Duk-Jae Woo

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

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.

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

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 planes 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 -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 0.32λ0 × 0.19λ0 (where λ0 is the free-space wavelength at the first resonant frequency).

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

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

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.

Circularly Polarized Antenna with Wide Axial-Ratio Bandwidth

This paper deals with a TT&C circularly polarized turnstile antenna for LEO satellites. The turnstile antenna consists of radiator for radiating power to free-space and power divider for generating circularly polarized wave. we presents a radiator to tolerate in space environments and a power divider to provide flat phase difference at wide bandwidth. The bandwidth of the proposed antenna covers the frequency bands of up- and down-link. The antenna shows wide beamwidth and enhanced axial ratio for unfavorable space environments.

A Simple Model for a DGS Microstrip Line with Stepped Impedance Slot-Lines

In this paper, a simple equivalent circuit model for a defected ground structure (DGS) microstrip line with stepped impedance slot-lines in the ground plane is presented. In addition, an analytic expression for the resonance frequency of the proposed structure is derived. In equivalent circuit modeling, the capacitance and the inductance of the resonance circuit are evaluated from the dimensions of the etched pattern in the ground plane. The resonance frequencies calculated from the proposed method are compared with those obtained with an electromagnetic (EM) simulation.

Power enhancement of microwave oscillator using a high-Q spiral-shaped DGS resonator

In this paper, a microwave oscillator using a high-Q spiral-shaped defected ground structure (DGS) resonator is proposed. The DGS resonator can be modeled by using the parallel LRC circuit of the transmission line to reject the RF signal at the resonant frequency. The high Q-factor of the spiral-shaped DGS provides high carrier output power and low phase noise. The output power is obtained as 14.2 dBm at 2.438 GHz with 2.0 V DC supply and 24 mA current consumption. It can be seen that the Q- factor of spiral-shaped DGS is 14, the phase noise is observed about -120 dBc/Hz at the 1 MHz offset and DC to RF conversion ratio is calculated 52.8%. The microwave oscillator using a DGS is fabricated on RT Duroid substrate using ATF13786 GaAs MESFET. A considerable enhanced output power was produced using the spiral-shaped DGS developed here.

Multi-band Rejection DGS with Improved Slow-wave Effect

New techniques to suppress multiple frequency bands with a single defected ground structure(DGS) unit are developed. The proposed stacked spiral DGS, in which the spiral-shaped defects with different size are aligned in the transverse direction to the guiding direction of the coplanar waveguide (CPW), provides multiple resonance frequencies. Also, a composite spiral-rectangular DGS is proposed to provide two resonance frequencies with the same characteristic of the cascaded spiral-and dumbbell-shaped DGS units. The slow-wave effects for the proposed DGSs are greater than that of conventional spiral-or dumbbell-shaped DGS. The proposed DGSs are successfully designed and fabricated and the measured results are in a very good agreement with the simulated results.

TT&C Antenna Design for LEO Satellite

In this paper, we study a TT&C link to obtain a required specifications of TT&C(Telemetry Tracking and Command system) antenna for an LEO(Low Earth Orbit) satellite. The premised mission orbit is the sun-synchronized and circular orbit and it performs earth-space observations. We design minimum TT&C link-budget to obtain required antenna beamwidth and gain. The proposed turnstile antenna provides wide beamwidth and circular polarization. We suggested the attaching position that shows the most effective results by confirming the variation of antenna performance when the proposed antenna is adapted to satellite`s various positions. Also we proved the proposed antenna`s ability while it is performing the mission through the orbit simulation based on the electrical performance of the proposed turnstile antenna.

Multi-Band Rejection Slot-Shaped DGS and Its Equivalent Circuit Model

This paper presents a slot-shaped defected ground structure(DGS) which has multi-band rejection property. The proposed structure, in which the spiral slot-shaped defects with different size are aligned in the transverse direction to the guiding direction of the coplanar waveguide(CPW), provides multiple resonance frequencies. Compared with the simulated results, the band rejection characteristic is in good agreement with the measurement. Also, an equivalent circuit model of the proposed structure is presented, where the DGS on the ground plane is modeled as LC-resonators. This resonators are inductively coupled to the signal line through mutual inductance. From the equivalent circuit model, multi-band rejection property was derived.