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 directivity coefficient of the antenna, expressed in decibels, it can be deduced mathematically that the maximum gain coefficient of antenna is equal to the product of antenna directivity coefficient and antenna efficiency.

It refers to the ratio of the power radiated by the antenna (that is, the power that effectively converts the electromagnetic wave part) to the active power input to the antenna. It is a value that is always less than 1.

1. Antenna efficiency

2. Antenna polarized wave

When an electromagnetic wave propagates in space, if the direction of the electric field vector keeps fixed or rotates according to a certain rule, this electromagnetic wave is called polarized wave, also known as antenna polarized wave, or polarized wave. Generally, it can be divided into plane polarization (including horizontal polarization and vertical polarization), circular polarization and elliptical polarization. 

3. Direction of polarization

The electric field direction of polarized electromagnetic wave is called polarization direction. 

4. Polarization plane

The plane formed by polarization direction and propagation direction of polarized electromagnetic wave is called polarization plane.

5. Vertical polarization

The polarization of radio waves is usually based on the earth. Any polarized wave whose polarization plane is parallel to the geodetic normal plane (vertical plane) is called vertical polarized wave. Its electric field direction is perpendicular to the earth. 

6. Horizontal polarization

Any polarized wave whose polarization plane is perpendicular to the geodetic normal plane is called horizontal polarized wave. Its electric field direction is parallel to the earth.  

7. Plane polarization

If the polarization direction of electromagnetic wave is kept in a fixed direction, it is called plane polarization, also called linear polarization. When the component of electric field parallel to the earth (horizontal component) and the component perpendicular to the earth's surface have arbitrary relative amplitude, plane polarization can be obtained. Vertical polarization and horizontal polarization are special cases of plane polarization. 

8. Circular polarization

When the periodic angle change between the polarization plane of radio waves and the geodetic normal plane is from 0 to 360°, that is, the magnitude of the electric field is constant, the direction changes with time, and the trajectory at the end of the electric field vector is projected as a circle on the plane perpendicular to the propagation direction, which is called circular polarization. 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 has a right spiral relationship with the propagation direction of electromagnetic waves, it is called right circular polarization; On the contrary, if it is in a left spiral relationship, it is called left circular polarization.

9. Elliptic polarization

If the angle between the polarization plane of radio waves and the normal plane of the earth changes periodically from 0 to 2π, and the trajectory at the end of the electric field vector is projected as an ellipse on the 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.

10. Long wave antenna and medium wave antenna

It is a general term for transmitting antenna or receiving antenna that works in long-wave and medium-wave bands. Long and medium waves are transmitted by ground waves and sky waves, while sky waves are continuously reflected between the ionosphere and the earth. According to this propagation characteristic, long and medium wave antennas should be able to generate vertically polarized electric waves. Among the long and medium wave antennas, vertical, inverted L, T and umbrella vertical grounding antennas are widely used. Long and medium wave antennas should have good grounding network. There are many technical problems in long and medium wave antennas, such as low effective height, low radiation resistance, low efficiency, narrow passband and low directivity. In order to solve these problems, the antenna structure is often very complex and huge.

11. Shortwave antenna

The transmitting or receiving antennas operating in the short wave band are collectively referred to as short wave antennas. Short wave is mainly transmitted by the sky wave reflected by the ionosphere, and it is one of the important means of modern long-distance radio communication. There are many forms of short-wave antenna, among which symmetrical antenna, in-phase horizontal antenna, double-wave antenna, angle antenna, V-shaped antenna, rhombus antenna and fishbone antenna are the most widely used. Compared with long-wave antenna, short-wave antenna has the advantages of high effective height, high radiation resistance, high efficiency, good directivity, high gain and wide passband.

12. Ultrashort wave antenna

The transmitting and receiving antennas working in the ultrashort wave band are called ultrashort wave antennas. Ultra-short waves mainly propagate by space waves. There are many forms of this kind of antenna, among which Yagi antenna, disk cone antenna, biconical antenna and "Batwing" TV transmitting antenna are the most widely used.

