Performance Parameters Passive Components of RF Antenna System

Antenna system is a system composed of transmitting antenna and receiving antenna. The former is a transmission mode converter that converts the radio-frequency current or electromagnetic wave in guided wave mode into space electromagnetic wave in diffusion wave mode; The latter is the transmission mode converter of its inverse transform.

The transmitting antenna used for the mode conversion from guided wave to guided wave and the receiving antenna I used for the mode conversion from guided wave to guided wave can be used interchangeably except that the power bearing capacity and voltage bearing capacity of the transmitting antenna are much greater than that of the receiving antenna, and the basic characteristic parameters of the antenna remain unchanged. This is called the reciprocity theorem. Another important function of the antenna is to concentrate the electromagnetic wave energy, that is, when it is used as a transmitting antenna, it concentrates the energy in the transmitting direction while reducing the energy in other directions; As a receiving antenna, more energy can be intercepted from incoming waves in the receiving direction, while the input energy can be reduced by phase cancellation for incoming waves in other directions. This is the directivity of the antenna. Compared with non directional antenna, the increase of energy concentration is called antenna gain. The extended meaning of antenna directivity is the negative gain (attenuation) in the non communication direction, which can be used to describe another relevant performance index of the antenna, that is, the sidelobe (interference) radiation suppression regime of the transmitting antenna or the incoming wave interference suppression regime of the receiving antenna in the non communication direction.

Description of performance parameters of base station antenna

Electrical indicators

1. Frequency range

Operating frequency band: no matter the antenna or other communication products, they always work within a certain frequency range (frequency bandwidth), which depends on the index requirements. Generally, the frequency range that meets the index requirements can be the operating frequency of the antenna.

The width of the operating frequency band is called the operating bandwidth. Generally, the operating bandwidth of the Omni-directional antenna can reach 3-5% of the central frequency, and the operating bandwidth of the directional antenna can reach 5-10% of the central frequency.

2. Input impedance

Input impedance: the ratio of signal voltage and signal current at the antenna input is called the input impedance of the antenna. The input impedance of a general mobile communication antenna is 50 Ω.

The input impedance is related to the structure, size, and operating wavelength of the antenna. Within the required operating frequency range, the imaginary part of the input impedance is very small and the real part is quite close to 50 Ω, which is necessary for the antenna to be in good impedance matching with the feeder.

3. Voltage standing wave ratio (VSWR)

Voltage standing wave ratio: the voltage standing wave ratio of the antenna is the ratio of the maximum value to the minimum value on the voltage standing wave pattern generated along the transmission line when the antenna is used as the load of the lossless transmission line.

The generation of the standing wave ratio is caused by the superposition of reflected waves generated when the incident wave energy is transmitted to the input end of the antenna and is not fully absorbed (radiated). This article comes from the filter WeChat official account. The larger the VSWR, the greater the reflection, and the worse the matching. In a mobile communication system, the standing wave ratio is generally required to be less than 1.5.

4. Isolation

The degree of isolation represents the proportion of signals fed to one port (one polarization) of the dual-polarization antenna in the other port (the other polarization).

5. Third order inter modulation

Third order intermodulation signal: refers to the parasitic signal after the second harmonic of one signal and the fundamental wave of the other signal are beat (mixed) due to the existence of nonlinear factors in a linear system.

Intermodulation is the phenomenon that two or more carrier frequencies outside the frequency band mix and fall into the new frequency components in the frequency band, resulting in the degradation of system performance

6. Power capacity

Power capacity: the power capacity of the antenna refers to the maximum continuous RF power that can be continuously added to the antenna without degrading its performance within the specified time period according to the specified conditions.

Space radiation index

7. Gain

The ratio of the radiation power flux density of the antenna in a specified direction to the maximum radiation power flux density of the reference antenna (usually an ideal point source) at the same input power;

Antenna gain is used to measure the ability of an antenna to transmit and receive signals in a specific direction. It is one of the important parameters for selecting a base station antenna. The higher the antenna gain, the better the directivity, the more concentrated the energy, and the narrower the lobe.

8. H/v-plane half power beam width

In the main lobe of the power pattern, the beam width angle between two points where the relative maximum radiation direction power is reduced to half or less than the maximum 3dB is called the half power lobe width.

