Earticle

밀리미터파 위상배열시스템에 위상변환기는 개별안테나의 위상을 조절하는 핵심 부품이다. 본 논문은 손실이 큰 실리콘 웨이퍼의위상변환기에 적용을 위한 설계 기법을 5GHz에서 검증한 내용을 담는다. 0/180도 2-State 위상변환기가 제작되었으며 그것은 2개의2-Stage AMP를 병렬로 구성하였다. 각 State의 Gain을 동일하게 유지하기 위해서 0/180도 Delay 라인을 2-Stage AMP의 각 Stage 중간에 삽입하였다. 통상적으로 AMP를 병렬 연결할 때 Wilkinson Power Combiner/Divider과 같은 수동회로를 추가하지만 실리콘웨이퍼에서는 이것으로 인해 큰손실이 발생할 수 있으므로 생략하고 직접 연결하였다. 제작결과 5GHz에서 12dB이득, 174도 위상차를 확인하여 본 설계 기법을 검증하였다.

A phase shifter is one of the key components that change the phase of an individual antenna in millimeter-wave phased array system. This paper presents a low-loss phase shifter design with two parallel 2-state amplifiers. To get the same gain of 0 〬/180 〬 each state, delay lines are in the middle of each stage of the 2-Stage amplifiers. Normally, when adding AMPs in parallel, a power combiner/divider such as Wilkinson Power Combiner/Divider is added, but they are directly connected because it can cause added losses in silicon wafer. The measured data shows 12dB gain and 174-degree phase difference at 5GHz.

A 94-GHz phased array antenna using a log-periodic antenna has been developed on a GaAs substrate. The developed phased array antenna comprises four log-periodic antennas, a phase shifter, and a Wilkinson power divider. This antenna was fabricated using the standard microwave monolithic integrated circuit (MMIC) process including an air bridge for unipolar circuit implementations on the same GaAs substrate. The total chip size of the fabricated phased array antenna is 4.8 mm × 4.5 mm. Measurement results showed that the fabricated phased array antenna had a very wide band performance from 80 GHz to 110 GHz with return loss characteristics better than -10 dB. In the center frequency of 94 GHz, the fabricated phased array antenna showed a return loss of -16 dB and a gain of 4.43 dBi. The developed antenna is expected to be widely applied in many applications at W-band frequency.

본 논문에서는 X-Band에서 동작하는 광대역의 빔 조향이 가능한 테이퍼 슬롯의 위상배열 안테나 설계기법을 제시하 고 제작, 측정하여 성능을 분석하였다. 안테나 성능을 만족하기 위하여 전자파 특성과 견고성, 추가로 가공성이 뛰어난 진행파의 테이퍼 슬롯 안테나(Tapered Slot Antenna)를 위상배열 안테나의 단일 복사소자로 설계하였고 설계된 단일 복사소자를 이용, 목표성능에 도달하는 체계적이고 효과적인 광대역 위상배열 안테나 구조를 제안하였다.

본 논문에서는 256 능동위상배열 기반의 연직바람 관측장비(RWP)의 송수신 채널의 크기 및 위상을 보정하는 방법등이 논의된다. 별도의 모듈 추가 없이 송수신 전단기 및 송수신 전환기 에 커플러 및 스위치를 사용하여 송신 및 수신 보정 경로를 확보하였고, Gain 및 Phase Detector를 사용하여 256 송수신 채널의 크기 및 위상을 독립적으로 보정하였다. 보정된 256 능동위상배열 안테나는 근접전계 시험을 통해 5개의 빔 (연직, 동, 서, 남, 북)의 빔폭 및 사이드 로브가 시뮬레이 션 계산 값과 일치함을 확인하였다. 제안된 보정방법은 실외 환경에서 운용되는 능동위상배열 기반의 시스템에 용이하게 적용이 가능하다.

In this paper, the phased-array transceiver (TRX) channel amplitude and phase calibration method for a radar wind profiler (RWP) based on the 256 active phased array is discussed. Without the additional module, the TX and RX calibration paths were secured using couplers and switches in the TRX front ends and the TRX switching duplexers, and the amplitude and phase of the 256 TRX were calibrated using a gain and phase detector. The beam widths and side lobes of five beams (vertical, east, west, south, and north) of the calibrated 256 active phased array antenna were confirmed by a near-field which agreed well with the simulation results. The proposed calibration method can be easily applied to a system based on an active phased array operated in an outdoor environment.