13. Microwave antenna

The transmitting or receiving antennas working in meter wave, decimeter wave, centimeter wave, millimeter wave and other bands are collectively referred to as microwave antennas. Microwave is mainly spread by space waves, and the antenna is erected higher in order to increase the communication distance. Among microwave antennas, parabolic antenna, horn parabolic antenna, horn antenna, lens antenna, slot antenna, dielectric antenna and periscope antenna are widely used.

14. Directional antenna

Directional antenna is a kind of antenna that emits and receives electromagnetic waves in one or several specific directions, but emits and receives electromagnetic waves in other directions at zero or minimal. The purpose of adopting directional transmitting antenna is to increase the effective utilization rate of radiation power and increase confidentiality. The main purpose of adopting directional receiving antenna is to increase anti-interference ability.

15. Undirected antenna

Antennas that radiate or receive electromagnetic waves uniformly in all directions are called non-directional antennas, such as whip antennas for small communication machines.

16. All channel antenna

An antenna whose directivity, impedance and polarization characteristics remain almost unchanged in a wide band is called a broadband antenna. Early broadband antennas include diamond antenna, V-shaped antenna, double-wave antenna, disk cone antenna, etc. New broadband antennas include log-periodic antenna, etc.

17. Tuned antenna

An antenna with a predetermined directivity in only a narrow frequency band is called a tuned antenna or a tuned directional antenna. Usually, the directivity of a tuned antenna remains unchanged only in the 5% band around its tuning frequency, while on other frequencies, the directivity changes so badly that the communication is destroyed. Tuning antenna is not suitable for shortwave communication with variable frequency. Cophased horizontal antenna, folded antenna and meandering antenna are all tuned antennas.

18. Vertical antenna

Vertical antenna refers to the antenna placed vertically with the ground. It has two forms: Symmetry and asymmetry, while the latter is widely used. Symmetrical antennas are often fed from the center. The asymmetric antenna feeds between the bottom of the antenna and the ground, and its maximum radiation direction is concentrated in the ground direction when the height is less than 1/2 wavelength, so it is suitable for broadcasting. Asymmetric antenna is also called vertical grounded antenna.

19. Inverted-L antenna

An antenna formed by connecting a vertical down conductor at one end of a single horizontal conductor. Because its shape resembles the English letter L upside down, it is called inverted L antenna. The word Γ in Russian is just the reverse of the English letter L. Therefore, it is more convenient to call Γ type antenna. It is a form of vertical grounding 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, and the radiation generated by this part can be ignored, while the vertical part generates radiation.

Inverted-L antenna is generally used for long wave communication. Its advantages are simple structure and convenient erection; Disadvantages are large floor space and poor durability.

20. T antenna

In the center of the horizontal conductor, a vertical down lead is connected, which is shaped like the English letter T, so it is called T-shaped antenna. It is the most common antenna with vertical grounding. Its horizontal part of radiation can be neglected, but the vertical part produces radiation. In order to improve efficiency, the horizontal part can also be composed of multiple wires. T-shaped antenna has the same characteristics as inverted L-shaped antenna. It is generally used for long-wave and medium-wave communication.

21. Umbrella antenna

At the top of a single vertical conductor, several inclined conductors are led down in all directions. The antenna formed in this way is shaped like an open umbrella, so it is called an umbrella antenna. It is also a form of vertical grounding antenna. Its features and uses are the same as those of inverted L-shaped and T-shaped antennas.

22. Whip antenna

A whip antenna is a flexible vertical rod antenna, and its length is generally 1/4 or 1/2 wavelength. Most whip antennas use ground nets instead of ground wires. Small whip antenna often uses the metal shell of small radio station as a ground net. Sometimes, in order to increase the effective height of the whip antenna, some 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.

The whip antenna can be used in small communication machines, walkers, car radios, etc.

23. Symmetric antenna

Two wires with equal length, broken center and fed can be used as transmitting and receiving antennas. The antenna formed in this way is called symmetric antenna. Because antennas are sometimes called vibrator, symmetric antennas are also called symmetric vibrator or dipoles. The symmetric vibrator with a total length of half a wavelength is called a half-wave vibrator, which is also called a half-wave dipole antenna. It is the most basic unit antenna, and it is also widely used. Many complex antennas are composed of it. Half-wave oscillator has simple structure and convenient feeding, so it is widely used in short-distance communication.

