• Journal of electromagnetic engineering and science
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• v.3 no.1
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• pp.62-66
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• 2003

Novel coupled line phase shifters and its equivalent phase delay line for compact broadband phased array antennas are proposed. These phase control circuits are designed to be less complex, small size and to use a less number of active devices. The phase shifter is able to control a 120$^{\circ}$ phase shift continuously, and the phase delay line for a reference phase has a fixed 60$^{\circ}$ shifted phase. Both have the low phase error of less than $\pm$3.5$^{\circ}$ and the low gain variations of less than 1 ㏈ within the 300 MHz bandwidth. These proposed circuits are adequate to form the efficient beam-forming networks with compactness, broadband, less complexity, and low cost.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.49 no.1
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• pp.74-79
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• 2012

Scalar quantification of the angular prediction error covariance matrix is considered for characterizing tracking performances in phased array radar tracking. Specifically, the maximum eigenvalue and the trace of the covariance matrix are examined in terms of consistency in parameterizing the probability of detection, taking antenna beam-pointing losses into account, and it is shown numerically that the latter is more consistent.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.4
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• pp.467-474
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• 2019

Recently, optical phased array(OPA) based laser detection and ranging(LADAR) has gained great interest to replace the traditional mechanical light detection and ranging technique(LiDAR). In OPA-based LADAR, it is well known that phases of laser pulses traveling through each of channels should be the same to obtain a narrow free-space single beam without noise-like ripples in the far field. However, it is difficult to provide such ideal condition due to the fabrication errors. To tackle this problem, any algorithms should be necessary to compensate the initial random phases of each channel in OPA antenna. In this paper, we propose a hill-climbing based phase calibration algorithm and evaluate the performance of the proposed algorithm.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.6
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• pp.812-819
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• 2012

Interference and jamming are becoming increasing concern to a radar system nowdays. AESA(Active Electronically Steered Array) antennas and adaptive beamforming(ABF), in which antenna beam patterns can be modified to reject the interference, offer a potential solution to overcome the problems encountered. In this paper, we've developed a planar active phased array radar system, in which ABF, target detection and tracking algorithm operate in real-time. For the high output power and the low noise figure of the antenna, we've designed the S-band TRMs based on GaN HEMT. For real-time processing, we've used wavelenth division multiplexing technique on fiber optic communication which enables rapid data communication between the antenna and the signal processor. Also, we've implemented the HW and SW architecture of Real-time Signal Processor(RSP) for adaptive beamforming that uses SMI(Sample Matrix Inversion) technique based on MVDR(Minimum Variance Distortionless Response). The performance of this radar system has been verified by near-field and far-field tests.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.11
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• pp.1217-1224
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• 2009

This paper newly proposes a methodology towards computing antenna element weights which are satisfying asymmetric sidelobe levels(SLLs) specified arbitrarily on both sides of the main beam pattern, in the linear phased array antenna pattern synthesis problem. Opposite to the conventional methods in which the element weights are directly optimized from the array factor, this method is based on the optimum perturbations of complex roots inherent to the Schelkunoff's polynomial form which is described for the array factor. From the proposed methodology, the capability of nulling the directions of multiple jammers is also possible by independently perturbing only the complex roots corresponding to each jamming direction, hence allowing an enhancement of the simplicity of the numerical procedure by means of a proper reduction of the dimension of the solution space. The complex weights over the array are then easily computed by substituting the optimally perturbed complex roots to the Schelkunoff's polynomial. Some examples are examined and numerically verified by substituting the extracted weights into the array factor equation.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.6
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• pp.306-309
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• 2004

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 Journal of The Korea Institute of Intelligent Transport Systems
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• v.21 no.5
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• pp.162-170
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• 2022

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.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.289-294
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• 2002

We propose optical true time-delays (TTDs) for phased-array antennas (PAAs) composed of 2${\times}$2 MEMS switches and fiber delay lines, and implement a TTD which shows a maximum scan angle of $120^{o}$ with $30^{o}$ resolution. Since this structure uses only one fixed wavelength laser diode, it provides several advantages such as easy control, high speed operation, and low cost compared with those of the optical TTDs using tunable laser sources. We design a four element linear PAA using the proposed TTDs at 10 ㎓. Simulation results show that the maximum gain is 11.6 dB at the radiation angle $0^{o}$, 11.2 dB at $\pm$$30^{o}$, and 10.6 dB at $\pm$$60^{o}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.8
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• pp.665-675
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• 2016

With the development of active phased array radar technology in recent years, active phased array antennas, which digitally combine signals received from subarray units using dozens of digital receiver, have been developed. The beam characteristics are greatly affected by the shape of the subarray structure as well as the weight of subarray in digital beamforming. So in this paper, the method to generate subarray structures by using recursive element exchanging method and the method to optimize subarray structures that can minimize sidelobes of operating beams are proposed. Additionally it presents the result to find the optimized subarray structure to minimize the maximum sidelobe of monopulse beam and pencil multi-beam respectively or simultaneously which are commonly used for digital beamforming by applying the algorithm propsed in this paper.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.6
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• pp.504-511
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• 2016

In this paper, the method is proposed that the equivalent result can be obtained by compensating the variation of gain and phase in the comparison with the result of near-field measurement which is obtained in the steady state, although the gain and phase variation of rx-channels occurred in the near-field rx-measurement of digital active phased array antenna. The proposed concept has the time section for monitoring the state of the rx-channels through the calibration path in the measurement timeline, and is the method for compensating the variation of state. For validating the proposed method, the fabricated X-band digital active phased array antenna and the planar near-field measurement facility is utilized. The proposed method is validated in the comparison with the compensated pattern which the unstable state of rx-channels is calibrated and the reference pattern obtained under the steady state of the rx-channels.