Taek-Kyung Lee

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.

Modified S-Band Satellite Antenna With Isoflux Pattern and Circularly Polarized Wide Beamwidth

A modified isoflux pattern antenna suitable for S-band satellite communication is introduced and investigated with respect to its beam pattern and axial ratios. For uniform coverage over the Earths surface, an isoflux pattern antenna is required because of its uniform power density over a wide coverage area. A final optimization for the parameter values is carried out from the parametric studies of the antenna, and a simple analysis of the combination of horizontal dipoles and vertically attached top-hat elements is also carried out. The electrical performances of the proposed antenna are verified in terms of the reflection coefficients, radiation pattern, and axial ratios according to a wide beamwidth rather than at a fixed observation angle such as a 0° main beam direction.

Circularly Polarized S-Band Satellite Antenna With Parasitic Elements and Its Arrays

A structural modification of S-band turnstile antenna with cylindrical parasitic elements around a main radiator is introduced and investigated with respect to its gain, axial-ratio (AR) beamwidth, and radiation pattern. The overall structure is composed of a main radiator of two crossed bowtie-shaped dipole antennas and a feeding network using a Wilkinson power divider with phase differences between two parts. A final optimization of the parameter values for the enhancement of AR beamwidth is carried out from the parametric studies. The proposed antenna has not only a broad 5-dB AR bandwidth of 12.3% ranging from 2025 to 2290 MHz, but also a stable peak gain of 7.6 dBic with circular polarization (CP) characteristic.

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.

An Equivalent Circuit Model for a Dumbbell-Shaped DGS Microstrip Line

This paper presents an equivalent circuit model for a dumbbell-shaped defected ground structure (DGS) in a microstrip line. The effects of equivalent circuit elements of a dumbbell-shaped DGS and their magnetic coupling to the host transmission line are modeled as a simple lumped-element circuit. In addition, simple approximate expressions to determine the main circuit parameters for this model are presented. The transfer characteristic calculated by the proposed circuit model is compared with the results of EM simulation and measurement.

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.

Bandwidth Enhanced Planar Inverted-F Antenna with Modified Ground Structure

In this paper, we present a wideband design of planar inverted-F antenna (PIFA) using modified ground structure (MGS). The antenna consists of two-layer patches with common feed and modified ground structure. The bandwidth of the designed antenna covers the frequency bands of services such as DCS1800, DCS1900, UMTS (WCDMA), WiBro, WLAN (IEEE 802.11b), satellite DMB, HLAN (IEEE 802.11a) in Korea. The radiation patterns are consistent with frequency change in the bandwidth.

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.