Plasma-based microwave power limitation in a printed transmission line: a self-consistent model compared with experimental data

Micro hollow cathode discharges (MHCD) were produced using 250 μm thick dielectric layer of alumina sandwiched between two nickel electrodes of 8 μm thickness. A through cavity at the center of the chip was formed by laser drilling technique. MHCD with a diameter of few hundreds of micrometers allowed us to generate direct current discharges in helium at up to atmospheric pressure. A slowly varying ramped voltage generator was used to study the ignition and the extinction periods of the microdischarges. The analysis was performed by using electrical characterisation of the V-I behaviour and the measurement of He*(3S1) metastable atoms density by tunable diode laser spectroscopy. At the ignition of the microdischarges, 2 μs long current peak as high as 24 mA was observed, sometimes followed by low amplitude damped oscillations. At helium pressure above 400 Torr, an oscillatory behaviour of the discharge current was observed just before the extinction of the microdischarges. The same type of instability in the extinction period at high pressure also appeared on the density of He*(3S1) metastable atoms, but delayed by a few μs relative to the current oscillations. Metastable atoms thus cannot be at the origin of the generation of the observed instabilities.

In this work, diagnostics and comparative analysis of microhollow cathode discharges with an open and covered external surface of the cathode in helium at atmospheric pressure were carried out. It is shown that by covering the external surface of the cathode, it is possible to achieve the effect when the current–voltage characteristics of the discharge grows in a wider range of discharge currents. Obviously, in this case, the negative glow (NG) plasma of the hollow cathode occupies a significant part of the discharge cell, as evidenced by the measurements carried out with the additional electrode. The electron temperature values determined from the I–U characteristic of the additional electrode are 0.3–0.4 eV for a microhollow cathode discharge with a covered external surface, which indicates that the plasma of such discharge is similar to NG plasma of glow discharge. The fast parts of the second derivatives of the I–U characteristic of the additional measuring electrode demonstrate the detection of the spectra of fast electrons produced as a result of Penning ionization reactions. Moreover, by covering the external surface of the cathode, conditions are created under which the entire discharge volume is occupied by a NG plasma, which makes it possible to achieve a better resolution for recording the spectra of fast electrons.

One aspect of the electromagnetic compatibility (EMC) analysis of RF circuitry is the accurate modeling of the coupling between printed transmission lines. Correct modeling of this coupling is essential because unwanted noise voltages can be substantial and create adverse effects on sensitive components. Recently, the development of composite right-/left-handed transmission lines (CRLHTLs) has received considerable attention due to the unique propagation characteristics. Because of this increase in applications, CRLHTLs are being implemented in RF systems with other printed circuitry, such as microstrip transmission lines, in very close proximity. In many of these instances, the coupling may not be intentional. To study this interaction between CRLHTLs and other printed circuitry from an EMC point of view, this paper presents derived analytical expressions for computing the nearand far-end voltage coupling between right-handed (printed microstrip transmission lines) and CRLHTLs. More specifically, these expressions are used to determine the nearand far-end voltages weakly coupled to the CRLHTL when the conventional microstrip right-handed transmission line is driven with a source and terminated with a load. These expressions are then used to illustrate how the induced voltages on the CRLHTL can be reduced by the capacitance and inductance values that support left-handed propagation. This can be a useful alternative to conventional shielding. Furthermore, design guidelines and tradeoffs are presented on the layout of CRLHTL near other printed transmission lines. The expressions derived in this paper are validated with simulations and measurements.

New guiding structure for millimeter-wave integrated circuits was proposed in this paper. Since surfaces of dielectric substrates for printed boards are usually roughened to make tight copper-coating, it was found out that effective conductivities of surfaces of the copper foils, attaching on the dielectric substrate, more degraded than those of the opposite surfaces of the copper foils, facing an air region, at frequency range beyond centimeter waves. To overcome such difficulty, a technique to reduce transmission losses was devised for printed transmission lines at millimeter-wave frequencies. By symmetrically-loading metal patterns on both sides of the dielectric substrate and by biasing equi-voltage to both metal patterns, the currents on the under surfaces of the metal patterns decrease, and thus the transmission loss may be relatively unaffected by the roughness of the dielectric surfaces. Based on this consideration, a bilaterally metal-loaded tri-plate strip transmission line was fabricated and its unloaded Q factor was measured at 60 GHz, compared with that of a unilaterally metal-loaded tri-plate transmission line, namely conventional tri-plate transmission line. The Q factor of the bilaterally metal-loaded tri-plate transmission line was measured to be 700, while that of the unilaterally metal loaded tri-plate strip transmission line was 200, and thus the capability to realize low-loss printed millimeter-wave ICs was confirmed by using the proposed transmission line.