기존의 레이다는 RF Sub-Array 방식의 레이다 알고리즘을 적용하여 개발되어 왔고, 최근 차량용 레이다용으 로 Full 디지털 방식의 Multiple-Input Multiple-Output (MIMO) 레이다 알고리즘을 적용하여 구현되고 있다. 본 논문에서는 미확보 기술인 RF Sub-Array 방식의 하드웨어에 Phased MIMO 방식을 적용한 레이다 알고리즘을 실시간 가능하도록 구현 및 검증하였다. RF Sub-Array 방식의 Phased MIMO 알고리즘 기술 확보 차원에서 FPGA 기반의 실시간 신호처리를 위한 하드웨어 구조를 제시하고 이에 대한 설계 및 시뮬레이션을 통하여 성능을 먼저 예측하였으며, 이를 통하여 FPGA 기반의 광대역 MIMO FMCW 레이더의 디지털 송수신 신호처리 하드웨어 를 개발하였고 최종적으로 RF Sub-Array 방식의 Phased MIMO 레이다 알고리즘을 실시간 구현 및 검증하였다. 이를 바탕으로 향후 테라헤르츠 대역 레이다 등에 필요한 핵심 기술 확보 및 응용할 수 있을 것으로 판단된다.

Existing radars have been developed by applying RF sub-array algorithms, and recently, fully digital Multiple-Input Multiple-Output (MIMO) radar algorithms have been implemented for vehicle radars. In this paper, the radar algorithm applying the Phased MIMO method to the hardware of the RF sub-array method, which is an unsecured technology, was implemented and verified in real time. In order to secure RF sub-array Phased MIMO algorithm technology, a hardware structure for FPGA-based real-time signal processing was presented, and performance was first predicted through design and simulation. Through this, the digital signal of FPGA-based broadband MIMO FMCW radar The processing hardware was developed, and the Phased MIMO radar algorithm of the RF sub-Array method was finally implemented and verified in real time. Based on this, it is judged that it will be possible to secure and apply core technologies necessary for terahertz band radar in the future.

This paper presents the analysis of increasing the resolution of True-Time-Delay (TTD) by 0.5-bit for phasedarray antenna system which is one of the Multiple-Input and Multiple Output (MIMO) technologies. For the analysis, a 5.5-bit True-Time Delay (TTD) integrated circuit is designed and analyzed in terms of beam steering performance. In order to increase the number of effective bits, the designed 5.5-bit TTD uses Single Pole Triple Throw (SP3T) and Double Pole Triple Throw (DP3T) switches, and this method can minimize the circuit area by inserting the minimum time delay of 0.5-bit. Furthermore, the circuit mostly maintains the performance of the circuit with the fully added bits. The idea of adding 0.5-bit is verified by analyzing the relation between the number of bits and array elements. The 5.5-bit TTD is designed using 0.18 μm RF CMOS process and the estimated size of the designed circuit excluding the pad is 0.57×1.53 mm2. In contrast to the conventional phase shifter which has distortion of scanning angle known as beam squint phenomenon, the proposed TTD circuit has constant time delays for all states across a wide frequency range of 4 ‒ 20 GHz with minimized power consumption. The minimum time delay is designed to have 1.1 ps and 2.2 ps for the 0.5-bit option and the normal 1-bit option, respectively. A simulation for beam patterns where the 10 phased-array antenna is assumed at 10 GHz confirms that the 0.5-bit concept suppresses the pointing error and the relative power error by up to 1.5 degrees and 80 mW, respectively, compared to the conventional 5-bit TTD circuit.

본 논문에서는 광대역 특성을 가지는 능동위상배열 안테나의 설계, 검증 및 분석에 대하여 기술하였다. 능동위상 배열 안테나를 항공기 혹은 미사일에 적용하려면 배열 안테나의 소형화 및 광각 빔조향 특성을 확보하는 것은 피할 수 없는 안테나 설계 고려 사항이 될 수 있다. 특히 전자적으로 광각 빔조향 시 능동반사계수 특성은 시스템의 생존 및 성능 측면에서 최소화되어야 하는 설계 파라미터이다. 광대역 특성 및 광각 빔조향에 적합한 복사 소자로 본 논문에서는 Step Flared Notch(SFN)를 적용한 배열 구조를 설계하고 구좌표계 θ 각도 기준 최대 40° 빔조향에 따른 능동반사계수 를 최소화하였다. 복사소자의 대역폭은 Ka대역에서 능동반사 기준으로 3GHz를 확인하였다. 또한 실제 제작된 8by8 배열 안테나는 근접전계 시험을 통해 복사소자의 단일 패턴을 측정하고, 수학적으로 합성하여 탐색기 시스템에 사용하는 송/수신빔을 예측하여 성능을 분석하였다.

