A method to predict multipath effects on a line-of-sight link

A method that computes the quality of a digital microwave line-of-sight link affected by multipath propagation is presented. The use of a statistical propagation model and of the signature concept allows the propagation effects to be separated from the characteristics of the equipment. Since the variations of the statistical mode coefficients with respect to the characteristics of the link under consideration are not known, experimental results have been achieved using assumptions based on physical considerations. A single channel is considered and the same principles, although more speculative because of the lack of data, are applied to a diversity channel     

Characteristics of double-groove guide at 3 mm wavelength

A groove guide having two parallel grooves may simultaneously propagate two modes with a small difference in phase constant. Experimental measurement of this difference for three groove separations at 100 GHz gives results close to theoretical predictions. The attenuation of one mode is a little less than for a guide with a single groove.     

Groove guide propagation characteristics at 3mm wavelength

Measurements of moding characteristics and attenuation on groove guide with appropriate dimensions for 3 mm wavelength operation show that it can be made with convenient dimensions, can operate with only the single dominant mode, and have a loss less than 1 dB/m.     

Amplitude and phase scintillation measurements on 8.2 km line-of-sight path at 30 GHz

The letter summarises results of amplitude and phase scintillation measurements at 30 GHz on an 8.2 km line-of-sight path in the Netherlands. The measured results compare favourably with those obtained from weak-scattering theory.     

Depolarization at 11.6 GHz on a terrestrial radio link

This paper presents some early data from an 11.6 GHz, 18 km terrestrial radio link operating in circular, linear horizontal and vertical polarizations. Rain, snow and clear weather effects are presented and analysed together with cumulative statistics over a fourteen month period. Observations indicate that rain depolarization is most severe on the circularly polarized transmission followed in order of magnitude by horizontal and vertical polarizations. Linear polarizations usage on a practical microwave link appears to be limited primarily by clear weathereffects. A good agreement with theoretical models for rainfall is obtained on circular and linear polarizations. During snow the variability of effects precludes a definitive classification of this type of precipitation, however, circular polarization exhibits a marked sensitivity to depolarization, generally less than that for the same rain attenuation level. The attenuation experienced during snow can be markedly different from event to event.     

Probability distribution of amplitude scintillations on a line-of-sight link at 36 GHz and 55 GHz

The probability distributions of the amplitude scintillations on 36 GHz and 55 GHz millimetre wave links along a 4.1 km path across central London have been obtained. These show that the log-normal distribution applies for the case of 36 GHz, but for 55 GHz, on the side of the oxygen absorption peak, the distribution departs significantly from log-normal.     

A comparative study of scintillation analysis over two line-of-sight paths at 6.7 GHz and 7.6 GHz

A comparison of the signal intensity fluctuations or scintillation of signal level, observed over two line-of-sight links is presented. These links are situated over Calcutta, DumDum-Andul (6.7 GHz) and Delhi, Delhi-Sonepat (7.6 GHz). The study reveals departures, in the occurrence and variation of the scintillation over the Calcutta path as compared with the path over Delhi. This deviation has been attributed to the large variation in humidity which exists in the coastal region, and also which plays a major role in microwave propagation in the troposphere.     

The effect of the outer scale of turbulence and wavelength on scintillation fading at millimeter wavelengths

Amplitude scintillation measurements made on two-millimeter microwave links at 36 GHz and 110 GHz along a common 4.1 km path across central London are deseribed. The variances of the logarithmic amplitude scintilliations at these two frequencies are compared for different ranges of the outer scale of turbulence. A comparison is made between the experimental results and the theoretical predictions of Tatarski. Good agreement has been found for the two cases when the outer scale of turbulence is greater than and smaller than the Fresnel zone size.     

Orotron with a two-row periodic structure at a wavelength of 1.3 mm with a wide electron beam

A discrete nonlinear theory is used to optimize the efficiency and output power of orotron at a wavelength of 1.3 mm. The device works at the first spatial harmonic of the two-row periodic structure (TRPS) with an increase in the width of electron beam. The dependence of the optimal length of TRPS at which the maximum efficiency is reached for a plane electron beam with a width of three radii of caustic on the plane mirror of the open resonator on the ohmic loss in the TRPS is obtained.     

Sunrise and sunset effects as observed on microwave propagation over a line-of-sight path

Microwave signal propagation provides an effective measure of studying the variable nature of the atmosphere. Sunrise and sunset periods are characterized by the dissolution and formation of nighttime temperature inversions. Signal amplitude recordings at 6.7 GHz over DumDum-Andul line-of-sight (LOS) communication link during post-sunrise period are characterized by the appearance of an enhancement in signal strength (as high as 20 dB). The sunset effect or the evening transition is observed as an enhancement in signal amplitude of about 10- 12 dB over the link. The signal characteristics observed during transition periods over the 6.7 GHz DumDum-Andul link are studied herein.     

Performance of a cryogenic 3 mm Schottky-mixer receiver on the Mets?hovi 14 m radio telescope

A cooled receiver with some novel features and a noise temperature of 80?140 K double sideband in the frequency range 75?95 GHz has been built for radio astronomical observations. The quasioptical beam switch is followed by a 3 mm Schottky mixer and FET amplifier at 1.4 GHz. For calibration the receiver is provided with a cold reference load within the Dewar.     

Large anomalous dispersion at short wavelength and modal properties of a photonic crystal fiber with large air holes

We investigated the dispersion and modal properties of a photonic crystal fiber (PCF) with larger air holes (LAH). The theoretical and numerical results show that large anomalous group-velocity dispersion at short wavelength down to around 700 /spl sim/ 800 nm can be achieved in a LAH-PCF with small pitch. Furthermore, the high-order modes usually are excited in a LAH-PCF when the optical field is launched from a traditional single-mode fiber, and all the excited modes will interfere when they propagate along the PCF. Finally, the properties of the excited modal spectrum and the multimode interference are determined by the normalized pitch and the normalized hole size of the PCF. All of these will provide references for the smoothing applications of the LAH-PCF.     

