Search

An enhanced microstrip antenna is proposed that incorporates a patch that rotates around the inner conductor of the coaxial line or dielectric shaft and a novel coaxial line feeding technique that offers constant electromagnetic coupling. This proposal addresses the disadvantages in our previous patch antenna in which the resonant frequency diverges from the center frequency of the personal handy-phone system (PHS) band and the bandwidth decreases as the patch rotates because of the changing electromagnetic coupling between the patch and microstrip line due to the patch rotation. We verify that this enhanced patch antenna achieves the antenna gain of approximately 0 dBd, which is the same as that of the previously proposed antenna, while suffering no significant gain degradation due to unit inclination over inclination angles from [+ or -] 45[degrees] compared to a conventional quarter-wavelength whip antenna, which experiences a degradation of approximately 2.7 dB. We show that the maximum resonant frequency separation from the center frequency of the PHS band is reduced to 15 MHz from 31.4 MHz of the previous antenna using the novel coaxial line feeding technique. The effective bandwidth needed for PHS is achieved over the inclination angles of -20[degrees] to +40[degrees]. Approximately 93% of the total bandwidth needed for PHS is achieved while the previous microstrip line type achieved only 58% coverage; accordingly, an adequate bandwidth for PHS use is obtained. Index Terms--Electromagnetically coupled microstrip antenna, new coaxial line feeding technique, personal handy-phone system (PHS), rotatable patch antenna.

Air-filled copper Ka-band resonators with heights between 250-700 [micro]m are demonstrated with measured unloaded Q factors between 440-829. The low-profile quasi-planar resonators are fabricated using a sequential metal deposition process. Miniaturization of up to 70% with respect to a [TE.sub.101] quasi-planar resonator is accomplished by reducing the footprint of the resonator while maintaining the height. Finite-element simulations predict the measured resonant frequency within less than 1%. Due to fabrication imperfections, [Q.sub.un] is measured to be approximately 15% less than predicted. The resonators are compatible with air-filled rectangular microcoaxial feed lines fabricated in the same metal-deposition process. Index Terms--Cavity resonator, coaxial transmission line, photolithography, quality (Q) factor.

It has been shown recently that the use of modified assigned material parameters (MAMPs) within the finite-difference time-domain (FDTD) method provides a systematic, readily extensible, accurate, and efficient approach to the electromagnetic analysis of microstrip structures. In this paper, it is shown that this technique can also be applied with equal effect to lossless and lossy coaxial lines, wires in a lossy medium such as earthing grids, and more complex structures which include coaxial feeds and shorting posts. The modified parameters are calculated directly from the known asymptotic fields near the wire and do not rely on the concept of 'equivalent radius.' Results are given which show equal or superior performance compared to those obtained using other methods but with the added advantage of flexibility and rigor. Index Terms--Coaxial transmission lines, finite-difference time-domain (FDTD) methods, wire grids.

Byline: Y.P. Zhang (1), J.T. Ong (1) Keywords: leaky feeder; indoor radio propagation channel; personal communication systems Abstract: This paper presents the results of narrowband and wideband propagation measurements carried out at 2.0 GHz in a large enclosed area using a coaxial cable with leaky sections as the transmitting antenna. The narrowband measurements were devised to measure attenuation of radio signals and the wideband techniques to measure multipath impulse responses and their associated root mean square delay spread. Analysis of the narrowband data files shows that the received signal levels in the direction parallel to the cable generally decay and display peaks in front of leaky sections due to the specific attenuation and special structure of the cable. The received signal levels in the direction radial to the cable decrease slowly and the distance-power law exponent is found to be slightly larger than one. The slow and fast variations of the received signal levels are also examined. The results reveal that the slow variations do not follow the lognormal distribution, while the fast variations fit the Rayleigh distribution in both parallel and radial directions. Analysis of the wideband data files yields that the maximum value of the root mean square delay spread is 86.1 ns and the root mean square delay spread values are less than 55 ns 50% of the time. One therefore can conclude that the enclosed area channel excited by the coaxial cable with leaky sections has a broad coherent bandwidth and can support the data rate up to 2.3 Mb/s without equalization. Author Affiliation: (1) School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore Article History: Registration Date: 11/10/2004