The half power beam width in horizontal plane is called horizontal beam width; The half power beam width of the vertical plane is called the vertical beam width.

9. Electrical down tilt

The electric dip angle refers to the angle between the maximum radiation direction on the vertical radiation surface of the communication antenna and the normal of the antenna.

The communication antenna can be divided into fixed downward tilt antenna and electric adjustment antenna according to whether it supports electric downward tilt adjustment: fixed downward tilt antenna refers to the fixed downward tilt antenna generated by shaping the amplitude and phase of the antenna radiation unit array according to the wireless coverage requirements; This article comes from the filter wechat official account. The electrically tunable antenna refers to changing the phase difference of different radiation units in the array through the phase-shifting unit, resulting in different radiation main lobe dip states. Generally, the dip state of the electrically tunable antenna is only within a certain adjustable angle range.

10. Front to back ratio

The front to back ratio of the antenna refers to the ratio of the power flux density in the maximum radiation direction (specified as 0 °) of the main lobe to the maximum power flux density near the opposite direction (specified as 180 ° ± 30 °) f/b=10log (front to back power / backward power).

11. Elevation upper side lobes & null fill

Side lobe suppression: the side lobe of the main lobe in the vertical direction (i.e. in the positive direction of the zenith angle) is called the upper side lobe. In order to achieve coverage effect, the base station antenna usually adopts a certain mechanical downward inclination in the network planning. This may cause the first (or within a certain angle range) upper side lobe of the antenna to be in the horizontal position or even lower than the horizontal position, which is easy to cause adjacent cell interference. Therefore, it is necessary to suppress it, that is, upper side lobe suppression.

The upper sidelobe not only wastes the energy radiated by the antenna, but also interferes with the adjacent cells, especially the high-rise buildings in the adjacent cells. This paper comes from the filter wechat official account, so the upper sidelobe should be suppressed as much as possible, especially the first upper sidelobe with large energy.

Zero point filling: refers to filling the first zero point of the lower sidelobe in the vertical plane of the antenna with a beam forming design, so as to improve the coverage of the near area of the base station and reduce the dead zone and blind spot of the near area coverage.

12. Cross polarization ratio

Difference between the power level of antenna co polarized reception (maximum reception level) and the power level of different polarized reception (minimum reception level) within 3dB beam width of the pattern

13. Circularity of pattern

The circularity of omnidirectional antenna pattern refers to the deviation between the maximum or minimum level value and the average value in the horizontal pattern.

The average value refers to the arithmetic mean of the level dB value in the direction of the horizontal plane with the maximum interval not exceeding 5 °.

14. Polarization mode

The electric field direction of the electromagnetic wave radiated by the antenna is the polarization direction of the antenna. If the electric field direction of the electric wave is perpendicular to the ground, we call it a vertically polarized wave; If the electric field direction of the electric wave is parallel to the ground, it is called horizontal polarization wave; If the electric field direction of the radio wave is at an included angle of 45 ° with the ground, it is called ＋ 45 ° or -45 ° polarization.

Types of RF antennas

Indoor distributed and cell coverage antenna products

1. ceiling antenna

Ceiling antennas are generally used in indoor wireless coverage scenes. According to their different radiation forms, they can be divided into directional ceiling antennas and Omnidirectional ceiling antennas. Omnidirectional ceiling antennas can be divided into single polarization ceiling and dual polarization ceiling.

2. wall-mounted antenna

Indoor wall-mounted antenna is a typical small plate antenna product, which is mainly used for indoor wireless coverage scenarios. According to different polarization modes, it can be divided into single polarization wall mounted antenna and dual polarization wall mounted antenna.

3. Yagi antenna

Yagi antenna is mainly used for link transmission and repeater, with low cost and good front and rear reflectance in two-dimensional plane.

4. log periodic antenna

The log periodic antenna is similar to the Yagi antenna. It is a multi-element bidirectional antenna with broadband coverage. It is mainly used for link relay.

5. parabolic antenna

Parabolic antenna is a high gain bidirectional antenna, which is composed of a parabolic reflector and a central feed antenna.

