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As the market for internet of things (IoT) is growing and due to Ofcom's decision to reassign parts of the very high frequency (VHF) spectrum in the UK for IoT use, a propagation study has been conducted using the newly released VHF spectrum and the currently commercially operated ultra‐high frequency (UHF) spectrum, in order to compare and contrast the suitability of the VHF spectrum for IoT use. The authors conducted their study in a number of different environments (rural, suburban, urban and dense urban), with measurement equipment deployed in a manner suitable for a portable IoT use case. Results are presented in comparison to other propagation studies available in the literature and widely used propagation models such as the Hata model. Shadowing and noise are also measured and examined. It is found that current propagation models do not provide adequate predictions within the considered use case, but found it is possible to calculate log‐distance based models that provide good predictions. Path‐loss is found to be constantly lower at VHF than UHF, but radio frequency noise is consistently higher. The newly released spectrum is found to be suitable for IoT deployments in all the examined environments. [ABSTRACT FROM AUTHOR]

With the characteristics of higher electron density and lower ion bombardment energy, large-area VHF (very high frequency) plasma enhanced chemical vapor deposition has become an essential manufacturing equipment to improve the production throughput and efficiency of thin film silicon solar cell. However, the combination of high frequency and large electrodes leads to the so-called standing wave effect causing a serious problem for the deposition uniformity of silicon thin film. In order to address this issue, a technique based on the idea of simultaneously launching two standing waves that possess similar amplitudes and are out of phase by 90° in time and space is proposed in this study. A linear plasma reactor with discharge length of 54 cm is tested with two different frequencies including 60 and 80 MHz. The experimental results show that the proposed technique could effectively improve the non-uniformity of VHF plasmas from > ±60% when only one standing wave is applied to < ±10% once two specific standing waves are launched at the same time. Moreover, in terms of the reactor configuration adopted in this study, in which the standing wave effect along the much shorter dimension can be ignored, the proposed technique is applicable to different frequencies without the need to alter the number and arrangement of power feeding points. [ABSTRACT FROM AUTHOR]

Abstract Through concurrently measurements by Communication/Navigation Outage Forecasting System (C/NOFS), Sanya VHF radar and GPS ionospheric scintillation receiver on 12 March 2010, five plasma bubbles were found and three of them were observed by all those instruments. Two well-developed plumes with strong backscatter echoes were measured by Sanya radar and their corresponding depletions were observed by C/NOFS in Orbit 10317, 10318 and 10319. Broad plasma depletions resulting from merging process were found in orbit of 10318. The occurrence time and geophysical positions of scintillations correlate well with observations implemented by Sanya VHF radar and C/NOFS. Observations from three types of instrument indicate that the spread F irregularities have distinct scale. There were longitudinal differences between Sanya VHF radar and C/NOFS as irregularities measured, and the eastward drift of developed bubbles are responsible for these differences. [ABSTRACT FROM AUTHOR]

This paper leads a discussion on how to form a Synthetic Aperture Radar (SAR) image without knowing the relative track. That is, within the scope of factorized geometrical autofocus (FGA). The FGA algorithm is a base-2 fast factorized back-projection (FFBP) formulation with six free geometry parameters (per subaperture pair). These are tuned step by step until a sharp image is obtained. This innovative autofocus concept can compensate completely for an erroneous geometry. The FGA algorithm has been applied successfully on two ultrawideband (UWB) data sets, acquired by the CARABAS II system at very high frequency (VHF)-band. The relative tracks are known (measured accurately). We, however, adopt and modify a basic geometry model. A linear equidistant track at fixed altitude is initially assumed. Apart from deviations due to linearization, a ~2.5-m/s along-track velocity error is also introduced. Resulting FGA images are compared to reference images and verified to be focused. This indicates that it is feasible to form a wavelength-resolution SAR image at VHF-band without support from a motion measurement system. The execution time for the examples in this paper is about five times longer with autofocus than without. Hence, the FGA algorithm is now fit for use on a regular basis. [ABSTRACT FROM AUTHOR]

In this letter, we report simulation results of streamer propagation and collision that produce electromagnetic radiation in the very high frequency (VHF) and ultra high frequency (UHF) bands. The streamers are initiated in overbreakdown field conditions, 1.5Ekand2Ek, respectively, which may be found during the corona flash stage of negative leader stepping processes. We find that while streamer propagation produces stronger VHF radiation, the head‐on collision of streamers dominates UHF, and even higher‐frequency radiation. Analysis of the energy spectral densities obtained from different simulation cases shows that the total length and radii of colliding streamers, as well as the ambient field, are important parameters for the UHF radiation produced by streamer collisions. The larger those parameters are, the stronger UHF radiation produced. Finally, by comparing with the measured spectral magnitude of lightning field in the VHF range, it is found that there are probably 105–107 streamers involved during the lightning corona flash stage. Plain Language Summary: Despite being a familiar phenomenon, the physics of lightning initiation and propagation is not well understood. An effective approach to study lightning is to observe their radio frequency (RF) signals, which is especially critical for understanding the lightning activities inside thunderstorms, because clouds are opaque for other signals. The RF signals with frequencies above about 10 MHz are commonly used to map/image lightning development. They are believed to be produced by the physical process electrically breaking down virgin air. Previous work has shown that electrical breakdown processes known as streamers, which are the precursors of lightning, can produce RF radiation below hundreds of megahertz. Our study investigates a physical process that enables lightning to produce RF radiation above hundreds of megahertz. We find that collisions between streamers can generate rapid increases of electrical current to produce RF emissions extending to tens of gigahertz. The results will be helpful for understanding and interpreting RF observations/measurements of lightning and will generate impact in the field of atmospheric and space electricity. Key Points: Colliding streamers can produce electromagnetic radiation in the UHF, SHF, and even higher‐frequency rangePropagating streamers produce insignificant electromagnetic radiation beyond the VHF rangeUnder otherwise the same conditions, longer and larger streamers in higher ambient field produce stronger VHF and UHF radiation [ABSTRACT FROM AUTHOR]

