• Journal of electromagnetic engineering and science
• /
• 제17권1호
• /
• pp.1-8
• /
• 2017

This paper introduces a technique to obtain the broadband characteristics of circularly polarized antennas using an L-shaped probe. A waveguide antenna is suitable for obtaining high gain and handling convenience in some applications; however, the asymmetrical structure of the L-shaped probe results in cross-polarization and frequency dependence on the field distribution of higher-order modes (HOM). In addition to the basic characteristics of a waveguide antenna with an L-shaped probe, the author discusses some techniques to reduce the HOM and cross-polarization. As a result, the 3-dB axial ratio (AR) is obtained with the fundamental mode even when the frequency is expanded to the region for HOM of TM. This reduction is mainly due to the cutoff structure to the TM mode around the short wall of the waveguide. Furthermore, some aperture modification techniques can reduce the cross-polarization in a wide range of angles in the radiation pattern. Such techniques and their mechanisms are discussed in this paper. The obtained performance shows that the proposed antennas have a wide range of angles of 3-dB AR in the radiation pattern, broadband characteristics in impedance and AR, and low variation in group velocity.

• 한국전자파학회논문지
• /
• 제15권7호
• /
• pp.635-643
• /
• 2004

본 논문에서는 무선 LAN 시스템에서 편파 다이버시티를 사용하기 위한 이중편파 특성을 가지는 2${\times}$2 배열 안테나를 설계, 제작하였다. 이중편파 안테나의 대역폭과 격리특성을 개선하고자 개구면 결합 급전 구조와 L형 이중 프루브 급전 구조를 사용하였다. 제작된 안테나의 -15dB 기준 반사손실 대역폭은 개구면 결합 급전에서 210MHz, L형 이중 프루브 급전에서 280MHz로 측정되었다. 두 입력포트간의 격리특성은 -40dB 이하이며, 안테나 이득은 무선 LAN 동작주파수 대역에서 14.3$\pm$0.2dBi로 측정되었다.

• 한국가시화정보학회지
• /
• 제18권3호
• /
• pp.122-128
• /
• 2020

In the field of experimental fluid dynamics, the 5-hole probe is one of the most widely used tools to measure flow velocity and pressure. We hereby describe the development of an inexpensive laboratory-based flow calibration system for 5-hole probes. The system is applied to a custom L-shaped probe, and the probe performance is compared against a standard commercial probe in a custom wind tunnel. The setup allows rotation of the probe around the yaw and pitch axes. Static and total pressure values are calculated, and then calibration maps are constructed based on the yaw and pitch angles. Using these maps, errors of the custom probe are found to be ±5% for velocity magnitude and ±3° for direction, compared to the commercial probe, when both pitch and yaw angles are within 40°.

• 정보통신설비학회논문지
• /
• 제5권1호
• /
• pp.43-59
• /
• 2006

A compact and broadband $4\times1$ array antenna was developed for 3G smart antenna system testbed. The $4\times1$ uniform linear away antenna was designed to operate at 1.885 to 2.2GHz with a total bandwidth of 315MHz. The array elements were based on the novel broadband L-probe fed inverted hybrid E-H (LIEH) shaped microstrip patch, which offers 22% size reduction to the conventional rectangular microstrip patch antenna. For steering the antenna beam, a commercial variable attenuator (KAT1D04SA002), a variable phase shifter (KPH350SC00) with four units each, and the corporate 4-ways Wilkinson power divider which was fabricated in-house were integrated to form the beamforming feed network. The developed antenna has an impedance bandwidth of 17.32% $(VSWR\leq1.5)$, 21.78% $(VSWR\leq2)$ with respect to center frequency 2.02GHz and with an achievable gain of 11.9dBi. The design antenna offer a broadband, compact and mobile solution for a 3G smart antenna testbed to fully characterized the IMT-2000 radio specifications and system performances.

• 정보통신설비학회논문지
• /
• 제7권1호
• /
• pp.41-58
• /
• 2007

A compact and broadband $4{\times}1$ array antenna was developed for 3G smart antenna system testbed. The $4{\times}1$ uniform linear array antenna was designed to operate at 1.885 to 2.2GHz with a total bandwidth of 315MHz. The array elements were based on the novel broadband L-probe fed inverted hybrid E-H (LIEH) shaped microstrip patch, which offers 22% size reduction to the conventional rectangular microstrip patch antenna. For steering the antenna beam, a commercial variable attenuator (KAT1D04SA002), a variable phase shifter (KPH350SC00) with four units each, and the corporate 4-ways Wilkinson power divider which was fabricated in-house were integrated to form the beamforming feed network. The developed antenna has an impedance bandwidth of 17.32% ($VSWR{\leq}1.5$), 21.78% ($VSWR{\leq}2$) with respect to center frequency 2.02GHz and with an achievable gain of 11.9dBi. The design antenna offer a broadband, compact and mobile solution for a 3G smart antenna testbed to fully characterized the IMT-2000 radio specifications and system performances.

