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This letter presents the design and measurement of high OIP3, low flicker noise double-balanced Gilbert cell down conversion mixer in CMOS process. The key features of proposed mixer are dynamic current injection and derivative superposition. Since the flicker noise (1/f noise) have a strongly affect mixer's noise figure (NF), a dynamic current injection is used to reduce the flicker noise. The derivative superposition method has an auxiliary common gate stage of radio-frequency (RF) input stage to cancel each third order intermodulation distortion (IMD3) and can provide a high third order output intercept point (OIP3). The proposed down conversion mixer is fabricated in 0.18 μm CMOS technology. And this letter highlights the performances of the proposed mixer in terms of: flicker noise (i.e., noise figure: 5 dB at 100 kHz), third order output intercept point (i.e., OIP3, typically 35 dBm), and the conversion gain (i.e., typ. 17.3 dB) from −20 dBm RF input at 2.4 GHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1720–1723, 2016

This article presents a feedforward 3rd harmonic cancellation scheme for ultra-high frequency (UHF) wireless communication system in 834–879 MHz. The major features are highlighted: a special notch filter with sharp skirt performance (e.g., both lower and higher band edge from 834 to 879 MHz yield lower than −40 dB cutoff), and micro-controller based amplitude/phase control on feedforward path signal generation for fine harmonic cancellation. A prototype was implemented; it works out 47.36 dB Hz−1 cut-off and 60 dBc ACLR. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1006–1010, 2016

In this article, special type of RF Charger is proposed for Wireless RF power harvesting system. RF charger is consisted of impedance matching circuit, full bridge CMOS rectifier, active diode, hysteresis switch, and DC–DC booster. The proposed RF charger is to obtain maximum available RF power through adjusting impedance matching circuitries. The proposed RF charger is matched to Korean WCDMA frequency band from 1960 to 1980 MHz. The minimum input RF power for charging 5 V battery is −10 dBm. The RF to DC conversion efficiency of the RF charger is 81% at 30 mA load current with 5 V battery, and the maximum output voltage is 5.5 V. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1622–1625, 2015

This article presents an adaptive tuning technique for improving the power flatness of an X-band frequency multiplier. The major features are highlighted: a tunable band-pass filter, and a microcontroller process. Simulation and measurement results show the power flatness is improved from 5–5.5 dB to 0.5–1 dB. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1056–1060, 2015

An extended work on DGS modulator, which was presented before on Microwave and Optical Technology Letters Society, shall be adaptive performance and practical implementation and measurement. A DGS modulator is motivated from three benefits that can be obtained from defected ground structure; an extensive resonance, size reduction, and excellent stopband characteristic. An extensive resonance via a microstrip ground plane configuration, which includes a varactor diode bridging microstrip transmission line with variable capacitance provision that can be controlled, gives on/off switching and its attenuation level (OOK is a 100%, and which less than 100% can be ASK) that plays the key role of the ASK and OOK modulation process. A varactor diode is under control of a micro control unit that can be controlled by user interface software; therefore, user can monitor communication states while each operational sequence of a varactor diode can be controlled. Sharper phase and more precise data modulation can be achieved after several tuning works and practical trials. A modulation index (about 90–93%) with stable tag responses over the target bands (860–960 MHz, centered 912 MHz) was verified through the practical measurements on the RFID reader communication using ASK. And when a modulation index was nearly 99% (∼98.8%), this is considered to be an OOK. Overall radio communications are with EPC class-1 Gen2 Type-B and Type-C passive tags, respectively. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2646–2651, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23780

This article represents a microchip balun for UHF mobile RFID system at 910 MHz. This balun is designed by transforming coupled transmission lines into lumped-element equivalent circuit, and thus monolithic elements that are fabricated by IPD technology replace it for entirely miniaturized size. The corresponding balun performs under 3 dB return loss, with nearly 176 (176.42) degree of phase difference characteristic; therefore, this meets the UHF mobile RFID reader system consideration. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2203–2206, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23617

Radio characteristic evaluations of each component through the entire communication system can be performed by using the signal sampling methods, which give information of the precise statistics and high qualified specifications. Particular modern trends on electrical devices demand extremely miniaturized dimensions to meet the hand-held system units, such as personal communication services, mobile RFID applications and other possible products including crucial factors of low-profile and mobility. It is eventually aimed to avoid unnecessary waste of manufacturing products, and guarantee the mobility, ease of use and so forth. Thus the multi-mode electrical devices providing numerical advances in a single structure are needed and this is the motivation of further experiments. In this study, we propose a novel dual directional coupler design schemes including derivative calculations and its completely manufactured prototype. It has been designed by promoting three parallel coupled transmission lines with novel mathematic formula and auxiliary simulation systems. Outstanding technical features can be high isolation and directivity characteristics and these will be illustrated within the statistical tables and graphics for verification. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 775–780, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23188

In order to offer RFID services on mobile phones, the RFID reader must be embedded on the handset as a chip. However, the directional coupler was used as a ceramic passive component in conventional handsets. RFID system using an identical Tx/Rx carrier frequency has a significant volume limitation compared with active components. This article presents the directional coupler design for UHF RFID mobile reader using IPD (Integrated Passive Device) process. T and π-type coupler with dimensions of 1.74 × 1.6 and 1.32 × 1.4 mm2 were assembled. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1501–1504, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22497

A novel compact microstrip patch antenna is proposed for quad band, GSM850, GSM900, GPS (L1–1575 and L2–1227), and UMTS-2110 application for cellular telephone system. Design is particularly unique since it supports the new generation mobile phone where multiband operation with minimum size is greatly desired. Two microstrip line feeds placed in orthogonal directions are used for the excitation of the proposed antenna. Microstrip patch has been meandered to lengthen the electrical paths and to achieve quad frequency bands. Detail of design criteria with respect to physical parameters is described. Radiation Patterns and impedance bandwidths are measured and shown. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 997–1001, 2007; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.22341

In this paper, a DPDT (Double-Pole Double-Throw) switch with defected ground structure (DGS) is newly proposed for transceiver systems. A biased varactor diode is introduced to control the on/off operation of the proposed switch. In order to confirm the validity of the switch, we design and implement the switch at the 2.45-GHz frequency. It is designed specifically for antenna-diversity switching for WLAN applications. The experimental results show very low insertion loss, excellent power handling, and high isolation performances. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1127–1130, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21561

This article presents a TX leakage cancellation scheme for UHF RFID readers. A prototype is implemented on a UHF RFID reader board, which includes a circulator, directional coupler, microcontrol unit (MCU)-controlled variable attenuator, and phase shifter. The difference between a conventional TX leakage canceller and this new one is that, reflected signals caused by mismatches between the front-end and the antenna are included; in addition, high isolation is supplemented at variable frequencies. About 10% of the frequency range is recovered by the best suited parameter values that provide a predetermined process of MCU; and thus, peak isolation characteristics are constantly guaranteed at each center frequency by phase-shifted signal generation that follows references stored in MCU. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2043–2045, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23592

A new approach is proposed to design a frequency-variable dual-band microstrip antenna. Two unbalanced microstrip lines are used to feed microstrip patch vertically with a branch-line coupler. The entire structure is designed on a single-layer substrate. The resonant frequencies of the microstrip patch can be changed by varying the dimensions of the unbalance feed lines. A prototype of the proposed antenna is fabricated and measured. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 11991–1201, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21581