We describe a multioctave power-combiner structure using finline arrays in an oversized coaxial waveguide. The spectral-domain method (SDM) is used to compute the propagation constant in this structure, and is verified with HFSS simulations. The SDM method is then employed to synthesize broad-band tapered impedance transformers in finline for coupling energy to and from a set of monolithic microwave integrated circuit (MMIC) amplifiers. A modular assembly is described using a sectoral tray architecture. The concept is demonstrate for a 32-MMIC system using low-power traveling-wave amplifier MMICs, providing a 3-dB bandwidth of 13 GHz (3-16 GHz). An output combining loss of 1 dB is estimated from the small-signal measurements, suggestion a combining efficiency of ~75% for 32 MMICs. Index Terms--Coaxial waveguide, slotline array, spatial power combining, ultra-broad-band.

A stainless steel open-ended coaxial probe was developed to measure the complex permittivity of solid dielectric materials at elevated temperatures and over a broad frequency range. The spring loading of the inner conductor insured that the probe maintained contact with the sample up to 1000 [degrees] C and eliminated errors due to differential thermal expansion of the probe. Comparison with an industry standard probe demonstrated that the spring-loaded probe accurately and reproducibly measured the complex permittivity of several samples over a broad frequency range of 0.3-6 GHz at room temperature. At temperatures up to 1000 [degrees] C, dielectric measurements of a glass ceramic and of a porous alumina composite performed with both a spring-loaded probe and a resonant cavity agreed to within 8% for the real part and 15% for the imaginary part of the complex permittivity. The probe's insensitivity in measuring low-loss materials constrained accurate dielectric measurements to materials with tan b[greater than or equal to]0.05. Finally, optimization of an open-ended probe by varying the probe dimensions is presented. Index Terms - Coaxial probe, high temperature, permittivity measurements.

A 'thin outer conductor coaxial cable' was designed for high-temperature superconducting (HTS) filters. The proposed coaxial cable is made of copper film and has an optimum thickness of 0.005 mm. Performance testing of the device showed that it optimizes both low electric loss and low thermal leakage for HTS filters. In addition, the 'thin outer conductor coaxial cable' has the bending capability similar to that of the semi-rigid coaxial cable.

There is a growing interest to extend existing coax CATV networks to enable interactive multimedia services. In this paper we describe necessary modifications and additions of CATV network components to provide broadband upstream channels in the range of 6 to 40 MHz. To investigate linear and nonlinear distortions, reflexions, noise and ingress, suitable digital modulation shemes and adaptive equalization, the CATV network components are modelled and a computer simulation program using PTOLEMY is established. It is shown that all 3370 subscribers of an existing CATV sub-network can be provided with up to 25 kbit/s collision free on the physical network layer. Using appropriate teletraffic and media access control protocols, user bit rates of up to 2 Mbit/s are feasible in upstream direction.

Two types of linear coaxial antennas, coaxial-colinear antennas, and slotted coaxial antennas are studied to check the possibility of using them as the base-station antenna in personal communication systems. The slot voltages and input impedance of linear coaxial antennas are obtained by using a transmission-line analysis where the radiation effect is accounted by a shunt and a serial admittance, respectively. The current distribution is obtained by solving an integral equation using the method of moments. The radiation pattern and directivity are then obtained from the current distribution and the reflection coefficient inside the coaxial cable. Factors analyzed include frequency, coaxial filling permittivity, and segment number. Index Terms - Coaxial-colinear antenna, field pattern, gain, input impedance, slotted coaxial antenna, transmission line analysis.

Optical implementation of a large-scale neural network with 32 x 32 neurons is reported. The experimental setup is described, error caused by limited precision of hardware is analyzed, and experimental results are presented. Key words: Optical neural network, interconnection, lenslet array, error.

