Measurement 1 - Ranges

Reference: http://www.radartutorial.eu/01.basics/Distance-determination.en.html


Distance/Range

Range is the distance from the radar site to the target measured along the line of sight.

Direction-determination

The angular determination of the target is determined by the directivity of the antenna. Directivity, sometimes known as the directive gain, is the ability of the antenna to concentrate the transmitted energy in a particular direction. An antenna with high directivity is also called a directive antenna. By measuring the direction in which the antenna is pointing when the echo is received, both the azimuth and elevation angles from the radar to the object or target can be determined. The accuracy of angular measurement is determined by the directivity, which is a function of the size of the antenna.


 In actual practice, search radar antennas move continuously; the point of maximum echo, determined by the detection circuitry or visually by the operator, is when the beam points direct at the target. Weapons-control and guidance radar systems are positioned to the point of maximum signal return and maintained at that position either manually or by automatic tracking circuits.


Maximum Unambiguous Range

- Definition: The maximum unambiguous range (Rmax)is the longest range to which a transmitted pulse can travel out to and back again between consecutive transmitted pulses.

 Rmax is the maximum distance radar energy can travel round trip between pulses and still produce reliable information.

The relationship between the PRF or their reciprocal value interpulse period T (PRT) and Rmax determines the unambiguous range of the radar. Suppose the radar emits a pulse that strikes a target and returns to the radar in round trip time t:

    If t < T then the return signal arrives before the next pulse has been emitted.

    If t = T then the return signal arrives exactly when the next pulse has been emitted.

    If t > T then the return signal arrives after the next pulse has been emitted and there is an ambiguity, ie the radar

The reflection of a target of the first pulse is received after the second pulse has been transmitted. This causes some confusion since the radar, without any additional information, cannot determine whether the received signal is a reflection of the first pulse or of the second pulse. This leads to an ambiguity in determining the range, this received echo signal be mistaken as a short-range echo of the next cycle.

The pulse repetition time (PRT) of the radar is important when determining the maximum range because target return-times that exceed the PRT of the radar system appear at incorrect locations (ranges) on the radar screen. Returns that appear at these incorrect ranges are referred to as ambiguous returns, second-sweep echoes or second time around echoes.

Exemptions

More modern 3D- radar sets with a phased array antenna (like the RRP-117) don't have this problem with an ambiguous range. The system computer steers the transmitted beams so that ambiguous returns from the previous pulses are not received while the antenna beam points in another direction.

If the radar uses intrapulse modulation and uses a different waveform in each transmit pulse, the maximum unambiguous measuring distance is of no significance for the radar. Each received echo signal can be assigned to exactly its origin (the individually transmitted pulse) and thus the runtime over several pulse periods can be measured.

Radar sets in satellites for the remote sensing of the earth can, however, also represent targets at the correct distance, if they are actually ambiguous. The general height of the orbit is known, so only a distance can be measured that differs by a few kilometers from the height of the orbit. Compared to Fig. 1, this means that at an altitude of 400 km only the measurement result received in the second pulse period can be valid.


Minimal Measuring Range


Monostatic pulse radar sets use the same antenna for transmitting and receiving. During the transmitting time, the radar cannot receive: the radar receiver is switched off using an electronic switch, called duplexer. The minimal measuring range Rmin (“blind range”) is the minimum distance which the target must have to be detected. Therein, it is necessary that the transmitting pulse leaves the antenna completely and the radar unit must switch on the receiver. The transmitting time τ and the recovery time recovery should are as short as possible if targets shall be detected in the local area.

Minimal Measuring Range

Targets at a range equivalent to the pulse width from the radar are not detected. A typical value of 1 µs pulse width of a short-range radar corresponds to a minimum range of about 150 m, which is generally acceptable. However, radars with longer waveforms suffer a relatively large minimum range, notably pulse compression radars, which can use pulse lengths of the order of tens or even hundreds of microseconds. Targets at ranges closer than this minimum are said to be eclipsed.

