• Geophysics and Geophysical Exploration
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• v.23 no.4
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• pp.223-229
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• 2020

Small-loop EM techniques have been used in many geophysical investigations, including shallow engineering and environmental surveys. Even though geometric and frequency soundings have been widely used, there is a debate regarding the effectiveness of frequency sounding, especially when the coil spacing is small. In this study, we analyzed the effectiveness of geometric as well as frequency soundings via the one-dimensional modeling of small-loop EM surveys. The numerical results reveal that geometric sounding can effectively provide underground information. Conversely, the frequency soundings are only effective when the loop spacing is relatively large, that is, when the induction number is large. On the contrary, the frequency soundings fail to provide any information concerning the subsurface layers if the loop spacing is not large.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.9 s.100
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• pp.862-871
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• 2005

In this paper, the modified design equation of shielding effectiveness was presented to predict more accurately the shielding effectiveness of honeycomb structure with hexagonal waveguide. The design equation of shielding effectiveness in honeycomb was represented from adding shielding effectiveness of single lattice to shielding effectiveness of infinite array of single lattice. This paper proposed the generalized design equation of shielding effectiveness by analyzing basis lattice of hexagonal waveguide which composes honeycomb structure and infinite array structure of basis lattice. To provide the validity of the modified design equation of shielding effectiveness in this paper, comparison with other available date using 3D EM commercial software is made.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.3
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• pp.269-276
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• 2016

This paper presents a 2.65 GHz Doherty power amplifier with internally-matched GaN HEMT. Internal matching circuits were adopted to match its harmonic impedances inside the package. Simultaneously, due to the partially matched fundamental impedance, input and output matching networks become simpler. Bond wires and parasitic elements of transistor package were predicted by EM simulation. For the LTE signal with 6.5 dB PAPR, the implemented Doherty power amplifier shows a power gain of 13.0 dB, a saturated output power of 55.4 dBm, an efficiency of 49.1 %, and ACLR of -26.3 dBc at 2.65 GHz with an operating voltage of 48 V.

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.69-76
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• 2007

High-frequency electromagnetic (EM) wave propagation associated with borehole ground-penetrating radar (GPR) is a complicated phenomenon. To improve the understanding of the governing physical processes, we employ a finite-difference time-domain solution of Maxwell's equations in cylindrical coordinates. This approach allows us to model the full EM wavefield associated with crosshole GPR surveys. Furthermore, the use of cylindrical coordinates is computationally efficient, correctly emulates the three-dimensional geometrical spreading characteristics of the wavefield, and is an effective way to discretise explicitly small-diameter boreholes. Numerical experiments show that the existence of a water-filled borehole can give rise to a strong waveguide effect which affects the transmitted waveform, and that excitation of this waveguide effect depends on the diameter of the borehole and the length of the antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.8
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• pp.709-716
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• 2016

In this paper, A duplexer module with temperature-insensitive electrical characteristics was proposed for remote wireless communication system. Duplexer modules are required to have performances of low insertion loss, high isolation between transmitted band and received band, harmonic suppression as well as high power durability in the system for transmitting guided information to missile flying a free space on the ground. The proposed duplexer module are consist of transmission bandpass filter and receiving bandpass filter which are connected to common antenna port, planar coupler for output power monitoring and low pass filter for harmonic attenuation of power amplifier and coaxial cavity resonator. The material and dimensions of the resonator are determined for minimum frequency shift by temperature variation using 3D EM simulation. The measured results of the prototype showed a good agreement with the simulation results, and it should be well applied not only for guided weapon systems but also for any other communication systems such as remote radio head.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.1
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• pp.31-37
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• 2002

