Duk-Jae Woo

Bio: Duk-Jae Woo is an academic researcher from Seoul National University. The author has contributed to research in topics: Microstrip & Equivalent circuit. The author has an hindex of 6, co-authored 17 publications receiving 464 citations.

Suppression of harmonics in Wilkinson power divider using dual-band rejection by asymmetric DGS

Abstract: In this paper, we present an effective technique of second and third harmonic suppression for a Wilkinson power divider by using an asymmetric spiral defected ground structure (DGS). With the proposed technique, a single asymmetric DGS provides two different resonance frequencies because of the different sizes of spiral-shaped defects on the ground plane. The transfer function of the asymmetric DGS shows signal rejection characteristics at two different resonance frequencies and the characteristics of asymmetric DGS is modeled by two parallel RLC resonance circuits in cascade. With the insertion of asymmetric spiral DGS into a quarter-wave line of the Wilkinson power divider, the second and third harmonics are suppressed simultaneously. In experimental results, 18-dB suppression for the second harmonic and 15-dB suppression for the third harmonic, respectively, are achieved. Using asymmetric DGS, the size of a quarter-wave line is reduced by 9.1% compared to that of the conventional divider without a DGS.

Novel U-slot and V-slot DGSs for bandstop filter with improved Q factor

Abstract: Novel slot-shaped defected ground structures (DGSs) on the microstrip line are presented to provide a band-rejection property with an improved Q factor. Two different geometries (U-slot and V-slot) are investigated. U-slot and V-slot DGSs have simple shapes compared to the conventional DGSs, however, they provide more steep rejection characteristics. The Q factor of the band-rejection property for the U-slot DGS increases when the distance between two slots in the U-shape decreases. Similarly, the V-slot DGS provides a higher Q characteristic when the slot angle is reduced. Two bandstop filters are designed and fabricated employing three cascaded U-slot DGSs and V-slot DGSs, respectively. Experimental result shows that the high-Q band-rejection filter with three U-slot DGSs provides Q of 38.6. A fabricated filter with three cascaded V-slot DGSs also rejects the signals at the frequencies from 3.5 to 4.3 GHz with more than 20-dB suppression

Compact and Bandwidth-Enhanced Asymmetric Coplanar Waveguide (ACPW) Antenna Using CRLH-TL and Modified Ground Plane

Abstract: A novel compact and broadband asymmetric coplanar wave guide (ACPW) antenna is presented. A method to extend the bandwidth of a metamaterial-inspired antenna based on a composite right/left-handed transmission line (CRLH-TL) and a modified ground plane is proposed. The ACPW antenna has a broadband characteristic by placing the zeroth-order resonance (ZOR), first-positive-order resonance (FPOR) of short-ended CRLH-TL and the modified ground plane’s two resonances, which are half and one lambda resonances, at all different frequencies with proper frequency intervals. The prototype of the proposed antenna has been implemented and measured. The measured $-\hbox{10-dB}$ fractional bandwidth is 109.1% (from 2.69 to 9.15 GHz) with high efficiency of over 65% and a low profile of $0.32{{{\lambda}}_0}\times 0.19{{{\lambda }}_0}$ (where ${{{\lambda }}_0}$ is the free-space wavelength at the first resonant frequency).

High-Q band rejection filter by using U-slot DGS

Abstract: This paper presents a new U-slot defected ground structure (DGS) in the microstrip line for the use in the design of high-Q band rejection filter. Compared to the conventional DGS, a U-slot DGS has a simple shape but the slope of its rejection characteristic is more steep. The Q factor of the band rejection property for the U-slot DGS increases when the distance between two slots in the U-shape decreases. By employing three cascaded U-slot DGSs, a high-Q band stop filter is designed and fabricated. Experimental results show that the Q factor of the band stop filter with three U-slot DGSs is 38.4.

Equivalent Circuit Model for a Simple Slot-Shaped DGS Microstrip Line

Abstract: In this letter, an analytic expression is derived for the resonance frequency of a simple slot-shaped DGS. In equivalent circuit modeling, the capacitance and inductance of the resonance circuit are evaluated from the dimensions of the DGS structure. The effects of equivalent circuit elements of a one-turn spiral DGS in the ground plane and their magnetic coupling to the host transmission line are modeled as a simple lumped-element circuit. The resonance frequencies calculated from the proposed method are compared with those obtained by EM simulation.

An Overview on Defected Ground Structure

Abstract: This paper focuses on a tutorial overview of defected ground structure (DGS). The basic conceptions and transmission characteristics of DGS are introduced and the equivalent circuit models of varieties of DGS units are also presented. Finally, the main applications of DGS in microwave technology field are summarized and the evolution trend of DGS is given.

Defected Ground Structure: Fundamentals, Analysis, and Applications in Modern Wireless Trends

Abstract: Slots or defects integrated on the ground plane of microwave planar circuits are referred to as Defected Ground Structure. DGS is adopted as an emerging technique for improving the various parameters of microwave circuits, that is, narrow bandwidth, cross-polarization, low gain, and so forth. This paper presents an introduction and evolution of DGS and how DGS is different from former technologies: PBG and EBG. A basic concept behind the DGS technology and several theoretical techniques for analysing the Defected Ground Structure are discussed. Several applications of DGS in the field of filters, planar waveguides, amplifiers, and antennas are presented.

Single- and Dual-Band Power Dividers Integrated With Bandpass Filters

Abstract: This paper presents a novel device integrating a power divider with two bandpass filters. It is capable of splitting power and selecting frequency at the same time. The phase shift of the filter is found to be ±90° at the center frequency. Therefore, when it is matched to 70.7 Ω, it can replace the conventional quarter-wave length transmission line in the power divider. The isolation elements are loaded at the filters' open ends to get a good isolation between the output ports. As a result, both the transmission and isolation property are satisfied. The equivalent even- and odd-mode circuits of the proposed structure are analyzed and design equations are derived. They are used to guide the design of the devices. For demonstration, filter-integrated power dividers with single- and dual-band operation are implemented, respectively. Comparisons of the measured and simulated results are presented to verify the theoretical predications.

Novel U-slot and V-slot DGSs for bandstop filter with improved Q factor

Abstract: Novel slot-shaped defected ground structures (DGSs) on the microstrip line are presented to provide a band-rejection property with an improved Q factor. Two different geometries (U-slot and V-slot) are investigated. U-slot and V-slot DGSs have simple shapes compared to the conventional DGSs, however, they provide more steep rejection characteristics. The Q factor of the band-rejection property for the U-slot DGS increases when the distance between two slots in the U-shape decreases. Similarly, the V-slot DGS provides a higher Q characteristic when the slot angle is reduced. Two bandstop filters are designed and fabricated employing three cascaded U-slot DGSs and V-slot DGSs, respectively. Experimental result shows that the high-Q band-rejection filter with three U-slot DGSs provides Q of 38.6. A fabricated filter with three cascaded V-slot DGSs also rejects the signals at the frequencies from 3.5 to 4.3 GHz with more than 20-dB suppression