﻿ 基于非自由空间缩短效应的水下航行器海面天线优化方法
 舰船科学技术  2022, Vol. 44 Issue (10): 80-83    DOI: 10.3404/j.issn.1672-7649.2022.10.015 PDF

The optimization method of the antenna on the sea surface of the underwater vehicle based on the non-free space shortening effect
LI Li-hua, WANG Shi-yu, XIU Meng-lei, WANG Yong-bin
College of Electronic Engineering, Naval University of Engineering, Wuhan 430033, China
Abstract: When the half-wave dipole antenna is used as a low-power bidirectional sea surface antenna, the mismatch loss caused by the shortening effect becomes an urgent problem to be improved. Based on the induction electromotive force method, this paper proposes that the existing formulas for shortening length calculation in free space cannot be applied in non-free space, and proposes an optimization method for shortening effect of the symmetrical dipole antenna in non-free space. The method is applied and verified in a symmetrical dipole antenna in the sea surface environment. The actual antenna is made and verified by experiments, theoretical derivation, and simulation calculation. The results show that the optimization method based on the shortening effect of non-free space makes the symmetrical dipole antenna on the sea surface in the resonant state at the operating frequency, which reduces the power loss caused by the mismatching of the antenna and improves the antenna gain.
Key words: underwater communication     non-free space     shortening effect
0 引　言

1 自由空间中缩短长度的计算

 $\Delta {{l = }}\frac{{42.54L}}{{60{\text{π}} \ln \dfrac{\lambda }{{{\text{π}} d}}}} 。$ (1)

2 非自由空间中缩短效应分析

 ${X_{{\text{in}}}} = {R_m} + {X_m}，$ (2)

 $G = - 2\cos \left( {\dfrac{{kL}}{2}} \right)\dfrac{{\cos \left( {kr} \right)}}{r} + \dfrac{{\cos \left( {k{R_1}} \right)}}{{{R_1}}} + \dfrac{{\cos \left( {k{R_2}} \right)}}{{{R_2}}}，$

 $\begin{split} {X_m} =& \frac{\eta }{{4{\text{π}} }}\int_{ - \frac{L}{2}}^0 {\sin \left[ {k\left( {\frac{L}{2} + z} \right)} \right] \times G{\rm{d}}z} + \\ & \frac{\eta }{{4{\text{π}} }}\int_0^{\frac{L}{2}} {\sin \left[ {k\left( {\frac{L}{2} - z} \right)} \right]} \times G{\rm{d}}z 。\end{split}$ (3)

 $\begin{split} M =& \int_{ - \frac{L}{2}}^0 {\sin \left[ {k\left( {\frac{L}{2} + z} \right)} \right] \times G{\rm{d}}z } + \\ & \int_0^{\frac{L}{2}} {\sin \left[ {k\left( {\frac{L}{2} - z} \right)} \right]} \times G{\rm{d}}z 。\end{split}$ (4)

 ${X_m} = \frac{\eta }{{4{\text{π}} }}M ，$ (8)

 $\eta = \sqrt {\frac{\mu }{\varepsilon }} 。$ (9)

 $\begin{split}\Delta X=&30\;\mathrm{sin}\;2\alpha \left(\dfrac{L}{2}\text-\Delta \text{l}\right)\times\\ &\left(0.57721+\mathrm{ln}\alpha \dfrac{L}{2}+ci2\alpha L-2ci\alpha L-2\mathrm{ln}\dfrac{L}{d}\right)。\end{split}$ (10)

${X_m} + \Delta X = 0$ ，可以得出天线单臂缩短长度与介质、频率和天线长度的关系如下式：

 $\Delta l = \dfrac{{{X_m}L}}{{60{\text{π}} \ln \dfrac{\lambda }{{{\text{π}} d}}}} = \dfrac{{\sqrt {\dfrac{\mu }{\varepsilon }} ML}}{{240{{\text{π}} ^2}\ln \dfrac{c}{{{\text{π}} df\sqrt \varepsilon }}}} 。$ (11)

 $\Delta {{l = }}\frac{{{X_{{m}}}L}}{{60{\text{π}} \ln \dfrac{\lambda }{{{\text{π}} d}}}} ，$ (12)

3 仿真计算与实验验证 3.1 优化前后天线在漂浮线缆工作环境中的电气特性

 图 1 空气-发泡聚乙烯-海水分层电磁模型 Fig. 1 Air-foamed polyethylene-seawater layered electromagnetic model

 图 2 半波振子在分层电磁模型中的阻抗特性 Fig. 2 Impedance characteristics of a half-wave oscillator in the layered electromagnetic model

 图 3 缩短后对半波振子天线在分层电磁环境中的阻抗特性 Fig. 3 Impedance characteristics of the optimized symmetric oscillator in the stratified electromagnetic environment

 图 4 半波振子天线缩短长度与反射系数的关系 Fig. 4 The relation between the fine-tuning length of half-wave oscillator antenna and reflection coefficient

3.2 优化前后天线的实验测试

 图 5 缩短前天线在工作环境中阻抗特性 Fig. 5 Impedance characteristics of the antenna in a simulated working environment before optimization

 图 6 缩短后天线在工作环境中阻抗特性 Fig. 6 Impedance characteristics of the optimized antenna in a simulated working environment

4 结　语

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