respectively, may suffer from sidelobe contamination. We note, however, that these cells account for less than 20% of the population of greater than 400 range-azimuth cells measured in this experiment. They are included in the reported database to accurately represent the median NRCS (50% level); their impact on the mean NRCS estimate is expected to be less than IdB. Summary: Large bistatic angle vertically polarised NRCS (propagation factors included) exceeds horizontally polarised NRCS by -6dB for rolling forested hills at low grazing angles, with average values of -36 and 4 2 d B , respectively. Defoliation of the deciduous portion of the canopy does not significantly change the NRCS. Additional measurements are needed to verify these results and investigate any possible dependence of NRCS on cell size and bistatic scattering angle. These measurement results should be of interest to system designers requiring estimates of bistatic clutter levels. tion bands will naturally provide a limited operational range. Our propagation studies were carried out as the prelude to the design of a 6OGHz secure digital microcellular communication system in rural environments. The measurements were conducted to determine the effect of natural obstacles obstructing the line of sight (LOS) path. Several configurations were tested with a wideband sounder using a network analyser to measure the channel transfer function. Channel model: In the studied radio propagation environment, the signals are received via a scattering mechanism. Therefore, multiple propagation paths occur (multipath) with different time delays, attenuations and phases. This channel is classically modelled as a complex time-varying linear filter associated with the following complex impulse response [I]: T(t) h(t. .A(t, rt)cxp(ja(t,T,))J(t- ~ ~ ( t )(1) ) = t=O Acknowledgment: This work was supported by the US Air Force Rome Laboratory, Hanscom AFB, MA, under contract number F19628-91-k-0047. The authors are grateful to M. Sowa for his support and R. Chanley for his assistance in performing these experiments. where N ( t ) is the number of multipath components received, and A(t,.r,), @(t,.rj) and .r,(r) are, respectively, the magnitude, phase, and delay associated with the multipath component i. 22 July 1YY4 0 IEE 1994 Electronics Lerrers Online No: 19941024 D.J. McLaughlin, E. Boltniew, Y . Wu and R.S. Raghavan (ECE Department, Northeastern University. Boston. M A 02115, USA) References BOREL. C.C., MCINTOSH. R E., NARAYANAN, R.M., and SWIFT, C T : ‘File of normalized radar cross sections (FINRACS) - A computer program for research and the scattering of radar signals of natural surfaces’, IEEE Trans., 1986, GE-24, (6), pp. 1020-1022 HANLE. w., FARINA. A., and PELL, c.: ‘Bistaticimultistatic radar bibliography’, IEE Proc. F, 1986, 133, (7), pp. 666668 WILLIS, H.J.: ‘Bistatic radar’ (Atrech House, Nonvood, MA, 1991) HSU. Y.s., and LORTI, D.c.: ‘Spaceborne bistatic radar - An overview’, IEE Proc. F, 1986, 133, (7), pp. 6 4 2 4 8 SOWA, M.J., and MCLAUGHLIN. D.J : ‘A bistatic radar test bed for signal-to-clutter enhancement studies’. Proc. 1993 Bistatic Radar Workshop, Griffiths AFB, Rome, NY, 1993 JACKSON, M.c.: ‘The geometry of bistatic radar systems’, IEE Proc. F, 1986, 133, (7), pp. 604412 MOYER, L.R.,MORGAN. c J . , and RUGGER, D.A.:‘An exact expression for resolution cell area in special case of bistatic radar systems’, IEEE Trans., 1989, AES-25, (4), pp. 58&587 ULABY. PT., MOORE. R.K. and FuNG.A.K.:‘Microwave remote sensing, active and passive, Volume 11’ (Addison-Wesley Publishing Co., Reading. MA, 1982) MEEKS, M.L.: ‘Radar propagation at low altitudes’ (Artech House, Dedham, MA, 1982) Outdoor millimetre-wave propagation measurements with line of sight obstructed by natural elements N. Daniele, D. Chagnot and C. Fort 1 Fig. 1 60GHz channel sounding syAtem Channel measurement technique: The measurement system (Fig. 1) is built up around an HP 8753B vector network analyser (VNA) which performs the frequency domain measurements of the channel transfer function (&, determination) between 59 and 61 GHz. The impulse response can be calculated via the inverse Fourier transform of the frequency data [2]. At port 1 of the VNA the frequency is swept between 2 and 4GHz and is kept as the reference for further calculations. A 200111 flexible coaxial cable allows mobility of the autonomous upconverter module. This module converts the 2 4 G H z I F signal to the 59-61GHz sounding frequency which is radiated through a biconical antenna positioned 0.5m above the ground. At the receiver the down-converter is identical to the up-converter; the 2 4 G H z I F signal is amplified and fed into the return signal port 2 of the VNA which displays the channel transfer function. Both LO frequencies are derived from a unique IOOMHz temperature compensated crystal oscillator (stability 5 x 10 *). A phaselocked oscillator is used to generate a I9GHz signal, which is tripled to give the 57GHz LO signal. A personal computer equipped with a GPIB card controls the acquisitions, and computes the correction for the line of sight path loss (free space loss) and for the antenna gains; finally it calculates statistical values from the data. Indexing terms: Radiowuve propago tion, Multiparh The authors present widehand measurements of outdoor radio channels operating within a 2GHz frequency band around a 60GHz carrier. Statistical analyses such as the RMS delay spread and cumulative distribution function (CDF) of the received signal envelope are presented. Investigations into the multipath effect and data rate limitation are discussed. Description of environments