**3. A case study for NIM OATS**

**Figure 7** shows a photo of NIM OATS taken in 2014. It is located in NIM's Changpin Campus. The white part is the reflective GP, and usually, there are a motorized mast and a manual mast for holding the antennas to be measured. The masts are made of low permittivity dielectric materials. The motor of the motorized mast is located under the metal GP to avoid unwanted reflections. Obviously, these setups will imitate the theoretical model shown in **Figure 1**.

**Figure 7.** *Photo of NIM OATS.*

*Design, Construction and Validation of a High-Performance OATS DOI: http://dx.doi.org/10.5772/intechopen.99727*

BTW, in this photo, there are two more masts on the upper right corner of the GP, which is for backup, and it would better be moved away. There is also a beautiful lake in the north of the OATS. Some sand cypress trees are planted around to keep the soil wet and as fences to prevent the entrance of unintentional persons and trucks.

The structure of the OATS is illustrated in **Figure 8**.

The whole system is designed carefully. The metal GP will suffer more than 80 degrees temperature variations seriously during four seasons in Beijing. In order to cope with this critical problem, the large metal GP is placed "freely" on the top 2501 pieces (41 by 61) of the ceramics plate. The metal GP can move freely in the horizontal plane but is kept fixed in the vertical direction. The ceramics plates are mounted on adjustable bolts, which are mounted on the steel frames. These steel frames are mounted on the box-layered concrete structure. The whole concrete structure is located on 138 pile foundations, which are over 20 m deep into the rock layer, to maintain a very stable foundation.

As shown in **Figure 8**, the equipment room (ER) is located under the bottom of antenna masts, which can make sure the shortest cable routing from antenna masts

**Figure 8.** *The structure illustration of NIM OATS.*

**Figure 9.**

*The grounding of the triangular wire mesh. (a) Triangular wire mesh and (b) tip of the triangular wire mesh.*

to the ER. The control room is located under the GP, but near the entrance, to make sure a short way for operators to make measurements.

The dimesion of the GP and stainless triangular wire mesh are shown in **Figure 9**.

As shown in **Figures 4**–**6**, the triangular is very useful for reducing the reflections from the edge of the GP. **Figure 9(a)** is the photo for the stainless triangular wire mesh, and **Figure 9(b)** shows the tips of the triangular wire mesh connected each other and being grounded to the soil with resistance less than 1 Ω.

Lots of precise "measurements" are carried out for this OATS. The deviation *ΔA* shown in Eq. (1) measured with a pair of calculable dipole antennas (CDAs) at 24 resonant frequencies is shown in **Figure 10** for HP and **Figure 11** for VP [7].

**Figure 10.** *The deviation of NIM's OATS at HP.*

**Figure 11.** *The deviation of NIM's OATS at VP.*

*Design, Construction and Validation of a High-Performance OATS DOI: http://dx.doi.org/10.5772/intechopen.99727*

**Figure 12.**

*Deviation of NIM's OATS over sweeping frequencies, HP,* R *= 10 m. (a) the comparison of measured and calculated site insertion loss (A). (b) the difference of site insertion loss between measurements and calculations.*

The deviation is less than 0.26 dB for HP and 0.34 dB for VP. Obviously, it meets the requirements for both CALTS and REFT, though the uncertainty *ΔA*<sup>m</sup> is over-estimated. Thus, we can conclude that the performance of this OATS is wonderful.

In order to investigate the results at other frequencies, sweeping measurements between a pair of broadband calculable dipole antennas separated by 10 m and HP are shown in **Figure 12**. The difference between *A*<sup>m</sup> and *A*<sup>c</sup> are quite less at resonant frequencies, e.g., 50 MHz, 300 MHz, 500 MHz, 700 MHz, and 1000 MHz; however, it is larger at non-resonant frequencies.
