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A new structure of on-off keying(OOK) transmitter with low power consumption and high data rate is proposed using a current-reused CMOS differential LC-VCO [1] for wireless capsule endoscope application.The carrier frequency (440MHz) of the transmitter is determined as the minimum loss frequency point considering the antenna loss and the loss property of human body, etc. The transmitter is able to output OdBm of power at the single-ended output to a monopole 50-Ohm antenna to meet the demands of high-data rate speed (4OMb/s) and short range (15-cm) wireless communication. This transmitter, has been fabricated using 0.18-,um CMOS technology, consumes only 860-uA of current from a 3V supply.

A coupled‐line passive circulator is proposed for improving the TX/RX isolation of the UHF radio frequency identification (RFID) reader. The increased isolation is realized by generating and adding the canceling signal to the leakage. The input return loss of the reader antenna, which can degrade TX‐to‐RX isolation, as well as the inherently imperfect isolation characteristic of a coupled‐line directional coupler, are included in the design of the coupled‐line passive circulator. The proposed coupler exhibits up to 60‐dB isolation characteristic with the mismatch of the employed reader antenna. The performance comparison between the proposed and the conventional coupled‐line directional couplers shows a significant improvement in the leakage‐to‐signal ratio by up to 35 dB. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2597–2600, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23705

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. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ

This letter proposes a novel calibration method for a multiport amplifier (MPA) to achieve optimum port-to-port I. IntroductionModern satellite communication systems generally adopt various techniques to increase the flexibility of the antenna and the power allocation of their coverage [1]. To adaptively control communication traffic during the lifetime of a satellite, using an architecture based on the multiport amplifier (MPA) is an effective approach in multibeam systems. The theoretical analysis of an MPA with respect to classical power amplification architectures reflects that it has lower DC power consumption with lower saturation power amplifiers (PAs) [2].In this case, the isolation characteristic among the output ports of the MPA is important for successful operation. A fair port-to-port isolation characteristic can be achieved by Manuscript received Dec. 1, 2012; revised Feb. 2, 2013; accepted Feb. 12, 2013. Seong-Mo Moon (phone: +82 42 860 0862, smmoon@etri.re.kr), Dong-Hwan Shin (dhshin@etri.re.kr), Hong-yul Lee (hylees@etri.re.kr), Man-seok Uhm (msuhm@etri.re.kr), and In-Bok Yom (ibyom@etri.re.kr) are with the Broadcasting