Dong-Hoon Park

A Reconfigurable Directional Coupler Using a Variable Impedance Mismatch Reflector for High Isolation

This letter proposes a reconfigurable directional coupler that uses a variable impedance mismatch reflector to achieve high isolation characteristics in the antenna front end. The reconfigurable coupler consists of a directional coupler and a single-pole four-throw (SP4T) switch with different load impedances as a variable load mismatch reflector. Selection of the load impedance by the reflector allows cancellation of the reflected signal due to antenna load mismatch and the leakage from the input to isolation port of the directional coupler, resulting in high isolation characteristics. The performance of the proposed architecture in separating the received (Rx) signal from the transmitted (Tx) signal in the antenna front end was verified by implementing and testing the reconfigurable coupler at 917 MHz for UHF radio-frequency identification (RFID) applications. The proposed reconfigurable directional coupler showed an improvement in the isolation characteristics of more than 20 dB at the operation frequency band.

Reconfigurable 2

This letter presents a new 2 × 2 multi-port amplifier (MPA) structure using switching mode hybrid matrices (SMHMs) that can improve both system reliability and flexibility by controlling signal paths without complicated circuitry. Unlike previously reported MPA structures which have fixed input and output relations, the proposed MPA can select the number of PAs for signal amplification and produce flexible output patterns depending on the mode selection of the switches. For a 2 × 2 structure, the input signal can be amplified by a single PA or two PAs and then be delivered to any one of the two output ports. In addition, the amplified signal by a single PA or two PAs can also be delivered to both output ports with a 90 ° phase difference. To verify the proposed structure, a simplified MPA is tested at 900 MHz ISM band.

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This paper presents a bio-radar system using a compact lumped six-port demodulator and a Quadrifilar Helix Antenna (QHA) for remote respiration and heartbeat monitoring. Since bio-radar applications require low power characteristics and six-port structure has an advantage in low power operation, the proposed system is configured with a six-port demodulator replacing active frequency mixers. For the compactness and minimization in size at low frequency applications, the six-port demodulator which consists of three hybrid couplers and a power divider is implemented by lumped elements. Also, the proposed system adopts a QHA module that has high Tx and Rx isolation characteristics. The system performance is verified at 917 MHz by monitoring respiration and heartbeat.

2 Multi-Port Amplifier Using Switching Mode Hybrid Matrices

In this paper, a quadruple linear polarization (LP) and circular polarization (CP) diversity antenna with a reconfigurable coupler is presented. The proposed antenna has two linear (vertical and horizontal) and two circular (right-handed and left-handed) polarizations. In order to implement real-time polarization diversity antenna, the electrical switches are used in the proposed antenna feeding network which is four mode reconfigurable coupler. The measured gains and the axial ratios of the proposed antenna are 5.6 ~ 6 dBi and 0.5 ~ 1.5 dB in four operation modes and two CP modes.

RF bio-radar system using a compact lumped six-port demodulator and Quadrifilar Helix antenna

In this paper, quadruple polarized antenna system with a reconfigurable feeding network is presented. The proposed antenna system consists of the reconfigurable feeding network for fourth polarization such as vertical/horizontal linear polarization and right-handed/left-handed circular polarizations or 45 degree tilted vertical/horizontal linear polarization and patch antenna to receive the signals with various polarizations. In order to receive a signal in any direction, the proposed antenna is designed by electrical switches for reconfigurable polarization. The insertion loss of the designed feeding network in the proposed antenna system is approximately 1.2 dB. The measured 3 dB axial bandwidth and gain of the proposed antenna are about 2 % and 4 dBi(c).

Quadruple linear and circular polarized diversity antenna with reconfigurable coupler

In this paper, we have designed and manufactured 10MHz power source for the application of short distance wireless power transmission. The designed power source consists of a DDS(direct digital synthesizer) signal generator, a buffer driver and a balanced power amplifier. Short range wireless power transmission is usually carried out by near-field inductive coupling between source and load. The distance variation between source and load gives rise to the change of load impedance of power amplifier, which has effect on the operation of power amplifier. To overcome this problem due to load variation of power amplifier, we have adopted the balanced power amplifier using the quadrature hybrid implemented by lumped capacitors and a mutually coupled coil. The experiment results show the above 40dBm output power, frequency range of 9 to 11MHz, and total DC power consumption of 36W.

Quadruple Polarized Antenna System with a Reconfigurable Feeding Network

In this paper, we propose an antenna module with high isolation between Tx and Rx in RFID reader module. The proposed module consists of a quadrafilar antenna and a directional coupler with a switchable dummy load to improve the directivity. The proposed module achieves the isolation higher than 20 dB between Tx and Rx. To show the validity of the proposed scheme, we have performed the measurement of tagging range and multi-tagging ability. The experiment results show that the detecting range and multi-tagging ability are enhanced by 81% and 200%, respectively.

Design of the 10MHz and 10W Power Source for Short Distance Wireless Power Transmission

We propose a new four-port BPSK direct conversion receiver based on 0.18 ¿m CMOS technology for the first time. The proposed direct conversion receiver is composed of two active combiners, an active balun, two power detectors and a decoder. The designed direct conversion receiver is successfully demonstrated by demodulating BPSK signal with 40 Mbps in the L-band.

RFID Antenna Module with High Isolation Characteristic between Tx and Rx

In this paper, a new six-port direct conversion receiver for high-speed multi-band multi-mode wireless communication system such as software defined radio(SDR) is proposed. The designed receiver is composed of two CMOS four-port BPSK receivers and a dual-band one-stage polyphase filter for quadrature LO signal generation. The four-port BPSK receiver, implemented in 0.18 CMOS technology for the first time in microwave-band, is composed of two active combiners, an active balun, two power detector, and an analog decoder. The proposed polyphase filter adopt type-I architecture, one-stage for reduction of the local oscillator power loss, and LC resonance structure instead of using capacitor for dual-band operation. In order to extent the operation RF bandwidth of the proposed six-port receiver, we include I/Q phase and amplitude calibration scheme in the six-port junction and the power detector. The calibration range of the phase and amplitude mismatch in the proposed calibration scheme is 8 degree and 14 dB, respectively. The validity of the designed six-port receiver is successfully demonstrated by modulating M-QAM, and M-PSK signal with 40 Msps in the two-band of 900 MHz and 2.4 GHz.

Design of K-Band CMOS Four-Port Direct Conversion Receiver for BPSK Demodulation

We propose and demonstrate an I/Q demodulator using four-port BPSK demodulator base on additive mixing and reflection-type phase shifter using hybrid technique. Previously, the conventional I/Q demodulator base on multiplicative or additive mixing method divides I/Q signal path from mixer to parallel-to-serial converter. In this paper, we propose new I/Q demodulator without dividing I/Q baseband signal path. The proposed schematic requires half size in implementation and half power consumption in baseband path compared with the conventional receiver. Also, the proposed receiver eliminates parallel-to-serial converter after data decoding. The proposed circuit has been successfully demodulated a QPSK signal with the L-band carrier frequency and 20 Mbps data rate.