This letter presents a new 2 2 multi-port amplifier (MPA) structure using switching mode hybrid matrices (SMHM's) 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 PA's 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 PA's and then be delivered to any one of the two output ports. In addition, the amplified signal by a single PA or two PA's 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.Index Terms-Balanced amplifier, multi-port amplifier (MPA), reconfigurable divider/combiner, switching mode hybrid.

This article presents a reconfigurable antenna feeding network for circular and linear polarization diversity. The proposed circuit consists of two hybrid couplers and two single pole four throw switches for four configuration modes: left‐hand circular polarization, right‐hand circular polarization, vertical linear polarization, and horizontal linear polarization. For verification, a reconfigurable antenna with the proposed feeding network is designed at 917 MHz and measured for switchable circular and linear polarizations. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:893–896, 2014

This article presents a compact attenuator integrated phase shifter with switchable trimode operations. The proposed structure consists of simple reflection‐type attenuator and phase shifter with Lange coupler for wideband performance. The reflective circuits for attenuator and phase shifter are implemented with HEMT's and varactor diodes. By separately adjusting the control voltages for attenuator and phase shifter, the designed circuit can operate in trimode: attenuation‐mode, phase shift‐mode (PS‐mode), and loss variation compensated phase shift‐mode (LVC‐PS‐mode). The proposed circuit is implemented in 0.15‐µm GaAs low noise pHEMT process and provides the input and output return losses always better than 12 and 15 dB, respectively. Using LVC‐PS‐mode, the measured maximum phase shifting range of 80° with the measured insertion loss variation within ±0.05 dB from 15 to 25 GHz can be achieved. The chip size of the fabricated core is about 1.5 × 0.65 mm2 excluding test pads. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1798–1800, 2014

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.Index terms -Bio-radar system, six-port demodulator, lumped six-port architecture, quadrifilar antenna

A new automatic resonant frequency matching technique based on voltage detection by sampling the output transformer loop of the radio-frequency power amplifier (PA) in ultrasonic medical applications is proposed. The proposed automatic resonant frequency matching circuitry is composed of a single-loop coil added to a PA output transformer, voltage divider, diode detector and micro-controller unit for frequency adjustment. Using the proposed circuitry, the resonant frequency shift due to output load variations can be effectively tracked and compensated to provide optimised power transfer to a nonlinear load. For verification, a prototype ultrasonic medical application using a piezoelectric transducer is implemented and examined with silicone oil to check the resonance.Introduction: Resonant frequency or load impedance variations are common phenomena in applications in which radio-frequency (RF) power sources are required such as wireless power transfer and highpower ultrasonic transducers [1,2]. In ultrasound operations, using a transducer at its exact resonant frequency is critical in terms of highest power conversion. If an application is not matched to the resonant frequency of a transducer, the overall system performance is degraded by low-power efficiency and unstable vibration amplitude.To solve these problems, there have been several techniques to track the working frequency around the resonant frequency of ultrasonic transducers and the phase-locked loop (PLL)-based tracking system has been considered the most common method [3,4]. However, the configuration with a PLL increases system complexity and exact calculations on phase difference must be conducted. Therefore, in this Letter, a simple automatic resonant frequency matching structure with a class-D power amplifier (PA) is proposed and verified with an ultrasonic transducer for medical applications.