전자파 잔향실(Reverberating Shielded Enclosure)의 개념은 전자파 차폐실(Shielded Enclosure)에서 얻어진 측정결과를 개선하기 위하여 1968년도에 제안되었다. 이후 Reverberating 또는 Mode-Stirred Chamber는 EM Immunity 측정뿐만 아니라 EMI측정에서도 많이 적용되어 왔지만, 국제 표준 방식으로 적용되어 오지 못하다가 최근 EMI 복사 전력 측정 및 EM Immunity 측정시설로 유용하게 사용될 수 있다는 점이 부각되어 국제 표준 방식으로 적용하자는 분위기가 무르익어 이에 대한 활발한 논의가 계속되어 오고 있다. 이러한 전자파 잔향실을 이용하여 EMI 및 EMS 시험을 실시할 수 있는 방법을 규격화시키자는 제안이 '96년 프랑스 Mandelieu 국제 전자파 장해 특별위원회(CISPR:International Special Committee on Radio Interference)회의에서 검토된 후 '97년 일본 Yokosuka CISPR 회의에서 정식의제로 채택되었다. 이 안건에 대하여 대부분의 국가들이 제안 취지에 찬성하여 NWIP(New Work Item Proposal) 문서가 각국에서 회람되었다. 초기 전자파 잔향실은 전자파 장해 및 복사 내성 측정을 위한 대용시험 시설로서 1968년 미국 Mendes에 의해 전자파 차폐실 구조에 Stirrer를 이용하여 필드의 균일도를 확보할 수 있다는 전자파 잔향실 개념이 처음으로 제안되었다. 이후 이 분야의 연구는 미국 표준 기술 연구소(NIST: National Institute of Standard and Technology)등에서 연구가 활발히 진행되고 있으며, 국제 표준화 기구인 CISPR에서 전자파 장해 및 내성 시험을 위한 대용시험 시설로서 활용하기 위하여 규격 작업이 진행중에 있다. 또한 최근 전자파 장해 방지를 위한 규제 주파수가 1∼18㎓ 까지 확장됨에 따라 이 주파수 대역에서 시험장으로 활용할 수 있는 전자파 잔향실이 새롭게 부각되고 있다. 전자파 잔향실은 기본적으로 공진 모드를 활용하기 때문에 일정한 크기의 잔향실 내부에서 전자파 균일성을 확보할 수 있는 모드 수에 의해 하한 주파수가 결정되며 충분한 모드 분포상태에서 Stirrer를 사용하여 필드 경계를 이동시킴으로서 확률적으로 균일한 필드분포를 확보하게 된다. 주파수가 증가함에 따라 모드수는 증가하기 때문에 하한 주파수 이상의 대역에 대한 시험시설로 활용할 수 있으며, 특히 ㎓ 대역에서 사용하기에 적합한 대용시험시설이라고 볼 수 있다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.8
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• pp.943-953
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• 2007

In this paper, we propose a Cassegrain antenna with a scalar feed horn opt rating in Ka-band. For an effective EM simulation of the Cassegrain antenna, the near-field of the feed hone is used ai the equivalent source of the Cassegrain antenna using the surface equivalent theorem. A corrugated circular horn operating with $HE_{11}$ mode is used as the feed horn. The angle and feed center of the main and sub reflectors are optimized to achieve maximum antenna efficiency. The designed feed horn shows the gain of 19dBi, the side-lobe level of less than -25dB and the half power beam width of $20^{\circ}$ at 33 GHz. The Cassegrain antenna shows the gain of 41dBi, the efficiency of 60%, the side-lobe level of less than -20dB and the half power beam width of $1.2^{\circ}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.7
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• pp.613-619
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• 2015

In this paper, we proposed a paper-based pattern-switchable antenna using inkjet-printing technology. The proposed antenna is composed of two bow-tie antennas and a switching network. The bow-tie antennas are inkjet-printed on paper using a low cost home printer. The switching network is built on a printed-circuit-board(PCB) and consists of a single-pole-double-throw(SPDT) switch and balun element. A double-sided parallel-strip line(DSPSL) can convert the unbalanced microstrip mode to the balanced strip mode. Two bow-tie antennas have different radiation patterns because of the different orientation of the reflectors. It is demonstrated from EM simulation and measurement that the radiation patterns of the proposed antenna are successfully switched by the SPDT.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.6
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• pp.608-618
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• 2004

In this paper, modifying the diode star double balanced mixer of Maas, a novel resistive 60 GHz pHEMT MMIC star mixer is suggested. Due to star configuration, troublesome IF balun for ring configuration FET mixer is not necessary. In addition, the sysematic design method of dual balun through EM simulation is suggested rather than the design by inspection as Maas. The mixer circuit is fabricated as MMIC on CPW base using 0.1 um GaAs pHEMT Library of MINT in Dongguk University. The size is 1.5 ${\times}$ 1.5 $\textrm{mm}^2$ and its performance is adjustable by DC supply. It can be operated as both up and down converters and it shows the conversion loss of about 13∼18 ㏈ over the full V-band frequencies.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.6
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• pp.552-559
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• 2002

The EM(Engineering Model) LO(Local Oscillator) is designed for Ka-band satellite transponder. The VCO(Voltage Controlled Oscillator) is implemented using a high impedance inverter coupled with dielectric resonator to improve the phase noise performance out of the loop bandwidth. The phase of VCO is locked to that of a stable OCXO(Oven Controlled Crystal Oscillator) by using a SPD(Sampling Phase detector) to improve phase noise performance in the loop bandwidth. This LO exhibits the harmonic rejection characteristics above 43.83 dBc and requires 15 V and 160 mA. The phase noise characteristics are performed as -102.5 dBc/Hz at 10 KHz offset frequency and -104.0 dBc/Hz at 100 KHz offset frequency, respectively, with the output power of 13.50 dBm$\pm$0.33 dB over the temperature range of -20~+7$0^{\circ}C$.