In this paper, we describe measurement results of the signal-in-space of very high frequency (VHF) omnidirectional range (VOR) facilities. In aviation VOR are used to display the current course of the aircraft in the cockpit. To understand the influence of wind turbines (WT) on the signal integrity of terrestrial navigation and radar signals, the signal content and its changes, respectively, must be investigated. So far, only numerical simulations have been carried out on the frequency-modulation (FM) part of the Doppler-VOR (DVOR) signal to estimate the influence of WT on DVOR. Up to now, the amplitude-modulated (AM) part of the DVOR was not assessed at all. In 2016, we presented an unmanned aerial system (UAS) as a carrier for state-of-the-art radio-frequency (RF) measurement instrumentation (Schrader et al., 2016a, c; Bredemeyer et al., 2016), to measure and to record the true signal-in-space (both FM and AM signal) during the flight. The signal-in-space (which refers to time-resolved signal content and field strength, respectively) is measured and sampled without loss of information and, furthermore, synchronously stored with time stamp and with precise position in space, where the measurements were taken. [ABSTRACT FROM AUTHOR]

Magnetic pulse compression (MPC) systems are suitable for generating dielectric barrier discharges (DBDs) owing to their capability of producing high-amplitude, short pulse voltage waves. This paper proposes a high-frequency, bipolar magnetic compression system to study DBD plasma characteristics. First, the principle of bipolar MPC is explained [a bipolar MPC system comprises a full bridge inverter circuit, pulse transformer (PT), and magnetic switch (MS)]. Additionally, the design of the PT and MS is described. Then, the waveform of the resistive load is tested and compared with PSpice simulation results. It was found that the nanosecond pulse generator produces a pulse on a resistor with an amplitude of 0–13 kV, a rise time of approximately 100 ns, and a repetition frequency of 0 to several kHz. Finally, this paper studies the plasma characteristics under the application of a high-frequency bipolar pulse, and the charge–voltage Lissajous figure of the discharge waveform is analyzed. Combining discharge photographs and theoretical calculation results yields the relationship between the discharge characteristics and the frequency, which enriches the theoretical study of high-frequency bipolar discharges. [ABSTRACT FROM AUTHOR]

This paper presents an extremely low-profile frequency-tunable composite antenna with enhanced gain and an omnidirectional radiation pattern. The antenna is based on a recently developed very short two-legged monopole antenna and consists of one driven element and eight identical parasitic coupled elements. By utilizing the mutual coupling between elements, the radiation resistance of the antenna is significantly increased, leading to considerable gain enhancement and better matching performance. The composite antenna has the same height as the single monopole ( $\lambda _{0}/150$ ) but a larger lateral dimension ( $\lambda _{0}/16$ ). The performance of the proposed antenna is compared with that of a single monopole antenna. It is shown that the peak gain of the composite antenna is about 10 dB higher than that of the monopole antenna. The design is then modified for frequency tunability to achieve frequency agility and higher bandwidth for certain modulations like frequency hopping spread spectrum. The fractional bandwidth of the tunable antenna is 3.32%, and the gain is further improved at higher frequencies. A new method of effectively measuring a monopole antenna with an electrically small ground plane using cascaded transformers is also presented and discussed. [ABSTRACT FROM AUTHOR]

Biologists interested in using radio telemetry to track the movements of birds should concurrently conduct studies to assess potential impacts on study organisms, particularly when monitoring threatened or endangered species. We investigated the effects of traditional and digital very high frequency (VHF) radio transmitters on daily nest survival and chick survival rates of Piping Plovers ( Charadrius melodus) along the Atlantic Coast in 2012, 2013, and 2015. We attached 1.0-1.2 g transmitters to 110 plovers and monitored their 160 nest attempts. We also monitored 221 nest attempts by 161 control pairs with no transmitters. There was no evidence that nest or chick survival differed between tagged and control pairs. Transmitters did not seem to adversely impact Piping Plover daily nest and chick survival and are a valuable tool to monitor movements of this threatened species. [ABSTRACT FROM AUTHOR]

One-dimensional particle-in-cell simulation is used to simulate the capacitively coupled argon plasma for a range of excitation frequency from 13.56 MHz to 100 MHz. The argon chemistry set can, selectively, include two metastable levels enabling multi-step ionization and metastable pooling. The results show that the plasma density decreases when metastable atoms are included with higher discrepancy at a higher excitation frequency. The contribution of multistep ionization to the overall density increases with the excitation frequency. The electron temperature increases with the inclusion of metastable atoms and decreases with the excitation frequency. At a lower excitation frequency, the density of Ar** (3p5 4p, 13.1 eV) is higher than that of Ar* (3p5 4s, 11.6 eV), whereas at higher excitation frequencies, the Ar* (3p5 4s, 11.6 eV) is the dominant metastable atom. The metastable and electron temperature profile evolve from a parabolic profile at a lower excitation frequency to a saddle type profile at a higher excitation frequency. With metastable, the electron energy distribution function (EEDF) changes its shape from Druyvesteyn type, at a low excitation frequency, to bi-Maxwellian, at a high frequency plasma excitation; however, a three-temperature EEDF is observed without metastable atoms. [ABSTRACT FROM AUTHOR]

The problem of inferring the location and time of occurrence of a very high frequency (VHF) lightning source emission from Lightning Mapping Array (LMA) network time-of-arrival (TOA) measurements is closely examined in order to clarify the cause of retrieval errors and to determine how best to mitigate these errors. With regard to this inverse problem, the previous literature lacks a comprehensive discussion of the associated forward problem. Hence, the forward problem is analyzed in this study to better clarify why retrieval errors increase with increasing source horizontal range and/or decreasing source altitude. Further insight is obtained by performing carefully designed Monte Carlo inversion simulations that provide specific retrieval error plots, which in turn lead to clear recommendations for mitigating retrieval errors. Based on all of the numerical results, the following strategies are recommended for mitigating retrieval errors (when possible, and without obstructing the line of sight): expand the horizontal extent of the LMA network, maximize the vertical sensor baseline by using mountainous terrain if available, and improve TOA measurement timing accuracy. Adding sensors to the network is relatively ineffective, unless of course the addition of sensors expands the horizontal extent and/or vertical baseline of the network. It is also shown how the standard retrieval method can be generalized by considering, in addition to the regular (unpolarized) point VHF source, the polarized transient very low frequency/low frequency (VLF/LF) electric point dipole source. Multiple observations (i.e., VHF arrival time and power, and VLF/LF arrival time and electric field amplitude) are simultaneously implemented into the new generalized mathematical framework, and the potential benefits are indicated. [ABSTRACT FROM AUTHOR]