• Journal of electromagnetic engineering and science
• /
• 제7권3호
• /
• pp.122-128
• /
• 2007

In this paper, we present the design and measurement of a side-fed circularly-polarized patch antenna with a dielectric loading. The antenna consists of a comer-truncated rectangular patch, an L-shaped ground plane, a dielectric loading material, and a coaxial probe. An antenna operating at the UHF band (910 MHz) for the RFID reader applications is optimized using a commercial software. The size of the patch is reduced by a factor of 1.73 by loading the patch with mono-cast(MC) nylon. Measurements of the fabricated antenna show performance characteristics comparable to those of much larger commercial RFID reader antennas.

• 한국전자파학회논문지
• /
• 제27권5호
• /
• pp.416-423
• /
• 2016

본 논문은 광대역 시스템에서 이용 가능한 빔 틸트 특성을 가지는 Conformal 구조의 $1{\times}4$패치 어레이 안테나를 설계 및 제작하였다. E자 형태의 패치 안테나 및 L-probe 급전 방식을 이용하여 광대역 단일 패치를 설계하였고, 전방으로 20도의 빔 틸트 특성을 얻기 위해 $1{\times}4$ 안테나 어레이를 T-junction 전력분배기와 42 psec의 마이크로스트립 전송선을 이용하였다. 3.6~4.4 GHz에서 9 dB 이상의 반사 손실이 측정되었으며, 3.75~4.25 GHz에서 10 dBi 이상의 안테나 이득을 가지며, 30도 이하의 HPBW 특성이 측정되었다.

• ALGAE
• /
• 제24권3호
• /
• pp.139-147
• /
• 2009

Microalgae using a submersible fluorescence probe in water column (up to 100 m) were measured during the austral summer of 2006 (February) in Prydz Bay, East Antarctica (triangular-shaped embayment in the Indian sector of Southern Ocean). Concurrently, environmental parameters such as temperature, salinity and nitrogen (nitrate, ammonium, urea) uptake rates were measured. The concentration of phytoplankton is relatively high due to availability of high nutrients and low sea surface temperature. Phytoplankton community is dominated by diatoms whereas cryptophytes are in low concentration. The maximum concentration of total chlorophyll is 14.87 ${\mu}g\;L^{-1}$ and is attributed to upwelled subsurface winter water due to local wind forcing, availability of micro-nutrients and increased attenuation of photosynthetically available radiation (PAR). Concentration of blue-green algae is low compared to that of green algae because of low temperature. Comparatively high concentration of yellow substances is due to the influence of Antarctic melt-water whereas cryptophytes are low due to high salinity and mixed water column. Varied concentrations of phytoplankton at different times of Fluoroprobe measurements suggest that the coastal waters of Prydz Bay are influenced by changing sub-surface water temperature and salinity due to subsurface upwelling induced by local winds as also melting/freezing processes in late summer. The productivity is high in coastal water due to the input of macro as well as micro-nutrients.

• 한국결정성장학회지
• /
• 제12권2호
• /
• pp.68-72
• /
• 2002

Iodine ($I_2$)을 이용한 기상성장법(chemical vapour transport CVT)으로 상용 FeSi$_2$분말로부터 $\beta$-$FeSi_2$ 및 $\alpha$-$FeSi_2$단결정을 제조하였다 $FeSi_2$ 분말은 iodine과 함게 석영 ampoule에 넣은 후 진공배기하여 two-zone 전기로 내에서 기상성장 시켰다. CVT법에 의한 기상성장시 고온부분의 source측 온도는 $1050^{\circ}C$이었으며 $\beta$-$FeSi_2$와 $\alpha$-$FeSi_2$ 단결정이 얻어지는 성장측 온도는 각각 $750^{\circ}C$ 및 $950^{\circ}C$이었다. 이때 얻어진$\alpha$-$FeSi_2$ 단격정은 $l0\times10 \textrm{mm}^2$크기의 판상결정이었고 orthorhombic 구조의 $\beta$-$FeSi_2$, 단결정은 길이 10mm의 needle형 결정임을 알 수 있었다. $\alpha$-$FeSi_2$ 단결정의 조성을 EPMA로 조사한 결과 Si이 화학양론비보다 많은 $FeSi_{2.58}$ 이었다. CVT법으로 합성된 $\beta$-$FeSi_2$ 격정의 승온에 따른 상의 안정성을 조사한 결과 $930^{\circ}C$ 이상에서 $\alpha$-$FeSi_2$로 상변태함을 알 수 있었다.