Ell-Kou Kim

Integrated mixer based on composite right/left-handed leaky-wave antenna

This paper presents a novel balanced mixer receiver front-end design based on a metamaterial structure applicable to differential-/common-mode excitation. This metamaterial structure functions as a leaky-wave antenna and provides intrinsic common-mode suppression. Low LO leakage and high RF to LO isolation are achieved without additional filters for the LO and RF paths. The metamaterial is based on a unit-cell which under a differential-mode excitation behaves like a composite right/left-handed (CRLH) metamaterial. In contrast, the metamaterial unit-cell is below cut-off under a common-mode excitation. Experimental results are used to verify the proposed metamaterial’s differential-/common-mode characteristics. The metamaterial is integrated with a balanced mixer design resulting in an operation frequency range of 1.96 GHz – 2.40 GHz with an optimum mixer conversion loss of 21.1 dB at 2.4 GHz.

A Series Feedback Predistorter using Junction Resistance of Schottky Diode

This paper proposes a series feedback predistorter using junction resistance of schottky diode to compensate for AM/AM and AM/PM in the nonlinear characteristics of amplifier. This consists of common- emitter amplifier and schottky diode that is connected between emitter and ground. The common-emitter amplifier with varying resistance of schottky diode operates to increase amplitude and lead phase. To demonstrate the general usefulness of this predistorter, the series feedback predistorter was applied to linearize amplifier for cellular CDMA system. The test results show that IMD3 can be removed by more than lOdB in case of CW 2-tone signals. Also, the adjacent channel power ratio (ACPR) can be improved by more than 9.6dB for IS-95 CDMA 1FA signals.

Tunable band-stop filter with combined Right/Left-Handed Transmission Line

In this paper, a tunable band-stop filter based on Right-Handed Transmission Lines (RHTLs) of low-pass characteristics and Left-Handed Transmission Lines (LHTLs) of high-pass characteristics are developed. This filter consists of a parallel connection of the RHTLs and LHTLs. Varactor diodes and chip inductors are used to make the unit cells of RHTLs and LHTLs. The cut-off point of the RHTLs becomes the lower cutoff frequency of the band-stop filter and the LHTL becomes the upper cut-off frequency. Therefore, upper and lower cut-off frequencies of the proposed band-stop filter can be controlled by the voltages of the varactor diodes, individually, and it is easy to change the center frequency and the bandwidth. The measured results of the tunable band-stop filter show a minimum bandwidth at 85.8% and a maximum at 133% from a center frequency of 600MHz. While the minimum insertion losses at pass-band are −0.9dB.

Size reduction and wide bandwidth rat-race coupler with shunt capacitors and composite Right/Left-Handed Transmission Line

This paper introduces a rat-race coupler, with size reduction and bandwidth enhancement, using shunt capacitors, high impedance lines and Composite Right/Left-Handed Transmission Lines (CRLH-TLs). The reduced method of line length is used to combine a short length high impedance line and two shunt capacitors. Also, there is combined CRLH meta-material, using nonlinear phase characteristic of CRLH-TL that consists of series capacitors and shunt inductors, so as to obtain wide bandwidth. The implemented rat-race coupler shows a novel design with compact size that is smaller by 10% and a bandwidth that is larger by 60% than that of a conventional rat-race coupler.

Attenuator using lossy left-handed transmission line and its applications

This paper proposes a design of a variable attenuator based on meta-material structuring and its application. The unit-cell of attenuator, based on the lossy transmission line, consists of the composite right/left-handed transmission line (CRLH-TL) and PIN diodes to control internal loss according to resistance variation of diode. Also, to reduce the initial losses, a parallel connection of PIN diodes is used. Because of constituting a periodic structure to increase attenuations, an attenuator with a cascade unit-cell is connected. The attenuation quantities of the unit-cell are about 10dB and phase variations are a maximum of 15° at 1.5 GHz ∼ 2.5 GHz. To attenuate more than 10dB, the unit-cell of attenuator must be connected to a cascade. Also, its application is represented by a vector modulator.