A novel broadband horizontally polarized (HP) omnidirectional antenna is proposed for meteor-burst communication system in VHF. The proposed antenna is composed of three bowtie dipoles, which are concentrically placed to form a loop antenna. The bowtie dipole is shorted at the terminal by folded elements in order to reduce antenna size. The bowtie dipoles are fed by a three-way power divider. A slotted line balun is employed to achieve broadband impedance matching and realize balanced-to-unbalanced transformation. The designed HP omnidirectional antenna exhibits a fractional bandwidth of 24.7% with VSWR < 2 ranging from 39 to 50 MHz. Uniform omnidirectional radiation patterns in the azimuth plane with HP have been obtained. The loop antenna provides a relatively low gain of no more than 1.5 dBi. Therefore, a two-element HP antenna array is developed to enhance its gain. In order to reduce longitudinal dimension of the array, the two loop antenna elements are placed in reverse and employ differential feeding method to realize in-phase current. Both the simulation and measured results are used to verify the design approach. [ABSTRACT FROM PUBLISHER]

This paper addresses the self-interference (SI) cancellation for full-duplex operation in the presence of imperfect radio-frequency (RF) components. In particular, we develop a new scheme to jointly estimate and cancel the in-phase/quadrature mixer imbalance, power amplifier nonlinearities, up-/down-conversion phase noise, and the SI channel. First, we develop a detailed baseband model that captures the most significant transceiver RF imperfections, for both separate- and common-oscillator structures used in the up- and down-conversions. Then, a basis expansion model is derived to approximate the time-varying phase noise and to transform the problem of estimating the time-varying phase noise into the estimation of a set of time-invariant coefficients. Subsequently, the likelihood function is derived in the presence of the unknown intended signal to formulate the joint estimation of the intended channel, SI channel, nonlinear impairments, and phase noise, under the maximum likelihood (ML) criterion. An iterative procedure is developed to find the ML estimate of the different parameters based on the known transmitted data, the known pilot symbols, and the statistics of the unknown intended signal received from the intended transmitter. The full use of the received signal significantly reduces the required number of pilot symbols as compared to training-based techniques. We consider the two pilot-insertion structures used in LTE for the frequency-multiplexed pilots and the time-multiplexed pilots. Simulation results indicate that the proposed ML algorithms can offer a superior SI-cancellation performance with the resulting intended-signal-to-SI-and-noise ratio very close to the intended-signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

In this study, a four-way power combiner using four equally designed 2-way power combiners is introduced. The physical structure of the combiner is such that the components and connections are symmetrically arranged. In the final section of the power combiner, two 2-way combiners are connected in parallel, which helps for easier circuit alignment and better electrical properties. The 2-way power combiner is the building block of the 4-way power combiner. The 2-way power combiner is analysed by even and odd method and its performance is verified by measurements. The analysis method can be extended to 4-way or N-way power combiners. The proposed 4-way power combiner is fabricated and its performance is measured. The amplitude imbalance of the 4-way power combiner is <0.2 dB in the path between the input ports and the summing port. The attenuation above the theoretical 6 dB insertion loss is 0.5 dB from 30 to 500 MHz. The 4-way power combiner has the same performance as the 2-way power combiner, regarding the added insertion loss above the theoretical ideal value. Ease of fabrication, simple circuit connections and use of equally constructed 2-way power combiners result in repeatability and reduce electrical mismatch. [ABSTRACT FROM AUTHOR]

This paper investigates the Additional Secondary Phase Factor (ASF) characteristics of Automatic Identification System (AIS) signals spreading over a rough sea surface. According to the change of the ASFs for AIS signals in different signal form, the influences of the different propagation conditions on the ASFs are analyzed. The expression, numerical calculation, and simulation analysis of the ASFs of AIS signal are performed in the rough sea surface. The results contribute to the high-accuracy propagation delay measurement of AIS signals spreading over the rough sea surface as, well as providing a reference for reliable communication link design in marine engineering for Very High Frequency (VHF) signals. [ABSTRACT FROM AUTHOR]

The ability of very high frequency (VHF) (~50 MHz) windprofilers to measure backscatter, winds and turbulence in the troposphere and the lower stratosphere gives them a unique perspective not available with many other remote sounding radar techniques. This capability has been utilized to study the environment of 31 tornadoes generated in the provinces of Ontario and Quebec in Canada over an 11‐year period. Tornadoes were mostly of Enhanced Fujita (EF) types EF0 to EF2, with one being EF3. Focus is on events which produced visible damage. Signals detected show characteristics demonstrating new informative—and potentially predictive—capabilities. A large enhancement in backscattered power immediately above the common volume of the radar and the tornadic supercell, reaching to the tropopause and beyond, when coupled with radar measurements of strong turbulence and wind speeds, provides good radar evidence of tornadic activity. [ABSTRACT FROM AUTHOR]

Plasma-enhanced atomic layer deposition (PE-ALD) has many advantages for the deposition of thin films. However, an appropriate control of the plasma frequency in the PE-ALD process is required to reduce the plasma-induced damage of the thin films during deposition. In this study, we comparatively studied the effects of conventional 13.56 MHz, radio frequency (RF) and 60 MHz, very high frequency (VHF) plasma reactants in the PE-ALD during the deposition of Al 2 O 3 . The plasma damage and the degree of strain of the substrate are investigated by transmission electron microscopy at the atomic scale. In addition, a correlation between the atomic structure and plasma damage at RF and VHF is suggested. Compared to the RF PE-ALD, Al 2 O 3 thin films deposited with VHF PE-ALD show a clearly effective reduction of the plasma-induced damage. Moreover, the Al 2 O 3 thin films are grown into a tetrahedral structure near the surface and are then further grown into an octahedral structure, indicating the presence of an increased number of ions and radicals during the plasma-enhanced process. It is evident that the VHF PE-ALD is a more important deposition process for reducing plasma-induced damage to thin films than its RF counterpart. [ABSTRACT FROM AUTHOR]

