An unbalanced microstrip bandpass filter (BPF) in dual‐extended doublet topology with source‐load (S‐L) coupling is first presented and researched based on dual‐layer capacitive‐loaded dual‐mode loop resonators. The input and output ports are located on the upper substrate layer. The lower dual‐mode loop resonator is coupled to the upper loop resonator using four coupling apertures in the middle metal layer. Single‐ and dual‐band responses with four controllable finite‐transmission zeros (FTZs) are analysed. Then, a balanced BPF in dual‐extended doublet topology without S‐L coupling on the basics of the proposed unbalanced filter is presented and researched. Single‐ and dual‐band differential mode responses with three controllable FTZs can be realised with good common mode suppression. Some design examples are provided to illustrate the performances of the realised single‐ and dual‐band unbalanced and balanced filters with controllable FTZs. The measured results agree well with simulated ones.
This article presents a design method for balanced substrate integrated waveguide (SIW) filters with controllable finite transmission zeros (FTZs). The balanced SIW filters are designed by combining one dual‐mode and four single‐mode SIW cavities. Characteristics of the proposed balanced SIW filters without and with cross‐coupling path are analysed in detail. The proposed balanced SIW filters can realize one or two controllable FTZs. Based on the characteristic of dual‐mode SIW cavity, good performance of common mode suppression can also be achieved. For the demonstration, some design examples with the centre frequency of 12.5 GHz are presented, and two design examples are fabricated to verify the performance of the proposed balanced SIW filters and the design method.
We present a high-power white supercontinuum (SC) all-fiber laser source with average power of 67.9 W, spectrum ranging from 500 to 1700 nm, and spectral width exceeding 1000 nm for spectrum with flatness below 10 dB (except pump wavelength). Also, the visible waveband power (below 850 nm) occupies about 21% of the total SC power. A 145 W high-power picosecond pulse fiber laser is specially designed with high repetition frequency of 656 MHz to reduce nonlinear effects. Meanwhile, a homemade high-power mode field adaptor that can operate stably at hundreds of watts of pulse power has high coupling efficiency of 82%. To our knowledge, the 67.9 W white SC fiber laser source we achieved is the highest reported with such a wide and flat optical spectrum.
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