Quarter-wavelength Filter Research Articles

Experimental and numerical characterization of a radio-frequency plasma source with a DC-grounded electrode configuration using a quarter-wavelength filter

We present a combined experimental and numerical investigation of the plasma properties in an asymmetric capacitively coupled radio frequency plasma source using argon discharge. Besides driving the system in the conventional way, which results in a high negative self-bias voltage due to the asymmetric configuration, we also connect a ‘quarter-wavelength filter’ to the powered electrode, which lifts its DC potential to zero. At the powered side of the plasma, we employ electrodes with conducting and insulating surfaces, as well as electrodes combining both in different proportions (‘hybrid electrodes’). Measurements are carried out for the plasma potential, the electron density and temperature in the bulk plasma, as well as for the flux-energy distribution of the ions at the grounded surface of the system. The nature of the surface of the powered electrode as well as the presence of the quarter-wavelength filter are found to highly influence the plasma potential, . For the electrode with a conducting surface 20 V and ∼150 V are found in the absence and the presence of the filter, respectively. For the electrode with an insulating surface, the self-bias voltage builds up directly at the plasma interface, thus the filter has no effect and a plasma potential of ∼20 V is found. For the electrodes with different conducting/insulating proportions of their surface, ranges between the above values. Particle-in-Cell/Monte Carlo Collisions calculations for identical conditions with hybrid electrodes predict double-peaked ion energy distribution at the powered electrode with peaks corresponding to and along with a lowering of the plasma potential (whencompared to wholly conducting electrode), a trend that is observed experimentally. These studies are of great importance for the application of similar plasma sources with in-situ cleaning of mirrors in fusion devices and the results can be extended to a variety of plasma processing applications.

Design of Lightning Protector Compatible for Both 2g and 3g Cellular Systems

A novel multi-passband lightning protector simultaneously compatible for base stations of 2G and 3G cellular systems is designed, fabricated and measured. Based on the theory of extended quarter wavelength filter, this protector successfully acquires 3 transmission poles. The VSWRs in three passbands, 800–1000 MHz, 1700–2200 MHz and 2300–2500 MHz, are lower than 1.10,1.12,1.08, respectively. It indicates that this device transmits 2G and 3G signals with very low losses while effectively protecting inner circuits from lightning induction. By applying the approach presented in this paper, other multi-band protectors can also be realized to fit different frequency regulations for various 2G and 3G standards.

Vision at the workplace: Part II — Knowledge base for the guide

This chapter discusses vision problems in workstations. Visual problems can be due to deficiencies in the person, the place, or the procedure. Some personal deficiencies can be corrected with lenses (contact lenses, spectacles). Place deficiencies can be corrected by (1) increasing the quantity of the illumination or (2) improving the quality of the illumination. Visual problems at workplaces are unlikely to affect the worker's health although they may cause unnecessary stress on the visual system, sometimes resulting in headaches and fatigue. Visual performance may be affected, resulting in increased errors and time/unit. Offices are mostly composed of visual display terminals (VDTs). The screen is relatively vertical, but more importantly, the ambient light washes out the contrast on the screen. So lighting must be designed for both vertical screens and vertical paper (in document holders) and horizontal paper. Reflections on the screen can be diffuse or specular. Diffuse (veiling) reflections are caused by ambient light, as well as the phosphor. Diffuse reflections increase the luminance of both the screen background and characters, thereby reducing the contrast ratio. Specular reflection produces a mirrorlike image. Coatings, such as quarter-wavelength filters (like the coating on camera lenses) and matte treatment (frosting), can reduce specular reflection.

Synthesis of Symmetrical TEM-Mode Directional Couplers

Exact synthesis procedures are derived for symmetrical three-section and five-section TEM-mode directional couplers. These synthesis procedures are based on the equivalence between the theory of directional couplers and stepped quarter-wavelength filters as previously described by Levy and Young. Explicit formulas for the parameters of three-section couplers are presented. A realizable insertion-loss function is derived for the five-section coupler resulting in an equal-ripple response. Although this function has an equal-ripple characteristic, it is not expressible in terms of Chebyshev polynomials. Results obtained for the five-section coupler show considerable improvement in bandwidth over a three-section coupler. For example, a five-section coupler of -3 /spl plus mn/ 0.5 dB has a bandwidth of 9.6:1 as compared with 5.8:1 for a three-section coupler of -3 /spl plus mn/0.5 dB. A five-section coupler of -10 /spl plus mn/ 0.5 dB was designed on this theoretical basis for the 555-4000 Mc band, and the measured shows good agreement with the theoretical coupling sponse, yielding a minimum directivity of 18.0 dB at 3.7 Gc.

A Wide Stop Band UHF Coaxial Band-Pass Filter (Correspondence)

A narrow-band coaxial filter is described which has a stop band fourteen times the fundamental frequency, and is relatively simple to design. Since the well-known multiresonator coaxial band-pass filter having quarter-wavelength resonators is probably the most commonly used coaxial filter for narrow-band frequency selection, the design to be described herein is most meaningful. Identical construction techniques used in the common quarter-wavelength filter can also be used for this design. Rather than employing the normal quarter-wavelength resonators, the filter being described here makes use of resonators which are approximately one-tenth of a wavelength long. The one-tenth wavelength coaxial sections are made to resonate by capacitively loading the open-circuit end of the cavities. The capacitors are formed by placing a disk on the end of the center conductor and inserting a low-loss dielectric between the disk and the end wall of the cavity. Fig. 1 shows a cutaway view of a four-stage filter using the above loading scheme. The dielectric section is bonded to the end of the cavity and the center conductor disk is completely captured by the dielectric in order to insure complete support of the center conductor under extreme vibration. It has been found that this type of capacitive loading does not appreciably reduce the unloaded cavity Q nor cause an increase in insertion loss of the filters.