• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.8
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• pp.688-693
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• 2009

In this paper, a half wave-length microstrip antenna was proposed to be able to continuously tune the resonant frequency in the stated area of UHF ISM band. By loading varactor diodes at both edges of the half wavelength antenna, where the electric field is the strongest, and varying the voltage in order to tune the electrical resonance length continuously, it is possible to automatically recover the resonant frequency and input impedance shifted by surrounding environment. When the microstrip antenna(center resonant frequency: 425 MHB) was tested, by adjusting the each voltages of varactor diodes from DC 0.6 to BC 3.0 volts, the resonant frequency under 20 dB return loss was varied 385 to 465 MHz. The peak gain was -0.2 dBd and return loss -10 dB bandwidth was 3.3 MHz(0.8 %).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.7
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• pp.560-570
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• 2017

Recently, well-known SAR imaging algorithms have been developed to form the focused SAR images for stationary targets. In general, the conventional methods exploit the range variation only defined by the motion of radar platform and SAR geometry. However, for SAR imaging of ground moving targets, the motion of the targets induces an additional range shift, yielding the blurred SAR images. To overcome the problem, in this paper we propose an effective motion compensation algorithm operated under a multi-channel SAR, named along-track interferometry(ATI) and phase unwrapping to directly estimate the motion parameters of the targets. In simulations, 50 Monte-Carlo simulation results show the effectiveness of the algorithm in the presence of noise.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.9
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• pp.693-700
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• 2018

In this paper, we propose a method to generate SAR(synthetic aperture radar) images for bistatic radar. The bistatic SAR can overcome several limitations of monostatic SAR, because the former can be applied to a variety of scenarios, compared to the latter. However, no study has been conducted on bistatic SAR imaging so far. In this paper, we propose a method to generate bistatic SAR images using the monostatic equivalent model and conventional monostatic SAR imaging algorithms. Simulations using airborne SAR in the bistatic geometry validated the efficacy of the proposed method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.10
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• pp.810-818
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• 2017

This paper presents the approaching target above ground tracking based on Kalman filter applied to the proximity sensor for the active defense system. The proximity sensor located on the front of the countermeasure is not easy to detect when the anti-tank threat enters a fragment dispersion range due to limited antenna beamwidth. In addition, it is difficult for the proximity sensor to detect the anti-tank threat accurately at a terrestrial environment including various clutters. To solve these problems, this study presents the approaching target above ground tracking based on Kalman filter and applies the novel estimation method for a noise covariance matrix to improve a tracking performance. Then, a high tracking performance of Kalman filter applied the proposed noise covariance matrix is presented through field firing test results and the validity of the proposed study is examined.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.6
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• pp.555-563
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• 2015

This paper presents signal processing algorithms of a frequency-modulated continuous-wave(FMCW) radar altimeter and provides a practical assessment technique. The radar altimeter is initially operated in search mode, when the radar altimeter detects a valid altitude, search mode is switched to track mode and a altitude being tracked is displayed. The sweep bandwidth in each mode is a function of altitude to narrow the beat frequency bandwidth. In addition, transmit power and receiver gain in each mode are controlled to compensate for the dynamic range of wide altitude range. To assess more realistic operation, the radar altimeter was tested using the crane setup. The crane test demonstrated that signal processing algorithms described in this paper resulted in a reduced measurement error rate.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.18-25
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• 2000

In this paper, we have designed a microwave level meter based on the FM-CW radar theory using a YIG-tuned oscillator (YTO). YTO has an excellent frequency linearity, so a linearizer circuit is not necessary for the level meter. It is shown that interference signals reflected from nearby obstacles can be removed by using a digital band-pass filter. An FIR band-pass filter is designed using the Kaiser window. The distance measurement has been performed in the outdoor test field. The measurement data have been obtained for the range of 1~40m with 1m step, and the results show that the standard deviation of the measured data is 2.33 cm. The level meter manufactured in this study can be applied usefully in the industrial facilities which are not accessible easily, for example, to measure the level of molten metal in the iron and steel company.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.3
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• pp.321-330
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• 2010

In this paper, the theoretical background and the specific implementation method of a compressive receiver for RFID signal detection as well as the design method of DDL(Dispersive Delay Line) and chirp LO are described. DDL, which is one of the main components of the compressive receiver, is designed to have $13{\mu}s$ dispersive delay time and 6 MHz bandwidth using the SAW technique based on $LiNbO_3$ material. The chirp LO is designed using DDS(Direct Digital Synthesizer). Also the compressive receiver is fabricated to be installed into the RFID reader. Test results show the maximum frequency error of 25 kHz for single signal input, the receiver sensitivity of -44 dBm, and the maximum frequency error is 75 kHz for 6 multi-tone input signals. These results indicate that the fabricated compressive receiver is working well even in dense RFID operating environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.10
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• pp.900-908
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• 2016

In this paper, we have studied the tracking system with a single channel monopulse receiver that has a comparative advantage of costs, size, weight, and power consumption over the general 3-channel monopulse receivers. After the single channel monopulse system was composed of an antenna, a monopulse receiver, a servo unit, a RF signal processor unit and a power supply unit, we analyzed the basic tracking performance of the tracking error angle and the pointing loss. And we proved the tracking performance to a moving target in the outdoor environment. On the Analysis of the tracking test results, the single channel monopulse system shows a equal or higher performance over the general 3-channel monopulse system and also has advantages of the system implementation. Also, it is concluded that this study is useful to apply a single channel monopulse receiver with benefits of production price and miniaturization when the monopulse tracking systems will be developed in the future.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.5
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• pp.339-347
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• 2019

The power circuit design of an on-board S-band transmitter for KSLV-II with derating(operation of a component at less than its maximum rated specification to enhance reliability) is investigated. The power circuit of the transmitter consists of linear voltage regulators, DC/DC converters for regulating the DC supply, and diodes for reverse voltage protection. After analyzing the load current of the components, derating requirements are explored. Furthermore, power dissipation and junction temperature rise are considered with respect to the load current. The analysis is compared to the results from an engineering model of the transmitter. The temperature of the components is derated by >$40^{\circ}C$ in an environment where the ambient temperature is $+60^{\circ}C$, which is the acceptance test specification of high temperature.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.1
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• pp.50-60
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• 2018

In this paper, we developed a broadband multi-layered radome applicable for high-power applications. In this regard, we presented the wave propagation characteristics of the broadband multi-layered radome with the ABCD matrix and obtained the optimal thickness and the material constant for each layer by an optimization algorithm called "particle swarm optimization," implemented by a commercial numerical modeling tool. Further, we redesigned it in view of mechanical properties to reflect environmental conditions such as wind, snow, and ice. The power transmission property was reanalyzed based on the recalculated data of each layer's thickness to consider the limitations of the fabrication of a large structure. Under the condition of a peak electric field strength that is 10 dB above the critical electric field strength in air breakdown, we analyzed the air breakdown by radio frequency(RF) in the designed radome using the commercial full-wave electromagnetic tool. The radome was manufactured and tested by continuous wave(CW) RF small signal and large signal in an anechoic chamber. The test results showed good agreement with those attained by simulation.