Balancing the energy production and consumption in smart grids influences the integration of new high-speed communication technologies, to support monitoring services. Sharing the television white space (TVWS) spectrum between licensed and unlicensed users has been recommended by the federal communications commission in 2004. Federal communications commission allows the unlicensed users to access both the very high frequency (VHF) and the ultra-high frequency channels in TVWS. On the other hand, broadband power line communication (BPLC) has drawn the researchers' attention over the last decade as a high-speed indoor communication technology. One application for BPLC is the multimedia service in smart grid applications. In this article, we present an overview of the standards, regulations, and channel models of the TVWS and BPLC as 2 separate technologies. We then propose the deployment of the BPLC technology in the TVWS VHF band to build up the white BPLC (WBPLC) communication systems. The WBPLC incorporates the TVWS and the BPLC technologies into multiple-input multiple-output communication systems in the VHF band. The simulation results show significant throughput enhancement in the WBPLC over both the TVWS and BPLC communication systems, indicating that WBPLC can be a promising technology to serve the growing needs for the multimedia services in future smart grids. [ABSTRACT FROM AUTHOR]

Radar sounding from aircraft or ground-coupled radars has long provided scientists with a powerful technique to sound through ice layers to retrieve local depth and layering structure. More recently, it has been used to detect shallow aquifers in warm, dry, and desert regions. At Mars, a long-wavelength radar sounding from low orbit altitudes has produced global maps that reveal the presence of ice layering at all latitudes and glacial deposits on the flanks of volcanoes. Until now, sounding from the earth orbit at wavelengths long enough to penetrate ice sheets and arid sand was thought to be infeasible, because of the electromagnetic properties of the ionosphere. In this paper, we show that a radar sounding at frequencies as low as 45 MHz is, in fact, theoretically possible under viewing conditions that occur often enough to be practical. This conclusion opens up a previously unutilized portion of the electromagnetic spectrum for large-scale, spaceborne remote sensing of subsurface features on the earth. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the reasons behind the absence of ionospheric VHF scintillation over Pingtung, Taiwan during the March 17, 2015 St. Patrick’s Day geomagnetic storm. What makes it more interesting is the fact that the absence of scintillation on the storm day was preceded by observations of scintillation for 6 consecutive days before the storm. A combination of data from VHF receivers, ionosonde and in situ plasma density observations from European Space Agency (ESA)’s SWARM constellation were used for this purpose. Also, global hmF2 maps obtained from International Reference Ionosphere (IRI) Real-Time Assimilative Mapping (IRTAM) were utilised for a better picture of the ionospheric conditions. The main driver behind the absence of the scintillation in the Taiwanese sector was a reduced pre-reversal enhancement (PRE) electric field caused due to westward prompt-penetration electric field (PPEF). This caused the post-sunset ionosphere to drift downwards in altitude causing unfavourable conditions for Rayleigh-Taylor instability. On the contrary, the PPEFs were found to strongly enhance the PRE electric fields in the Indian sector leading to ionospheric irregularities/scintillations in the post-sunset sector. [ABSTRACT FROM AUTHOR]

Two miniaturized wire antennas using a 3D space-filling Hilbert-curve (HC) fractal geometry were constructed on a Kodak photo paper using inkjet printing. The proposed antennas each had the 3D dimensions of an 8 cm3 box and operate at very high-frequency band frequencies of 238 and 147 MHz. We wrapped 4- and 2-mm-thick planar wires around a 3D box made of photo paper using second- and third-order HC space-filling fractal designs. The electrical volumes of the proposed second-order HC and third-order HC fractal antennas were 0.004 λ0 × 0.004 λ0 × 0.004 λ0 and 0.002 λ0 × 0.002 λ0 × 0.002 λ0, respectively. The operation of the proposed antennas was verified using simulation and measurement results. [ABSTRACT FROM AUTHOR]

In this paper, a highly nonlinear, fuzzy logic based, composite scheme is proposed by combining a pre-processing and a post-processing operation to efficiently restore high frequency (HF) and very high frequency (VHF) details in an up-scaled image. The blurring in case of an up-sampled image is caused by the degradation of HF and VHF image details that correspond to fine details and edge regions during the up-sampling process. The degradation of HF and VHF image details is more significant than that of the flat and slowly varying regions. In order to resolve this problem effectively, a fuzzy composite scheme is developed which is based on the inverse modeling approach of HF degradation. During the pre-processing operation, the VHF components of an image are boosted up using recursive Laplacian of Laplacian (LOL) operator prior to image up-scaling. Subsequent to the image up-scaling, a fuzzy local adaptive Laplacian post-processing scheme is used which enhances the HF image details more than the low frequency image details based on local statistics in the up-scaled image. The HF restoration performance of the fuzzy based composite scheme is enhanced by improving its nonlinearity through the variations of different parameters of the fuzzy inference system (FIS) such as slope, width and the number of input-, and output membership functions. The effective fusion of pre-processing and post-processing operations makes the proposed scheme much effective to tackle the non-uniform blurring than the standalone pre-processing and post-processing techniques. Experimental results reveal that the proposed composite scheme gives much less blurring in comparison to the standalone schemes and performs better than most of the widely used interpolation schemes in terms of objective and subjective measures. [ABSTRACT FROM AUTHOR]

This paper presents for the first time single metal layer step-down on-chip transformer. The design is characterized for VHF and UHF frequency ranges. The prototype is coreless (air core), which is suitable for high frequency operations. The design is fabricated in a standard Metal-MUMPs fabrication process, which offers a single structure layer. The primary inductance of 10.7 nH and the transformer quality factor of 8.8 have been achieved at 1 GHz. The coupling coefficient is 0.60 and the efficiency is 76% with matched load at 1 GHz. The total footprint area of micro-transformer is 0.49 mm 2 . [ABSTRACT FROM AUTHOR]

Following the standard approach envisioned by the Federal Communication Commission (FCC), we consider database as a tool to plan the utilization of very high frequency/UHF spectrum by white space (WS) radios. Our approach, however, differs from the FCC one in the sense that the proposed geolocation database is not limited to process terrain information based on antenna height above average terrain (HAAT). Our primary contour prediction (PCP) algorithm processes detailed regional topographic data with the Fresnel diffraction theory while allowing flexibility in conservativeness to accommodate local regulations. This renders more realistic contour predictions in regions of rough terrain. Moreover, due to the current broadcast antenna height limitation of 200 m in existing propagation models, we revisit the work of Okumura et al. and derive a new model applicable to a broader antenna height range. Specifically, we utilize $n$ th order polynomials to fit Okumura curves in the least-square sense and obtain remarkable accuracy with low orders, i.e., $n = 3$ . As a result, contours of broadcasters as high as 1000 m are easily predicted in regions ranging from quasi-flat to mountainous with the proposed geolocation database, which is composed of the novel yet simple propagation model and the PCP algorithm based on the diffraction theory. Finally, we perform an extensive analysis of TV WS (TVWS) spectrum availability in Japan based on NASA topography data, demographic information from the Statistic Bureau of Japan, and broadcaster-related information obtained from the Japanese Ministry of Communications. This analysis suggests that HAAT-based techniques should not be utilized in countries with rough terrain due to HAAT inherent lack of sensitivity to detailed topography, which hinders the potential of TVWS technology. We also computed the TVWS availability considering all (more than 2000!) transmitters, translators, and boosters across Japan and adjacent channel restrictions as required per regulations. We found that processing detailed topographic data by diffraction-based algorithms almost triple the expected TVWS bandwidth compared with HAAT-based techniques in this country. [ABSTRACT FROM AUTHOR]