This paper dedcribes the design. verification, and analysis techniques for an advanced phased array antenna. When applying an active phased array antenna to an aircraft or missile, miniaturization of the array antenna and wide-angle beam steering characteristics can be unavoidable antenna design considerations. In particular, the active reflection coefficient characteristics when electronically steering a wide-angle beam is a design parameter that must be minimized in terms of system survival and system performance. As a radiator suitable for broadband characteristics and wide-angle beam steering, this paper designed an array structure using SFN and minimized the active reflection coefficient according to beam steering of up to 40° based on the spherical coordivate system angle. The bandwidth of the radiator was confirmed to be 3GHz based on active reflection in the Ka-band. In addition, the performance of the actually manufactured 8by8 array antenna wsa analyzed by measuring the single pattern of the radiator through a near-field test, mathematically synthesizing it, and predicting the Tx/TRx beam used in the seeker system.

최신의 무기체계 및 전자장비들은 아군의 생존성 향상을 위해 스텔스 기술에 대한 요구가 증가하고 있기 때문에, 레이다 반사 면적을 줄이는 저피탐 기술 구현이 필요하다. 이러한 스텔스 기술을 위해 형상 설계나 전파 흡수체를 적용 한 저피탐 특성 구현 방법이 널리 사용되는데, 능동위상배열 안테나는 형상 설계에 구조적인 한계가 있고 전파 흡수체 적용 시 안테나의 전기적 성능이 저하되는 단점이 있다. 따라서 본 논문에서는 X-대역에서 동작하는 능동위상배열 안테 나의 저피탐 특성 구현을 위해 전파 흡수체를 적용하기에 적합한 개별 복사소자를 선정하고, 13x13 배열 안테나를 설계 및 제작하였다. 다음으로 제작된 안테나의 흡수체 유무 및 종류에 따른 상대 RCS와 전기적 성능 측정 결과 비교를 통해 저피탐 특성은 확보하면서 전기적 성능은 동등 이상의 수준으로 유지됨을 보임으로써, 본 논문에서 제안한 저피탐 특성 구현 방법이 유효함을 보이고 전파 흡수체 적용 시 안테나 성능이 저하되는 한계를 극복할 수 있음을 확인하였다.

As the latest weapon systems and electronic equipments are increasingly demanding stealth technology to improve the survivability of allies, it is necessary to implement low-observability technology that reduces the radar cross section(RCS). In order to implement this stealth technology, a method for low RCS characteristics by applying a shape design or a electromagnetic wave absorber is widely used. However, active phased array antennas have structural limitations in shape design, also when a absorber is applied to it, the performance of the antenna is degraded. Therefore, in this paper, in order to realize the low RCS characteristics of the active phased array antenna operating in the X-band, individual radiating elements suitable for applying the radio wave absorber were selected, and a 13x13 array antenna was designed and manufactured. Next, by comparing the measured results of the relative RCS and electrical performance for the manufactured antenna according to the presence and type of the absorber, it is shown that the electrical performance is maintained at an equal or higher level while obtaining the low RCS characteristics. Thereby the method proposed in this paper for implementing the low RCS characteristics was validated. Finally, it was confirmed that when the wave absorber is applied to the array antenna, the limitation of its performance deterioration can be overcome.

본 논문에서는 디지털 능동위상배열 안테나를 간략히 소개하고 주 빔의 부엽을 차단하기 위해 적용된 이중 채널 부엽 차단 빔 형성 방법에 대해 기술하였다. 그리고 안테나 주 빔 및 부엽 차단 빔 설계 결과와 안테나 근접전계 측정 결과로부터 안테나 성능을 검증하였다. 다음으로 기존의 이중 채널 부엽 차단 빔 운용 방식 보다 채널수를 줄이기 위해 단일 채널 부엽 차단 빔 형성 방법을 제안하고, 제안한 방법으로 부엽 차단 안테나에 대한 소자별 가중치 분포를 설계하 였다. 마지막으로 설계된 단일 채널 부엽 차단 빔 패턴과 차단 능력을 검증하고 이중 채널 부엽 차단 빔과 비교하였다. 또한, 디지털 능동위상배열 안테나의 수신 근접전계 시험을 통해 측정한 이중 채널 부엽 차단 빔과 제안된 단일 채널 부엽 차단 빔 패턴 및 부엽 차단 성능을 비교/검증함으로써 제안된 부엽 차단 빔 형성 방법에 대한 유효성을 확인하였다.

