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A novel and compact microstrip ultra-wideband (UWB) bandpass filter (BPF) based on a triple-mode resonator is designed, fabricated and measured. The proposed resonator is composed of a coupled line with a half-pass characteristic, which is connected directly with each other at one end and is short-circuited to the grounding plane at the other end. A simple structure and design approach to the proposed filter is provided and demonstrated. To implement the design on a microstrip, the directly tapped-transition input/output ports are used to excite the coupled-line multi-mode resonator. The measured results are in good agreement with the electromagnetic simulated results. The proposed filter shows a 3 dB fractional bandwidth of 117.3% at the central frequency (/)) with a return loss of better than 12 dB and an insertion loss of < 0.5 dB within the passband response. [PUBLICATION ABSTRACT]

A broadband hybrid power amplifier using a gallium nitride (GaN) high electron mobility transistor (HEMT) is presented. A discrete GaN HEMT bare die with 1.25 mm of gate width is used, and a compact size of 8.3 × 12.7 mm is achieved by using a feedback technique based on lumped elements. The power amplifier operates from 100 to 1000 MHz, and shows more than 12.8 dB gain and higher than 30.7 dBm output power in the overall bandwidth. Power added efficiency of 61.3% was acquired at the mid-band frequency and more than 54.5% throughout the bandwidth. [PUBLICATION ABSTRACT]

This paper presents an ultra-low-power second-order Chebyshev active-RC complex filter for a low-IF ultra-low-power receiver. By utilising a pole-cancellation push-pull buffer with feedforward phase compensation technology, the operational amplifier (opamp) realises superior stability while maintaining high gain bandwidth and ultra-low power consumption. A second-order complex filter with four proposed opamps and an adaptive bias fabricated in standard 180 nm CMOS process consumes only 460 mu W at 1.8 V power supply. The measured centre frequency is 3 MHz and bandwidth is 2 MHz, while it achieves 32 dB image rejection ratio at the centre frequency.

The bandwidth of tapered slot antennas (TSAs) is usually limited by the bandwidth of the feed used and typically does not exceed a few octaves, even though the TSA itself possibly can operate at a wider frequency range. Presented, and discussed, is a planar TSA feeding scheme that makes use of an external 1808 hybrid. Design guidelines and analytical formulas are presented for this hybrid connection scheme.

A compact triple-band coplanar waveguide (CPW)-fed antenna for WLAN/WiMAX applications is proposed. The radiation patch is fed by capacitive coupling of the top transmission line. By only using one metallic strip etched on the bottom of the substrate, tri-band resonances of the antenna are generated. The proposed antenna has a compact size of 30 × 27 mm2, which can provide stable omnidirectional radiation patterns in three bands. The measured − 10 dB impedance bandwidths are 150 MHz (2.39–2.54 GHz), 360 MHz (3.37–3.73 GHz) and 1170 MHz (5.02–6.19 GHz), which is suitable for WLAN/WiMAX applications.

Following a brief review of current progress in the field of nonlinear targeted energy transfer (TET), we discuss some general ideas and methods in this field and describe certain possible future venues for further developments; these go beyond the current paradigm of implementing TET by means of nonlinear energy sinks. Four such emerging research fields are discussed, namely (i) the new and promising concept of intermodal targeted energy transfer, (ii) the implementation of TET in nonlinear acoustic metamaterials, (iii) the break of classical reciprocity in elastodynamics in the context of TET, and (iv) the role of TET on the bandwidth of general classes of nonlinear resonators. Our aim is to describe the main ideas, summarize recent developments, outline possible directions for future work, and possibly trigger further research in the discussed topics and also in other possible TET-related topics not discussed herein.

A passively mode-locked laser system featuring cavity filtering and cavity-enhanced nonlinear interactions within an integrated microring resonator produces nanosecond optical pulses with a spectral width of 104.9 MHz. Most mode-locking techniques introduced in the past 1 , 2 focused mainly on increasing the spectral bandwidth to achieve ultrashort, sub-picosecond-long coherent light pulses. By contrast, less importance seemed to be given to mode-locked lasers generating Fourier-transform-limited nanosecond pulses, which feature the narrow spectral bandwidths required for applications in spectroscopy 3 , the efficient excitation of molecules 4 , sensing and quantum optics 5 . Here, we demonstrate a passively mode-locked laser system that relies on simultaneous nested cavity filtering and cavity-enhanced nonlinear interactions within an integrated microring resonator. This allows us to produce optical pulses in the nanosecond regime (4.3 ns in duration), with an overall spectral bandwidth of 104.9 MHz—more than two orders of magnitude smaller than previous realizations. The very narrow bandwidth of our laser makes it possible to fully characterize its spectral properties in the radiofrequency domain using widely available GHz-bandwidth optoelectronic components. In turn, this characterization reveals the strong coherence of the generated pulse train.

A century-old tenet in physics and engineering asserts that any type of system, having bandwidth Δω, can interact with a wave over only a constrained time period Δt inversely proportional to the bandwidth (Δt·Δω ~ 2π). This law severely limits the generic capabilities of all types of resonant and wave-guiding systems in photonics, cavity quantum electrodynamics and optomechanics, acoustics, continuum mechanics, and atomic and optical physics but is thought to be completely fundamental, arising from basic Fourier reciprocity. We propose that this “fundamental” limit can be overcome in systems where Lorentz reciprocity is broken. As a system becomes more asymmetric in its transport properties, the degree to which the limit can be surpassed becomes greater. By way of example, we theoretically demonstrate how, in an astutely designed magnetized semiconductor heterostructure, the above limit can be exceeded by orders of magnitude by using realistic material parameters. Our findings revise prevailing paradigms for linear, time-invariant resonant systems, challenging the doctrine that high-quality resonances must invariably be narrowband and providing the possibility of developing devices with unprecedentedly high time-bandwidth performance.

A symmetrical Fe2O3/BaCO3 hexagonal cone structure having a height of 10 um and an edge length of -4um is reported, obtained using a common solvothermal process and a mirror growth process. Focused ion beam and high-resolution transmission electron microscopy techniques revealed that α-Fe2O3 was the single crystal feature present. Ba ions contributed to the formation of symmetrical structures exhibited in the final composites. Subsequently, porous magnetic symmetric hexagonal cone structures were used to study the observed intense electromagnetic wave interference. Electromagnetic absorption performance studies at 2-18 GHz indicated stronger attenuation electromagnetic wave ability as compared to other shapes such as spindles, spheres, cubes, and rods. The maximum absorption frequency bandwidth was at 7.2 GHz with a coating thickness d = 1.5 mm. Special structures and the absence of BaCO3 likely played a vital role in the excellent electromagnetic absorption properties described in this research.