This paper presents a negative impedance converter (NIC) based on graphene field effect transistors (GFETs) for VHF applications. The NIC is designed following Linvill's open circuit stable (OCS) topology. The DC modelling parameters of GFET are extracted from a device measured by Meric et al. [IEEE Electron Devices Meeting, 23.2.1 (2010)] Estimated parasitics are also taken into account. Simulation results from Keysight Advanced Design System (ADS) show good NIC performance up to 200 MHz and the value of negative capacitance is directly proportional to the capacitive load. In addition, it has been shown that by varying the supply voltage the value of negative capacitance can also be tuned. The NIC stability has been tested up to 2 GHz (10 times the maximum operation frequency) using Nyquist stability criterion to ensure there are no oscillation issues. [ABSTRACT FROM AUTHOR]

The paper presents Direct Numerical Simulations of sinusoidal pulsating turbulent flow, at low bulk Reynolds numbers, with high frequency, in a straight pipe. Our objective is to study pulsating flow considering it as the superposition of a temporal unsteadiness on a mean current, and from this viewpoint, to decompose the flow in a mean and an oscillating part. Firstly, we examine the time-averaged statistics, which show that the parent flow retains its properties. Then, we analyze the oscillating part of the flow, and confirm the notion that for rapidly pulsating flow, the amplitude of the streamwise velocity and the phase lag at different radial locations follow the solution of the laminar Stokes problem. In addition, we find that the modulation of the turbulent fluctuations follows approximately the sinusoidal form of the imposed pulsation, and that the ratio of the frequency parameter to the amplitude of the streamwise velocity can be used as a scaling factor. We investigate the effects of the amplitude and the frequency of the imposed unsteadiness on the modulation of the time-averaged properties and the turbulence statistics, through a systematic analysis. Finally, we examine the time evolution of the mean velocity and the turbulent fluctuations. These results indicate that a lower limit for the high frequency regime can be identified, based on the level of conformity of the phase-averaged profiles on their steady-state counterparts. For very high frequencies, we find that that the flow behavior does not change, indicating the absence of an upper limit for the high frequency regime. [ABSTRACT FROM AUTHOR]

The Thunder and VHF lightning Locating System (termed TVLS) is established and utilized to observe leader behaviors of negative cloud to ground (CG) flashes. This system takes advantages of VHF broadband interferometer and thunder imaging technique, which could provide the temporal and quasi-3D spatial evolution of lightning discharges. In conjunction with synchronized electric field changes ( E -changes) and electric field derivatives (d E /d t ) records, 10 leaders from two CG flashes are presented and analyzed. Based on the characteristic evolution of leader velocities, E -changes, d E /d t waveforms and VHF intervals, three stepped leaders, five dart leaders and two dart-stepped leaders are identified. The stepped leaders behave impulsive while approaching ground, with average speed (1.3∼3.9)×10 5 m/s. All normal dart leaders presented here exhibit irregular (or termed “chaotic”) fluctuations in E -change and d E /d t waveforms, with the similar speeds ((1.0∼2.9)×10 7 m/s) and durations ((300∼700) μs) of the “chaotic” leaders observed by other investigators. The irregular fluctuations would be weak if the channels keep conductive until the leader enters the less conductive branches, coinciding with VHF radiations in time sequence. The dart-stepped leader could be divided into the dart stage and the stepped stage by a transition region, which usually lies around the branch junctions of previous active channel. The dart stage resembles the normal dart leader, and the stepped stage usually associates with regular pulse trains in E -change and d E /d t waveforms. [ABSTRACT FROM AUTHOR]

We produced a VHF H 2 plasma (frequency, 60 MHz) by a narrow-gap discharge and examined the plasma parameters as a function of pressure and power, where two parallel plate electrodes (400 × 300 mm 2 ) were used. The plasma density reached a peak at a certain pressure, and when the power was increased, the peak pressure at which the density reached this peak shifted to higher pressures. Measured sheath potentials were lower than the theoretical values while the electron temperature was relatively high. An estimation of plasma uniformity was attempted by measuring the ion saturation current distribution, and the uniformity of about 4% was achieved. [ABSTRACT FROM AUTHOR]

Multifrequency range imaging technique (RIM) has been implemented on the Chung- Li VHF-array radar since 2008 after its renovation. This study made a more complete examination and evaluation of the RIM technique tofacilitate the performance of the radar for atmospheric studies. Various experiments of RIM with different radar parameters such as pulse length, pulse shape, receiver bandwidth, transmitter frequency set, and so on, were conducted. The radar data employed for the study were collected from 2008 to 2013. It has been shown that twofactors, the range/time delay of the signal traveling in the media and the standard deviation of Gaussian-shaped range-weighting function, play crucial roles in ameliorating the RIM-produced brightness (or power distribution); the two factors are associated with some radar parameters. In addition to radar parameters, long-term RIM data show that the aging of cable lines or key components of the radar system may result in an increase of the range/time delay of signal. It is also found that the range/time delay was visibly different for the echoes from the atmosphere with and without the presence of significant precipitation. A procedure of point-by-point correction of range/time delay was thus conducted to minimize the bogus brightness discontinuity at range gate boundaries. With the RIM technique, the Chung- Li VHF radar demonstrates its first successful observation of double-layer structures as well as their temporal and spatial variations with time. [ABSTRACT FROM AUTHOR]

