Analysis and design of integrated active circulator antennas

A study on the analysis and design of active integrated antennas based on active quasi-circulators is reported in this paper. The antenna consists of a novel hybrid active circulator and a short-circuited quarter-wavelength microstrip antenna, which combine to form an active antenna with transmit and receive action at the same frequency. A full-wave model of the configuration using the extended finite-difference time-domain method is devised to analyze its operation, to study parasitic electromagnetic coupling effects, and to derive design guidelines. Experimental results for a hybrid model are also presented     

Three-Dimensional FDTD Simulation of Micro-Pillar Microcavity Geometries Suitable for Efficient Single-Photon Sources

We present the results of calculations of the microcavity mode structure of distributed-Bragg-reflector (DBR) micro-pillar microcavities of group III-V semiconductor materials. These structures are suitable for making single photon sources when a single quantum dot is located at the center of a wavelength scale cavity. The 3-D finite difference time domain (FDTD) method is our primary simulation tool and results are validated against semi-analytic models. We show that high light extraction efficiencies can be achieved (>90%) limited by sidewall scattering and leakage. Using radial trench DBR microcavities or 2-D photonic crystal structures, we can further suppress sidewall emission, however, light is then redirected into other leaky modes     

n/sup k/-pulse position modulation for optical wireless communication

An original analysis is presented for n/sup k/-PPM in which the information is conveyed by the position of k pulses, each within their own frame of n slots, giving n/sup k/ PPM symbols. Comparisons are made with multiple PPM (MPPM) and it is demonstrated that n/sup k/-PPM offers improved orthogonality, a simplified circuit implementation and comparable receiver sensitivity.     

Harmonic control in active integrated patch oscillators

The authors present a set of experimental results which demonstrate that it is possible to control the level of harmonic and spurious radiation emitted from a microstrip patch oscillator by means of at least two mechanisms. A discussion of these mechanisms is included, and it is also argued that an unambiguous method of classifying similar results is required     

Performance analysis of self-synchronized optically preamplifiedPPM

The performance of a hybrid erbium-doped fiber amplifier pulse position modulation (EDFA PPM) system is investigated under self-synchronization. Sensitivity results are presented for a system operating at 622 Mb/s and λ=1.53 μm. These indicate that EDFA PPM offers 7.9 dB sensitivity improvement over an equivalent EDFA PCM system and is beyond the fundamental PCM limit. An original expression is derived for the EDFA PPM power spectral density (PSD) under jitter. Original results are presented for the timing variance and the jitter wrong slot error (JWSE) probability due to the extracted self-timing. An original analysis and results are given for the system sensitivity penalty due to jitter. The penalty varied between 0.15 and 1.9 dB for the range of parameters considered. The selection of the system parameters that minimizes the penalty is investigated     

Human Mycobacterium bovis infection in the south-west of Ireland 1983-1992: a comparison with M. tuberculosis

Epidemiological and bacteriological aspects of human Mycobacterium bovis disease were investigated in south-west Ireland (counties Cork & Kerry, population 536,000) over the years 1983-92 inclusive and compared to M. tuberculosis. Results showed a small, stable incidence of culture positive M. bovis human disease, mean annual incidence 0.56 per 100,000 population compared to a higher but declining incidence of culture positive M. tuberculosis (15.3 per 100,000 in 1983, 9.0 per 100,000 in 1992). Male patients were the majority, 63.4 per cent of M. bovis; 62.4% of M. tuberculosis (p = 0.03). Fifty three per cent of M. bovis cases (n = 30) were pulmonary, compared to 85% of M. tuberculosis (n = 626; p = 0.0001). M. bovis patients were older (p = 0.02), mean age 58.4 years (SD 18.9) compared to 48.5 (SD 22.2). The mycobacterial smear positive rate was similar in both groups taken as a whole. No rural-urban difference in incidence was found in either disease, suggesting in the case of M. bovis initial infection in childhood via contaminated milk in the pre-pasteurisation era.     

Integrated active antenna with simultaneous transmit-receiveoperation

The authors present results for a novel two element active transmit-receive array using dual linear polarisation and sequential rotation. Each element includes an integrated oscillator and amplifier mounted on orthogonal edges of a square patch, such that transmit and receive paths are isolated and polarisation duplexed. The array gives in excess of 55 dB transmit-receive isolation at 3.77 GHz     

Overcoming the effects of polishing induced stress when fabricating fused polished couplers

The tendency of the polished fibres to separate due to the thermal relaxation of polishing induced stress during the fabrication of fused polished couplers is overcome by depositing a thin layer of silica in the form of either a silica sol-gel or an aqueous suspension of silica powder on the parallel fibre assembly prior to the application of heat.<>     

ATM infrared wireless LANs: a proposed architecture

As infrared wireless LANs for in-building applications become more popular because of their many advantages, it is of interest to design such LANs to support the ATM protocol and therefore provide wireless access to fixed ATM networks. The architecture of such a LAN is presented in this article. Emphasis is placed on the protocol stacks of the model to provide seamless operation with the wired network, on the cellular topology, and on the MAC protocol. Under the proposed topology the system performance is revealed in terms of packet dropping probability, average access delay, channel throughput, and statistical multiplexing gain for a range of system parameters     

Spectral characterisation and frame synchronisation of optical fibre digital PPM

The discrete time decoding of data in pulse position modulation calls for accurate timing synchronisation, particularly at the frame rate. The spectral properties of optical fibre digital PPM are considered. An original expression is presented for predicting the spectrum and it is shown that, unlike satellite PPM, a component exists at the frame rate which may be used for timing extraction purposes. Further, it is illustrated that the modulation index can be used to enhance this component by up to 19 dB. This has been verified practically, with the results agreeing to within 1 dB of those predicted from the original expression presented.<>