Coaxial Switch Research Articles

Model-based method for improvements in the calibration of ultrasonic power measurements at low-power levels

The measurement uncertainty in the calibration of ultrasonic power measurements at low-power levels was reduced by a model-based signal-processing method. The ultrasonic power measurement system is based on the radiation force balance method according to IEC 61161. Outputs of an electronic balance and the excitation voltage were simultaneously sampled and recorded. A computer-controlled coaxial switch that utilizes data lines of the parallel port of a desktop computer was used for power-on and power-off control. Power-on and power-off intervals were finely controlled by the desktop computer. The Electroacoustic radiation conductance, defined as the ratio of the ultrasonic power of a transducer and the square of the rf voltage at its input, was calculated from the recorded data. During data processing, a simple model for drifting and switching was proposed and a least-mean-squares algorithm was used to estimate parameters of the model. Good measurement reproducibility was also observed that resulted in the reduction of total measurement uncertainty.

Scaling microsecond-conduction-time plasma opening switch operation from 2 to 5 MA

We describe experiments in which conduction currents were successfully scaled from 2 to 5 MA for conduction times around 1 /spl mu/s in a coaxial geometry plasma opening switch (POS) on the 4 MJ ACE 4 driver. Simple models of POS operation, derived from previous work, were used to scale successful results from drivers that operate at microsecond conduction times, but at currents below 1 MA. An MHD model for the conduction phase was verified in which the square root of the plasma density is approximately proportional to the product of conduction time and peak conduction current divided by the switch radius and length. For the opening phase, a model where the POS gap is approximately constant when the local plasma conditions at the beginning of the conduction phase are kept roughly the same is consistent with the observed POS opening voltages of at least 1 MV. The conduction current was increased by increasing the POS cathode radius from 6 to 20 cm while maintaining roughly the same plasma density. This increase in radius resulted in the observed increase in the conduction-current/conduction-time product from 2 to 5 MA /spl mu/s while maintaining MV POS voltages.

Fast switching with laser-generated continuous plasma columns

A novel approach to laser triggering of spark gaps is proposed. The method is based on switch initiation by Besselian laser beams. This results in the fast generation of a continuous conducting plasma column(s) and almost instantaneous electrical connection of electrodes. Experiments showed excellent performance of a gas-filled coaxial switch triggered with 2 ns laser pulses: 1.5–2.5 ns rise time, approximately zero delay, and 0.2–0.3 ns jitter obtained within a broad operational voltage range of three orders of magnitude. Depending on the type and pressure of the gas used in the spark gap, the experimentally determined laser energy required for triggering ranged from 40 to 500 mJ. It can be further reduced by factor of 5 by optimization of the focusing system. The unique feature of the proposed triggering method is independence of the required driving energy and switching parameters on the voltage applied to the gap in the range from nearly zero up to standoff voltage. Comparison of this approach with previously developed methods is presented. The switch in single- or multichannel modifications can be used as closing or crowbar devices.

A method for measuring transients caused by interrupting current using a transmission line terminated in its characteristics impedance

A measurement method of transients caused by interrupting a current is described. In consideration of the fast transients and high-frequency discharge phenomena due to interrupting the current, a transmission-line system was introduced. It consists of a coaxial switch, coaxial cables as transmission lines on the right and left sides of the switch, and termination resistors. When the current is interrupted by the switch, the waveform across the termination resistor is measured by an oscilloscope. The impedance-matching technique for the cables was employed to minimize the effects of reflected waves. That is, the resistors were designed to match the characteristic impedance of the cables. The characteristics of the system were measured by a network analyzer. The VSWR of the system was within 1.33 in the frequency range below 500 MHz. The time-domain measurement using a transmission-line system terminated in its characteristic impedance clears up the process of the complicated transients caused by interrupting current. >

Experiments on high-power ion beam generationin self-insulated diodes

Experimental results are given on high-power ion beams (HPIB) generation in a vacuumspherical focusing diode with self-magnetic insulation, obtained from the nanosecond accelerator PARUS with 0.2-TW power and 60-ns pulse duration for a matched load. When the passive plasma source of the ions was used, the efficiency of the HPIB generationwas measured to be as high as 20% for 700-kV diode voltage and 10-kA/cm2 beam density in the focal plane.The application of a coaxial plasma opening switch (POS) prior to the diode resultedin a factor-of-1.8 increase in the diode power in comparison with a match operation inthe absence of a POS.