A Resonance Power Combining Technique Using CRLH-Transmission Line

This paper proposes a resonance power-combining technique using CRLH-transmission line. The circuits using proposed technique consist of the parallel capacitances and transmission lines to satisfy matching conditions and to combine power of amplifiers. The CRLH(Composite Right/Lefi-Handed) transmission lines are used to reduce the circuit size. As a result, the power combining amplifier using proposed techniques is measured that a gain is equal and the output power is increased about 2.2 dB higher than the single amplifier. Also, a size of amplifier is 78.3 % smaller than the conventional amplifier using RH transmission line.

An individual order predistorter based on diode series feedback using controlling bias voltages

In this paper, a third- and fifth-order analog predistorter using series feedback constituted individual predistorter of common-emitter amplifiers and schottky diodes has been developed. The individual order predistorters of the proposed circuit have shown the gain and phase control characteristics in order to compensate nonlinearity of amplifier with wide dynamic range. The individual predistorters with improvement of AM/AM and AM/PM is controlled the optimum condition of third- and fifth-IMD by the diode bias. The proposed circuit consists of the individual predistorters, power splitter and divider. The test results show that the third- and fifth-IMD of power amplifier is cancelled maximum 13.5 dB and 13.4 dB for two-tone signals, respectively. Also, its improved the adjacent channel leakage ratio (ACLR) approximate 2.5 dB and 3 dB each other for CDMA 2FA signals at 1.23 MHz and 1.98 MHz offset points. The proposed predistorter provides moderate distortion improvement and control individual-orders at little extra cost. It also is realized with advantages of miniaturized size, low complexity, and stable operation.

Individual Order Intermodulation Distortion Generator Using Series Feedback of Diode and Its Application

This paper proposes an individual order predistortion linearizer using intermodulation distortion(IMD) generator for cancellation the third and the fifth IMD of power amplifier. The IMD generator for controlling the third and the fifth IMD consist of common Emitter amplifier and Schottky diode. These signals are generated by series feedback of Schottky diode to obtain the inverse AM/AM and AM/PM characteristics of power amplifier. The individual order predistorters are consisted of individual IMD generator, power splitter and combiner. The test results show that the third and the fifth IMD can be improved by a maximum 13.5 dB and 0.9 dB in case of CW 2-tone signals. Also, the Adjacent Channel Leakage Ratio(ACLR) can be improved 2.3 dB, 2.5 dB at MHz, MHz offset frequency for CD-MA IS-95 2FA signals.

Dual-Band Power Divider Using CRLH-TL

This paper proposes a power divider based on meta-material structure with dual-band operation. The meta-material structures of left-hand characteristic are constituted of series capacitors and shunt inductors, but they have parasitic series inductance and shunt capacitance effects. There is represented the composite right/ left-handed transmission line (CRLH-TL) model. When the power divider is implemented by using the CRLH-TL, the power divider can operate dual band. To verify the power divider with dual band, we are implemented to operate dual-band that is 0.88 GHz and 1.67 GHz. The characteristics of divider have the return loss less than each 21.0 dB and 15.8 dB and the insertion loss better than 3.83 dB and 3.64 dB at each frequency. Also, the output phase difference is .

Tunable Bandstop Filter with Combined Right/Left-Handed Transmission Lines

A novel tunable bandstop filter was proposed. It is composed of a right-handed transmission line, which has lowpass characteristics, and a left-handed transmission line which has highpass characteristics. Dispersion relations for the unit cells of RHTL and LHTL were derived by the method of ABCD parameter analysis. Varactor diodes and chip inductors were used to make the unit cells of RHTL and LHTL. A tunable bandstop filter was designed and fabricated by the parallel connection of RHTL and LHTL. The measured results of the proposed tunable bandstop filter are agreed well with the simulated results.