24. Cage antenna

It is a wide-band weak directional antenna. It is made of a hollow cylinder surrounded by several wires instead of a single wire radiator in a symmetrical antenna. Because its radiator is cage-shaped, it is called cage antenna. Cage antenna has a wide working band and is easy to tune. It is suitable for short-distance trunk communication.

25. Angular antenna

It belongs to a kind of symmetrical antenna, but its two arms are not arranged in a straight line, but are 90° or 120° angle, so it is called angle antenna. This kind of antenna is generally horizontal, and its directivity is not significant. In order to obtain wide-band characteristics, the arms of angle antenna can also adopt cage structure, which is called angle cage antenna.

26. Folded antenna

Dipole antennas that bend oscillators into parallel ones are called folded antennas. There are several kinds of folded antennas, such as two-wire folded antenna, three-wire folded antenna and multi-wire folded antenna. When bending, the currents at the corresponding points on each line should be in phase, and from a distance, the whole antenna looks like a symmetrical antenna. However, compared with symmetrical antenna, the radiation of folded antenna is enhanced. The input impedance is increased, which facilitates coupling with feeder. Folded antenna is a tuned antenna with a narrow working frequency. It is widely used in shortwave and ultrashort wave bands. 

27. V antenna

It is an antenna which is composed of two wires at an angle to each other and shaped like the English letter V. Its terminal can be open circuit or connected with a resistor, and its resistance is equal to the characteristic impedance of the antenna. The V-shaped antenna is unidirectional, and the maximum radiation direction is in the vertical plane along the corner line. Its disadvantages are low efficiency and large floor space.

28. Diamond antenna

It is a broadband antenna. It consists of a horizontal rhombus suspended on four pillars, with one acute angle of the rhombus connected to the feeder, and the other acute angle connected to a terminal resistance equal to the characteristic impedance of the rhombus antenna. In the vertical plane pointing to the direction of terminal resistance, it is unidirectional. The diamond antenna has the advantages of high gain, strong directivity, wide use band and easy erection and maintenance. The disadvantage is that it occupies a large area. After the rhombus antenna is deformed, there are three forms: double rhombus antenna, feedback rhombus antenna and folded rhombus antenna. Diamond antennas are generally used in large and medium-sized short-wave receiving stations.

29. Discone antenna

It's an ultrashort wave antenna. The top is a disc (i.e. radiator), fed by the core wire of the coaxial cable, and the bottom is a cone connected to the outer conductor of the coaxial cable. The function of cone is similar to that of infinite ground. Changing the inclination angle of cone can change the maximum radiation direction of antenna. It has a very wide frequency band.

30. Fishbone antenna

Fish-shaped antenna, also called broadside antenna, is a special short-wave receiving antenna. It is composed of two symmetrical oscillators connected at regular intervals on two collection lines. These symmetrical oscillators are connected to the collection lines through a small capacitor. At the end of the collection line, that is, the end facing the communication direction, a resistor equal to the characteristic impedance of the collection line is connected, and the other end is connected to the receiver through a feeder. Compared with diamond antenna, fishbone antenna has the advantages of small side lobe (that is, strong reception ability in the main lobe direction and weak reception in other directions), small mutual influence among antennas and small occupied area; the disadvantages are low efficiency and complicated installation and use.

31. Yagi antenna

It is also called director 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. The radiator usually uses a folded half-wave oscillator. The maximum radiation direction of the antenna is the same as that of the director. Yagi antenna has the advantages of simple structure, portability, firmness and convenient feeding. Disadvantages are narrow frequency band and poor anti-interference. Application in ultrashort wave communication and radar.

32. Fan antenna

It has two forms: metal plate type and metal wire type. Among them, it is a sector metal plate type and a sector metal wire type. This kind of antenna broadens the antenna frequency band because it increases the cross-sectional area of the antenna. The wire sector antenna can use three, four or five metal wires. Sector antenna is used for ultrashort wave reception.