Outdoor base station antenna products

1. omnidirectional base station

The omnidirectional base station antenna is mainly used for 360 degree wide coverage and is mainly used to cover sparse rural wireless scenes.

2. directional base station antenna

Directional base station antenna is the most widely used fully enclosed base station antenna at present. It is divided into several types, mainly including vertical polarization antenna, vertical and horizontal polarization antenna, ± 45 ° dual polarization antenna, multi band antenna, etc. This paper comes from the filter wechat official account. According to the different tilt angle electric adjustment methods, it can be divided into fixed tilt angle antenna, electric adjustment antenna, and three sector cluster antenna.

3. electric control base station antenna

Electrically tunable antenna means that the phase difference of different radiating elements in the array is changed by phase-shifting elements, so as to produce different downward inclination states of radiation main lobe. Generally, the downward inclination state of electrically tunable antenna is only within a certain adjustable angle range. There are manual adjustment and RCU electric adjustment for electric adjustment of tilt down.

4. smart antenna

The dual polarization radiation unit is used to form a directional or omnidirectional array, which can scan the beam in 360 degrees or a specific direction; The smart antenna is an antenna array that can determine the spatial information of the signal (such as the propagation direction) and the intelligent algorithm for tracking and locating the signal source, and can perform spatial filtering based on this information.

5. multimode antenna

The main difference between the multi-mode base station antenna product and the ordinary base station antenna is that more than two antennas of different frequency bands are integrated in a limited space. This article comes from the filter wechat official account. Therefore, the product focuses on eliminating the interaction between different frequency bands (decoupling effect, isolation, near-field interference)

6. multi beam antenna

Multi beam antenna an antenna that produces multiple sharp beams. These sharp beams (called meta beams) can be combined into one or several shaped beams to cover a specific airspace. There are three basic forms of multi beam antenna: lens type, reflector type and phased array type.

RF communication feeder passive components and others

1. RF feed cable

RF feeder cable can be divided into semi flexible coaxial cable and semi-rigid coaxial cable; According to different models, they can be divided into different sizes, such as 1/4 ″, 3/8 ″, 1/2 ″, 5/8 ″, 7/8 ″, 1-1/4 ″, 1-5/8 ″, which are mainly used for indoor and outdoor RF signal transmission.

The RF cable inside the mobile communication antenna is also an RF feed cable, which is mainly used for jumper joint feeding, power division network feeding, network impedance matching, etc.

2. combiner and splitter

The combiner is mainly used to combine multiple system signals into a set of indoor distribution system. In engineering application, a set of indoor distribution system can work in different communication frequency bands at the same time by using combiner. The combiners used in mobile communication systems generally include two-way combiners, three-way combiners, four-way combiners and so on.

3. filter

The function of the filter is to allow the signals with partial frequencies to pass smoothly, while the signals with other partial frequencies are greatly suppressed. This paper comes from the WeChat official account of the filter. The filter is generally divided into an active filter and passive filter. The cavity filter in the passive filter is generally used in the mobile communication system. Its main characteristics are wide frequency coverage, high reliability, good stability, input and output impedance matching, easy cascade use, flat in band amplitude frequency characteristics, small insertion loss, high out-of-band suppression system, etc.

4.POI

Point of interface, a multi system integration platform. It is mainly used for indoor coverage of metro, convention and Exhibition Center, exhibition hall, airport and other large buildings. The system uses frequency combiner and Bridge combiner to combine mobile signals of multiple operators and systems, and then introduces the antenna feeder distribution system, so as to make full use of resources and save investment.

To avoid interference, POI is divided into uplink and downlink platforms, which transmit uplink and downlink signals separately. As a bridge between wireless communication donor signals and distributed coverage signals (leaky cables, antenna arrays, etc.), POI comes from the filter wechat official account. Its main function is to combine and branch the uplink and downlink RF signals of various operators, and filter out the interference components between various frequency bands. The main function of the uplink part of the POI is to collect the signals sent by mobile phones of different systems through the antenna and transmit them to the uplink POI through the feeder. The signals of different frequency bands are detected by the POI and sent to the base stations of different operators. The main function of the downlink part of the POI is to synthesize carrier signals of various operators and different frequency bands and send them to the antenna feeder distribution system in the coverage area.