Antenna Radiation Characteristics Measurement Classification
Antenna radiation characteristics of the measurement method shown in Figure 6. Far field method can be divided into outdoor field, indoor field and tight field; near field method can be divided into plane, spherical, cylindrical near field test method.
1. Far field method
Far field method is also known as direct method, the far field data obtained do not need to calculate and post-processing is the pattern. But it often takes a long distance to test the characteristics of the antenna, so most of the far-field methods are carried out in the outdoor test site. Outdoor field is divided into elevated field and ramp field, collectively referred to as free space test field, the main drawback is vulnerable to external interference and site reflection. Far field method if the dark room is called indoor field. Because the space required is large, the indoor field is often costly.
The compact field is classified as far field test field, but it does not use a large test field, but with a parabolic antenna and feed, the feed is placed in the focal area of the parabolic antenna, and the parabolic reflected wave is a plane wave. So that the measured antenna in the plane wave area. Tightening field equipment processing accuracy requirements are high, change the work band need to replace the feed, the cost is greater.
2. Near field method
Near-field measurement technique is to use a known probe on a surface of the near-field region of the antenna to sample the amplitude and phase characteristics of the field and to obtain the far-field radiation characteristics of the antenna by rigorous mathematical transformation. According to the shape of the sampling surface, the near field test field is divided into three kinds, namely, the plane test field, the cylinder test field and the spherical test field.
The main advantage of the near field measurement technique is that the required space is small and can be measured with high precision in the microwave darkroom, eliminating the difficulty of building a large microwave chamber. Measure the impact of the surrounding environment is minimal, to ensure that all-weather can be carried out smoothly. The measured information is large and the far field amplitude phase and polarization characteristics of the antenna can be accurately obtained by sampling a certain surface in the near field region. Near field measurement techniques are discussed in detail in Chapter 7.
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