This letter proposes a compact and wideband absorptive bandpass filter (ABPF) with flat-in-band group delay and multiple out-of-band transmission zeros (TZs). The presented absorptive filter consists of a quarter-wavelength three-line coupled structure (TLCS) and four stubs that are basically a series connection of a lumped resistor and a short-circuited quarter-wavelength transmission line. The TZs are expressed by the adjacent and cross-coupling coefficients. It is revealed that the four stubs affect the filter’s bandwidth and TZ frequencies. To verify the design concept, a wideband absorptive filter operating at 2.4 GHz is fabricated and measured, whose simulated and measured results are in good agreement.

There are many researches on Z-source/Quasi-Z-source inverters since the topology was proposed in 2002 by Professor F.Z. Peng. This inverter can cover the shortage of traditional inverters. Almost all of the researches are studied in a circuit structure of single-stage. The original Z-source/Quasi-Z-source cannot achieve electrical isolation between input and output. The high frequency transformer isolated Z-source/Quasi-Z-source inverter proposed by F.Z. Peng in 2011 completes and perfects the circuit topologic family of Z-source inverter. It integrates the Z-source impedance network into the two-stage DC-DC-AC inverter by high frequency transformer. This paper makes an in-depth study of high frequency transformer isolated cascaded quasi-Z-source inverter. First the paper analyzes its basic principle and an abnormal working state discontinuous conduction mode (DCM). Based on the formulas, the paper gives some advice of how to choose desirable component parameters and working parameters. At last the paper gives a simulation of the inverter working in photovoltaic power generation system.

In this communication, a compact absorptive bandpass filter (ABPF) characterized by adjustable bandwidth and phase, low group delay (GD), a high absorptive ratio and low insertion loss (IL) is proposed. The presented ABPF consists of a bandpass section that is made of a quarter-wavelength coupled line and four stubs that are basically a lumped resistor in series with a short-circuited quarter-wavelength transmission line. The stubs not only perform the function of absorption but also have the advantage of adjustable bandwidth and phase. To verify the design concept and analysis formulas, an ABPF operating at 2.4 GHz is fabricated and measured; its simulated and measured results are in good agreement.

A unified-mode analysis method for modeling symmetric networks is proposed in this paper. Adjusting to the characteristics of Marchand balun circuits, a unified-mode circuit model is constructed by introducing virtual impedance. The tenable condition of a Marchand balun with connecting segments is then derived. The parameter constraint of Marchand balun’s input matching is given in a quarter-saddle diagram. Simulated results under different parameter conditions verify the validity of the derived formulas. Based on the derived formulas, the traditional isolation circuit and impedance matching circuit are merged with a Marchand balun to achieve matching for all ports and full-frequency isolation between output ports. A microstrip balun with input and output impedance values of 50 Ω, operating at 1.5 GHz, is simulated, fabricated, and measured. The simulated and measured results of the microstrip balun are in good agreement. When the core parameters remain unchanged, an impedance transformer is inserted in front of the input port of the balun to realize a balun with a topology characterized by flexible impedance transformation. A balun with an input impedance of 35 Ω and different output impedances of 50 Ω and 75 Ω is simulated and fabricated to verify the design concept. Measured results show that an amplitude balance of less than 0.4 dB and a phase balance of less than 3° for a fractional bandwidth of 50%. It should be mentioned that all design equations are closed-form and can be readily employed to design symmetric networks.

This letter proposes a compact triple-band bandpass filter with ten transmission zeros (TZs) and large frequency ratio, which is composed of a three-line coupled structure (TLCS) and four open-circuited stubs (OCSs). By classifying the coupled lines ports and utilizing the voltage and current constraint relationships at its ports, the Z-matrix of the input and output ports was obtained, and then the S-parameters were derived. To validate the theoretical analysis and design concept, a triple-band filter with center frequencies (CFs) of 0.86, 2.07, and 3.18GHz was simulated, fabricated, and measured. The filter has three bandwidths (BWs) of 0.12, 1.1, and 0.13 GHz, respectively, with insertion losses (ILs) of 0.34, 0.29, and 0.36dB. The theoretical predictions, simulated, and measured results are in good agreement.