Research on Fast Measurement Method for Active Element Pattern of Phased Array Antenna

I. INTRODUCTION In order to achieve desired radiation pattern performance, such as main beam shape and low sidelobes, it is necessary for the array to be well calibrated [1]. As for modern large-scale, sophisticated phased array antennas, measuring its radiation characteristics have become a complex technical task in recent years. Near-field and far-field pattern testing methods are two main methods for measuring antenna radiation characteristics currently [2]. However, the above methods haven ’t taken the characteristics of antenna under test (AUT) into consideration. Thus, the approach can be used to test any type of antenna. Supposing that the characteristics of antenna under test is reliable enough, use these information effectively will simplify the process of measurement. With regard to phased array antennas, the geometric dimension, the types and active element pattern, phase-shifters and feed-networks are prior information which will be the essential and significant messages for the measurement process [3]. According to the definition, in the circumstances that only specified element’s port generates unitary excitation, while others are connected to the matched loads. The radiation pattern is defined as active element pattern (AEP), in other words, is called the patterns of elements operating in the unique excited array [4]. On the basis of the mathematical model of fast measurement, the active element pattern is not only used in the process of solving each channel transmission
coefficient, but also needed in the recovery of whole pattern, and it determines the affiliation between antenna ’s gain and scanning range as well as affects the polarization characteristic. Therefore, to determine the active element pattern will be of great importance in the phase-shift measurement method introduced by Russian scientist than other fast measurement methods such as the rotating element electronic field vector (REV) method proposed by Japanese scientists [5]. Measuring active element pattern proves to be a very heavy and difficult task in engineering application. In fact, it is impossible for the engineers to connect to matched loads for each radiating element. However, as long as the number of radiating elements is large enough, the entire active element pattern in array will have insignificant differences. In this paper, the average active element pattern is introduced. This paper is organized in the following manner. In Section II mathematical model for fast measurement process is developed. In Section III we will describe the relationship between far-field radiation pattern and channel excitation. In section IV we will demonstrate our approach with meaningful examples. The correctness and feasibility of this approach is verified by simulation experiment. The study shows that the proposed method simplifies the mathematical model, reduces the number of measurements and improves the efficiency of testing simultaneously. II. MATHEMATICAL MODEL Assuming that there exists a phased array antenna consists of N elements, each of which is connected to a feeding-network that includes phase-shifter as well as an amplifier and an attenuator. The phase-shifter is usually formed by binary digital phase-shifter, which consists of p discrete bits. The states of phase-shifter make up a collection of
{0,1,2,...L 1} , where L 2 p , L is the state number. The set t {lt (n), lt , n 1,2,...N 1} in t moment is
called phase configuration of phased array antenna. The prominent characteristic of phased array antenna is that its radiation pattern depends heavily on each state of phase-shifter. In other words, any phase configuration is determined by each channel excitation. Therefore, the characteristics of phased array antenna can be determined by measuring the amplitude and phase of transmission coefficient
Research on Fast Measurement Method for Active Element Pattern of Phased Array Antenna
Li Wei1, 2, Tian Shulin1, Liu en1, 2, Huang Jianguo1
1. School of Automation Engineering, University of Electronic Science and Technology of China, Chengdu, China 2. The 5th Lab of Engineering Research Center of Electronic Measurement Technology and Instrument, Ministry of Education Phone: +86 18200112855, Email: liwei0600820315@
Abstract – A novel fast measurement approach in the phase-shift measurement method to obtain the active element pattern in phased array antenna is investigated in this paper. The active element pattern is not only used in the process of solving each channel excitation, but also needed in the recovery of whole pattern. Since the accuracy of active element pattern will directly affects the precision of fast measurement results, it is more important to determine the active element pattern accurately compared with other measurement methods. In this paper, the elements in the phased array antenna are composed of half-wave dipoles, and a novel determination method of active element pattern which achieves accurate pattern calculations with less computer memory and computation time is introduced. The calculating formulas are presented, and the correctness along with the feasibility of this proposed method is verified and illustrated through experimental simulation. Keywords – phased array antenna, half-wave dipoles, active element pattern, fast measurement.