33. Biconical antenna

Double-cone antenna consists of two cones with opposite cone tops, which feed at the cone tops. The cone can be made of metal surface, metal wire or metal mesh. Just like cage antenna, as the cross-sectional area of antenna increases, the frequency band of antenna also widens. Double cone antenna is mainly used for ultrashort wave reception.

34. Parabolic antenna

Parabolic antenna is a directional microwave antenna, which consists of a parabolic reflector and a radiator, and the radiator is mounted on the focal point or focal axis of the parabolic reflector. The electromagnetic wave emitted by the radiator is reflected by the paraboloid to form a highly directional wave beam. The parabolic reflector is made of metal with good electrical conductivity, and there is mainly the following four forms: paraboloid of revolution, cylindrical paraboloid, truncated paraboloid of revolution and elliptic edge paraboloid, among them, the paraboloid of revolution and the cylindrical paraboloid are the most commonly used. The radiator generally adopts half-wave oscillator, open-ended waveguide, slotted waveguide, etc. Parabolic antenna has the advantages of simple structure, strong directivity and wide working frequency band. Disadvantages: Because the radiator is located in the electric field of the parabolic reflector, the reflector has a great reaction to the radiator, and it is difficult to get a good match between the antenna and the feeder; the radiation on the back is large; poor degree of protection; and the manufacturing precision is high. This antenna is widely used in microwave relay communication, troposcatter communication, radar and television.

35. Horn parabolic antenna

Horn parabolic antenna consists of horn and paraboloid. The paraboloid is covered on the horn, and the vertex of the horn is located at the focus of the paraboloid. A horn radiator radiates electromagnetic waves to a paraboloid. The electromagnetic waves are reflected by the paraboloid, focused into a narrow beam and emitted. The advantages of a parabolic horn antenna are: The reflector has no reaction to the radiator, the radiator has no shielding effect on the reflected electric waves, and the antenna is well matched with the feeding device; Low back radiation; High degree of protection; the working frequency band is very wide; Simple structure. parabolic antenna is widely used in trunk relay communication.

36. Horn antenna

Also known as horn radiator. It consists of a uniform waveguide and a trumpet-shaped waveguide with gradually increasing cross-section. There are three types of horns: fan horn antenna, pyramid horn antenna and cone horn antenna. 

Horn antenna is one of the most commonly used microwave antennas, generally used as radiator. Its advantages are wide working frequency; the disadvantage is that it is bulky, and its directivity is not as sharp as that of parabolic antenna in terms of the same aperture.

37. Horn lens antenna

It is composed of a horn and a lens mounted on the horn aperture, so it is called a horn lens antenna. For the principle of lens, please refer to lens antenna. This kind of antenna has a wide working frequency band, and has a higher degree of protection than parabolic antenna. It is widely used in microwave trunk communication with more channels.

38. Lens antenna

In centimeter band, many optical principles can be applied to antenna. In optics, the spherical wave radiated by a point light source placed at the focal point of the lens can be refracted by the lens to become a plane wave. The lens is made by using this principle. It consists of a lens and a radiator placed at the focal point of the lens. There are two kinds of lenses: 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. The spherical wave emitted from the radiation source is decelerated when it passes through the dielectric lens. Therefore, the path of the spherical wave being decelerated in the middle part of the lens is long, and the path of the spherical wave being decelerated in the peripheral part is short. Therefore, the spherical wave becomes a plane wave after passing through the lens, that is, the radiation becomes directional. The lens is made up of many metal plates with different lengths placed in parallel. The metal plate is perpendicular to the ground, and the closer it is to the middle, the shorter it is. Electric waves are accelerated when propagating in parallel metal plates. 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 accelerated path is, and the shorter the accelerated path is in the middle. Therefore, the spherical wave after passing through the metal lens becomes a plane wave.  

The lens antenna has the following advantages:

1. The side lobe and the back lobe are small, so the radiation pattern is good;

2. The precision of lens manufacturing is not high, so it is convenient to manufacture. Its disadvantages are low efficiency, complex structure and high price. The lens is used in microwave relay communication.