Hollow cathode discharge devices with hole dimensions in the range from 0. 1 —0.5 mm (microhollow cathode discharges or MHCDs) can be operated at high pressure (up to and exceeding atmospheric pressure). MHCDs are known to be efficient sources of non-coherent ultraviolet (UV) and vacuum ultraviolet (VUV) radiation when operated in rare gases, rare gas — halide mixtures, and gas mixtures containing rare gases and trace amounts of gases such as H2, 02, and N2. Highest internal efficiencies in direct current MHCD excimer sources of close to 10% were obtained in xenon at a pressure of 400 Ton. By applying nanosecond electrical pulses to the dc discharge the efficiency could be increased to approximately 20%. The radiative emittance which for dc discharges in xenon was measured as 1 .4 W/cm2 could be increased to over 15 W/cm2 through pulsed operation. In addition to rare gas and rare-gas halide excimer emission, intense, monochromatic atomic line emissions have been reported from high-pressure MHCD plasmas in pure rare gases and in rare gases admixed with trace amounts (less than 1 %) of H2, O2, and N2. . The atomic line emission is the result of a near-resonant energy transfer process involving the excimers and the diatomic molecules. For instance, Ne2* excimers in the bound 3?u state have enough energy to dissociate H2 and excite one of the H atoms to the n —2 state. The subsequent decay of the excited H atom results in the emission ofthe 121.6 nm H Lyman-? line. We discuss the results of dc and time-resolved emission spectroscopy in the UV and VUV to elucidate the microscopic mechanisms of the rare gas excimer formation and emission processes, the properties of the MHCD plasma, and microscopic details of the near-resonant energy transfer processes that lead to the emission of the intense atomic line radiation in the range 100 — 1 30 nm.

Antennas made with dielectric membranes rigidized with pressurized gas are taking a ground in practical applications. Variety of applications will broaden when inflated antennas are wisely integrated with platforms carrying them. The antenna integration prefers thin profile and conformal structures. However, antenna arrays are much more challenging to be developed in a form of inflated structures than wave reflecting surfaces. To develop complete feeding networks with the same technology as thin-membrane antenna elements are made, a lot of inventiveness is required. This paper presents transmission lines and discusses problems related to microwave couplers made entirely with thin membranes and rigidized with pressurized gas.

The transient response sensitivity analysis of the transmission line is a new hotspot problem in transmission line problems. In this paper, a sensitivity analysis method based on fast Fourier transform is proposed in the transient response sensitivity analysis of the transmission line network. The method firstly establishes the circuit equation of the whole transmission line network characteristic, and transforms the partial differential equation in the time domain into the ordinary differential equation in the frequency domain by Fourier transform. Then we find the derivative of a certain distribution parameter of the transmission line by the ordinary differential equation. The network transient response sensitivity problem is transformed into solving the transient response of the transmission line network and the partial derivative of the network parameter matrix to the circuit parameters, which greatly simplifies the analysis of the transient response sensitivity of the transmission line network, and the sensitivity analysis of the transient response of any node of the transmission line network to any network parameters is realized. The method does not need to decouple the coupled transmission line, and can accurately and quickly calculate the transient response sensitivity of any type of transmission line network. The result of the example shows that the method is correct and effective. This method provides a new reference method for the sensitivity analysis of transmission line network transient response.