This paper presents the characterization of a very high frequency, differentially powered, capacitively coupled, multi-tile plasma source, MAMELUKE. Specifically, this work concentrates on the plasma enhanced chemical vapor deposition of nano-crystalline silicon suitable for application in thin film solar manufacturing. The use of a differentially-fed multi-tile source has several benefits, but imposes a spatial structure on the plasma. Sections of dielectric insulator between the differentially-fed tiles interrupt both the electrode structure and the local gas delivery to the plasma volume, both of which contribute to the gas phase chemistry uniformity profile. We investigate the affect of these factors on the plasma spatial structure by measuring the uniformity of deposited films. We examine films deposited using the MAMELUKE source focusing on the ability to produce uniform, high quality films over large areas, with high deposition rates. Spatially resolved measurements of film thickness and crystalline fraction are presented. These measurements are then used in combination with the known behaviors of very high frequency plasma systems established by previous research to draw conclusions regarding the behavior of plasma uniformity with changing process parameters. The measurements indicate that changes in the uniformity of film properties are primarily driven by gas phase chemistry effects. Changes in local gas phase chemistry are attributed to a combination of non uniformities in both the power and gas delivery in the MAMELUKE source. [ABSTRACT FROM AUTHOR]

We reported in this paper the observation of a very bright long-delayed dancing sprite with distinct horizontal displacement from its parent stroke. The dancing sprite lasted only 60 ms, and the morphology consisted of three fields with two slim dim sprite elements in the first two fields and a very bright large element in the third field, different from other observations where the dancing sprites usually contained multiple elements over a longer time interval, and the sprite shape and brightness in the video field are often similar to the previous fields. The bright sprite was displaced at least 38 km from its parent cloud-to-ground (CG) stroke and occurred over comparatively higher cloud top region. The parent flash of this compact dancing sprite was of positive polarity, with only one return stroke (approximately +24 kA) and obvious continuing current process, and the charge moment change of stroke was small (barely above the threshold for sprite production). All the sprite elements occurred during the continuing current stage, and the bright long-delayed sprite element induced a considerable current pulse. The dancing feature of this sprite may be linked to the electrical charge structure, dynamics and microphysics of parent storm, and the inferred development of parent CG flash was consistent with previous very high-frequency (VHF) observations of lightning in the same region. [ABSTRACT FROM AUTHOR]

Biomass burning aerosols seasonally overlie the subtropical southeast Atlantic stratocumulus deck. Previous modeling and observational studies have postulated a semidirect effect whereby shortwave absorption by the aerosol warms and stabilizes the lower troposphere, thickening the low-level clouds. The focus herein is on the dynamical and moisture effects that may be convoluted with the semidirect effect. Almost-daily radiosonde data from remote St. Helena Island (15.9°S, 5.6°W), covering September-October 2000-11, are combined with daily spatial averages (encompassing the island) of the MODIS clear-sky fine-mode aerosol optical depth (). Increases in are associated with increases in 750-500-hPa moisture content. The net maximum longwave cooling by moisture of almost 0.45 K day−1 reduces the aerosol layer warming from shortwave absorption. ERA-Interim spatial composites show that polluted conditions are associated with a strengthening of a deep land-based anticyclone over southern Africa, facilitating the westward offshore transport of both smoke and moisture at 600 hPa. The shallower surface-based South Atlantic anticyclone exhibits a less pronounced shift to the northeast, strengthening the low-level coastal jet exiting into the stratocumulus deck and cooling 1000-hPa potential temperatures. Warm continental outflow further increases the 800-hPa potential temperatures (), reinforcing the lower tropospheric stability () over the stratocumulus deck. Enhanced southerly dry air advection also strengthens the cloud-top humidity inversion. The increased stability helps explain an observed decrease in cloud-top heights despite an anomalous reduction in subsidence. The changes to the horizontal dynamics enhance low-level cloudiness. These are separate but not necessarily distinct from an aerosol semidirect effect, encouraging care in attribution studies. [ABSTRACT FROM AUTHOR]

A printed two-dipole array antenna with a high front-back ratio is proposed for ultra-high-frequency (UHF) radiofrequency identification handheld readers. The proposed antenna is a parasitic dual-element array with the ends of both elements folded back towards each other for additional coupling. The antenna features a compact size of 89 mm × 87 mm and works properly with satisfactory gain and total efficiency in the wide UHF band of 860-960 MHz. Furthermore, the front-to-back ratio of 15-26.8 dB, the peak gain of 3.7-4.4 dBi and the total efficiency of more than 80% in the Federal Communication Commission (FCC) band make the proposed antenna attain high performance in the FCC band. [ABSTRACT FROM AUTHOR]

Abstract: Flow quantification with high-frequency (>20 MHz) power Doppler ultrasound can be performed objectively using the wall-filter selection curve (WFSC) method to select the cutoff velocity that yields a best-estimate color pixel density (CPD). An in vivo video microscopy system (IVVM) is combined with high-frequency power Doppler ultrasound to provide a method for validation of CPD measurements based on WFSCs in mouse testicular vessels. The ultrasound and IVVM systems are instrumented so that the mouse remains on the same imaging platform when switching between the two modalities. In vivo video microscopy provides gold-standard measurements of vascular diameter to validate power Doppler CPD estimates. Measurements in four image planes from three mice exhibit wide variation in the optimal cutoff velocity and indicate that a predetermined cutoff velocity setting can introduce significant errors in studies intended to quantify vascularity. Consistent with previously published flow-phantom data, in vivo WFSCs exhibited three characteristic regions and detectable plateaus. Selection of a cutoff velocity at the right end of the plateau yielded a CPD close to the gold-standard vascular volume fraction estimated using IVVM. An investigator can implement the WFSC method to help adapt cutoff velocity to current blood flow conditions and thereby improve the accuracy of power Doppler for quantitative microvascular imaging. [Copyright &y& Elsevier]

