1、 Antenna principle
1.1 definition of antenna：
A device that can effectively radiate electromagnetic waves in a specific direction of space or effectively receive electromagnetic waves from a specific direction of space.
1.2 functions of antenna：
Energy conversion - conversion of guided wave and free space wave;
Ø Directional radiation (reception) - has a certain directivity.
1.3 antenna radiation principle
1.4 antenna parameters
U radiation parameters
Ø Half power beam width and front to rear ratio;
Ø Polarization mode, cross polarization discrimination rate;
Ø Directivity coefficient and antenna gain;
Ø Main lobe, side lobe, sidelobe suppression, zero filling, beam dip
U circuit parameters
Ø VSWR, reflection coefficient Γ、 Return loss RL;
Ø Input impedance Zin, transmission loss TL;
Ø Isolation ISO;
Ø Passive third-order intermodulation PIM3
U antenna sidelobe
U horizontal beam width
U front to back ratio: Specifies the forward radiation power and backward & plusmn; 30° Ratio of internal radiation power
Relationship between u gain and antenna size and beam width
Flatten the "tire", the more concentrated the signal, the higher the gain, the larger the antenna size and the narrower the beam width;
Several key points of u antenna gain:
Ø The antenna is a passive component and cannot generate energy.
Antenna gain is only the ability to effectively concentrate energy to radiate or receive electromagnetic waves in a specific direction.
Ø The gain of the antenna is generated by the superposition of oscillators.
The higher the gain, the longer the antenna length.
The gain is increased by 3dB and the volume is doubled.
Ø The higher the antenna gain, the better the directivity, the more concentrated the energy and the narrower the lobe.
1.5 radiation parameters
U polarization: refers to the trajectory or changing state of the electric field vector in space.
1.6 circuit parameters
U return loss
In this example, the return loss is 10log (10 / 0.5) = 13dB VSWR (standing wave ratio) is another measure of this phenomenon
U isolation: it is the proportion of signals received by one polarization to signals received by another polarization
U passive intermodulation (PIM):
When two frequencies F1 and F2 are input to the antenna, due to the nonlinear effect, the signal radiated by the antenna includes other frequencies in addition to frequencies F1 and F2, such as 2f1-f2 and 2f2-f1 (third order).
2、 Antenna products
2.1 antenna naming method
Antenna category:
ODP (outdoor directional plate antenna), OOA (outdoor omnidirectional antenna), IxD (indoor ceiling antenna), OCS (outdoor bidirectional antenna), OCA (outdoor cluster antenna), oyi (outdoor Yagi antenna), ora (outdoor polished antenna), IWH (indoor wall mounted antenna), etc
Half power angle:
032065090105360 (base station antenna)
02030040050060075090120160360 (repeater antenna)
Polarization mode:
R (dual polarization), V (single polarization)
Gain:
According to the actual indicators, the current maximum is 21dbi
Joint type:
D (DIN head), n (n-type head), s (SMA head), t (TNC head), etc
Frequency band:
Specification code:
The Roman alphabet indicates the generation of products The following letters and numbers indicate the dip angle, shape, electric adjustment and other information F type; V electric regulation; RV remote electric regulation
2.2 base station antenna
Omnidirectional antenna
Dual band antenna
Tri band antenna
2.3 distributed system antenna
Smoke sensor type ceiling antenna
Lamp type ceiling antenna
Wall mounted antenna
2.4 outdoor antenna
Donor antenna:
Ø Narrow beam and strong directivity & Oslash; High front rear ratio
Yagi antenna
Angular reflector antenna
Paraboloid antenna
User antenna
3、 Overview of passive components
3.1 overview of microwave passive components
Ø Passive devices are divided into linear devices and nonlinear devices.
Ø Linear passive devices can be divided into reciprocal and non reciprocal.
Ø The linear reciprocity element only linearly transforms the microwave signal without changing the frequency characteristics, and meets the reciprocity principle.
Generally, the passive components we call refer to linear reciprocity components.
3.2 linear reciprocal component tree view
3.3 power divider
Ø Power divider is a device that divides one output signal energy into two or more outputs.
