertical rod antenna, typically measuring 1/4 or 1/2 wavelength in length. Most whip antennas do not use ground wires but instead use grounding grids. Small whip antennas often use the metal casing of small radio stations as a grounding network. Sometimes, in order to increase the effective height of the whip antenna, small radial blades can be added to the top of the whip antenna or inductors can be added to the middle of the whip antenna. Whip antennas can be used for small communication devices, walkie talkies, car radios, etc.
Symmetric antenna
A symmetrical antenna is an antenna composed of two equal lengths of wires that are disconnected at the center and connected for feeding, and can be used as a transmitting and receiving antenna. Because antennas are sometimes referred to as oscillators, symmetrical antennas are also called symmetrical oscillators or dipole antennas. A symmetrical oscillator with a total length of half a wavelength is called a half wave oscillator, also known as a half wave dipole antenna. It is the most basic unit antenna and widely used, and many complex antennas are composed of it. The half wave oscillator has a simple structure and convenient feeding, and is widely used in short-range communication.
Cage antenna
It is a wideband weakly directional antenna. It is formed by enclosing several wires into a hollow cylinder instead of a single wire radiator in a symmetrical antenna. Because its radiator is cage shaped, it is called a cage antenna. The working band of the cage antenna is wide and easy to tune. It is suitable for close range trunk communication.
Angular antenna
It belongs to a type of symmetrical antenna, but its two arms are not arranged in a straight line and form a 90 ° or 120 ° angle, hence it is called an angular antenna. This type of antenna is usually installed horizontally, and its directionality is not significant. In order to obtain wideband characteristics, the dual arms of the angular antenna can also adopt a cage structure, called an angular cage antenna.
folded antenna
Bending the oscillator into symmetrical antennas that are parallel to each other is called a folded antenna. There are several forms of folded antennas, including double line folded antenna, triple line folded antenna, and multi line folded antenna. When bending, the current at each corresponding point on each line should be in phase. From a distance, the entire antenna looks like a symmetrical antenna. However, compared to symmetrical antennas, the radiation of folded antennas is enhanced. The input impedance increases, making it easier to couple with the feeder line. Equivalent antenna is a type of tuned antenna with a narrow operating frequency. It has been widely used in the short wave and ultra short wave bands.
V-shaped antenna
It is an antenna composed of two wires at an angle to each other, shaped like the English letter V. Its terminal can be open or connected with a resistor, whose resistance is equal to the characteristic impedance of the antenna. The V-shaped antenna has unidirectionality, and the maximum transmission direction is in the vertical plane of the dividing line direction. Its disadvantages are low efficiency and large footprint.
Diamond shaped antenna
It is a broadband antenna. It consists of a horizontal diamond suspended on four pillars, with one acute angle of the diamond connected to the feed line and the other acute angle connected to a terminal resistor with an impedance equal to the characteristic impedance of the diamond antenna. It has unidirectionality in the vertical plane pointing towards the terminal resistor direction.
The advantages of diamond shaped antennas are high gain, strong directionality, wide bandwidth, and easy installation and maintenance; The disadvantage is that it occupies a large area. After deformation, diamond shaped antennas come in three forms: double diamond shaped antennas, feedback diamond shaped antennas, and folded diamond shaped antennas. Diamond shaped antennas are generally used for large and medium-sized shortwave receiving radio stations.
Conical antenna
It is an ultra short wave antenna. The top is a circular disk (i.e. radiator) fed by the centerline of the coaxial line, and the bottom is a cone connected to the outer conductor of the coaxial line. The function of a cone is similar to that of an infinite ground. By changing the inclination angle of the cone, the maximum radiation direction of the antenna can be altered. It has an extremely wide frequency band.
Fishbone antenna
Fishbone shaped antenna, also known as edge shooting antenna, is a specialized shortwave receiving antenna. Composed of symmetrical oscillators connected at regular intervals on two assembly lines, these oscillators are all connected to the assembly line through a small capacitor. At the end of the collection line, facing the communication direction, connect a resistor with a characteristic impedance equal to that of the collection line, and the other end is connected to the receiver through a feeder line. Compared with diamond shaped antennas, fishbone shaped antennas have the advantages of smaller sidelobes (i.e. stronger reception ability in the main lobe direction and weaker reception in other directions), less mutual influence between antennas, and smaller footprint; The disadvantage is low efficiency and complex installation and use.
