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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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K-band 0°/180°phase shifter MMIC based on balanced structure which can be applied to BPSK or QPSK modulator with dc-offset cancellation is presented. The proposed balanced phase shifter consists of four Lange couplers, two quarter-wave transmission lines and four switches for open and short terminations. The proposed structure implemented in GaAs 0.15-µm low noise pHEMT process ensures stable 0/180°phase shift while common-mode signals due to the mismatch in reflections by open and short are fed to the isolation port. The proposed phase shifter is verified by the phase shift of 179 ± 1.5°with the insertion loss of 4.5 ± 0.8 dB from 17.5 to 22.5 GHz. The fabricated phase shifter size is 2.2 × 2.85 mm including test pads.Introduction: Phase shifters are one of the most widely used components in microwave applications, such as phased-arrays and communication systems. For reliable system performances, phase shifters must generate a desired relative phase shift with low insertion loss variation and good return characteristics. Thus, there have been many techniques such as a reflection type phase shifter with series and parallel LC terminating circuits [1], vector-sum based phase shifter [2] and modified rat-race structure with the Lange coupler [3]. In addition, 0/180°phase shifters configured with the combinations of directional couplers, Wilkinson dividers, or 3-dB couplers are used as BPSK modulators [4,5]. However, these structures undergo the dc-offset problem [1,2] or degradation in return characteristics [3] by common mode signals returning to the input owing to the mismatch in reflective circuitry. Thus, a new balanced phase shifter structure that generates stable 0/ 180°phase shift and cancels unwanted common-mode signal which results in dc-offset is proposed.

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Two types of compact broadband phase shifter MMICs (monolithic microwave integrated circuits) with constant insertion loss variations are presented. Both phase shifters are reflection‐type phase shifters using a Lange coupler as a 3‐dB coupler and LC resonance terminations. The first type phase shifter uses a single diode with reverse biasing as a varactor and adopts a miniaturized Lange coupler to maximize compactness and to minimize parasitic loss. The second type adopts back‐to‐back connected diodes with reverse biasing as a varactor for wider tunable phase range and parallel resistors for constant insertion loss variation. For both types, MMIC's are fabricated in GaAs 0.15‐μm low noise pHEMT (p‐high electron mobility transition) process and required indcutances are implemented by microstrip lines. The implemented MMIC phase shifter of the first type shows the measured relative phase shift range of 80° and measured insertion loss of 2.1 ± 0.2 dB at 20 GHz. The measured relative phase shift range of 72 ± 9° and the measured insertion loss variation of ±0.2 dB are obtained from 15 to 25 GHz. Similarly, the second type phase shifter shows the measured relative phase shift range of 104° and measured insertion loss of 2.4 ± 0.1 dB at 21 GHz. Also, the broadband characteristic of the second type is verified by the measured relative phase shift range of 96 ± 8° with the constant insertion loss variation of ±0.2 dB from 17 to 25 GHz. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:394–400, 2014