This paper reports on the basic theory of operation and experimental results obtained from an electric field imaging system for planar microwave circuits that employs the method of modulated scattering with monolithically integrated probes. The low-cost system is capable of mapping the normal and tangential electric field intensities and electrical phase delays above reciprocal microwave circuits in the frequency range of 0.5-18 GHz with a spatial electric field resolution of better than 100 [[micro]meter]. Monolithic probes incorporating silicon Schottky diodes integrated with electrically small dipole and monopole antenna scatterers on a 40-[[micro]meter]-thick high-resistivity silicon substrate are used. Electric field intensity and electrical phase delay images are presented for a 55-[Omega] coplanar waveguide line (CPW), a three-turn microstrip meander line at 8.8, 11.7, and 13.4 GHz, a microstrip coupled-line directional coupler at 10 GHz, and a microstrip patch antenna at 12.85 GHz. The results demonstrate that the modulated scattering technique is a valuable low-cost tool for microwave circuit diagnostics.

The performance of zero cross-over timing system of the amplitude rise time compensated type using coaxial Ge(Li) detectors is analyzed, using an average pulse-shape method. Standard deviation of walk and noise jitter as a function of energy deposited in the detector are computed and FWHM of ARC timing spectra are identically verified with experimental results published elsewhere. Deviations of the centroid of ARC prompt time distributions from the corresponding peak positions are studied through mathematical expressions.

Radiation from a cavity-backed annular slot array antenna fed by a coaxial probe is studied. The Hankel transform and mode-matching techniques are utilized to obtain a solution in convergent series. A prototype antenna was fabricated and its characteristics were measured at C-band to verify the accuracy of our approach. Index Terms--Annular slot, cavity-backed antenna, coaxially-fed, mode matching.

Time-domain reflectometry (TDR) is a cheaper, faster and quicker technique for monitoring unstable slopes than traditional methods. TDR uses coaxial cables in place of inclinometers which reduces the costs of monitoring landslides sites. The cables are embedded in the ground and changes in their impedance are determined. The changes are due to ground movements that deform the cable. The location of the change is determined and the rate of change gives the rate of movement. TDR stores data in a computerized datalogger which can be accessed by a cell phone.

Coaxial waveguides are very commonly used in many microwave subsystems for the connection of various components. Significant size reduction could, therefore, be achieved by integrating the design of the coaxial transition in the computer-aided design (CAD) of microwave filters. In this context, we first discuss in this paper a coaxial transition, which can be efficiently designed interactively using an accurate and efficient CAD procedure. The key elements of the CAD tool developed are then described and a specific example of a microwave filter is discussed. In addition to theory, measured results are also presented, thereby fully validating both the CAD tool and the structures proposed. Index Terms--Coaxial waveguides, electromagnetic launching, waveguide excitation, waveguide filters.

The Green's functions for determining the electromagnetic fields inside a semiinfinite coaxial line due to a radially directed, infinitesimally thin, and short-current element have been derived. In addition to the TEM mode, TE and TM modes are alto considered. Based on the Green's functions, a closed-form formula for determining the input impedance of a probe in a coaxial line terminated at an arbitrary load has been derived. Good agreement is observed between the theoretical results and experimental measurements over a wide frequency band for several configurations of interest. At low frequencies where the TEM mode is dominating, there is practically no difference between the results obtained by the rigorous analysis and those by a simple formula derived from the transmission-line theory. However, at frequencies where TE and TM modes are no longer insignificant, there is a noticeable discrepancy between the results obtained by the rigorous and not-so-rigorous methods. Index Terms--Coaxial line, Green's functions, input impedance, junctions, probe.

A methodology useful to derive exact and higher order surface impedance/admittance boundary conditions (HOI/ABC's) for complex geometries is presented. It is shown that exact surface boundary conditions are always expressed through dyadic integral operators involving the tangential magnetic and electric fields all over the surface of the body. Quasi-local surface boundary conditions that include curvature effects are shown to be computable through an asymptotic approximation of the integral operators. Finally, an example of a surface admittance boundary condition useful to analyze a structure exhibiting discontinuities along its surface boundary is presented. Practical examples to demonstrate the feasibility of the proposed methodology, as well as the accuracy of the resulting surface boundary conditions are also presented. Index Terms--Complex geometries, dielectric rod, Leontovich, lossy coaxial cable, radiation admittance, surface boundary conditions, surface waves, uniform asymptotic.