A long-term study to compare harbor seal ( Phoca vitulina) survival rates between 2 study areas was conducted in Alaska, in Glacier Bay (GB) and Prince William Sound (PWS). Very-high-frequency (VHF) transmitters with 3.5- to 5-year batteries were subcutaneously implanted into 277 harbor seals; 122 in PWS from 2003 to 2005, and 155 in GB from 2004 to 2006. The presence of radiotagged seals was remotely monitored using VHF data-loggers, which transmitted data via the Geostationary Operational Environmental Satellite (GOES) system. The GOES site is administered by the National Oceanic and Atmospheric Administration, National Environmental Satellite Data and Information Service; data were accessible to researchers via telnet. Initial data-logging was plagued with ambient electronic interference ('noise'); subsequent equipment revisions substantially reduced the noise and resulted in 8,129 total 'seal-days' (≥ 1 detection calendar day−1 seal−1) of telemetry detections ( X̄ = 29 days/seal ± 3.4 SE; maximum 424 days spanning 4.15 years). Although 84% of radiotagged seals were detected at least once during the year they were radiotagged, the proportion of tagged seals detected in subsequent years dropped to 59%, 28%, 0.9%, and 3% in the 1st through the 4th year, respectively. Tag failure and tag rejection, including 1 tag rejected 11.75 months after implantation surgery, were documented. There was almost no evidence of health problems at the time of implanting the tags in the harbor seals. Survey effort outside the study areas did not detect evidence of high emigration rates. Although subcutaneously implanted transmitters could be radiotracked during and after molt and the long battery life provided multiyear data on a subset of individual seals, this method of subcutaneously implanting radiotags was not effective for assessing the long-term survival rate of free-ranging harbor seals. [ABSTRACT FROM AUTHOR]

Background Pulse rate (PR) indicates heart beat rhythm and contains various intrinsic characteristics of peripheral regulation. Pulse rate variability (PRV) is a reliable method to assess autonomic nervous system function quantitatively as an effective alternative to heart rate variability. However, the frequency range of PRV is limited by the temporal resolution of PR based on heart rate and it is further restricted the exploration of optimal autoregulation frequency based on spectral analysis. Methods Recently, a new novel method, called instantaneous PRV (iPRV), was proposed. iPRV breaks the limitation of temporal resolution and extends the frequency band. Moreover, iPRV provides a new frequency band, called very high frequency band (VHF; 0.4-0.9Hz). Results The results showed that the VHF indicated the influences of respiratory maneuvers (paced respiration at 6-cycle and 30-cycle) and the nonstationary condition (head-up tilt; HUT). Conclusions VHF is as a potential indication of autoregulation in higher frequency range and with peripheral regulation. It helps for the frequency exploration of cardiovascular autoregulation. [ABSTRACT FROM AUTHOR]

This short paper presents phase and coherence data from the cross-wavelet transform applied on longitudinally separated very high frequency (VHF) equatorial ionospheric scintillation observations over Christmas Island. The phase and coherence analyses were employed on a pair of scintillation observations, namely, the east-looking and westlooking VHF scintillation monitors at Christmas Island. Our analysis includes 3 years of peak season scintillation data from 2008, 2009 (low solar activity), and 2011 (moderate solar activity). In statistically significant and high spectral coherence regions of the cross-wavelet transform, scintillation observations from the east-looking monitor lead those from the west-looking monitor by about 20 to 60 (40±20) min (most frequent lead times). Using several years (seasons and solar cycle) of lead (or lag) and coherence information of the cross-wavelet transform, we envisage construction of a probability model for forecasting scintillation in the nighttime equatorial ionosphere. [ABSTRACT FROM AUTHOR]

Abstract: Three consecutive magnetic storms during the month of September 1982 were found to be associated with solar proton events (SPE) observed over a number of high latitude VLF propagation paths. The penetration of solar protons into the auroral zone produced a marked reduction in reflection height at night for high latitude VLF paths resulting in a reduced diurnal phase shift. This effect has been known for some 50 years. However in this paper, a previously unidentified response is described consisting of an increase in the night 90km reflection height over middle latitude and transequatorial VLF paths. Solar protons do not penetrate to these latitudes and this slight increase in VLF reflection height was associated with typical negative ionospheric storm effects in the F2 region. Dynamics at the 90km base of the night ionosphere are little known and difficult to investigate except at VLF. These results are the first to suggest a response of the night ionospheric base to events leading to the well known negative ionospheric storm seen at greater heights. Such negative storms seen in the F2 region have been associated with an equatorward wind surge and change in neutral atmospheric chemistry driven by joule heating in the auroral zone produced by solar proton precipitation. [Copyright &y& Elsevier]

Abstract: We report on EISCAT ionospheric heating experiments carried out on 13 September 2010 at Tromsø, Norway. This paper focuses on the long-lasting enhanced ion- and plasma-lines observed by the VHF incoherent scatter radar. In previous experiments, the enhanced ion-lines observed by VHF radar lasted ~200ms. Observations of long-lasting enhanced ion- and plasma-lines in the VHF radar have not been reported before. The enhanced lines may be caused by Parametric Decay Instability (PDI). In addition, the VHF data show that the enhanced ion-lines are descending in altitude with time during the heater-on period. Likewise, the temporal and spatial evolution of the enhanced plasma-lines also show a similar morphology and generally occur at the same height. At last a possible mechanism for the altitude evolution is given in this paper. [Copyright &y& Elsevier]

Very High Frequency (VHF) range covers the range of radio frequency electromagnetic waves from 156 MHz to 162.025 MHz. Marine VHF communication devices have a wide application in navigation onboard convention and non-convention vessels. VHF communication is also partly used in inland waterways, rivers, and lakes. The varied application of the VHF technology implies performing regular and emergency communication during the operation of various services that ensure the safe flow of navigation process by exchanging Maritime Safety Information (MSI). As for their construction and design, marine VHF equipment may be classified as portable and stationary. Regulations provided by local registers of shipping apply to their technical features and design requirements in case of new-built vessels or subsequent fitting of the vessels with such equipment. Although these regulations go into details as they refer to the design and the exploitation of vessels, it can be noticed that they are not sufficiently elaborated in the area of using VHF marine communication devices in dynamic conditions. This paper discusses the impact of dynamic conditions on the range of marine VHF equipment and the development of feasible improvements onboard various types of vessels. [ABSTRACT FROM AUTHOR]

Abstract: A lightning VHF radiation location system based on short-baseline time-difference of arrival (TDOA) technology is newly developed. Based on the orthogonal 10m-baseline antenna array with four identical broadband flat plane antennas, this system receives the lightning broadband VHF radiation signals and calculates TDOA between antennas in order to determine the location of lightning radiation sources in two dimensions (elevation and azimuth). To reduce noise and improve estimation accuracy of time delay, a general correlation time delay estimation algorithm based on direct correlation method and wavelet transform is proposed. Moreover, parabolic interpolation algorithm is used in the fractional delay estimation to improve the time resolution of the positioning system. In this paper, a rocket-triggered lightning discharge and a cloud lightning discharge are analyzed respectively, combining with simultaneous observations of high-speed camera and fast/slow electric field changes. The results indicate that the TDOA location system could effectively map the lightning radiation sources in 2 dimensions and are in a good agreement with the high-speed video camera images. [Copyright &y& Elsevier]

