The performance with respect to rain outage time of dual path diversity and non‐path diversity (tandem) arrangements for 18‐GHz short hop radio systems is computed and compared. The analysis is based on two extrapolations of R. A. Semplak's1 three‐year average of the measured probability distributions for rain attenuation at 18.5 GHz on a 6.4‐km hop in New Jersey. The effects of merge hops and joint fading between hops in the diversity system, dependence of the rain attenuation distribution on hop length, and uncertainty in the tail of the distribution are included. The results show that (i) the performance of tandem systems relative to diversity systems increases as the system length increases, (ii) the difference in the number of repeaters per unit length required for short and long tandem systems is small, (iii) the performance of the diversity system is strongly dependent on the amount of joint fading between parallel paths, and (iv) the performance of the tandem system is strongly dependent on the tail of the attenuation distribution. Neither of the latter two factors is known from rain attenuation measurements, but if the joint attenuation probabilities are sufficiently high, then diversity shows no advantage over tandem for either of the assumed extrapolations. The uncertainty in the tail of the attenuation distribution and the sensitivity of the tandem system performance to it emphasize the need for reliable attenuation measurements out to a probability of about 10−7.
This paper describes the procedures adopted at Bell Laboratories for using rain attenuation data to engineer 11‐GHz microwave radio hops and routes. Rain outage time charts, which show the rain outage time as a function of rain attenuation and hop length, are the basic tools in engineering the hops. The charts, their formulation, and the procedures for using the charts are described and illustrated with several examples. The procedures are used to demonstrate and quantify the sensitivity of allowable hop lengths to the available rain attenuation margin, the effects of a limited rain attenuation margin, and the effects of the variation in the outage in a single year from the 20‐year average outage. Guidelines for judging if a hop or route is performing as engineered are developed.
This paper reports a two‐hop system experiment, designed to demonstrate the viability of the concept described in previous papers. A single RF channel, instrumented in the 11 GHz common carrier band, is transmitted from a terminal to a repeater one and a half miles away. After passing through the repeater, the signal is transmitted back to the terminal. We discuss the system parameters in relation to the requirements of operation at frequencies above 10 GHz; we also describe design, construction, and performance, as well as the lessons learned from one year of operation.
This paper describes a design procedure for optimizing the performance of a varactor upconverter microwave power amplifier with respect to maximum pump efficiency, the procedure gives explicit diode and circuit parameters and operating levels. An optimum diode is selected by inclusion of an empirical relation between diode breakdown voltage and cutoff frequency. A fully driven abrupt junction diode is assumed. The bandwidth of an upconverter is limited by the intermediate frequency input circuit which typically has a 3 dB bandwidth of about 10 percent. We describe a method of obtaining broadband operation where the interface between the intermediate frequency source and the varactor diode is mismatched in an optimum way. Analysis shows that the frequency variation in mismatch loss just compensates for the frequency variation in upconverter gain predicted by the Rowe—Manley relations. The design procedure is illustrated by a 300 MHz to 10.960 GHz varactor upconverter built for use in the transmitter of the short hop radio system experiment. A bandwidth of 120 MHz between 1.4 dB points represents a bandwidth of more than 40 percent at the intermediate frequency. An output power of +16 dBm was obtained using a pump power of +20 dBm giving a pump efficiency of 40 percent. The normal input to the driver amplifier is +3 dBm giving an overall gain of +13 dB. The upconverter operates over a temperature range of −40°F to +140°F with only a small change in bandshape and output power.
Significant improvements in noise figure and band-icidth
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