Reflectionless filters are two-port networks that ideally present matched terminations at both filter ports to all frequencies, within both the filter’s passband and stopband. Standard lossless filter structures reflect out-of-band power back to the input, which can profoundly impact the performance of heterodyne instruments and contribute to generation of spurious sidebands, unwanted gain compression, reduced dynamic range or instability. Reflectionless filters, conversely, direct out-of-band power to one of the filter’s two “internal” resistive terminations. If either of these internal resistors is converted into a port, then the resulting circuit forms a matched frequency diplexer This paper reports a prototype lowpass “quasi-reflectionless” filter and diplexer architecture that exploits integration of passive elements on a silicon-on-insulator platform. The design employs suspended high-impedance transmission lines for the filter inductive elements as well as integrated metal-insulator-metal (MIM) capacitors and thin-film titanium resistors on a 15 mm thick high-resistivity silicon substrate. As proof-of-concept implementations, a filter designed for operation in the 0—220 GHz band with 3 dB roll-off at 150 GHz and a diplexer architecture designed for the 0—220 GHz band with target cross-over frequency at 170 GHz are described. The filter and diplexer are implemented using a silicon-on-insulator (SOI) micromachining process that has been used broadly as a platform for integration. Fabrication utilizes frontside lithography, sputter deposition and electroplating processes to form thin-film titanium resistors (nominal impedance of 50 W, 2 mm10 mm, 50 nm thick), metal-insulator-metal capacitors (radii of 4.6 mm and 3.8 mm with SiO2 insulator thickness of 200 nm) and meandered high-impedance microstrip transmission lines (width of 3 mm, lengths of 180 mm and 90 mm) on a 15 mm thick, high-resistivity (>20 kW-cm) silicon membrane. After the topside features of the filter and diplexer have been formed, the SOI wafer is bonded topside-down to a temporary carrier to allow backside processing. Scattering parameter measurements of the filter and diplexer both show the desired lowpass characteristic from lowband input port to output, but with a softer roll-off than anticipated from electromagnetic finite-element analysis and circuit simulations of the structures. Modeling suggests this soft roll-off characteristic is associated with parasitic inductance and resistance contributed by the metallized ground via. These parasitic elements associated with the via-to-ground are not observed in the electromagnetic simulation of the filter or diplexer and the observation that they occur consistently in the model for each circuit node connected to ground suggest they are associated with the electrical interface of the circuits to the tests fixtures used to characterize them. Moreover, it is also hypothesized that these parasitic elements are associated with discontinuities between the filter/diplexer metallized ground plane (on the silicon backside) and the metallized measurement housing platform to which the circuits are affixed for measurement. Disruptions to ground currents flowing beneath the silicon-supported microstrip circuit and the suspended transmission lines (where the measurement housing itself serves as the ground) will contribute to parasitics associated with the ground connection, consistent with the observed measurements.

The electron cyclotron heating (ECH) and current drive system is one of the main plasma heating systems for ITER. It uses high-power microwave beams with the power deposition location steerable across the plasma cross section. Microwave power is conveyed via transmission lines (TLs) that run from the gyrotrons in the radio frequency building through the assembly hall and tokamak building to the ECH launchers within the tokamak vacuum vessel. The ECH system includes a vast array of interconnected TL waveguides, in-line components, and support structures. Finite element (FE) modeling provides an essential means of simulating the system, applying loads and determining deflections, rotations, forces, moments, and stresses in order to evaluate various structural and microwave transmission performance metrics. A representative FE model of the overall ECH TL system is developed in ANSYS®. This top-level model defines the centerline of the waveguide system. Waveguide segments are represented by line elements (beams and pipes) with equivalent section properties, and support structures are represented by boundary conditions. A systematic approach is used to model each ECH component with lumped masses and structurally equivalent stiffness matrices or ANSYS superelements. The top-level TL FE model is used to evaluate the various loads (thermal, vacuum, seismic, etc.) and operating scenarios. The top-level model directly calculates stresses in the straight aluminum waveguide segments. The model provides the forces and moments acting on the in-line components for detailed submodel assessments. Displacement results from the top-level analysis feed into a separate microwave performance model to help determine operational efficiency. All TL performance and thermal-structural requirements are met, as specified by the applicable codes and standards, and successfully documented in numerous technical reports and demonstrated at the final design review.

