What Is a Network Analyzer?

Network Analyzer A comprehensive microwave measurement instrument that can perform sweep measurements over a wide frequency band to determine network parameters. The full name is microwave network analyzer. A network analyzer is a new type of instrument for measuring network parameters. It can directly measure the complex scattering parameters of active or passive, reversible or irreversible dual-port and single-port networks, and give the amplitude and phase of each scattering parameter in a sweeping manner. Frequency characteristics. Automatic network analyzer can correct 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) Transmission parameters such as phase shift and group delay, as well as isolation and directivity.

Vector network analyzer is the most important and widely used high-precision intelligent test instrument in the field of microwave and millimeter wave test instruments. It enjoys the reputation of "the king of microwave / millimeter wave test instruments" in the industry and is mainly used for the network under test. The measurement of amplitude, phase frequency and group delay of bidirectional S-parameters of scattering parameters is widely used in the research, development, production, maintenance and measurement of new generation military electronic equipment represented by phased array radar. It can also be applied In precision guidance, stealth and anti-stealth, aerospace, satellite communications, radar detection and surveillance, teaching experiments and antenna and RCS testing, component testing, material testing and many other areas ^[1]

The network analyzer was developed on the basis of a four-port microwave reflectometer (see standing wave and reflection measurements). Automated in the mid-1960s, using a computer to correct errors caused by directional coupler imperfections, mismatches, and leakage at each frequency using a certain error model, thereby greatly improving measurement accuracy. It can achieve the measurement accuracy of the most precise measurement line technology in the measurement room, and the measurement speed is increased by dozens of times ^[2]

When all the port terminals of an arbitrary multi-port network are matched, the incident traveling wave a n input from the n- th port will be scattered to all the remaining ports and transmitted. If the outgoing traveling wave of the m- th port is b m, the scattering parameter between the n- port and the m- port S mn = b m / an One

The parameter (scattering parameter) is used to evaluate the performance of the DUT reflected and transmitted signals. The parameter is defined by the ratio of two complex numbers and contains information about the amplitude and phase of the signal. The parameters are usually expressed as:

Input and output

Output: The DUT port number of the output signal.

Input: The DUT port number of the input signal.

For example, parameter S21 is the ratio of the output signal of port 2 on the DUT to the input signal of port 1 on the DUT.

When the balanced-unbalanced conversion function is activated, the mixed mode S-parameter can be selected.

In 1973, a six-port network analyzer was developed. It uses a six-port network consisting of a directional coupler and a hybrid connector (Magic T ) as the measurement unit. Except for two ports connected to the signal source and the device under test, the other four ports are connected to the amplitude detector or dynamometer. Through the appropriate combination of the detected four amplitudes, the mode and phase of the measured network scattering parameters can be obtained. It does not need to use a complicated two-channel receiver to obtain phase information, which greatly simplifies the hardware of the measurement system. In addition, it has more than the necessary number of redundant measurement ports, and can use the mutual verification of redundant data to improve the credibility of measurement results. But its calculation work is much more complicated than a four-port network analyzer. A dual six-port network analyzer is used to measure a dual-port network, that is, a six-port network analyzer is connected to port 1 of the network under test and the other is connected to port 2 to avoid switching or manual inversion of the network under test The input and output terminals further improve the measurement accuracy ^[3] .