Yagi antenna
Also known as directional antenna. It consists of several metal rods, one of which is a radiator, the longer one behind the radiator is a reflector, and the shorter ones in front are directors. Radiators typically use folded half wave oscillators. The maximum radiation direction of the antenna is the same as the direction of the director. The advantages of Yagi antenna are simple structure, lightweight and sturdy, and convenient feeding; Disadvantages include narrow frequency band and poor anti-interference performance. Applied in ultra short wave communication and radar.
Fan shaped antenna
It comes in two forms: metal plate and metal wire. Among them, it is a fan-shaped metal plate and a fan-shaped metal wire type. This type of antenna widens the antenna frequency band due to the increased cross-sectional area of the antenna. A linear fan-shaped antenna can use three, four, or five metal wires. Fan shaped antenna is used for ultra short wave reception.
Double cone antenna
A double cone antenna consists of two cones with opposite tips, and is fed at the tips of the cones. A cone can be constructed with a metal surface, metal wire, or metal mesh. Just like a cage antenna, as the cross-sectional area of the antenna increases, the frequency band of the antenna also widens accordingly. The double cone antenna is mainly used for ultra short wave reception.
Parabolic antenna
A parabolic antenna is a directional microwave antenna composed of a parabolic reflector and a radiator, with the radiator mounted on the focal point or focal axis of the parabolic reflector. The electromagnetic waves emitted by the radiator are reflected by a parabolic surface, forming a highly directional beam.
Parabolic reflectors are made of highly conductive metals and can be used in four main ways: rotating paraboloids, cylindrical paraboloids, truncated rotating paraboloids, and elliptical edge paraboloids. The most commonly used are rotating paraboloids and cylindrical paraboloids. Radiators generally use half wave oscillators, open waveguides, slotted waveguides, etc.
Parabolic antennas have the advantages of simple structure, strong directionality, and wide operating frequency band. The disadvantage is that due to the radiator being located in the electric field of the parabolic reflector, the reflector has a strong reaction on the radiator, making it difficult to achieve a good match between the antenna and the feed line; The back radiation is relatively high; Poor protection level; High production accuracy. This antenna is widely used in microwave relay communication, tropospheric scattering communication, radar, and television.
Horn parabolic antenna
A horn parabolic antenna consists of two parts: a horn and a parabolic surface. A parabolic surface is placed on top of a horn, and the vertex of the horn is located at the focal point of the parabolic surface. A horn is a radiator that radiates electromagnetic waves onto a parabolic surface. The electromagnetic waves are reflected by the parabolic surface and focused into a narrow beam before being emitted. The advantages of a horn parabolic antenna are: the reflector has no reaction to the radiator, the radiator does not obstruct the reflected radio waves, and the antenna matches well with the feeding device; Low back radiation; High degree of protection; The working frequency band is very wide; The structure is simple. The horn parabolic antenna is widely used in trunk relay communication.
Horn antenna
Also known as angular antenna. It is composed of a uniform waveguide and a horn shaped waveguide with a gradually increasing cross-section. There are three forms of horn antennas: fan-shaped horn antenna, conical horn antenna, and conical horn antenna. Horn antenna is one of the most commonly used microwave antennas, generally used as a radiator. Its advantage is a wide operating frequency band; The disadvantage is that it has a larger volume, and for the same aperture, its directionality is not as sharp as parabolic antennas.
Horn lens antenna
Composed of a horn and a lens mounted on the horn aperture, it is called a horn lens antenna. The principle of lens refers to lens antenna, which has a relatively wide operating frequency band and higher protection than parabolic antenna. It is widely used in microwave trunk communication with a large number of channels.
Lens antenna
In the centimeter band, many optical principles can be applied to antennas. In optics, a lens is used to refract spherical waves emitted by a point light source placed at the focal point of the lens into plane waves. Lens antennas are made using this principle. It consists of a lens and a radiator placed at the focal point of the lens. There are two types of lens antennas: dielectric deceleration lens antenna and metal acceleration lens antenna. The lens is made of low loss high-frequency medium, thick in the middle and thin around. Spherical waves emitted from a radiation source experience deceleration when passing through a dielectric lens. So the path of the spherical wave being decelerated in the middle part of the lens is long, and the path of deceleration in the surrounding parts is short. Therefore, spherical waves become plane waves after passing through a lens, which means that radiation becomes directional. A lens is made up of many metal plates of different lengths placed in parallel. The metal plate is perpendicular to the ground, and the closer it is to the middle, the shorter the metal plate. Radio waves on parallel metal plates
It is accelerated during transmission. When a spherical wave emitted from a radiation source passes through a metal lens, the closer it is to the edge of the lens, the longer the path of acceleration, while the path of acceleration in the middle is shorter. Therefore, the spherical wave after passing through the metal lens becomes a plane wave.