In this paper, a digital active phased array antenna is briefly introduced and beam forming method for a dual-channel side-lobe blanking applied to blank the side-lobe of the main beam is described. Next, the antenna performance was verified from results of design and antenna near-field measurement for the antenna main beam and side-lobe blanking beam. Then, a single-channel side-lobe blanking beam forming method was proposed to reduce the number of channels than the existing system operating dual-channel side-lobe blanking beam and weight distribution for each element of the side-lobe blanking antenna was designed with the proposed method. Finally, the designed single-channel side-lobe blanking beam pattern and blanking ability were verified and compared with the dual-channel side-lobe blanking beam. In addition, by comparing/verifying the conventional dual-channel and the proposed single-channel side-lobe blanking beam patterns measured through the receiving near-field test of the digital active phased array antenna and their ability to blank side-lobe of the main beam, validity of the proposed method for forming single-channel side-lobe blanking beam was confirmed.

일반적인 하나 또는 두개의 압전소자를 사용하는 트랜스듀서에 비하여 다수의 압전소자를 사용하는 어레이 트랜스듀서는 각 압전소자에 가해지는 펄스의 지연시간을 제어함으로써 초음파 빔을 임의의 지점에 집속시킬 수 있고 기계적 구동없이 임의의 방향으로 조향시켜 실시간 주사를 할 수 있는 장점이 있다. 페이즈드 어레이 트랜스듀서의 설계조건은 압전소자의 수. 압전소자의 크기 그리고 압전소자 사이 간격 등 여러가지가 있으며, 본 연구에서는 그 중에서 압전소자수의 변화에 따른 초음파 빔의 특성을 호이겐스의 원리를 이용한 수평횡파의 시뮬레이션을 통하여 평가하였다. 그 결과 초음파 빔은 조향각이 증가 할수륵 음압이 감소하며, 초음파 빔 특성도 점차적으로 분산됨을 알 수 있었고 또한, 초점거리가 증가할수록 초점에서의 집속효과는 감소하고, 압전소자의 수가 증가되면 집속효과는 향상됨을 알 수 있었다.

A phased array is a multi-element piezoelectric device whose elements are individually excited by electric pulses at programmed delay time. One of the advantages of using phased array in nondestructive evaluation (NDE) application over conventional ultrasonic transducers is their great maneuverability of ultrasonic beam. There are some parameters such as the number and the size of the piezoelectric elements and the inter-element spacing of the elements to design phased array transducer. In this study, the characteristic of ultrasonic beam for phased array transducer due to the variation of the number of elements has been simulated for ultrasonic SH-wave on the basis of Huygen's principle. Ultrasonic beam directivity and focusing due to the change of time delay of each element were discussed due to the change of the number of piezoelectric elements. It was found that ultrasonic beam was much more spreaded and hence its sound pressure was decreased as steering angle of ultrasonic beam was increased. In addition, the ability of ultrasonic bean focusing decreased gradually with the increase of focal length at the same piezoelectric elements. However, the ability of beam focusing was improved as the number of consisting elements was increased.

A new phased-array quadrature RF coil for one or two RF acquisition channels is developed for spine MR imaging. Quadrature RF coils for MRI have been useful to improve the signal-to-noise ratio (SNR) by $"\sqrt{2}"$ using two orthogonal RF coils in combination [1]. More recently, the phased-array RF coil has been proposed for more improvement of SNR by using an array of RF coil elements with a reduced size and coverage for each element. Two new schemes are proposed for the new phased-array quadrature RF coil as follows : (1) Proper overlapping of two quadrature RF coils thus removing the mutual inductance and (2) Attaching preamplifiers right after the coil section and combining the signal with proper phase delays. The coil has been implemented for receive- only mode. It has been tested through phantom and volunteer imaging. The experimental results show the utility of the proposed RF coil.