It is essentially an impedance converter.
Ø Can the power divider be used in reverse to replace the combiner?
Ø When used as a synthesizer, it not only needs high isolation and low standing wave ratio, but also focuses on bearing high power.
3.4 classification of power divider
3.5 power divider classification and comparison
3.6 characteristics of cavity power divider
Ø The cavity power divider adopts high-quality alloy as the conductor and the filling medium is air;
Ø It can withstand relatively high power, up to 200W; The dielectric loss and conductor loss are basically negligible, and the insertion loss is small, which can be less than 0.1dB.
Ø However, because there is no isolation resistance and the isolation of the output port is very small, the cavity power divider can not be used as a power synthesizer
3.7 schematic diagram of power divider test indicators
As shown in the figure, one port can measure the standing wave ratio; The insertion loss can be measured at ports 2 and 3. Due to the device characteristics of the cavity power divider, the standing wave at the output port and the isolation of the output port are not proposed as declared values.
4、 Coupler introduction
4.1 coupler
Ø Coupler is an element that distributes the energy of input signal through electric field and magnetic field coupling, part of which is output at the coupling end, and the rest is output at the output end to complete power distribution.
Ø The power distribution of the coupler is unequal.
Also known as power sampler.
4.2 schematic diagram of four port network coupler
4.3 coupler classification
4.4 directional coupler
Ø Directional couplers are often used to sample microwave signals with specified flow direction. The main purpose is to separate and isolate signals, or to mix different signals on the contrary. When there is no internal load, directional couplers are often a four port network
Ø Directional couplers are often implemented in two ways
4.5 cavity coupler
characteristic:
Carrying high power and low loss.
reason:
1. The filling medium inside the cavity is air. In the transmission process, the medium dissipation caused by air medium is much lower.
2. The coupling strip is generally made of conductors with good conductivity (such as silver plating on the copper surface), and the conductor loss is basically negligible.
3. Large cavity volume and fast heat dissipation Withstand high power.
4.6 schematic diagram of coupler index test
As shown in the figure, directionality = isolation - coupling, and data cannot be read.
5、 3dB bridge introduction
5.13db Bridge
3dB bridge coupler is a kind of directional coupler.
When used as a power synthesizer, the two input signals are isolated from each other, and the coupling output and direct output ports are reciprocal If it is used as two outputs without considering loss, the sum of input signal power and output power is divided into two outputs.
When used as a single port output, the other output must be connected with a matching power load to absorb the output power of the port, otherwise the system transmission characteristics will be seriously affected, which will also bring additional 3dB loss, which will affect the cost and reliability of the active part for system applications
5.2 main engineering applications
It is mainly used for combining between different carriers in the same frequency band.
Due to the discreteness of the circuit and processing assembly, the isolation of the input port of the bridge coupler is relatively low, so it is not recommended to be used in the combined application between different frequency bands.
In conclusion, in the application of different frequency combining, except that the adjacent carrier frequency in the same frequency band (such as the adjacent carrier frequency in the GSM downlink frequency band) can only use 3dB bridge instead of duplex / multiplex combiner, it is recommended to give priority to duplex / multiplex combiner in use, so as to improve the performance index of the system and increase the reliability
5.3 power divider vs coupler
6、 Introduction to combiner
6.1 combiner
Ø effect:
Synthesize multiple signals into one signal output
Ø Classification:
Classify according to the actual combined frequency band
6.2 combiner vs bridge vs power divider
7、 Introduction to attenuator
7.1 attenuator
Ø The attenuator is a two port reciprocal element
Ø The most commonly used attenuator is the absorption attenuator
Ø Coaxial attenuator is usually used in engineering, which is composed of "π" or "t" attenuation network.
Ø Coaxial Attenuators usually have fixed and variable attenuation.
Ø Attenuator is mainly used to control microwave signal transmission energy and consume excess energy in the detection system, so as to expand the dynamic range of signal measurement, such as power meter, spectrum analyzer, amplifier, receiver, etc.
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