“Antenna category: ODP (outdoor directional plate antenna), OOA (outdoor omnidirectional antenna), LCD (indoor ceiling antenna), OCS (outdoor two-way antenna), OCA (outdoor cluster antenna), OYI (outdoor Yagi antenna), ORA (Outdoor parabolic antenna), IWH (Indoor wall-mounted antenna), etc.
Introduction to the principles and functions of antennas and passive components commonly used by engineers
1. Antenna principle
1.1 Definition of antenna: Ø A device that can effectively radiate electromagnetic waves to a specific direction in space or can effectively receive electromagnetic waves from a specific direction in space.
1.2 The function of the antenna:
Ø Energy conversion-the conversion between guided traveling waves and free space waves; Ø Directional radiation (receiving)-has a certain directionality.
1.3 Principle of antenna radiation
1.4 Antenna parameters
ØHalf-power beam width, front-to-back ratio;
ØPolarization method, cross-polarization discrimination rate;
ØDirectivity coefficient, antenna gain;
ØMain lobe, side lobe, side lobe suppression, zero point filling, beam down tilt…
ØVoltage standing wave ratio VSWR, reflection coefficient Γ, return loss RL;
ØInput impedance Zin, transmission loss TL;
ØIsolation degree Iso;
ØPassive third-order intermodulation PIM3…
Antenna side lobe
Horizontal beam width
Front-to-back ratio: specify the ratio of the forward radiation power to the antenna and the backward radiation power within ±30°
The relationship between 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 antenna gain:
ØThe antenna is a passive device and cannot generate energy. Antenna gain is just the ability to effectively concentrate energy in a specific direction to radiate or receive electromagnetic waves.
Ø The gain of the antenna is produced by the superposition of the vibrator. The higher the gain, the longer the antenna length. The gain is increased by 3dB and the volume is doubled.
ØThe higher the antenna gain, the better the directivity, the more concentrated the energy, and the narrower the lobe.
1.5 Radiation parameters
Polarization: Refers to the trajectory or changing state of the electric field vector in space.
1.6 Circuit parameters
In this example, the return loss is 10log(10/0.5) = 13dB
VSWR (Standing Wave Ratio) is another measure of this phenomenon
Isolation: It is the ratio of the signal received by one polarization of the other polarization
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 the frequencies f1 and f2, such as 2f1-f2 and 2f2-f1 (3rd order).
2. Antenna products
2.1 Antenna naming method
Antenna category: ODP (outdoor directional plate antenna), OOA (outdoor omnidirectional antenna), LCD (indoor ceiling antenna), OCS (outdoor two-way antenna), OCA (outdoor cluster antenna), OYI (outdoor Yagi antenna), ORA (Outdoor parabolic antenna), IWH (Indoor wall-mounted antenna), etc.
Half power angle: 032,065,090,105,360 (base station antenna) 020,030,040,050,060,075,090,120,160,360 (repeater antenna)
Polarization mode: R (dual polarization), V (single polarization)
Gain: According to actual indicators, the current maximum is 21dbi
Connector type: D (Din head), N (N type head), S (SMA head), T (TNC head), etc.
Specification code: Roman letters indicate the generations of products. The letters and numbers that follow indicate ESC down angle, shaping, ESC and other information. F shaping; V ESC; RV remote ESC
2.2 Base station antenna
Dual frequency antenna
2.3 Distribution system antenna
Smoke detector type ceiling antenna
Lamp type ceiling antenna
2.4 Outdoor antenna
Donor antenna: ØNarrow beam, strong directivity ØHigh front-to-back ratio
Corner reflector antenna
3. Overview of passive components
3.1 Overview of microwave passive components
ØPassive devices are divided into linear devices and non-linear devices.
ØLinear passive components are divided into reciprocity and non-reciprocity.
ØLinear reciprocal components only perform linear transformation on microwave signals without changing the frequency characteristics, and satisfy the principle of reciprocity. Usually what we call passive devices refer to linear reciprocal components.
3.2 Dendrogram of linear reciprocal components
3.3 Power divider
Ø A power divider is a device that divides the energy of one output signal into two or multiple outputs. It is essentially an impedance converter.
