..标题：弗里斯传输方程
.. slug：rf-friis-传输方程
.. 日期: 2025-12-26 15:00:00 世界标准时间
..标签：网络、计算器、工具
..类别：计算器
..链接：
.. 描述：应用 Friis 传输方程根据发射功率、天线增益和路径损耗求出接收信号功率。用于射频链路预算规划。
..类型：文本
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</style>
<div class="calc-container">
<div class="calc-header">
<h2>弗里斯传输方程计算器</h2>
<p>使用 Friis 传输方程计算无线传输中的接收功率。输入频率和距离以确定自由空间路径损耗和菲涅尔区半径。</p>
<div class="form-section">
<div class="form-row">
<div class="form-group">
<label for="frequency">频率：</label>
<input autocomplete="off" id="frequency" type="text" value="2.4"/>
</div>
<div class="form-group">
<label for="freunit">频率单位：</label>
<select id="freunit">
<option value="ghz">千兆赫 (GHz)</option>
<option value="mhz">兆赫 (MHz)</option>
<option value="khz">千赫兹 (KHz)</option>
<option value="hz">赫兹 (Hz)</option>
</select>
</div>
</div>
<div class="form-row">
<div class="form-group">
<label for="distance">距离：</label>
<input autocomplete="off" id="distance" type="text" value="1"/>
</div>
<div class="form-group">
<label for="unit">距离单位：</label>
<select id="unit">
<option value="feet">英里</option>
<option value="meters">公里</option>
</select>
</div>
</div>
<div class="button-group">
<button class="calc-button" onclick="fresnelZone()" type="button">计算</button>
</div>
</div>
<div class="help-text">
<strong>笔记：</strong>Friis 传输方程计算理想条件下天线接收到的功率，假设另一根天线距离一定距离传输已知的功率。</div>
</div>
<div class="result-section" id="resultsSection" style="display: none;">
<div class="section-header">
<h3><span>📡</span>计算结果</h3>
</div>
<div class="section-content">
<div class="data-row">
<div class="data-label">菲涅耳区半径：</div>
<div class="data-value highlight" id="fnr">-</div>
</div>
<div class="data-row">
<div class="data-label">中心点：</div>
<div class="data-value" id="center">-</div>
</div>
</div>
</div>
<div class="info-section">
<h4>关于弗里斯传输方程</h4>
<p>Friis 传输方程将天线接收的功率与相隔一定距离的另一天线发射的功率联系起来。该方程考虑了天线增益和信号波长。</p>
<p><strong>公式：</strong></p>
<p><code>Pr / Pt = Gt × Gr × (λ / 4πR)²</code></p>
<p><strong>在哪里：</strong></p>
<ul style="margin: 10px 0; padding-left: 20px;">
<li><code>Pr</code>= 接收天线的功率</li>
<li><code>Pt</code>= 发射天线的输出功率</li>
<li><code>Gr</code>= 接收天线的增益</li>
<li><code>Gt</code>= 发射天线的增益</li>
<li><code>λ</code>= 波长</li>
<li><code>R</code>= 天线之间的距离</li>
</ul>
<p><strong>菲涅尔区：</strong>菲涅耳区是发射天线和接收天线之间的椭圆形区域。该计算器计算中心点的半径，这对于确定障碍物是否会干扰信号至关重要。</p>
</div>
</div>
<script>
/**
 * Friis Transmission Equation Calculator
 * Calculates Fresnel zone radius based on frequency and distance
 *
 * Equation:
 * Pr / Pt = Gt × Gr × (Lambda / 4 × Pi × R)²
 *
 * Where:
 * - Pr: Power at the receiving antenna
 * - Pt: Output power of transmitting antenna
 * - Gr: Gain of the receiving antenna
 * - Gt: Gain of the transmitting antenna
 * - Lambda: Wavelength
 * - R: Distance between antennas
 *
 * Fresnel Zone Calculation:
 * For Miles: radius = 72.05 × √(d1 × d2 / f)
 * For Kilometers: radius = 17.32 × √(d1 × d2 / f)
 * Where d1 and d2 are distances from each antenna to the center point
 */

'use strict';

function fresnelZone() {
    // Get input values
    const frequency = Number(document.getElementById("frequency").value);
    const freunit = document.getElementById("freunit").value;
    const distance = Number(document.getElementById("distance").value);
    const unit = document.getElementById("unit").value;

    // Validate inputs
    if (isNaN(frequency) || frequency <= 0) {
        alert("Please enter a valid frequency greater than 0");
        return;
    }

    if (isNaN(distance) || distance <= 0) {
        alert("Please enter a valid distance greater than 0");
        return;
    }

    // Convert frequency to GHz
    let sf;
    if (freunit === "ghz") {
        sf = frequency;
    } else if (freunit === "mhz") {
        sf = frequency / 1000;
    } else if (freunit === "khz") {
        sf = frequency / 1000000;
    } else {
        sf = frequency / 1000000000;
    }

    // Calculate center point (halfway)
    const d1 = distance / 2;
    const d2 = d1;

    // Calculate Fresnel zone radius based on unit
    let radius, distunit;
    if (unit === "feet") {
        // For miles: radius in feet
        radius = Math.round(36.03 * Math.sqrt(distance / sf));
        distunit = "Miles";
    } else {
        // For kilometers: radius in meters
        radius = Math.round(8.657 * Math.sqrt(distance / sf));
        distunit = "Kilometers";
    }

    // Display results
    document.getElementById("fnr").innerHTML = radius + " feet";
    document.getElementById("center").innerHTML = "The center of the Fresnel Zone is " + d1 + " " + distunit + " from the first antenna.";

    // Show results section
    document.getElementById("resultsSection").style.display = "block";

    // Scroll to results
    document.getElementById("resultsSection").scrollIntoView({ behavior: 'smooth', block: 'start' });

    console.log(`Calculation complete: Frequency=${sf}GHz, Distance=${distance}${distunit}, Radius=${radius}ft`);
}

// Add enter key support for inputs
document.addEventListener('DOMContentLoaded', function() {
    console.log('Friis Transmission Equation Calculator initialized');

    // Allow Enter key to trigger calculation
    const inputs = document.querySelectorAll('#frequency, #distance');
    inputs.forEach(input => {
        input.addEventListener('keypress', function(e) {
            if (e.key === 'Enter') {
                fresnelZone();
            }
        });
    });

    // Auto-focus first input
    document.getElementById('frequency').focus();
});
</script>