and experiments: Our measurements where carried out at two different sites: The first one is a large area with a water canal, rows of trees, some bushes and tall grass. U b The second one is a large area with different kinds of ground Introduction: Radio transmissions such as wireless communications, remote control, surveillance and local cellular radio networks require limited operational range. The use of a millimetre wave frequency which lies within one of the atmospheric absorp- ELECTRONICS LETTERS 1st September 1994 (grass, land, pebbles) and various topographies (hillocks, pits, trenches). For these two sites 25 channel transfer functions were measured. In each case the transmitter was placed on both sides of a Vol. 30 No. 18 1533 -. particular medium, the antenna being fixed 0.5m above the ground. The line of sight was always obstructed by the environment. The separation of the transmit and receive antennas lay between 2 and 150 m. For each measurement three graphs were recorded: C D F and the type of RMS delay spread that characterises this particular environment. The results show that propagation in this environment is possible in spite of scattering and diffraction by natural elements. Moreover, to avoid the undesirable effect of fading (which increases the bit error rate) a diversity technique can be used. These initial measurements show that a local cellular network can be established in this particular medium. * + + + + + + + + + f + t ~ + l + t t . t t + + f + ~. * + + + + t + t ~ . + + + + + + 0 + a t I * + ~ . + + + l + + + t + t f + t t + * t + * + f + t t t f + + * + t + + + * * * * * + * * + + + + * * + * + * . + + + + * + + + + .>&-d. * * + + 1. , 3 ti&,ns Fig. 4 R M S delay spreud Fig. 2 Module of a typiral impulse response (i) the medium tested channel transfer function between 59 and 61GHz. Acknowdedgment: This work has been supported by DRET from Direction Generale de I’Armement. The authors would also like to thank GlAT Industries for their contribution in the experiments scenarios. (ii) the impulse response after inverse Fourier transform of (i) (Fig. 2); two important parameters are calculated and displayed on this graph: TOA (time of arrival) and spread (RMS delay spread). 0 IEE 1994 26 July I994 Electronics Letters Online No: I9941047 N. Daniele, D. Chagnot, and C. Fort (LETI (CEA-Technologies Avancies) CEN.G. 17, rue des Martyrs-F38054 Grenoble Cedex 9, France) (iii) the C D F of the received signal envelope (Fig. 3); the straight line on the graph represents the well known Rayleigh distribution to be compared with the C D F of the different channels recorded. References -50 -40 -30 -20 -10 0 amplitude .dB IO 20 30 LO Fig. 3 CDF example Results: Scattering and diffraction were the main propagation phenomena giving rise to multipath in these environments. For the tested medium, reflection phenomena rarely occurred except in the case of metallic elements near the link. In the tested environment the vegetation loss difference is independent of the polarisation (vertical or horizontal). Other results [3] confirm this phenomenon. Sfatistical results: For 83% of the recorded channel transfer functions the cumulative distribution function of the amplitude components fits the log normal-Rayleigh distribution. This type of distribution is thus a good representation of the effect o f scattering generated by vegetation elements in obstructed sight (OBS) conditions. For 87% of the recorded cases the fades observed on the received signal envelope are less than 20dB. Fig. 4 shows the cumulative distribution of the RMS delay spread for all the performed measurements. For 88% of cases the RMS delay spread is less than 100ns. Discussion/conclusion: Propagation measurements were performed in a rural environment with natural elements obstructing the LOS. The purpose of these experiments was to investigate the type of 1534 DAVIES, R., BENSEBTI. M., BEACH. M.A., and MCGEEHAN, J.P.: ‘Wireless propagation measurements in indoor multipath environments at I.7GHz and 60GHz for small cell systems’. 41st IEEE Vehicular Technol. Conf., Gateway to the future, Technology in Motion, 1922 May 1991, (St. Louis, MO, USA), pp. 589-593 2 HOWARD, J.S., and PAHLAVAN, K.: ‘Autoregressive modelling of wideband indoor radio propagation’, IEEE Trans., 1992, COM-40, (9), pp. 1540-1552 3 VIOLETTE, E.I., ESPELAND, R.H., and MITZ, A.R.: ‘SHF-EHF propagation through vegetation on Colorado East slope’. Tech. Report CECOM-81-CS020-F,June 1981 1 Demonstration of direct bonding between InP and gadolinium gallium garnet (Gd3Ga5OI2)substrates M. Totoki, T. Mizumoto, K. Maru and Y. Naito Indesing terms: Indium phosphide. Garnets The authors demonstrate the direct bonding of InP/Gd,Ga,O,, (GGG) and InPGaInSb on GGG without glue. After chemical treatment, heat treatment was applied in an H, atmosphere without a weight. This technique makes feasible the integration of semiconductor and magneto-optic devices. Introduction: To realise photonic integrated circuits, a technology that is able to integrate different materials needs to be developed. Although individual photonic devices may have satisfactory performance characteristics, the integrating technology faces many problems when the physical properties of the constituent materials are very different, especially in case of materials with highly mismatched lattice constants. Most photonic devices, including active and passive components, such as optical switches and optical multi/demultiplexers, can he fabricated by using 111-V compound ELECTRONICS LETTERS __- 1st September 7994 Vol. 30 No. 18 - -
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