For more flexible and efficient use of radio spectrum, reconfigurable RF devices have important roles in the future wireless systems. In 5G mobile communications, concurrent multi-band operation using new SHF bands is considered. This paper presents a new configuration of dual-band SHF BPF consisting of a low SHF three-bit reconfigurable BPF and a high SHF BPF. The proposed dual-band BPF employs direct parallel connection without additional divider/combiner to reduce circuit elements and simplify the BPF. In order to obtain a good isolation between two passbands while achieving a wide center frequency range in the low SHF BPF, input/output impedances and external Qs of BPFs are analyzed and feedbacked to the design. A high SHF BPF design method with tapped transmission line resonators and lumped-element coupling is also presented to make the BPF compact. Two types of prototypes; all inductor-coupled dual-band BPF and C-L-C coupled dual-band BPF were designed and fabricated. Both prototypes have low SHF reconfigurable center frequency range from 3.5 to 5 GHz as well as high SHF center frequency of 8.5 GHz with insertion loss below 2.0 dB.

This paper proposes an independent control for parallel-connected multiple uninterruptible power supply (UPS) systems based upon a very simple control scheme. Here, the amplitude and phase angle of the output voltage are the controllable variables. With the only measurement of the output current, the active and reactive components are calculated to define the control variables. The entire system including the equations for the circuit, control and voltage limiters is well represented by a small-signal model, in which the computation of its eigenvalues constitutes the stability proof of the system. The root locus diagram gives an overall panorama of the system performance as a function of a certain gain and it aims to aid the further understanding and the design of the control. The experimental verification is carried out using a mere proportional-integral control scheme, which is a special case of the general control equation used in the theoretical analysis. For some situations, experiments show a flow of lateral current between UPS's, which causes an unbalanced current distribution. By increasing the proportional gain of the control equation for the output voltage amplitude, the lateral current can be substantially suppressed with a consequent improvement of the load sharing. Experimental results under various conditions show excellent results in terms of synchronization, load sharing and stability for three distinct output rating UPS's connected in parallel.