Study of backscattering from a complex scatterer at 3mm wave band

The backscattering characteristics of complex scatterer has been studied theoretically at 3 mm wavelength for the first time. RCS of the practial complex scatterer was calculated with GTD and the physical optics. The constrict model was also measured. The experimental results are in agreement with the theoretical calculations.     

Simulation of the effects of atmospheric scintillation on digital transmissions at centimeter and millimeter wavelengths

This paper describes the simulation of the effects of scintillation on digital transmissions. The scintillation is modelled by atmospheric turbulent cells whose parameters are determined by comparison with measured scintillation events. The effects of the cells crossing the communication link on the amplitude of the received signal are calculated as well as the transfer function. A complete communication link is simulated and the BER is calculated for different frequencies. The model can be used up to 100 GHz but this paper is focused on frequencies presently used in satellite communications.     

All-optical wavelength conversion of short pulses and NRZ signalsbased on a nonlinear optical loop mirror

Wavelength conversion of short pulses at 10 GHz based on a nonlinear optical loop mirror (NOLM) is experimentally and numerically investigated for the case of small group velocity dispersion and walkoff between the control pulses and continuous lightwaves. Experimental and numerical simulation results show that the pulsewidths of the converted signals at different wavelengths are almost the same, and the pulsewidths are compressed when the peak power of the control pulse is smaller than a certain value. An RZ optical source containing eight wavelengths having a high sidemode suppression ratio, equal amplitudes and almost the same pulsewidths is obtained by using wavelength conversion in a NOLM consisting of a common dispersion shifted fiber. 10 Gb/s NRZ wavelength conversion based on the NOLM is demonstrated for the first time and certain conclusions in some of the references are confirmed by our experimental results     

Optimization of orotron with two-row periodic structure at a wavelength of 1.3 mm in the framework of an approximate analytical theory

An approximate analytical theory is employed to optimize the parameters of an orotron with a two-row periodic structure (TRPS) and a semispherical open resonator at a wavelength of 1.3 mm. The TRPS period and length are chosen using the experimental verification of the optimization results. The optimization is performed for TRPS periods of 0.29 and 0.25 mm and mismatch parameter of b = 0.05. Under certain conditions, the output power of the orotron with TRPS at a wavelength of 1.3 mm may amount to tens of watts.     

Goodput and delay analysis of a radio link control protocol operating over a multicarrier DS-CDMA architecture

This work proposes an analytical model to investigate the behavior of a radio link control (RLC) protocol on the forward link of a mobile radio system and to relate its performance to transmission design. As a reference case, a multicarrier DS-CDMA architecture employing Walsh and quasi-orthogonal channelization codes, similar to the current cdma2000 system, is considered. Jointly modelling the features of the data link layer and of the underlying physical channels, it is possible to identify the interaction between transmission parameters and the RLC protocol behavior. The latter is assessed by analysis, determining the RLC protocol goodput and the average delivery time suffered by a data unit transferred over the radio channel, when two different coding approaches are adopted: namely, rate compatible punctured convolutional codes and code combining.     

Auroral and polar-cap ionospheric effects on radio propagation

Disturbances in the auroral and polar-cap ionosphere can have profound effects on radio signals traversing the high-latitude ionosphere (defined here as that latitudinal region poleward of approximately 55° corrected geomagnetic latitude). Some effects of the high-latitude ionosphere on polar radio paths were documented as early as the 1930s, but intensive investigations of this ionospheric global region started during the International Geophysical Year (IGY) 1957-1959. Starting in the mid-1960s it was realized that high-latitude ionospheric anomalies could affect radio signals from ELF through VHF on terrestrial and earth-space paths, especially during sunspot maximum, disturbed periods. A considerable effort has been made in the last two decades to model and predict the salient parameters of the auroral and polar-cap ionosphere. A somewhat lesser effort has been devoted to develop HF propagation programs which included high-latitude ionospheric effects. Salient past results are briefly reviewed, and developments in this field for the period 1970-91 are presented     

Ionospheric effects on radio communication and ranging pulses

Transionospheric radio pulses used for communication and ranging purposes are modified by propagation effects arising from dispersion and scattering. To describe these effects quantitatively it is convenient to use the concept of temporal moments. The zeroth temporal moment is proportional to energy flow in the wave and is constant in a dissipationless ionosphere under the forward scatter approximation. The first temporal moment is related to the mean arrival time which can be arranged as a series consisting of terms proportional tof_{c}^{-2n}, n = 0, 1, 2, ..., wheref_{c}is the carrier frequency. Here then = 0term in this series representation of the first temporal moment is just the free-space transit time which can be related simply to the geometric distance, a quantity required with great precision in ranging applications. Then = 1term, which is proportional to the electron content, has been investigated by various investigators in connection with navigational satellite applications. Then = 2term in the expansion of the first temporal moment given in this paper comes about through dispersion, finite bandwidth effect, and scattering from random irregularities; the numerical values of each of these terms are computed for a Chapman layer. The second temporal moment is related to the mean square pulsewidth. It is shown that an amplitude modulated pulse at a carrier frequency of 100 MHz may be stretched up to several hundred fold in width by dispersion and scattering, but such an effect diminishes rapidly in importance as the carrier frequency is raised. These results provide useful information to designers of satellite-based communication and ranging systems.