A dual-band dual-polarized microstrip antenna array for an advanced multi-function radio function concept (AMRFC) radar application operating at S and X-bands is proposed. Two stacked planar arrays with three different thin substrates (RT/Duroid 5880 substrates with $\varepsilon_r$=2.2 and three different thicknesses of 0.253 mm, 0.508 mm and 0.762 mm) are integrated to provide simultaneous operation at S band (3~3.3 GHz) and X band (9~11 GHz). To allow similar scan ranges for both bands, the S-band elements are selected as perforated patches to enable the placement of the X-band elements within them. Square patches are used as the radiating elements for the X-band. Good agreement exists between the simulated and the measured results. The measured impedance bandwidth (VSWR$\leq$2) of the prototype array reaches 9.5 % and 25 % for the S- and X-bands, respectively. The measured isolation between the two orthogonal polarizations for both bands is better than 15 dB. The measured cross-polarization level is ${\leq}-21$ dB for the S-band and ${\leq}-20$ dB for the X-band.

This paper presents a new active antenna consisting of a microstrip patch for the passive radiator, a mixer for frequency conversion, a voltage controlled oscillator (VCO) and a phase detector for phase control. The microwave signal frequency has been converted into intermediate frequency (IF) on the antenna elements by the mixer. The active antenna consists of two ports, the IF port has a transmitted IF signal via power combined to the baseband and the dc control port is under the control of the phase-detector. The input voltage of the VCO is controlled by the phase detector. The scan range of the array is determined by the phase detector and the VCO and is obtained between 30$^{\circ}$ and - 30$^{\circ}$

The reactor vessel body and closure head are fastened with the stud bolt that is one of crucial parts for safety of the reactor vessels in nuclear power plants. It is reported that the stud bolt is often experienced by fatigue cracks initiated at threads. Stud bolts are inspected by the ultrasonic technique during the overhaul periodically for the prevention of failure which leads to radioactive leakage from the nuclear reactor. The conventional ultrasonic inspection for stud bolts was mainly conducted by reflected echo method based on shadow effect. However, in this technique, there were numerous spurious signals reflected from every oblique surfaces of the thread. In this study, ultrasonic phased array technique was applied to investigate detectability of flaws in stud bolts and characteristics of ultrasonic images corresponding to different scanning methods, that is, sector and linear scan. For this purpose, simplified stud bolt specimens with artificial defects of various depths were prepared.

The expanded multi-Gaussian beam model has recently been developed that can calculate the radiation beam field from a single, rectangular transducer with great computational efficiency. In this study, this model is adopted to calculate the radiation beam field for a phased array transducer with various time delays to achieve steering and/or focusing. The calculation beam fields are compared to those obtained by well known Rayleigh-Sommerfeld integral that provides the exact solution in order to explore the validity of the expanded multi-Gaussian beam model And then, this study proposes a complete ultrasonic measurement model including the expanded beam model, far-field scattering model and system efficiency, Using the proposed model, phased array ultrasonic testing signals for a flat-bottomed hole with/without focusing were performed.

A phased array antenna was fabricated using four-element ferroelectric phase shifters with a coplanar waveguide (CPW) transmission line structure based on a $Ba_{0.6}Sr_{0.4}TiO_3(BST)/MgO$ structure. Epitaxial BST films were deposited on MgO (001) substrates by pulsed laser deposition. To attain the large differential phase shift and small losses for a ferroelectric CPW phase shifter, an impedance-matching-part adding technique between the effective transmission line and connecting cable was used. The return loss and insertion loss for this techniqueadapted BST CPW device were improved with respect to those for a normal BST CPW device. For an X-band phased array antenna system consisting of ferroelectric BST CPW phase shifters, power divider, dc block, patch antenna, and programmed dc power, the steering beam could be tilted by $15^{\circ}$ in either direction.

We describe a new method for removing non-linear phased array antenna aberration called "squint" problem. To develop a compensation scheme. theoretical antenna and artificial neural networks were used. The purpose of using the artificial neural networks is to develop an antenna system model that represents the steering function of an actual array. The artificial neural networks are also used to implement an inverse model which when concatenated with the antenna or antenna model will correct the "squint" problem. Combining the actual steering function and the inverse model contained in the artificial neural network, alters the steering command to the antenna so that the antenna will point to the desired position instead of squinting. The use of an artificial neural network provides a method of producing a non-linear system that can correct antenna performance. This paper demonstrates the feasibility of generating an inverse steering algorithm with artificial neural networks.