Summary of microwave network
Microwave circuits used to detect, transmit and process information or energy in various electronic systems. Microwave network theory mainly studies the analysis and design method of microwave circuit. It is the main theoretical basis of microwave field together with electromagnetic field theory (see basic theorem of electromagnetic field). Microwave network is a functional microwave circuit or system with several output and input ports of arbitrary shape and structure, which is composed of microwave components connected by waveguides or transmission lines.
Microwave network classification
1. Passive microwave network
The two port network includes microwave filter, mode converter (used to transform one electromagnetic wave mode into another), polarization converter (used to change the polarization property of electromagnetic wave in waveguide), phase shifter, ferrite and isolator. The three port network includes power distributor, ferrite Y-ring, etc. Microwave hybrid connector, directional coupler and directional filter belong to four port network. The multiplexer used in microwave multi-channel communication belongs to multi port network. Its function is to divide a wideband channel into several narrowband channels, so that the signals are output from different ports. The multiplexer can be composed of multiple directional filters or a combination of a bandpass filter and a matched double-T bridge.
2. Active microwave network
A typical two port network is a microwave transistor amplifier. Low noise amplifier, power amplifier, wide-band amplifier and narrow-band amplifier can be constructed by using bipolar transistor or field-effect transistor. A typical three port network is a microwave mixer. Schottky barrier diodes are often used as mixers. In order to reduce the noise of the mixer, two mixers can be used to form a balanced mixer. The parametric amplifier for low noise amplifier is also a three port network. Its typical structure consists of a three port y-circulator and a two port reflective amplifier. The signal is input from one port of the circulator, amplified by a reflective amplifier connected to the second port, and then output from the third port of the circulator. The reflective amplifier has a signal port and a pump source port. The input signal absorbs the pump source power through the nonlinear capacitance of the varactor to obtain the gain.
Practical application of microwave network
The significance of any computing tool is to be applied to practice. In the analysis of microwave network capacity, we can find its important working purpose. It can show the complex structure through clear charts, so that the staff can make clear the work priority and direction, which is more conducive to the smooth development of the work. In the process of calculation, first of all, we need to confirm the location of the city where the site belongs, and adjust it by changing the capacity. It is worth noting that the properties of the site can not be normal, so when setting, the relevant properties are adjusted to the state of not calculating the capacity. In the setting of “link table”, you need to adjust the current component capacity, change it to the current link capacity, and click Start calculation. If the demand capacity is too small, it means that there is no need to upgrade the optimized link. If the link needs to be upgraded, it needs to be upgraded and modulated by regular software. At the same time, the upgrade software can also solve the problem of insufficient capacity resources. The application of microwave network capacity computing equipment in real life can simplify the complex topology, make the staff understand the specific work content, and effectively solve the problem of insufficient site resource capacity, and provide convenience for the normal development of the project.
Measurement of two port microwave network parameters
1. Purpose of the experiment
(1) Understand the principle of variable circuit breaker to realize open circuit;
(2) Learn how to measure, analyze and calculate the reflection coefficient under different loads;
(3) Learn to use the three-point method to measure, analyze and calculate the [S] parameters of microwave network.
2. Experimental principle
The [S] parameter is an important physical quantity in the microwave network, and the three-point measurement method of [S] parameter is the basic measurement method. Its measurement principle is as follows: for the reciprocal two port network, there is S12 = S21, so only three quantities of S11, S12 and S21 can be measured. The network connection under test is shown in Figure 8-1
When the network to be tested is successively connected with Terminal Short-Circuit load (existing Γ I = – 1), terminal open circuit load (Γ I = 1) and terminal matching load (Γ I = 0), the measured input reflection coefficients are Γ s, Γ O and Γ m, respectively
This is the principle of three-point measurement.
In actual measurement, because the waveguide opening is not a real open circuit, the terminal equivalent open circuit l0 position (or the waveguide opening is equivalent to open circuit) is usually realized by using a precision movable short circuit breaker, as shown in Figure 8-2.
3. Content and steps of the experiment
(1) The matching load is connected to the terminal of the measuring line, and the measuring line test system is adjusted to the best working state;
(2) Connect the short circuit piece to the terminal of the measuring line, and rotate the position of the probe base (the big knob in front of the measuring line) from the terminal of the measuring line to the direction of the signal source, so that the indication of the frequency selective amplifier is zero (or minimum). At this time, the position is the equivalent short road surface, which is recorded as zmin0;
(3) At the terminal, remove the short-circuit chip and connect the variable short-circuit device. At the probe position zmin0, adjust the variable short-circuit device to make the frequency selection amplifier indicate zero (or minimum), and record the position L1 of the variable short-circuit device at this time;
(4) Continue to adjust the variable circuit breaker to make the indication of the frequency selective amplifier change to zero again, and then record the position L2 of the variable circuit breaker at this time;
(5) The variable circuit breaker is removed from the terminal and connected to the network to be tested, and the matching load is connected to the terminal of the network to be tested. The reflection coefficient Γ m is measured and calculated according to the method of Experiment 5;
(6) At the terminal of the network to be tested, the matching load is removed, the variable short circuit is replaced, and the variable short circuit is adjusted to position L1. The reflection coefficient Γ s is measured and calculated according to the method of Experiment 5;
(7) Adjust the VSC to the equivalent open circuit position of the terminal, i.e. l0 = (L1 + L2) / 2, and measure and calculate the reflection coefficient Γ O according to the method of Experiment 5;
(8) It is required to measure repeatedly for three times and process the data (i.e. referring to the method of Experiment 5, the corresponding reflection coefficient will be calculated according to the data of Imin, IMAX, zmin1, etc.); (9) the parameter [S] will be calculated according to equation (8-3).
4. Experimental results and data processing
zmin0 = 79.56mm li= 12.760mm l2 = 36.984mm
Matching: direct method
Through this experiment, we know the principle of realizing open circuit by VSC, learn the side quantity, analysis and calculation method of reflection coefficient under different loads, and master the [S] parameters of microwave network analyzed and calculated by side quantity of three-point method. In the first measurement of matching and open circuit, the method of large standing wave ratio is used. It is found that the standing wave ratio is less than 6 in the calculation process, so the direct method is used again.