A Study Of Near-field To Far-field And Near-field To Aperture-field Transformation

Antenna measurement is the most important technique of the process of the antenna development. With the rapid development of the wireless communication, we have higher precious and performance index of the antenna and the traditional far-field measurement can not satisfied this high index. Near-field measurement have been chosen in high-performance antenna testing in recent years both here and abroad. And the Planar Near-field measurement is one of this method. We use an antenna which we know its performance, and then we scanned in a plane which has an interval of several wavelength to the antenna under test. Then we can know the amplitude and phase of every point of this plane. Last we can calculate the amplitude and phase in far field by the mathematical transformation and data processing.The first part of this paper concerns the basic theory of near-filed antenna measurement.We begin with the coordinate system we used in the near-field antenna measurement.The principles of planar wave expansion and the basic theory of near-field antenna measurement are first introduced. And a method is presented for computing far-field antenna patterns from measured near-filed data measured by an array of planar dipole probes. An alternate method is presented for computing far-field antenna patterns from near-field measurements. Also the principle of selecting of the sampling parameters are introduced too. Under the theory foundation, a 2D near-field to far-field Fast Fourier Transform formulas comprising probe correction are. Besides, two antenna models which has low minor lobe are built and we calculated their near-field electric distribution. And then we use the theory of near-to-far transform to obtain the far-field patterns to validate the effectiveness of this theory. Besides the traditional mathematical model, this paper also use the software HFSS to built the 3D model to calculate the far-field patterns to compare with the mathematical model to further illustrate the effectiveness of the theory.The second part of this paper discusses diagnostic algorithm of near-field based on the principles of planar wave. First we discussed the coupled equation establish under the Lorentz reciprocity principle between the probe and the antenna under test.We deducedthe transformation formulas of near-field to aperture-field. Also we establishes a half-wave array antenna and horn aperture antenna model to verify the feasibility of the theory.The theoretical results agree well with the simulation result which indicate the feasibility of this method.