. Le journal technique de Bell System . gt;- comme la loi du carré inverse.puisque le pouvoir reçu implique le produit de ces deux facteurs, la relaa-tion devient : P, = x|;, ou, R-{K^y (1) où Pi et Pr représentent, respectivement, La puissance transmise et reçue, R la portée et K une constante déterminée par la conception de l'antenne, le caractère de la cible, etc. Dans des conditions de fonctionnement, un écart considérable de l'ahovQ relaa-tionship m.ay être éprouvé, en raison de facteurs tels que (1) la courbure de la terre, (2) interférence entre le faisceau direct et les re-sections simples ou multiples, et (3) atténuation due
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. The Bell System technical journal . gt;- as the inverse square law.Since the received power involves the product of these two factors, the rela-tion becomes: P, = x|;, or, R-{K^y (1) where Pi and Pr represent, respectively, the transmitted and received power, R the range and K a constant determined by antenna design, character oftarget, etc. Under operating conditions considerable departure from the ahovQ rela-tionship m.ay be experienced, due to such factors as (1) the curvature of theearth, (2) interference between the direct beam and single or multiple re-flections, and (3) attenuation due to atmospheric absorption. Except under 442 BELL SYSTEM TECHNICAL JOURNAL conditions of severe attenuation such as may occur at the very short wave-lengths, the received power commonly varies somewhere between the inversefourth power and the inverse 16th power of distance. To state it anotherway, the change in effective range is somewhere between the fourth andthe sixteenth root of the change in system performance. The former condi-. 10 IS 20 25 30 LOSS IN SYSTEM PERFORMANCE db Fig. 4—Effect of reduction in system performance on radar range. tion might hold for high angle plane-to-ship search in clear weather, thelatter for ship-to-ship search in fog. The loss of range resulting from a givendegradation of system performance is shown for 4th, 8th and 16th root lawsby the curves of Fig. 4. Whatever the propagation law, reduction in per-formance always means loss of range. Field sur^eys have shown that when test equipment is not available ornot used, radars in the field are likely to give no more than ^ to j of themaximum range of which they are capable. Hence it is necessary to know MICROWAVE RADAR TESTING 443 with good accuracy the over-all performance. Known, or so-called stand-ard, targets have often been used in the field for checking performance.Because of wide variations in transmission due to many factors, resultsobtained from such targets are frequently misleading. Si
