Network analyzer tests line loss


1、What is a network analyzer

Network analyzer is a new type of instrument to measure network parameters, which can directly measure the complex scattering parameters of active or passive, reversible or irreversible double-port and single-port networks, and give the amplitude and phase frequency characteristics of each scattering parameter in a sweeping manner.

2Classification of network analyzers

2.1. Scalar network analyzer

Only amplitude information is measured, phase measurement is not supported. The receiver uses diode detection, no frequency selection characteristics, and small dynamic range.

2.2. Vector network analyzer

Measure amplitude and phase information. The receiver adopts tuned reception, has frequency selection characteristics, can effectively suppress interference and spurs, and has a large dynamic range.

3、Test object of network analyzer

3.1 Single port or dual port

Antennas, matching terminals, filters, attenuators, isolators, amplifiers, connectors, cables

3.2 Multiport

Multiplexers, multiplexers, bridges, directional couplers, power dividers, circulators, transformers, balancing devices

3.3. Frequency conversion devices

Mixers, modulators, conversion frontends

4、The principle of network analyzer

In order to complete the test-in-test transmission/reflection characteristics, the network analyzer includes: excitation signal source; Provide the excitation input signal of the test piece; The signal separation device, including a power divider and a directional coupling device, extracts the input and reflected signals of the test piece, respectively. Receiver; Test the reflection, transmission, and input signals of the test piece; processing display units; Processing and display of test results.

5、Introduction to the main test parameters

The network analyzer can correct the error of the measurement results point by point, and convert dozens of other network parameters, such as input reflection coefficient, output reflection coefficient, voltage standing wave ratio, impedance (or admittance), attenuation (or gain), phase shift and group delay and other transmission parameters, as well as isolation and directionality (PS: general companies are mainly used for product transmission, reflection [S11, S12, S22], VSWR testing)

Device performance is described in two ways: transmission performance and reflection performance. Indicator definitions of transmission performance: Gain, Phase, Group delay. Indicator definitions of reflection performance: VSWR, Γ, ρ, impedance.

Therefore, when we usually use network analyzers to test R&D or produced products, we mainly pay attention to the reflection coefficient (return loss), gain/difference, isolation/directionality, group delay and other main parameter characteristics of microwave devices. No matter which instrumentation supplier provides the network analyzer is based on this principle and application to develop and design, but each supplier in the network analyzer implementation, man-machine operation interface, frequency coverage, test speed, indicators and other specific details are different, other functional aspects are similar, this depends on the user's habits and recognition.

6、How to improve the test accuracy of the network analyzer

There are three main categories of errors in the network analyzer test process: systematic error, random error, and drift error.

The system error is caused by the unsatisfactory test device inside the instrument. It is predictable and repetitive, and generally does not change over time, allowing it to be quantitatively described and systematic errors can be eliminated by calibration prior to testing (the portion that has been eliminated after calibration by calibration)

Random error is unpredictable because it exists in random form, changes over time, and therefore cannot be eliminated by calibration. The main sources of random error are the internal noise of the instrument, such as phase noise of the excitation source, sampling noise, the noise floor of the IF receiver, the repeatability of switching actions, etc. (related to the service life and quality of the network splitter, unpredictable) ...

Drift error is the drift in the performance of the test setup after the instrument is calibrated. Drift errors are primarily due to temperature variations and can be eliminated with further calibration. The length of time that a meter can maintain stable accuracy after calibration depends on the drift rate of the instrument in the measurement environment.

7、Basic classification of calibration

The test of coaxial structure is mainly calibrated with SOLT calibration parts and electronic calibration parts

8、Feature comparison

8.1. The accuracy of SOLT calibration is better than that of electronic calibration parts;

8.2. SOLT calibration is relatively cumbersome (Open, Short, Load, Through are used for calibration in turn), and the two electronic calibration pieces can be directly connected to the network splitter to calibrate in place at one time;

8.3. The SOLT calibration method is mostly used for laboratory calibration, and the calibration method for electronic calibration parts is mostly used for production line production.

For different test requirements, sometimes the four calibration parts Open, Short, Load, and Through do not need to be used at the same time; For example, when we only need to obtain the phase and insertion loss data of the DUT, we can use single-port calibration, and only need Open, Short, Load or Open, Short and Open to achieve the purpose of calibration (the network itself has a matching system algorithm according to different calibration conditions, and we can also connect to the computer to design a specific algorithm to achieve calibration)