RF Frequency Range Research Articles

Dispersion characteristics and radial field distribution of surface waves in the collisional regime

The influence of collisional damping and the radial electron density profile on the characteristics of the wave propagation as well as on the radial distribution of the electric field of electromagnetic surface waves is studied. The discussion is mostly addressed to the situation of surface wave plasmas in the RF frequency range in a strongly collisional case. Some aspects of the influence of the collisional damping on the wave propagation, particularly in view of diagnostic applications, are discussed. The range of validity of the 'thin cylinder approximation' in the collisional case is compared with predictions of the collisionless theory. Furthermore the possibility of the occurrence of a resonant field enhancement as the position of a local plasma resonance under microwave conditions is pointed out.

Radiation properties of a pigtail-terminated coaxial transmission line

The method of moments is used to study the shielding effectiveness of a pigtail-terminated shielded wire (coaxial line) above a perfectly conducting ground plane. Numerical computations are performed in the RF frequency range, i.e. 25-1000 MHz. Pigtail wires on either or both ends of the shield are considered. Results are compared to those from the ungrounded case (floating shield). Results show that the presence of pigtail wires as ground connections at RF frequencies is undesirable and may further enhance radiation. The impedance terminations have a small effect on the shielding effectiveness of the antenna structure. >

A low-current Ku-band GaAs monolithic image rejection down-converter

A single-chip image rejection downconverter has been designed, fabricated. and tested for broadcast satellite receivers operating in the 11.7- to 12.2-GHz range. The downconverter consists of an RF low-noise amplifier (LNA), a filter-type image rejection mixer (IRM), and an intermediate frequency amplifier (IFA). It receives 11.7- to 12.2-GHz RF signals and down converts to 1.0- to 1.5-GHz IF signals with an external local oscillator. Since the filter integrated on the downconverter produces an image rejection of more than 30 dB, the downconverter requires no off-chip circuits for the image rejection. A conversion gain of 37+or-1 dB and a noise figure of less than 3.5 dB have been achieved over the RF frequency range. The current dissipation is only 40 mA, and the chip size is 2.8 mm*2.8 mm*0.45 mm. >

A low current GaAs monolithic image rejection downconverter for X-band broadcast satellite applications

The design, fabrication, and performance of a fully integrated X-band monolithic image rejection downconverter are described. The downconverter consists of a low-noise amplifier, an image rejection mixer, and an IF amplifier. The downconverter receives RF signals between 11.7 and 12.3 GHz and converts them down to IF frequency between 1.0 and 1.6 GHz. A conversion gain of 46+or-1 dB, a noise figure of less than 3.3 dB, and an image rejection of 30 dB have been achieved over the RF frequency range. The chip size of the downconverter is 1.9 mm*2.2 mm, and its current dissipation is only 43 mA. Since the downconverter has sufficient image rejection due to an on-chip bandstop filter, it requires no off-chip circuits. Therefore, the use of this downconverter in X-band broadcast satellite applications will lead to a great reduction in size and current dissipation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Equal-gain loci and stability of a microwave GaAs MESFET gate mixer

The performance of a microwave GaAs MESFET gate mixer is theoretically investigated to clarify the existence of a conditionally stable RF frequency range as well as an unconditionally stable frequency range in which maximum available conversion gain (MACG) can be defined. For the unconditionally stable range, the MACG and load and source impedances are calculated as functions of RF frequency. For the conditionally stable range, the stability circle and equal gain loci are shown for source RF and load IF impedances. The conditionally stable region of the GaAs MESFET mixer appears around F/sub T/ of the MESFET. Higher conversion gain is easily obtained by choosing a MESFET for which the F/sub T/ is close to the RF frequency. >

Axial structure of a plasma column produced by a large-amplitude electromagnetic surface wave

Electromagnetic surface waves in the rf and microwave frequency range can be used to produce long large/small-diameter plasma columns. We propose a theory of surface-wave-produced plasmas at two different low-pressure gas-discharge regimes, diffusion and recombination, respectively. For a given regime the axial plasma density profile is specified by two quantities: a numerical parameter σ=ωR/c (ω being the wave frequency, R the tube radius, and c denoting the speed of light) and the collision frequency ν (ν≪ω). Our theory predicts the magnitude of the axial electron number density gradient. The very good agreement between the experimentally measured plasma density gradients and the theoretically calculated ones for diffusion-controlled surface-wave-produced plasma columns confirms the adequacy of the proposed model.

Optically detected electron-nuclear double resonance in hydrogenated amorphous silicon

Optically detected electron-nuclear double resonance (ODENDOR) measurements were carried out at 2 K and 9.6 GHz, monitoring total emitted light in hydrogenated amorphous silicon. ODENDOR signals were observed in the RF frequency range of 0.6 MHz – 15 MHz for the A centre (trapped hole centre) and dangling bond centre. The spatial distribution of weak hyperfine interaction with 29Si nuclear spins may be responsible for broad ODENDOR lines.

A folded-type integrated-optic spectrum analyzer using butt-coupled chirped grating lenses

A folded-type integrated-optic spectrum analyzer (IOSA) using reflection-type chirped grating lenses butt-coupled to a LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> waveguide Bragg cell is presented. The lenses can be easily fabricated by the well-established planar process, and the IOSA has good performance as well as a reduced device length. The spectrum analyzer function of 4.0 MHz resolution in 95-345 MHz RF frequency range is demonstrated.

Beam phase stabilisation at the sin injector cyclotron

A control system, designed to stabilize the phase of the extracted beam with respect to the Dee-voltage is described. Operating over the entire energy- and particle range of the SIN injector cyclotron, it requires no tuning over the rf frequency range of 4–17 MHz and at 51 MHz. Key components of the system are: A beam pick-up probe followed by wideband amplifiers with automatic gain control in the beam signal path, and a fast phase detector of high bandwidth, resolution and stability which features automatic gating for pulsed beam applications. The system's overall stability over a 2 h test period is better than 0.2° pp (rf, 51 MHz), with typical resolution at 0.01°, at beam currents above 1 μA at 72 MeVp (injector mode of the cyclotron).

The Low-Level Rf Beam Control System for the Booster of the Beijing Proton Synchrotron (BPS)

A prototype of a low level RF beam control system for the BPS Booster was designed and built at Fermilab during the past year. Machine parameters are: RF Frequency range 2.76-6.31 MHz, Harmonic number h= 3, Repetition rate 12.5 Hz, Maximum synchrotron frequency 12 KHz No phase transition occurs during acceleration. We have adopted computer controlled digital curve generators for the frequency program and other programs such as the radial position offset, radial position loop gain, etc. for the operational flexibility available with such programs. The frequency mixing method was chosen for the analog beam control loops, including the phase loop and radial position loop, for improving the signal to noise ratio within the wide frequency band and for convenience in signal processing. The system is composed of a series of modules which are to be operated in several modified NIM crates. This will allow maximum flexibility during the development phase of accelerator operation. Here we give a brief description of the LLRF system and some preliminary design and test results. Study and improvement of the system will be continued. A simplified block diagram of the system is shown in Figure 1.