©著作权归作者所有,转载或内容合作请联系作者
  • 序言:七十年代末,一起剥皮案震惊了整个滨河市,随后出现的几起案子,更是在滨河造成了极大的恐慌,老刑警刘岩,带你破解...
    沈念sama阅读 203,324评论 5 476
  • 序言:滨河连续发生了三起死亡事件,死亡现场离奇诡异,居然都是意外死亡,警方通过查阅死者的电脑和手机,发现死者居然都...
    沈念sama阅读 85,303评论 2 381
  • 文/潘晓璐 我一进店门,熙熙楼的掌柜王于贵愁眉苦脸地迎上来,“玉大人,你说我怎么就摊上这事。” “怎么了?”我有些...
    开封第一讲书人阅读 150,192评论 0 337
  • 文/不坏的土叔 我叫张陵,是天一观的道长。 经常有香客问我,道长,这世上最难降的妖魔是什么? 我笑而不...
    开封第一讲书人阅读 54,555评论 1 273
  • 正文 为了忘掉前任,我火速办了婚礼,结果婚礼上,老公的妹妹穿的比我还像新娘。我一直安慰自己,他们只是感情好,可当我...
    茶点故事阅读 63,569评论 5 365
  • 文/花漫 我一把揭开白布。 她就那样静静地躺着,像睡着了一般。 火红的嫁衣衬着肌肤如雪。 梳的纹丝不乱的头发上,一...
    开封第一讲书人阅读 48,566评论 1 281
  • 那天,我揣着相机与录音,去河边找鬼。 笑死,一个胖子当着我的面吹牛,可吹牛的内容都是我干的。 我是一名探鬼主播,决...
    沈念sama阅读 37,927评论 3 395
  • 文/苍兰香墨 我猛地睁开眼,长吁一口气:“原来是场噩梦啊……” “哼!你这毒妇竟也来了?” 一声冷哼从身侧响起,我...
    开封第一讲书人阅读 36,583评论 0 257
  • 序言:老挝万荣一对情侣失踪,失踪者是张志新(化名)和其女友刘颖,没想到半个月后,有当地人在树林里发现了一具尸体,经...
    沈念sama阅读 40,827评论 1 297
  • 正文 独居荒郊野岭守林人离奇死亡,尸身上长有42处带血的脓包…… 初始之章·张勋 以下内容为张勋视角 年9月15日...
    茶点故事阅读 35,590评论 2 320
  • 正文 我和宋清朗相恋三年,在试婚纱的时候发现自己被绿了。 大学时的朋友给我发了我未婚夫和他白月光在一起吃饭的照片。...
    茶点故事阅读 37,669评论 1 329
  • 序言:一个原本活蹦乱跳的男人离奇死亡,死状恐怖,灵堂内的尸体忽然破棺而出,到底是诈尸还是另有隐情,我是刑警宁泽,带...
    沈念sama阅读 33,365评论 4 318
  • 正文 年R本政府宣布,位于F岛的核电站,受9级特大地震影响,放射性物质发生泄漏。R本人自食恶果不足惜,却给世界环境...
    茶点故事阅读 38,941评论 3 307
  • 文/蒙蒙 一、第九天 我趴在偏房一处隐蔽的房顶上张望。 院中可真热闹,春花似锦、人声如沸。这庄子的主人今日做“春日...
    开封第一讲书人阅读 29,928评论 0 19
  • 文/苍兰香墨 我抬头看了看天上的太阳。三九已至,却和暖如春,着一层夹袄步出监牢的瞬间,已是汗流浃背。 一阵脚步声响...
    开封第一讲书人阅读 31,159评论 1 259
  • 我被黑心中介骗来泰国打工, 没想到刚下飞机就差点儿被人妖公主榨干…… 1. 我叫王不留,地道东北人。 一个月前我还...
    沈念sama阅读 42,880评论 2 349
  • 正文 我出身青楼,却偏偏与公主长得像,于是被迫代替她去往敌国和亲。 传闻我的和亲对象是个残疾皇子,可洞房花烛夜当晚...
    茶点故事阅读 42,399评论 2 342

推荐阅读更多精彩内容

  • rljs by sennchi Timeline of History Part One The Cognitiv...
    sennchi阅读 7,279评论 0 10
  • 人先天皆有不足,唯有后天多爱自己! 脾脏是女人的神,呵护好脾脏内健康外美丽 1脾为“气血生化之源”。 脾是女人气血...
    后爱书杭阅读 332评论 0 0
  • 你一定也有过很着迷的时候,只是,我遇到你的时候嫌晚了一些;而对我来说,遇到你却是太早了一些;那时,我还不懂得抓住一...
    冰星星阅读 1,693评论 0 0
  • 个人认为UC浏览器的主界面交互逻辑还是挺好的,界面过度流畅,动画具有引导性,美观大方。我们现在尝试实现它,先来一张...
    zibuyuqing阅读 2,007评论 4 27