Some properties of the circular waveguide with azimuthally magnetized ferrite

A comprehensive analysis of normal rotationally symmetric TE modes in a circular waveguide, filled with ferrite, magnetized azimuthally to remanence by a coaxial switching conductor of finite radius, is presented. The characteristic equation of the structure, derived in terms of Kummer and Tricomi confluent hypergeometric functions of complex parameter and variable, is solved numerically, using specially compiled tables of wave functions. Families of theoretically calculated nonreciprocal phase characteristics of the gyrotropic waveguide are shown in normalized form for the two latched states of remanent magnetization, a variety of ferrite parameters, and different values of switching conductor to waveguide radius ratio. The influence of structure geometry and parameters of anisotropic ferrite on normalized differential phase shift and cutoff frequency spectrum of the TE01 mode is discussed.

The Application of a Plasma Erosion Opening Switch to a Nanosecond Generator at the Power Level of 1010 W

This paper is devoted to experimental studies of a short-pulse (80 ns) inductive system with a coaxial plasma erosion opening switch (PEOS), operating at the 2-5 × 1010 W level. Scalings of the PEOS and ion diode characteristics with different parameters (PEOS plasma density and velocity, PEOS electrode geometry, load impedance, type and strength of an external magnetic field) were carried out. It was seen that for the most efficient energy and power switching to the load by the PEOS, the following conditions are preferable: high velocity and low density of the plasma flow, negative polarity of the inner PEOS electrode, coincidence of the switch current and injected plasma flow directions, the absence of an external magnetic field, and the presence of an additional self-field in the PEOS region. Power enhancement of a factor of 3 and pulse shortening by a factor of 2 were obtained under optimal conditions.

Refinement Procedures of Beam Position Measurement in the Tristan Accumulation Ring

High precision of about 0. 1 mm is required in the beam position measurement of TRISTAN MR(main ring) which is now under construction. In this respect, position measurement in the TRISTAN AR(accumulation ring) is reviewed. We found that the statistical study of the accumulated measuremnent data gives very useful information on the performance of the monitor system. For example, repeated COD measurements during a beam storage showed not only reproducibility of the position measurement (0. 05 mm) in the beam intens ity range of factor 50 but also pointed out troubles caused by poor contact in coaxial switches. Moreover, it suggested the criterion to abandon erroneous data. Programs for such check has been prepared and has improved the efficiency of COD correction. Improvements have also been made in the calibration and in the mechanical setting of the monitor chambers.

Attenuation Transfer Standards for International and National Intercomparisons

Some examples are given of mechanically and electrically stable attenuation transfer standards, developed or assembled for the international intercomparisons GT-RF 75-A 3 and 78-1 proposed by the radio frequency working group of the CCE. A 4-port directional coupler with matched loads terminating the ports of the side arm and a switchable short interrupting the power flow in the side arm between two coupling sections was constructed for 0.01 dB in waveguide R 140 at 15 GHz. At frequencies of 8 GHz ⩽ ν ⩽ 18 GHz in coaxial systems, switchable transfer standards consisting of commercially-available components incorporating a waveguide directional coupler and two isolators are the most stable and have the best repeatability. For comparing 100 dB at 30 MHz, two transfer standards applying the WBCO principles (using an R 100 rectangular waveguide) were developed, one of them for insertion into and removal from the line, the other fitted with a coaxial switch of optimal repeatability for remaining in line during the measurement. The total uncertainty of these standards is ⩽ 0.01 dB at 100 dB.

