Near-field Measurement Facility Research Articles

A Ku Wideband Circularly Polarized Microstrip Antenna Array with Low Profile Crossed-Dipole Element

This paper presents a novel Ku wideband circularly polarized (CP) antenna array composed of crossed-dipole element (CDE) and fed through sequential rotation (SR) feeding technique. Unlike the traditional CP-CDE fed by coaxial cable that usually works at low frequencies, the proposed CDE consists of two orthogonal heart-shaped patch dipoles that can work at frequencies as high as Ku-band, at the same time achieving a larger bandwidth. A feeding structure is proposed without welding, so potential errors in the antenna assembly process can be mitigated. A 2 × 2 CP antenna array with wideband SR feeding network is designed based on the CDE to further expand the axial ratio (AR) bandwidth. The designed antenna array is fabricated using the multilayer printed circuit board (PCB) technology and measured in anechoic chamber using the planar near-field measurement facility. The measured results show that −10 dB impedance bandwidth of 44% (11.6–18.15 GHz) along with 3 dB AR bandwidth of 38.7% (12–17.65 GHz) and 3 dB gain bandwidth of 34.6% (12.2–17.3 GHz) as well as 11.02 dBic peak gain have been achieved while maintaining a lower profile.

포토닉스 기반 송수신기 연동 광대역 능동위상배열 시스템

This paper describes the development of a wide-band active array system with a photonics-based optical transceiver module (OTM) and measurement results of Tx/Rx beam characteristics using near-field measurements. The proposed transceiver consists of an RF transceiver module and an OTM. The RF transceiver module was designed as a 2×8 array using a microstrip dipole antenna. The OTM performs frequency up/down conversion using an optical modulator and has four Rx channels of A/B/C/D for mono-pulse angle extraction. The transmit and receive modules include a true-time delay to electronically steer the wide-band beam over an azimuth angle of ± 20°. The Tx/Rx beam pattern is measured at a near-field measurement facility. The beam steering error is less than 0.9° over the ±20° azimuth angle in the wide Ku-band. In addition, the monopulse slope is obtained from the Rx 4 optic array, and the function of the monopulse calibration is verified using outdoor measurements.

근접 전계 시험 시설을 이용한 능동 위상 배열 안테나 송신 빔 패턴 측정

본 논문에서는 국내 최초로 개발되는 함상용 중거리 레이더에 사용되는 능동 위상 배열 안테나의 송신 빔 특성을 근접 전계 시험으로 측정하는 방안에 대하여 제시하였다. 측정하고자 하는 능동 위상 배열 안테나는 고출력 송신 빔을 펄스 형태로 방사하기 때문에 저출력의 연속적인 파형을 사용하는 일반적인 근접 전계 시험 시설에서는 측정하기 어렵다. 그래서 본 논문에서는 고출력 송신 시에도 견딜 수 있도록 설계된 근접 전계 시험 시설과 펄스 모드 측정을 지원하는 Agilent사의 PNA-X 네트웍 분석기를 이용한 근접 전계 시험으로 펄스 형태의 고출력 송신 빔을 방사하는 능동 위상 배열 안테나를 측정하는 방안에 대하여 제시하였고, 실제 개발된 능동 위상 배열 안테나의 고출력 송신 빔 패턴을 근접 전계 시험으로 측정하였다. 또한, 능동 위상 배열 안테나의 송신 특성인 EIRP(Effective Isotropic Radiated Power)를 측정하였고, 수학적인 계산을 통해 예측한 EIRP 값과 비교한 결과 0.1 dB의 오차 내에서 동일함을 확인하였다. In this paper, we proposed the transmit beam measurement method of active phased array antenna, which is installed in Korea's first developed naval medium range radar, using near-field measurement facility. The pulse-mode high power characteristics of active phased array antenna's trasmit-beam make it difficult to measure with general near-field measurement facilities where low power continuous RF signals are used. Thus, in this paper, the measurement method of active phased array antenna's transmit beam in conjunction with the near-field measurement facility, which is suitable for the high-power transmit beam measurement, and PNA-X network analyzer(Agilent Technologies), which can support pulse-mode measurement, was proposed and measured by near-field measurement techniques. And the EIRP(Effective Isotropic Radiated Power), the transmit characteristic of active phased array antenna, was measured by the near field measurement techniques and compared to numerical estimation which was nearly equal with small difference of 0.1 dB.

