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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

A wideband six-port-based demodulator is proposed and applied as a quadrature phase shift keying (QPSK) demodulator for optimal K-band multiport amplifier (MPA) calibration circuitry. The proposed six-port demodulator adopts wideband ring hybrids for optimal 180°p hase balance in local oscillator signal paths. In addition, a voltagecontrolled reflection-type phase shifter and an attenuator are integrated into the six-port structure to ensure accurate magnitude and phase balance over broadband operation, resulting in optimal phase and amplitude error detection for the MPA system. To verify the proposed structure, RF demodulation of the K-band QPSK modulated signal was demonstrated for purpose of MPA calibration.

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