GJB 2038A-2011 in English

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This standard replaces GJB 2038-1994 The measurement methods for reflectivity of radar absorbing material.

The following main changes have been made with respect to GJB 2038-1994:

a) The applicable measurement frequency range is extended from 8 GHz to 18 GHz to 0.5 GHz to 100 GHz;

b) The wedge radar absorbing material is added to the measurment material type of RCS method;

c) The oblique incidence reflectivity is added into the measurement parameters of RCS method;

d) The applicable temperature of reflectivity measurement is extended to high temperature;

e) The sample plate spatial translation measurement method in the former standard is not included in this standard.

Annexes A and B to this standard are informative.

This standard was proposed by the Electronic Information Foundation Department of the General Armaments Department of the PLA (Chinese People’s Liberation Army).

GJB 2038 was issued in 1994 as the first edition.


The measurement methods for reflectivity of radar absorbing material

1 Scope

This standard specifies the methods, procedures and requirements for measuring the reflectivity of radar absorbing materials (hereinafter abbreviated as RAM).

This standard is applicable to the measurement of vertical incidence and oblique incidence reflectivity of flat plate RAM and the measurement of vertical incidence reflectivity of wedge-type RAM. The reflectivity of other types of materials can be measured with reference to this standard. The frequency range of radar cross section (RCS) measurement method and bow measurement method is 0.5 GHz to 100GHz,and 1 GHz to 40 GHz respectively. The reflectivity measurement in other frequency bands can be carried out with reference to this standard.

2 Normative references

The following documents contain related provisions which, through reference, constitute provisions of this standard. For dated references, subsequent amendments (excluding corrections) to, or revisions, of any of these publications do not apply. However parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references or references with version not indicated, the latest edition of the normative document referred to applies.

GJB 3756 Expression and evaluation of uncertainty in measurement
GJB 4238 Terminology for military target and environment characteristics
GJB 5022 Method for measurement of radar cross section of scale target indoor range
GJB 5252 The requirements for the data to be stored of target and environmental characteristics

3 Terms and definitions

For the purposes of this standard, the terms and definitions given in GJB 4238 and the followings apply.

3.1
reflectivity of radar absorbing material (RAM) / RAM reflectivity
ratio of reflection power of the two electromagnetic waves in the mirror direction when they are incident on RAM and good conductor plane with the same dimension at the same power density from the same direction respectively, under the condition of given wavelength and polarization

3.2
equivalent reflectivity of background
ratio of the reflection power of the measured material plate to the reflection power of the calibration metal plate under the same emission power, wavelength and polarization

4 Measurement purpose

The RAM reflectivity is obtained by RCS measurement method or bow measurement method, which provides basis and data support for the evaluation of RAM absorbing performance and the development and application of stealth materials.

5 RCS measurement method

5.1 Measurement principle

RAM reflectivity is divided into vertical incidence reflectivity and oblique incidence reflectivity according to different incident angles. Vertical incidence reflectivity is generally measured by metal plate as reference plate; oblique incidence reflectivity can be measured by using metal plate or dihedral angle reflector as reference. If metal plate is used as reference plate, bistatic RCS measurement system or bow measurement system need be adopted for measurement. If the dihedral angle reflector is used as the reference, the mono-static RCS measurement system need be adopted for measurement, and the applicable oblique incident angle range is 20° to 70°.

For flat plate RAM, the far-field RCS measurement system is adopted. After the system is calibrated by a calibrator, the reflection power Pm of a good conductor metal plate with the same dimension and the reflection power Pa of a flat plate RAM sample plate are measured respectively, and the reflectivity of flat plate RAM is calculated by using Equation 1).

(1)

where,

Γ——the reflectivity of flat plate RAM;

Pa——the reflection power of flat plate RAM sample plate, mW;

Pm——the reflection power of a well-conducting metal plate of the same size, mW.

If expressed in dB, the reflectivity is calculated using Equation (2).

(2)

For wedge-type RAM, RCS is measured with reference to GJB 5022, and then reflectivity is obtained by data processing. Using standard metal ball calibration, the RCS value σRAM of wedge-type RAM sample plate with metal backing is measured first, and then compared with the theoretical RCS value σm of wedge-type RAM sample plate with metal backing plate, the reflectivity of wedge-type RAM is calculated by using Equation (3).

Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Measurement purpose
5 RCS measurement method
6 Bow measurement method
7 Analysis on measurement uncertainty
8 Measurement summary
9 Data storage
Annex A (Informative) Performance inspection of RAM reflectivity measurement system
Annex B (Informative) Example for format of RAM reflectivity measurement report