ØCan the power splitter be used in reverse to replace the combiner?
ØWhen used as a synthesizer, it not only requires high isolation and low standing wave ratio, but also focuses on the requirement to withstand high power. Taking into account the mismatch of the output ports of the commonly used cavity power dividers and large standing waves; the microstrip power divider reversely bears the characteristics of low power, we do not recommend using the power divider to replace the combiner.
3.4 Classification of power dividers
3.5 Power divider classification comparison
3.6 Features of Cavity Power Divider
ØThe cavity power divider uses high-quality alloy as the conductor, and the filling medium is air;
ØCan withstand relatively large power, up to 200W; the dielectric loss and conductor loss are basically negligible, and the insertion loss is small, which can be below 0.1dB.
ØBut because there is no isolation resistance, the isolation of the output port is very small, so the cavity power divider cannot be used as a power combiner.
3.7 Schematic diagram of power divider test indicators
As shown in the figure, 1 port can measure the standing wave ratio; 2, 3 ports can measure the insertion loss, and due to the characteristics of the cavity power splitter itself, the standing wave of the output port and the isolation of the output port are not proposed as declared values. .
Four, coupler introduction
Ø Coupler is a component that distributes part of the energy of the input signal through the electric field and magnetic field coupling to be output at the coupling end, and the remaining part becomes the 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 The schematic diagram of the four-port network coupler
4.3 Coupler classification
4.4 Directional coupler
Ø Directional couplers are commonly used to sample microwave signals in the specified flow direction. The main purpose is to separate and isolate the signals, or to mix different signals on the contrary. When there is no internal load, the directional coupler is often a four-port network.
Ø Directional couplers are often realized in two ways
4.5 Cavity coupler
Features: Carrying high power and showing low loss.
1. The filling medium inside the cavity is air. During the transmission process, the medium dissipation caused by the air medium is much lower.
2. The coupling band is generally made of a conductor with good conductivity (such as silver plated on the surface of copper), and the conductor loss is basically negligible.
3. The cavity is large in size and fast in heat dissipation. It can withstand high power.
4.6 Schematic diagram of coupler index test
As shown in the figure, where directivity = isolation-coupling, data cannot be accessed.
Five, 3dB electric bridge introduction
The 3dB bridge coupler is a kind of directional coupler. When used as a power combiner, the two input signals are connected to each other as isolated ports, and the coupled output and the direct output port are mutually reciprocal. If used as two outputs, regardless of loss, the input signal power is divided into the two output ports. When used as a single-port output, the other output end must be connected to a matched power load to absorb the output power of the port, otherwise it will seriously affect the system transmission characteristics, and at the same time, it also brings an additional 3dB loss, which is For system applications, it will affect the cost and reliability of its active parts.
5.2 Main engineering applications are mainly used in the combined application of different carriers in the same frequency band. Due to the discrete nature of the circuit and processing and assembly, the isolation of the input port of the bridge coupler is relatively low, and it is not recommended to be used in combined applications between different frequency bands. In summary, in the application of inter-frequency combining, except for the adjacent carrier frequency in the same frequency band (such as the adjacent carrier frequency in the GSM downlink frequency band), etc., only 3dB bridges can be used, and the duplex/multiplexer is not applicable. , It is recommended to use duplex/multiplex combiner first to improve the performance index of the system and increase reliability.
5.3 Power Divider VS Coupler
Six, introduction of combiner
ØFunction: combine multiple signals into one signal output
ØClassification: classified according to the actual combined frequency band
6.2 Combiner VS Bridge VS Power Divider
Seven, attenuator introduction
ØThe attenuator is a two-port reciprocal component
ØThe most commonly used attenuator is an absorptive attenuator.
ØThe coaxial attenuator is usually used in engineering, which is composed of “π” type or “T” type attenuation network.
ØThe coaxial attenuator usually has two kinds of fixed and variable attenuation.
ØAttenuators are mainly used to control microwave signal transmission energy and consume excess energy in the detection system, thereby extending the dynamic range of signal measurement, such as power meters, spectrum analyzers, amplifiers, receivers, etc.