<..It turns out that 38 GHz is right in a transmission window between an H20 absorption band at ~23 GHz and an oxygen absorption band at 60 GHz. The one at 24 GHz isn't too bad, maybe 0.2 dB/km attenuation, but the 60 GHz is horrid, with around 10 dB/km atten.>
Thanks for the details, David.
In NMR/MRI, one can "suppress" the infiltration of certain bands (like H2O) to bump up the SNR. Any work being done on this in radiowaves?
I just did a brief review of the literature on 38Ghz, and partly answered my above question. I'm going to post some of the abstracts here for collective comment, but if you (or anyone familiar with the field are interested) email me (take out the "_pam_" from my eddress) for more complete references.
[Note: Some of these abstracts date to 1993. And some MAY refer to 38Ghz OPTICAL systems]
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Abstract: High-performance tunable low-noise amplifiers for 38-42.5 GHz applications are presented based on a fully stabilized GaAs pseudomorphic high electron mobility transistor (PHEMT) 0.2 mu m technology. A single 1.5*3 mm/sup 2/ chip, incorporating six amplifying stages, shows a measured gain of 36-42 dB depending on the center frequency. Both maximum gain frequency and input impedance of the amplifier are accurately tunable on the chip. This means that the amplifier provides a narrow-band filtering function and can be matched to a fast p-i-n photodiode as well as to a 50 Omega load. This is the first time such performances are reported for single chip narrow-band tunable amplifiers using a GaAs PHEMT technology.
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Abstract: Factors affecting rain-induced depolarisation at 38 GHz have been investigated. The effect of raindrop canting on the crosspolar signal levels has been examined together with other, more minor, factors such as water temperature and drop shape model. The intervening medium between the two terminals is assumed to have constant rainfall rate and the crosspolar effects are evaluated for various link separations and for various rain intensities. Additionally, data obtained from the Chilbolton radar are used
and the depolarisation effects due to typical precipitation events are
assessed. Results indicate that, for a standard 38 GHz PCN (personal
communication network) system, the use of linear, orthogonal polarisations is not likely to present operational problems. Compared with the copolar fading of the wanted signal and the depolarisation introduced by antennas typically used by the operators, the effects of rain-induced crosspolarisation are shown to be almost negligible.
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Abstract: The last few years have seen a rapid growth in the use of the 38 GHz frequency band for fixed service. It was made available for commercial PCN (personal communications network) operators to be used for linking base stations. The links are fairly short, with separations ranging from 5 and 15 km. At the moment, all links use only vertical polarisation; however, the increase in demand for this spectrum could be provided by polarisation diversity so as to maximise spectrum utilisation. In order to examine the feasibility of using two linear, orthogonal polarisations at 38 GHz, the Rutherford Appleton Laboratory has installed a 9 km link operating at 38 GHz in southern UK. The primary intention of the campaign is to make a comprehensive set of co- and cross-polar measurements, under various conditions, using a typical system used by the PCN operators, and to make
recommendations on cross-polar isolation that may be required for the use of orthogonal polarisations. The link has been operating continuously for a year and we report examples of measurements taken during a variety of precipitation conditions, including drizzle, moderate to intense rain, sleet and snow. We also present the statistics of 1-year data and compare it with predictions from the relevant ITU-R recommendations.
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Abstract: New microwave or millimetre communication systems are designed to use dual-polarisation channels in order to increase the communication capacity without increasing the bandwidth. Even at 38 GHz, which is increasingly being brought into use, since its allocation for the interconnections of PCN base stations, the potential use of both horizontal and vertical polarisations has attracted much attention. A study of rain-induced depolarisation at 38 GHz is presented, including the effects of various rainfall rates, raindrop shape models, and water temperatures. The intervening medium between the two terminals is assumed to have constant rainfall rate and the cross-polar effects are evaluated for various link separations and for various rain intensities. Additionally, data obtained from the Chilbolton radar are used and the depolarisation effects due to
typical precipitation events are assessed.
(specific finding not available from ABS)
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Abstract: A high performance 38 GHz monolithic pseudomorphic high electron mobility transistor (PHEMT) power amplifier has been developed for commercial millimeter-wave radio systems. This highly integrated MMIC chip has three power PHEMT stages and achieved 25 dBm 1-dB compressed output power with 19 dB power gain using 6 V drain-source bias. The MMIC process utilized an optimized power PHEMT structure and has demonstrated high yield with excellent reproducibility making it suitable for high volume commercial applications.
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Abstract: A prototype down-converting mixer MMIC based on planar Schottky diodes and a production version based on HEMT diodes are reported. Measurements with a 1-2 GHz IF indicate conversion losses of 8-11 and 10-14 dB, respectively, and image rejections >20 dB. A HEMT-based mixer-amplifier MMIC with conversion gain of 3-8 dB and image rejection >18 dB is also reported. Simulations agree well with these measurements. Image rejection is produced by an on-chip IF coupler. This is the first report, to the authors' knowledge, of fully monolithic, image-reject downconverters of this type.
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Abstract: A short distance radio link working in the new 38 GHz frequency range is described. The 38 GHz link serves high speed data transmission in an Ethernet LAN of the dispatching centre at an Electrical Power Utility located in Karlsruhe, Federal Republic of Germany. It connects the computers of the dispatching centre to remote workstations placed in the headquarter building at a distance of 7 km. The 38 GHz radio link operates simultaneously with an optical fibre cable connection and thus provides redundancy Over a period of several years extensive tests were carried out. The bit error rate and the receiving level of the radio link were measured. The results achieved by using the 38 GHz technology are presented and discussed. It is confirmed that 38 GHz radio links for high speed data communications equal a transmission via cable up to a distance of 2.5 km maximum and that 38 GHz radio links are usefully applicable up to a distance of 10 km.
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Abstract: The utilization of frequency bands above 20 GHz for short distance digital radio links requires relatively small antennas (diameter less than one meter) adapted to the particular frequency band. Due to the competitive market situation the antennas have to be very cheap in series production. Furthermore, the antennas have to meet the system relevant stringent electrical requirements concerning reflection coefficients and the radiation pattern envelopes. In 1992, the ETSI published parameters of radio relay systems operating at 23, 26 and 38 GHz bands, among them antenna radiation pattern envelopes. According to local interference requirements antennas with moderate or very stringent sidelobe suppression may be necessary. Based on these requirements, an antenna family has been developed, which allows an easy adaption to different frequency bands and sidelobe requirements using low-cost components and technologies.
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Abstract: Work carried out in the development of commercial radio links at millimeter (MM) wave frequencies is presented. System aspects are discussed, and results are presented for the MM-wave components which have been developed. A modular common system approach has been used, thus enabling the economical reuse of most of the lower-frequency system functions. The modulation options which have been considered and their effect on the MM-wave components are discussed. From this analysis a low-cost system approach is presented based on the use of MMICs (monolithic microwave integrated circuits) and broadband RF components. Offset 4 QAM (quadrature amplitude modulation) was used in order to provide a good compromise between amplifier linearity and spectral efficiency. This system design has been implemented at 38 GHz, and various system results are presented.
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