A time domain spherical near-field measurement facility for UWB antennas employing a hardware gating technique

Abstract. A spherical near-field antenna measurement facility employing a time domain hardware gating technique is presented. On-off keyed sinusoidal impulses are used as stimuli requiring wideband antennas with a bandwidth in excess of 400 MHz. The received signal is evaluated in the time interval after reaching the steady state and before multipath components arising in the non-ideal anechoic chamber distort the signal. An application specific pulse generator synthesizing sinusoidal impulses with a sub-nanosecond settling time and a low-cost equivalent time (ET) sampling receiver developed and optimized for this particular purpose are described. Measurement results of typical ultra-wideband (UWB) antennas show a significant improvement of the measured antenna pattern compared to conventional techniques.

Application of cylindrical near-field measurement technique to the calibration of spaceborne radar antennas: NASA scatterometer and SeaWinds

Modern spaceborne radar scatterometers, such as the NASA scatterometer (NSCAT) and SeaWinds radar instruments, require precise determination of the normalized backscattered radar cross section within a few tenth of a decibel. This is needed to achieve the desired wind velocity and direction measurement accuracy of 2 m/s and 20/spl deg/, respectively. This high level of precision demands a priori prelaunch accurate knowledge and determination of the radar antenna's absolute gain and relative radiation patterns characteristics over wide angular range. Such characterizations may be performed on a far-field range, compact range, or in an indoor near-field measurement facility. Among the unique advantage of the near-field measurement is that most of the information of the radar antenna radiation properties can be obtained anywhere outside the near-field measurement surface. Two recently designed radar scatterometers are considered in this paper, NASA scatterometer (NSCAT) and SeaWinds, to demonstrate the utility of a newly completed cylindrical near-field measurement range. As an example of an advanced calibration methodology, the data based on a recently measured JPL/NASA scatterometer (NSCAT) radar antenna are used to experimentally demonstrate the role of the probe pattern compensation, probe multiple reflection effects, probe mispositioning effects, scan area truncation effects, etc. A measurement test on a standard gain horn (SGH) has been performed to achieve and verify the absolute gain calibration accuracy. A comparison between direct far-field measured data and those obtained from cylindrical near-field measurements for the SeaWinds radar antenna was found in excellent agreement. It is demonstrated that the near-field measurement technique is a viable approach in accurately characterizing the performance of spaceborne radar antennas.

An overview of near-field antenna measurements

After a brief history of near-field antenna measurements with and without probe correction, the theory of near-field antenna measurements is outlined beginning with ideal probes scanning on arbitrary surfaces and ending with arbitrary probes scanning on planar, cylindrical, and spherical surfaces. Probe correction is introduced for all three measurement geometries as a slight modification to the ideal probe expressions. Sampling theorems are applied to determine the required data-point spacing, and efficient computational methods along with their computer run times are discussed. The major sources of experimental error defining the accuracy of typical planar near-field measurement facilities are reviewed, and present limitations of planar, cylindrical, and spherical near-field scanning are identified.

Far-field patterns of spaceborne antennas from plane-polar near-field measurements

Certain unique features of a recently constructed plane-polar near-field measurement facility for determining the far-field patterns of large and fragile spaceborne antennas are described. In this facility, the horizontally positioned antenna rotates about its axis while the measuring probe is advanced incrementally in a fixed radial direction. The near-field measured data is then processed using a Jacobi-Bessel expansion to obtain the antenna far fields. A summary of the measurement and computational steps is given. Comparisons between the outdoor far-field measurements and the constructed far-field patterns from the near-field measured data are provided for different antenna sizes and frequencies. Application of the substitution method for the absolute gain measurement is discussed. In particular, results are shown for the 4.8-m mesh-deployable high-gain antenna of the Galileo spacecraft which has the mission of orbiting Jupiter in 1988.