This letter proposes a new hybrid EM wave absorber with the crossed-wedge shape, which can be applied to 3 m semi anechoic chambers. In this study, we designed a new hybrid EM wave absorber with the crossed-wedge shape, which consisted of the inorganic and organic thin corrugated dielectric lossy sheet containing organic conductive fibers. Then the 3 m semi anechoic chamber is constructed in the size of 9.0 m6.0 m5.7 m (LWH) using these absorbers, and also the normalized site attenuation (NSA) is measured according to ANSI C63.4 in the frequency range of 30 MHz to 1 GHz. As a result, the measured NSA is obtained within 3 dB of the theoretical one.

This letter proposes the thinnest hybrid EM wave absorber using a composite magnetic material, which can be applied to the 3 m semi anechoic chambers. We experimentally designed a new hybrid EM wave absorber of the wedge shape, which was made from the ferrite powder, the inorganic fiber and binder. As a result, the length of this absorber could be realized only 6 cm, which was ascertained having the nonflammable. The 3 m semi anechoic chamber is constructed in the size of L9 mW6 mH5.7 m using this absorber, and then the site attenuation is measured according to ANSI C63.4 in the frequency range of 30 MHz-1 GHz. As a result, the measured normalized site attenuation is obtained within 3 dB to the theoretical normalized site attenuation.

This paper investigates the 10 m semi anechoic chamber using a new type hybrid EM wave absorber consisted of the grid-ferrite and the open-top hollow pyramidal EM wave absorber. We designed a new type hybrid EM wave absorber, which length could be slightly realized 65 cm. The 10 m semi anechoic chamber was constructed in the size of L21.5 mW13.5 mH8.9 m as the result of the ray-tracing simulation using this absorber. Then, the site attenuation in the constructed anechoic chamber was measured by using the broadband calculable dipole antennas. As the result, the maximum deviations between the measured site attenuation and theoretical calculated one were obtained within 3.6 dB in the frequency range of 30 MHz to 300 MHz. It was confirmed the validity of a new type hybrid EM wave absorber. Moreover, it was confirmed that the measured results agree with the ray-tracing simulation results, in which the differences are about 1.5 dB.

The site attenuation is an important parameter to evaluate an anechoic chamber. The ray-tracing method has been applied to analyze it. However, the lowest applicable frequency has not been cleared. In this paper, the FDTD method has been applied to analyze the site attenuation of a compact anechoic chamber from 30 MHz to 250 MHz, and this has been compared with the calculated one by the ray-tracing method to evaluate the lowest frequency where the ray-tracing method could be applied. The compact anechoic chamber, where the absorbers are placed on the all walls, has been used for the calculation. For FDTD analysis, the dipole antenna and the absorber have been modeled by using the large cell, whose size is larger than the diameter of the antenna element. For verification, the site attenuation of a compact anechoic chamber has been measured and compared with the calculated values by the FDTD method and the ray-tracing method. As the results, the calculated values by the ray-tracing method have larger deviation than the ones by the FDTD method when the frequency is less than 180 MHz.

Theoretical values of site attenuation for broadband receiving antenna or the antenna factor of broadband antenna over the frequency range from 30 MHz to 1 GHz have been calculated or measured by some researchers. For a frequency range over 1 GHz, wire antennas or horn antennas should be used. However, the theoretical site attenuation or antenna factor over 1 GHz have never yet been calculated. A CLS (Conical Log-periodic Spiral) antenna is generally used for EMC/EMI measurements in the microwave band as a broadband wire antenna for the swept frequency method. However, this antenna has the defect that its use results in the loss of polarization information. So we proposed an improved CLS antenna which has linear polarization. This new CLS antenna has another wire wound symmetrically to that of the standard CLS antenna. For this reason, we named it a double-wire CLS antenna. The double-wire CLS antenna loses no polarization information. We calculated the height pattern and the frequency characteristics of CSA (Classical Site Attenuation) for the double-wire CLS antenna when used for receiving, or used for both transmitting and receiving, as well as the antenna factor. Moreover, NSA (Normalized Site Attenuation) when the double-wire CLS antenna is used for receiving or used for both transmitting and receiving in free space were calculated.