Lens antennas have the following advantages:
- The side lobes and back lobes are small, resulting in a better directional pattern;
- The precision of lens manufacturing is not high, so it is relatively convenient to manufacture. Its disadvantages are low efficiency, complex structure, and high price. Lens antennas are used in microwave relay communication.
slot antennas
The antenna formed by cutting one or several narrow slots on a large metal plate and feeding them with coaxial lines or waveguides is called a slotted antenna, also known as a crack antenna. In order to obtain unidirectional radiation, a cavity is made behind the metal plate, and the slot is directly fed by the waveguide. The slotted antenna has a simple structure and no protruding parts, making it particularly suitable for use on high-speed aircraft. Its disadvantage is that it is difficult to tune.
Dielectric antenna
A dielectric antenna is a circular rod made of low loss high-frequency dielectric material (usually polystyrene), with one end fed by a coaxial line or waveguide. 2 is the extension of the inner conductor of the coaxial line, forming a oscillator for exciting electromagnetic waves; 3 is coaxial line; 4 is a metal sleeve. The function of the sleeve is not only to clamp the dielectric rod, but also to reflect electromagnetic waves, thereby ensuring that the electromagnetic waves are excited by the coaxial inner conductor and propagate towards the free end of the dielectric rod. The advantages of dielectric antennas are small size and sharp directionality; The disadvantage is that the medium has losses, resulting in low efficiency.
Periscope antenna
In microwave relay communication, antennas are often placed on high supports, so feeding the antenna requires a long feeder line. A long feeder line can cause many difficulties, such as complex structure, high energy loss, and distortion caused by energy reflection at the feeder joint. To overcome these difficulties, a periscope antenna can be used, which consists of a lower mirror radiator placed on the ground and an upper mirror reflector installed on a bracket. The lower mirror radiator is generally a parabolic antenna, and the upper mirror reflector is a metal flat plate. The lower mirror radiator emits electromagnetic waves upwards, which are reflected off the metal plate. The advantages of periscope antennas are low energy loss, minimal distortion, and high efficiency. Mainly used in microwave relay communication with small capacity.
Spiral antenna
It is an antenna with a spiral shape. It is composed of metal spiral wires with good conductivity, usually fed by coaxial lines. The center line of the coaxial line is connected to one end of the spiral wire, and the outer conductor of the coaxial line is connected to a grounded metal mesh (or plate). The radiation direction of a spiral antenna is related to the circumference of the spiral line. When the circumference of a spiral is much smaller than a wavelength, the direction of strongest radiation is perpendicular to the spiral axis; When the circumference of a spiral is on the order of one wavelength, the strongest radiation occurs in the direction of the spiral axis.
Antenna tuner
An impedance matching network that connects a transmitter and an antenna is called an antenna tuner. The input impedance of the antenna varies greatly with frequency, while the output impedance of the transmitter is constant. If the transmitter is directly connected to the antenna, when the frequency of the transmitter changes, the impedance mismatch between the transmitter and the antenna will reduce the radiated power. By using an antenna tuner, impedance matching can be achieved between the transmitter and antenna, allowing the antenna to have maximum radiated power at any frequency. Antenna tuner is widely used in ground, vehicle, ship and aviation shortwave radio stations.
Logarithmic periodic antenna
It is a broadband antenna, or a frequency independent antenna. Among them, it is a simple logarithmic periodic antenna, whose dipole length and spacing follow the following relationship: the τ dipole is fed by a uniform double line transmission line, and the transmission line needs to be swapped between adjacent dipoles. This antenna has a characteristic: any characteristic that exists at frequency f will repeat at all frequencies given by τ ⁿ f, where n is an integer. These frequencies are plotted on a logarithmic scale at equal intervals, with a period equal to the logarithm of τ. The term logarithmic periodic antenna comes from this. Logarithmic periodic antennas only periodically repeat radiation patterns and impedance characteristics. However, for an antenna with such a structure, if τ is not much less than 1, the variation of its characteristics within one cycle is very small, so it is basically frequency independent. There are many types of logarithmic periodic antennas, including logarithmic periodic dipole antennas and monopole antennas, logarithmic periodic resonant V-shaped antennas, logarithmic periodic spiral antennas, etc. Among them, the most common is logarithmic periodic dipole antennas. These antennas are widely used in the short wave and above frequency bands.