The multipath signal and direct signal lying within a beamwidth of a receiving antenna are highly correlated, which degrades the performance of DOA in a VHF array radar. Especially on rough terrain, the reflection centers of elements are not at the same horizontal plane; thus the variation of indirect wave path difference from each element with respect to the target's depression angle is not linear. In this paper, we assume the two-path-component data model, with one direct component and one indirect component related to the ground reflection. This paper builds a highly deterministic multipath signal model which takes the curvature of the signal path and the terrain parameters of the reflection region into account based on the sphere model, gives calculation methods of the reflection coefficient and lengths of the direct path and indirect path, and proposes a synthetic steering vector super-resolution algorithm. The results for both simulated and measured data show that this method provides excellent performance in resolving the DOA problem in a multipath environment compared to the data model that only considers the flat-earth model. [ABSTRACT FROM AUTHOR]

The aspect angle, a measurement of the aspect sensitivity of atmospheric refractivity irregularities, was estimated with multiple-receiver coherent radar imaging (CRI) of very high frequency (VHF) atmospheric radar. Two CRI parameters retrieved by Capon's method were utilized to derive the aspect angle: brightness width from the vertical radar beam and the direction of arrival (DOA) of the echo center from the oblique radar beam. Differing from previous studies with CRI, the radar beam weighting effect on the CRI brightness distribution was considered, and moreover, the radar beamwidth used in study was adaptive to the signal-to-noise ratio (SNR) of data as well as the off-beam direction angle. The study is based on statistical results. It is shown that the brightness width, a representative of the aspect angle, obtained from the modified CRI brightness distribution of the vertical radar beam was generally larger than that without correction, and it was very close to the values derived from the DOA of the 1° oblique radar beam and the power distribution of multiple beam directions. Moreover, the aspect angle derived from the DOA varied with the radar beam direction, which was similar to that obtained from the comparison of echo powers of a radar beam pair; however, the DOA approach yielded a much larger aspect angle in the low-SNR condition. This study recommended a feasibility of improving the measurements of atmospheric parameters with CRI after removing the radar beam weighting effect suitably from the CRI brightness distribution. [ABSTRACT FROM AUTHOR]

We present a traceable calibration of a specially designed horizontally polarised reference antenna with an omnidirectional pattern in the E-plane for the frequency range between 105MHz and 120 MHz. This antenna is used as a validation tool for absolute ?eld strength measurements at the localizer transmitter of an instrument landing system (ILS) at airports and is carried by a helicopter. We investigate whether we can treat it as a dipole-like antenna in the calibration setup despite its disk-shape body. We also investigate the suitability of an anechoic chamber for antenna calibration though it was not designed for that purpose. The measurements are based on scattering parameters (S-parameters) which we apply in the 3-antenna-method (TAM or 3-AM) to obtain the antenna gain and the antenna factor, respectively. An uncertainty budget for the antenna gain calibration is derived. We also report on the first practical application of the calibrated reference antenna. [ABSTRACT FROM AUTHOR]

Abstract: Al-doped p-type hydrogenated nanocrystalline cubic silicon carbide (nc-3C-SiC:H) thin films were successfully deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) using dimethylaluminum hydride (DMAH) as an Al source. A high dark conductivity of 6.88×10−4 S/cm was obtained for a 27nm-thick film under high H2/MMS and plasma power conditions. We applied this optimized film to a heterojunction emitter of n-type c-Si solar cells. The solar cell showed high fill factor of 0.756. The internal quantum efficiency in the short wavelength region was improved to 0.87 with decreasing the thickness of a buffer layer. [Copyright &y& Elsevier]

In dim light, scarcity of photons typically leads to poor vision. Nonetheless, many animals show visually guided behavior with dim environments. We investigated the signaling properties of photoreceptors of the dark active cockroach (Periplaneta americana) using intracellular and whole-cell patch-clamp recordings to determine whether they show selective functional adaptations to dark. Expectedly, dark-adapted photoreceptors generated large and slow responses to single photons. However, when light adapted, responses of both phototransduction and the nontransductive membrane to white noise (WN)-modulated stimuli remained slow with corner frequencies ∼20 Hz. This promotes temporal integration of light inputs and maintains high sensitivity of vision. Adaptive changes in dynamics were limited to dim conditions. Characteristically, both step and frequency responses stayed effectively unchanged for intensities >1,000 photons/s/photoreceptor. A signal-to-noise ratio (SNR) of the light responses was transiently higher at frequencies <5 Hz for ∼5 s after light onset but deteriorated to a lower value upon longer stimulation. Naturalistic light stimuli, as opposed to WN, evoked markedly larger responses with higher SNRs at low frequencies. This allowed realistic estimates of information transfer rates, which saturated at ∼100 bits/s at low-light intensities. We found, therefore, selective adaptations beneficial for vision in dim environments in cockroach photoreceptors: large amplitude of single-photon responses, constant high level of temporal integration of light inputs, saturation of response properties at low intensities, and only transiently efficient encoding of light contrasts. The results also suggest that the sources of the large functional variability among different photoreceptors reside mostly in phototransduction processes and not in the properties of the nontransductive membrane. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to review current activities for the identification of earthquake (EQ) precursors and their epicentres. Starting with a brief description on the background to approaches using ultra-low (ULF), extremely low (ELF), very low/low (VLF/LF), medium (MF), high (HF), very high frequency (VHF) etc. radio waves for short-term EQ prediction, the paper concentrates on those characteristics of anomalous VHF reception from frequency-modulation (FM) radio transmissions and broadcast television (TV) signals in relation to EQ precursors. The possible ways to identify an impending EQ and its epicentre position as defined and observed by workers from a variety of studies fall within the purview of the paper. In attempts to find pre-EQ energy exchange and coupling processes between the lithosphere and atmosphere, the paper highlights some relevant observations of surface latent heat flux, sonic detection and ranging (SODAR) echograms and LF propagation. Explanations on possible causes leading to such anomalous reception are reviewed with reported results in association with pre-seismic induced modifications to tropospheric and ionospheric parameters. [ABSTRACT FROM AUTHOR]