39. Slot antenna

One or several narrow slots are cut in a large metal plate and fed by coaxial cable or waveguide. The antenna formed in this way is called slot antenna, also known as slot antenna. In order to obtain unidirectional radiation, the back of the metal plate is made into a cavity, and the slot is directly fed by the waveguide. The slotted antenna has simple structure and no protruding parts, so it is especially suitable for high-speed aircraft. Its disadvantage is that it is difficult to tune.

40. Dielectric antenna

The dielectric antenna is a round rod made of low-loss high-frequency dielectric material (polystyrene is used generally), and its one end is fed by coaxial cable or waveguide. 2. It is an extension of the inner conductor of the coaxial cable, forming a vibrator for exciting electromagnetic waves;3. It uses coaxial cable; 4. It uses a metal sleeve. The function of the sleeve is not only to clamp the dielectric rod, but also to reflect the electromagnetic wave, thus ensuring that the electromagnetic wave is excited by the inner conductor of the coaxial cable and propagates to the free end of the dielectric rod.

The advantages of dielectric antenna are small size and with sharp directivity. The disadvantage is that the medium is lossy, so the efficiency is not high. 

41. Periscope antenna

In microwave relay communication, the antenna is often placed on a very high bracket, so it takes a long feeder to feed the antenna. Too long feeder will cause many difficulties, such as complex structure, high energy loss, distortion caused by energy reflection at the feeder joint, etc. To overcome these difficulties, a periscope antenna can be adopted, which consists of a lower mirror radiator arranged on the ground and an upper mirror reflector mounted on a bracket. The lower mirror radiator is generally a parabolic antenna, and the upper mirror reflector is a metal plate. The lower mirror radiator emits electromagnetic waves upward, which are reflected off the metal plate. 

Periscope antenna has the advantages of low energy loss, low distortion and high efficiency. Mainly used in microwave relay communication with small capacity.

42. Helical antenna

It is an antenna with a spiral shape. It consists of a metal helix with good electrical conductivity, usually fed by a coaxial cable. The core of the coaxial cable is connected with one end of the helix, and the outer conductor of the coaxial cable is connected with a grounded metal net (or board). The radiation direction of spiral antenna is related to the circumference of spiral.

When the circumference of the helix is much smaller than one wavelength, the direction of the strongest radiation is perpendicular to the helix axis; When the circumference of the spiral is in the order of one wavelength, the strongest radiation appears in the direction of the spiral axis.

43. Antenna tuner

An impedance matching network connecting the transmitter and the antenna is called an antenna tuner. The input impedance of the antenna changes greatly with the frequency, while the output impedance of the transmitter is certain. If the transmitter is directly connected to the antenna, when the frequency of the transmitter changes, the impedance between the transmitter and the antenna does not match, which will reduce the radiation power. By using the antenna tuner, the impedance between the transmitter and the antenna can be matched, so that the antenna has the maximum radiation power at any frequency. Tuners are widely used in ground, vehicle, ship and aviation shortwave radio stations.

44. Log-periodic antenna

It is a broadband antenna, or an antenna independent of frequency. Among them, it is a simple log-periodic antenna, and its dipole length and interval conform to the following relationship:

 τ dipole is fed by a uniform two-wire transmission line, and the position of the transmission line should be changed between adjacent dipoles. This antenna has one feature: all the characteristics at f frequency will be repeated at all frequencies given by τⁿf, where n is an integer. These frequencies are equally spaced on the logarithmic scale, and the period is equal to the logarithm of τ. This is why the logarithmic periodic antenna is called. The logarithmic antenna only repeats the radiation pattern and impedance characteristics periodically. However, if τ of the antenna with this structure is not far less than 1, the change of its characteristics in a period is very small, so it is basically independent of frequency. There are many kinds of log-periodic antennas, including log-periodic dipole antenna and monopole antenna, log-periodic resonant V-shaped antenna, log-periodic helical antenna, etc., among which log-periodic dipole antenna is the most common one. These antennas are widely used in short wave and above.