Aviation Electronics

Details of Electrical and Electronic Apparatus with Applications in the Maintenance and Operation of Aircraft, Missiles and Space Vehicles. A miniature coaxial switch for use with Amphenol's recently introduced SMA connectors, has been developed by the company, based at Thanet Way, Whitstable, Kent, to give complete hermetic protection in all environments.

Measurement of RF Peak-Pulse Power by a Sampling-Comparison Method

A method is described whereby RF peak-pulse power may be measured by comparison with CW power at the same frequency. Comparison is made by first sampling the power in a small portion of the RF pulse width and subsequently sampling the same portion of the CW signal whose power level is accurately known. Sampling is accomplished with a fast SPDT coaxial solid-state switch synchronized with the RF pulse. A time delay network allows the sample to be taken anywhere along the RF pulse width. Estimated maximum error for peak power levels to 10 kw is 3 per cent. High CW levels are not necessary since the switch is used in conjunction with directional couplers to cover the power ranges of interest.

A Broad-Band Coaxial Ferrite Switch (Correspondence)

A broad-band strip-line reflective ferrite switch has been described by Johnson and Wiltse, who also referred to the possibility of a similar switch in coaxial line. This note describes a coaxial on-off switch which will operate over the band 2500-4100 Mc; two such units can be combined to make a two-way switch. An isolation of 40 db was achieved, with a very low loss for the transmitting path, which, in both these devices, was obtained by magnetizing the ferrite well beyond the value for isolation.

Theory of TEM Diode Switching

The theory of TEM diode switching is presented for purpose of understanding and designing TEM microwave diode switches. A few experimental results are reported for the purpose of supporting the theory and demonstrating the exceptional bandwidth possible. An analysis is given of the switching action of one and of two or more diodes as well as the biasing of the center conductor of a TEM transmission line over broad-frequency bandwidths without interacting the RF signal. The use of point-contact germanium, and gold-bonded germanium diodes for TEM switching is discussed. Some considerations of switching speed and maximum power-handling capacity are given. A coaxial transmission line switch has been constructed in which two gold-bonded diodes provide 26-db or greater isolation and insertion ranging from 1.6 db to less than 1 db from 40 Mc to 4000 Mc. The addition of a bias lead should increase the insertion loss 0.4 db or less over the 100-to-1 bandwidth, the maximum increase being at the upper and lower bounds.

Multidiode Switches (Correspondence)

The impedance of crystal diodes is known to depend on the applied bias voltage. This has suggested the use of diodes as switching elements in the control of microwave signal transmission. In the simplest form, the diode switch consists of a transmission line which is shunted by a diode. Coaxial cables as well as waveguides have been used for the transmission lines that are shunted by point-contact and p-i-n diodes. Slab line or coaxial switches where a diode is inserted in series with the center conductor of the line have also been developed.

20-Kilovolt Delta-Function Generator

An electronically triggered impulse generator has been developed which produces 20 kilovolt pulses having rise times of less than 0.6 millimicrosecond. When used with a shorting stub, this instrument produces delta-function pulses of less than 2.5 millimicrosecond total width at full amplitude. The functions of primary pulse generation and pulse sharpening are separated. A special 50-ohm coaxial switch was constructed of hydrogen thyratrons to produce 20 kilovolt primary pulses of arbitrary length and having rise times of less than 1.75 millimicroseconds. When triggered by a 2–500 volt pulse of 5 millimicroseconds rise time, the over-all jitter of the system is of the order of 1 millimicrosecond.

An aerial comparator and monitor unit

The paper describes a system for improved aerial selection and signal monitoring at receiving centers. The system enables any available ariel to be applied, via a coaxial switch, to a monitoring receiver whose output at intermediate frequency is displayed on the screen of a cathode ray tube; thus providing monitoring facilities at any frequency on any aerial.It also provides facilities for any two aerials to be switched alternately on to the monitoring receiver, either manually or at high speed by electronic means, in order that a visual comparison may be obtained between the two aerials on a cathode ray tube whose time base is locked to the aerial switching speed.