Truncation Error Study in Cylindrical Near-field Measurement Technique

A truncation error study in the cylindrical near-field (NF) measurement technique is proposed. The maximum angle span of the far-field (FF) radiation pattern from the bore-sight of the antenna under test (AUT) is studied. The truncated NF scan length will be varied. The cylindrical wave expansion is employed to transform the near-field to far-field (NF-FF), where the two-dimensional (2D) numerical integration is employed to calculate associated double integration in the cylindrical wave expansion. The referenced far-field radiation pattern of AUT is simulated by three-dimensional (3D) electromagnetic (EM) software. It is found that the maximum angle span of the FF radiation pattern is dependent on truncated NF scan length and AUT to probe distance. The simulated radiation patterns and the radiation patterns from numerical NF-FF transformation in the valid angle span are in good agreement. Therefore, the greater the truncated NF scans length, the higher the valid angle span of the FF radiation pattern. The actual valid angle span is a bit wider than the estimated maximum angle span, under the condition of the truncated NF scan length is two times larger than the antenna size.