<p style="margin-bottom: 5px; margin-top: 5px; text-align: left;"><span style="font-family: 微软雅黑,Microsoft YaHei; color: rgb(0, 176, 80);"><strong><span style="font-family: 微软雅黑,Microsoft YaHei; font-size: 24px;">计算:菲涅耳区半径</span></strong></span></p><p style="margin-bottom: 5px; margin-top: 5px; text-align: center;"><span style="font-family: 微软雅黑,Microsoft YaHei;"><strong><span style="font-family: 微软雅黑,Microsoft YaHei; font-size: 24px;"><img src="http://www.qxwlan.com/media/wuji/553b4f174437b8d195e8a_20160803083843.jpg" style="white-space: normal;"/></span></strong></span></p><p style="margin-bottom: 5px; margin-top: 5px; text-align: left;"><span style="font-size: 24px; font-family: 微软雅黑,Microsoft YaHei;"><br/></span></p><pre class="brush:js;toolbar:false">&lt;form&nbsp;action=&quot;&quot;&nbsp;id=&quot;FresnelZone&quot;&nbsp;class=&quot;calculate_form&quot;&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;input&nbsp;type=&quot;hidden&quot;&nbsp;name=&quot;calculate_item&quot;&nbsp;value=&quot;FresnelZone&quot;/&gt; &nbsp;&nbsp;&nbsp;&nbsp;&lt;h3&gt;参数输入&lt;/h3&gt; &nbsp;&nbsp;&nbsp;&nbsp;&lt;label&nbsp;for=&quot;distance&quot;&gt;发射点与接收点之间的直线距离:&lt;/label&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;input&nbsp;id=&quot;distance&quot;&nbsp;name=&quot;distance&quot;&nbsp;type=&quot;text&quot;/&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;select&nbsp;id=&quot;metric_imperial&quot;&nbsp;name=&quot;unit&quot;&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;option&nbsp;value=&quot;metric&quot;&gt;公里&lt;/option&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;option&nbsp;value=&quot;imperial&quot;&gt;英里&lt;/option&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;/select&gt;&lt;br/&gt;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&lt;label&nbsp;for=&quot;frequency&quot;&gt;频率:&lt;/label&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;input&nbsp;id=&quot;frequency&quot;&nbsp;name=&quot;frequency&quot;&nbsp;type=&quot;text&quot;/&gt;&nbsp;Ghz&lt;br/&gt; &nbsp;&nbsp;&nbsp;&nbsp;&lt;button&nbsp;class=&quot;submit&quot;&nbsp;type=&quot;button&quot;&gt;计算&lt;/button&gt; &nbsp;&nbsp;&nbsp;&nbsp;&lt;hr/&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;h3&gt;计算结果&lt;/h3&gt; &nbsp;&lt;div&nbsp;class=&quot;result&quot;&gt; &nbsp;&nbsp;&nbsp;&lt;div&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;span&nbsp;class=&quot;subtitle&quot;&gt;菲涅耳区半径:&lt;/span&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;span&nbsp;class=&quot;radius&quot;&gt;&lt;/span&gt;&lt;span&nbsp;class=&quot;unit&nbsp;metric_imperial&quot;&gt;m&lt;/span&gt; &nbsp;&nbsp;&nbsp;&nbsp;&lt;/div&gt; &nbsp;&nbsp;&nbsp;&lt;div&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;span&nbsp;class=&quot;subtitle&quot;&gt;80%菲涅耳区半径:&lt;/span&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;span&nbsp;class=&quot;radius8&quot;&gt;&lt;/span&gt;&lt;span&nbsp;class=&quot;unit&nbsp;metric_imperial&quot;&gt;m&lt;/span&gt; &nbsp;&nbsp;&nbsp;&nbsp;&lt;/div&gt; &nbsp;&lt;/div&gt; &lt;/form&gt;</pre><p style="margin-bottom: 5px; margin-top: 5px; text-align: left;"><span style="font-size: 24px; font-family: 微软雅黑,Microsoft YaHei;"></span><br/></p><p style="margin-bottom: 5px; margin-top: 5px; text-align: left;"><span style="font-size: 24px; font-family: 微软雅黑,Microsoft YaHei;"></span></p><h2 style="text-align: left;" class="title-text"><span style="font-family: 微软雅黑,Microsoft YaHei;"><span style="font-family: 微软雅黑,Microsoft YaHei; font-size: 20px;">1、定义</span><span style="font-family: 微软雅黑,Microsoft YaHei; font-size: 24px;"></span></span></h2><p style="text-indent: 2em; line-height: 1.75em; text-align: left;"><span style="font-family: 微软雅黑,Microsoft YaHei;">菲涅耳区是在收发天线之间,由电波的直线路径与折线路径的行程差为nλ/2的折点(反射点)形成的、以收发天线位置为焦点,以直线路径为轴的椭球面。其中n=1的区域是对信号作主要贡献的区域,称为第一菲涅耳区,亦称有效区。</span></p><p><img src="/media/wuji/0_20160803083843.png" style="width: 519px; height: 161px;" height="161" width="519"/><strong style="text-align: center; font-family: 微软雅黑, &quot;Microsoft YaHei&quot;;"><span style="font-size: 24px;"><img src="http://www.qxwlan.com/media/wuji/what-is-fresnel-zone_20160803083843.jpg"/></span></strong></p><p style="text-indent: 2em; line-height: 1.75em;"><br/></p><h2 style="text-align: left;"><span style="font-size: 20px; font-family: 微软雅黑,Microsoft YaHei;">2、有限区域<br/></span></h2><p dir="ltr" style="text-indent: 2em; line-height: 1.75em; text-align: left;"><span style="font-family: 微软雅黑,Microsoft YaHei;">当坚硬物体突入菲涅耳区内的信号通道时,锐边衍射就会使部分信号偏转,致使其到达接收天线的时间略微晚于直接信号。由于这些偏转的信号与直接信号有相位差,所以它们会降低其功率或者将其完全抵消。如果树木或其他“软”物体突入菲涅耳区,它们就会削弱通过的信号(降低其强度)。简而言之,尽管事实上你能够看到一个位置,但这并不意味着你就能够建立到该位置的优质无线微波电链路。</span></p><p dir="ltr" style="text-indent: 2em; line-height: 1.75em; text-align: left;"><span style="font-family: 微软雅黑,Microsoft YaHei;">未被遮挡区域应占整个<span style="font-family: 微软雅黑,Microsoft YaHei;">菲涅耳区</span>的60%以上,才能确保有效的无线传输。</span></p><p><br/></p>