Jeong Keun Ji

Bandwidth Enhancement of Metamaterial Antennas Based on Composite Right/Left-Handed Transmission Line

A method to extend the bandwidth of metamaterial (MTM) antennas using a composite right/left-handed transmission line (CRLH-TL) is presented. The resonance modes and wideband characteristics of MTM antennas are analyzed and described using dispersion diagrams based on the CRLH-TL theory. Based on the analysis, we propose an efficient way to extend the bandwidth of MTM antennas, which has been verified by both full-wave simulations and experiments. The proposed analysis can be used to design novel wideband MTM antennas and other microwave components for mobile handset applications.

Miniaturized T-DMB Antenna With a Low–Loss Ni–Mn–Co Ferrite for Mobile Handset Applications

In this paper, a low-loss Ni-Mn-Co ferrite (Ni0.76Mn0.24-xCoxFe2O4 with x = 0-0.04) has been developed for miniaturization and performance improvement of mobile handset antennas. The developed ferrite material has almost equal permittivity and permeability of 7-9, as well as sufficiently low dielectric and magnetic loss tangent less than 0.001 and 0.01 below 200 MHz, respectively. Miniaturization factor of about 8 and normalized impedance of about 1 were obtained at 200 MHz. A helical antenna operating at terrestrial digital multimedia broadcasting (T-DMB, 174-216 MHz) band was fabricated on the ferrite substrate, which has compact size, low loss, wide bandwidth, and good radiation performance.

A Compact Multiband Antenna Based on DNG ZOR for Wireless Mobile System

A compact multiband antenna using a double-negative (DNG) zeroth-order resonator (ZOR) for global system for mobile communications (GSM850/1800/1900, 824894/17101880/18501990 MHz), wideband code division multiple access (WCDMA, 19202170 MHz), and wireless broadband (WiBro, 2.32.4 GHz) operations is presented. The proposed antenna having a total volume of 40 times 6 times 3 mm3 comprises a lower-band ZOR antenna part and an upper-band ZOR antenna part. The zeroth-order resonant properties are analyzed by magnitude and phase distributions of the surface magnetic field using near-field scanning system. The performance of the antenna is verified by experimental data obtained from fabrication and measurement. The antenna offers omnidirectional radiation patterns and measured radiation efficiencies exceeding about 53% and 41% for lower and upper bands, respectively.

Design of a DSRR FSS for CDMA/RFID isolation

In the mobile communication systems, high-power repeaters produce intermodulation signals, which can create severe interference in other RF systems. For example, inter-modulation signals generated by a code division multiple access (CDMA; 824 MHz ~ 894 MHz) repeater might interrupt a radio frequency identification (RFID; 917 MHz ~ 923 MHz) tag signal; thus the RFID reader receives incorrect information. Frequency selective surfaces (FSSs) can overcome this problem. Extensive research on FSSs has been conducted [1–6], but few FSS had been reported which enhances isolation between CDMA and RFID.