The scattering characteristics of microwaves (MWs) by an underdense inhomogeneous plasma column have been investigated. The plasma column is generated by hollow cathode discharge (HCD) in a glass tube filled with low pressure argon. The plasma density in the column can be varied by adjusting the discharge current. The scattering power of X-band MWs by the column is measured at different discharge currents and receiving angles. The results show that the column can affect the properties of scattering wave significantly regardless of its plasma frequency much lower than the incident wave frequency. The power peak of the scattering wave shifts away from 0° to about ±15° direction. The finite-different time-domain (FDTD) method is employed to analyze the wave scattering by plasma column with different electron density distributions. The reflected MW power from a metal plate located behind the column is also measured to investigate the scattering effect on reducing MW reflectivity of a metal target. This study is expected to deepen the understanding of plasma-electromagnetic wave interaction and expand the applications concerning plasma antenna and plasma stealth.

ABSTRACTThis paper discusses a reference design to provide an interurban microwave-powered air-cushioned vehicle (impav) suitable for use in a high-speed ground transportation system. The microwave power transmission line, for both directions of travel, is achieved by a single pair of confocal parabolic reflectors extending in 30-km‡sections between the urban centers, which for the purpose of this study are at a distance of 600 km (Montreal–Toronto, Montreal–New York). Power transfer to an impav, moving in either direction, is achieved by means of an elevated power rectenna positioned on top of the vehicle. Microwave transmission line attenuation considerations indicate a 10 per cent power loss in a 15-km half-section at 915 MHz. The unit microwave power requirement is 3.5 MW, and the total power required is 140 MW. Each microwave power unit feeds an impav from the end of a half-section of the 30 km transmission line section.The impav cruising speed is 330 km/h, and the average speed for the 600-km distan...

This paper presents the fabrication of organic semiconductor (OS) rectifiers and an investigation of rectifying antenna (rectenna) under the effect of microwave power. As a source of microwaves, a patch antenna fed by a generator was used. The rectenna contains a built-in rectifier. The surface-type Ag/NiPc/Au cell, with organic semiconductor nickel phthalocyanine (NiPc) as the active material, was used as a rectenna. The rectifier was fabricated by thermal deposition of Ag, Au and NiPc thin films on thoroughly cleaned glass substrate. The measured I–V characteristics of the cell showed rectifying behavior. The rectenna was tested at frequency ranges of 8–16 GHz at different intensities of radiation and vertical and horizontal positions of the rectenna's axes. Under the effect of microwave power at the output of the rectenna, the output dc voltage and current were detected.

A miniaturized printed integrated inverted-F antenna (PIIFA) is proposed which operates in the Bluetooth frequency band (2.4-2.485 GHz). The antenna is derived from a modified Hilbert geometry and can be easily fed using a 50 /spl Omega/ printed transmission line. The antenna being an integral part of the printed circuit board (PCB) reduces the cost and complexity of manufacturing the whole unit. The antenna on a standard FR4 substrate (/spl epsiv//sub r/ = 4.5) measures 9.25 mm by 4.125 mm and has a bandwidth of 3.5% within 2.5:1 VSWR. The peak gain is 1.2 dBi. An overall size reduction of 67% can be achieved compared to a conventional inverted-F antenna.

Monopole antennas are widely used in communication systems because of features such as pure vertical polarization and omnidirectional radiation patterns in the horizontal plane. Conventionally, monopole antennas are fed through a ground plane by a coaxial probe. Recently, monopole antennas fed by printed transmission lines have attracted increasing attention. However, to the best of our knowledge, monopole antennas are seldom fed by a rectangular waveguide. We consider the problem of this type of feed because of our interest in designing an omnidirectional antenna at millimeter wave bands. At millimeter wave frequencies, rectangular waveguides are preferred to coaxial or microstrip lines because they exhibit very low loss, have a large power handling capacity and other waveguide components are readily available. The paper presents a design for monopole antennas fed by a rectangular waveguide. In order to achieve a good transition from a rectangular waveguide to the monopole antenna, a ridged waveguide section is introduced, and the vertical monopole is attached to the ridge through a circular aperture opened on the upper broad-wall of the rectangular waveguide, which is part of the ground plane. Two examples are provided and experimental tests of one of these antennas shows that the monopole can achieve about 24% bandwidth and 5 dBi gain.

The recently developed MRTD scheme is applied to the solution of printed transmission line problems. Specifically, the field pattern and the characteristic impedance of a membrane stripline is calculated. The results are compared to those obtained by use of the conventional FDTD scheme to indicate considerable savings in memory and computational times.