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Multipactor, a frequent detrimental effect in space high power systems, can degrade the performance of space microwave components or even cause devastation. Surface coatings with a low secondary electron yield (SEY) have been verified to mitigate multipactor efficiently, and some literature indicates that titanium nitride (TiN) coating is an excellent multipactor suppressor due to its recognized low SEY, whereas so far, the theoretical analysis for interpreting secondary electron emission (SEE) characteristics of TiN coatings is scarce. In this work, we experimentally and theoretically investigate the SEE characteristics of TiN coatings. We fabricate seven TiN coatings at different N2 concentrations by RF sputtering. The microscopic analysis indicates that the nanostructured TiN coatings are more likely to be formed at low N2 concentration, inversely, the compact TiN films are more likely to be formed at high N2 concentration. The SEE measurement shows that the nanostructured TiN coatings are more efficient to trap electrons than the compact TiN films do. Furthermore, via measuring resistivity, we find a novel regularity that the variation in true SEY largely depends on the resistivity for compact TiN films. Namely, the true SEY of compact TiN films linearly decreases as their resistivity exponentially declines. Then, we establish an equation to describe the true SEY as a function of resistivity via applying the semiconductor conductivity theory to Dionne's SEE model. The equation qualitatively interprets the experimental regularity. This work presents a probability to control the SEE level of TiN coatings by adjusting resistivity and is of significance to comprehend the SEE of semiconductors. [ABSTRACT FROM AUTHOR]

Multipactor induced by secondary electron emission (SEE) is a potential risk for many high-power systems. It is of great importance to suppress the total electron emission yield (TEEY) to mitigate the detrimental effect. Metal black has been reported as effective TEEY suppressor, but the theoretical model for describing its SEE characteristics is still scarce. In this work, we propose a periodic nanostructure model, with each unit composed of a combination of a top hemispherical nanograin and a fractal rectangular groove-like gap, to describe the silver black nanostructure. Using this model, we investigate the SEE characteristics of the silver black nanostructure theoretically. Simulation results indicate that the groove-like gaps in the nanostructure suppress the TEEY, while the top hemispherical nanograins enhance it; and the suppression on the true secondary electron yield is much stronger than that on the back-scattered electron yield (BSEY). In addition, we observe two interesting phenomena: first, the nanostructure enhances the BSEY even if it suppresses the TEEY when the proportion of top nanograins reaches 30%; second, the suppression on TEEY of the nanostructure becomes weak at relatively high primary electron energy. To verify the simulation results, we fabricate several silver nanostructures by thermal evaporation with gas pressure varied from 40 to 70 Pa. Measurement results indicate that all the fabricated nanostructures can suppress TEEY to some degree; and the more top hemispherical nanograins the nanostructure possesses, the higher TEEY revealed. For the measured SEE characteristics of the nanostructures fabricated at 40 and 45 Pa, we observe a higher BSEY than that of the flat surface. These experimental results qualitatively verify the simulated estimations. This work is of significance to comprehend SEE characteristics in related applications such as multipactor suppression. [ABSTRACT FROM AUTHOR]

The high-accuracy passive intermodulation (PIM) measurement shows great significance in PIM quality checking and related researches. As the key point to guarantee the test accuracy, the IM reference is essential in realizing precise PIM calibration. This paper presents a design of dual-port IM generator that can generate dynamic IM reference for this demand. The proposed generator employs a cascaded coupling network consists of two couplers, while a reverse biased Schottky diode is working as a tunable reflection IM source. The bias voltage and coupling coefficient are introduced to regulate the quiescent operation points of diode and the IM signal excitation strength respectively, they work together to put the IM reference signal on a desired level. Specially, a trimming strategy by using a compact terminal matching resistor is adopted to smartly regulate the IM tunable interval. These configurations can promote the utilization of this proposed IM generator to be flexible not only for design engineers but also for commercial users. The test results demonstrate that this generator can provide the tunable IM3 whose dynamic range can reach about 30 dB@2x43 dBm, 50 dB@2 × 31 dBm. Meanwhile, the significance of bidirectional dynamic IM reference signals is demonstrated. [ABSTRACT FROM AUTHOR]

Plenty of evidence has implied that animals like pigeons and sea turtles utilize geomagnetic information for long-distance migration and homing. In this paper, we conduct an ab initio investigation to imitate a migratory animal's geomagnetic homing across a long distance over the surface of the Earth. Based on a simple assumption that such animals have a natural ability to sense and compare the included angle between the vector geomagnetic field (GF) and a specific geographic direction such as the due north, we show that a long-distance geomagnetic navigation (GN) can be accomplished without any assistance of prestored geomagnetic and geographic information, as long as the navigation is inside a vast area where such a spatial angle can uniquely determine a geographic location. Without any requirement of measuring the strength of the GF, this GN will not be visibly affected by the recurrent fluctuation of the GF that severely hampers traditional GN. By introducing the extended-Kalman-filter algorithm, it is able to find a shortcut in the geomagnetic space, overcoming interferences of strong Gaussian and local-area geomagnetic anomaly. We believe that the proposed approach will find a wide range of potential applications in global, local, and indoor navigations based on magnetic field in the future. [ABSTRACT FROM PUBLISHER]

Nowadays, there is expanding interest in planar compact microstrip filters applied to microwave wireless system. The compact microstrip resonant cell (CMRC) and spiral compact microstrip resonant cell (SCMRC) are more and more popular in filter design due to their slow-wave and band-stop effects. In this paper, a novel double-folded SCMRC (DSCMRC) is proposed, analyzed and measured, which turns out to have more compact dimensions and distinctly broader stopband than CMRC and SCMRC. Furthermore, an improved DSCMRC circuit with two parallel open-ended stubs that are added into the DSCMRC structure is presented, which could introduce more transmission zeros in the stopband for better out-of-band rejection than the original DSCMRC. The measured results show the excellent performance of the improved DSCMRC circuit structure. Finally, a novel low-pass filter incorporating two improved DSCMRC in series is simulated and measured, which proves to have an excellent performance of out-of-band rejection up to 25 GHz with a really compact circuit size. [ABSTRACT FROM AUTHOR]

Artificially designed transformation medium offers great opportunity to control the field distributions inside a waveguide. By rigorously solving Maxwell’s equations in cylindrical and rectangular waveguides, we show that filling waveguides with properly designed transformation medium with a space gradient can reduce the electric field at boundary to zero. Full-wave finite element modeling is also performed to confirm this point. This property can be used to reduce the probability of multipactor discharge at the surface of conductor inside a waveguide. [ABSTRACT FROM AUTHOR]