A New Expression of Near-Field Gain Correction Using Photonic Sensor and Planar Near-Field Measurements

Abstract

We propose a new expression of the near-field gain correction to calculate the on-axis far-field gain from the onaxis near-field gain for a directive antenna. The new expression is represented by transversal vectorial transmitting characteristics of two antennas that are measured by planar near-field equipment. Due to the advantages of the photonic sensor, the utilization of the new expression realizes the measurements of the on-axis far-field gains for two kinds of double ridged waveguide horn antennas within 0.1 dB deviation from 1 GHz to 6 GHz without calibrating the photonic sensor system.Key words: Near-Field Gain, On-Axis Gain, Photonic Sensor, Planar Near-Field Measurements.Manuscript received August 25, 2011 ; Revised February 14, 2012 ; Accepted March 5, 2012. (ID No. 20110825-07J) National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan. Corresponding Author : Masanobu Hirose (e-mail : masa-hirose@aist.go.jp) This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Ⅰ. IntroductionThe accurate measurements of the on-axis far-field gains of antennas are of primary importance in antenna measurements. The conventional method for the on-axis far-field gains uses the transmission measurements between antennas whose distance are far enough to fulfill the far-field conditions [1], or the near-field gain corrections to the transmission measurements between antennas at finite distances less than the distances of the far-field conditions [2]～ [5]. As the most accurate method, the extrapolation method is used in national metrology laboratories [6].The conventional near-field gain correction is calculated using the electric and magnetic fields at the apertures of antennas. Usually the electric and magnetic field distributions are calculated at the apertures of pyramidal horn antennas from some theoretical models [2], [4], [5]. For some complicated antennas such as real doubleridged waveguide horns, it is difficult to calculate the field distributions theoretically.Ludwig [3] obtained the electric and magnetic fields for the near-field gain correction using spherical wave expansions determined from the far-field pattern of an antenna. This method is equivalent to the combination of the near-field gain correction and spherical near-field antenna measurements by the present point of view.We propose a new expression of the near-field gain correction combined with the planar near-field antenna measurements [7]. From the theory of the planar nearfield measurements, the transmission between antennas at any distance can be expressed by the transversal vectorial transmitting characteristics (omitting "transversal vectorial" below) of the antennas. Using the transmitting characteristics, the far-field gain ca...