Mobile terminal antenna design skills

发布时间：2014-08-11 18:59:32 来源：文档文库

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移动终端几乎都是使用小型天线，它的缺点是低效率、窄频宽，为了确保天线的性能，因此天线小型化有一定的极限，然而如此一来却违背移动终端小型化的时代趋势。所幸的是天线使用的元件大多是可以创造空间的导体，若与波长比较的话，只要导体具备一定大小，基本上就可以当作高天线使用，例如类似移动终端外壳等结构就符合以上条件（图1）。

　　目前移动终端使用频率大多介于800mMHz～2GHz之间，波长相当于150～350nm左右，因此100～200mm的终端尺寸对小型天线非常有利，也就是说只要巧妙应用移动终端的机壳，就可以获得小型、高性能的天线功能，有鉴于此本文以移动终端的机壳当作天线使用为例，依序介绍地表数位播放用天线与PDC（Personal;DigitalCellular）用Diversity天线的设计技巧。

Almost all of the mobile terminal using a small antenna, its disadvantage is the low efficiency, narrow bandwidth, to ensure the performance of the antenna, so that the antenna has a certain limit miniaturization, but contrary to the mobile terminal but result miniaturization trend of the times. Fortunately, most of the components used to create space antenna is a conductor, when compared with the wavelength, so long as a conductor with a certain size, basically you can use as a high antenna, such as housing and other similar structures on mobile terminals meet the above criteria (Figure 1).

Currently most frequently used mobile terminal between 800mMHz ~ 2GHz, the wavelength is equivalent to about 150 ~ 350nm, 100 ~ 200mm therefore the size of a small antenna terminals is very beneficial, that as long as the chassis ingenious application of mobile terminals, you can get small, high-performance antenna function, this thesis contributes to the cabinet as a mobile terminal antennas, for example, sequentially introduce digital playback antenna surface and PDC (Personal; DigitalCellular) with Diversity antenna design skills.

移动终端天线的特征

　　如上所述低效率、窄频宽是一般小型天线的主要缺点。天线的比频宽（以中心频率制定的频率范围）与天线大小有密切关系，小型天线的频宽则与天线的体积呈比例关系。天线的效率可以用下式表示：

　　η=Pr/（Pr+Pd）

　　η：天线的效率。

　　Pr：放射功率。

　　Pd：损失功率。

　　由上式可知如果缩任意小天线大小的话，Pr会比Pd小导致放射效率大幅降低，这种现象尤其是天线附近的电磁界更加明显。图2是提供相同电力给两种天线时，天线附近的实际电界分布状态，图中的单极（Monopole）天线高度为λ/4（此处λ表示天线频率的对应波长）属于中等大小天线，此时单极天线最大强度大约是-20dB；相较之下逆F天线的高度为λ/10属於小型天线，此时F天线最大强度则只有0dB，由此可知即使相同电力随着天线大小的差异，天线附近的电界（电压）分布状态则截然不同，同样的磁界亦即电流强度也不相同。对小型天线而言构成天线的导体与天线周围的空间，若是属于有耗损性的媒体时，会就导致极大的电力（功率）损失，相对的效率也会急遽劣化。

In the mobile terminal antenna

As mentioned above the low efficiency , narrow bandwidth is a major drawback of the average small antenna. Than the bandwidth of the antenna ( center frequency enacted frequency range) and antenna size is closely related to the bandwidth of the antenna is small and proportional relationship between the volume of the antenna . The efficiency of the antenna can be represented by the following formula :

η = Pr / (Pr + Pd)

η: efficiency of the antenna .

Pr: radiation power .

Pd: loss of power .

From the above equation , if any small antenna size reduction , then , Pr cause substantially smaller than the lower emission efficiency of Pd , in particular the phenomenon of electromagnetic more pronounced near the antenna sector . Figure 2 is a time to provide the same power of two antennas, the effective power distribution near the boundary antenna , a monopole diagram (Monopole) antenna height ( an antenna corresponding to the frequency where the wavelength λ) is a λ / 4 antenna moderate size in this case the maximum intensity of the monopole antenna is about -20dB; contrast inverse F antenna height is λ/10 is a small antenna , then F antenna maximum intensity only 0dB, can be seen even with the same power as the antenna size differences antenna near power sector ( voltage ) distribution is very different , the same magnetic field and current density that is not the same . Space around the antenna conductor constitutes a small antenna on the antenna, while if there is loss of belonging to the media will lead to great power ( power ) loss , the relative efficiency will rapidly deteriorate

天线的等化G与物理长度L可以用下式表示：G=8log（2L/λ）（dBd）（dBd）为接收电波时的强度（与半波长Dipole比较）指标。此处若将频率为/20nm移动终端的天线等化代入上式，可以求得-7.7dB左右的（理论）效率，然而实际上移动终端的效率大约只有-1dB。

　　图3是移动终端周围的电界分布状态，由图可知若对天线施加脉冲电界，天线周围的电界会随时间改变，例如右图的电界强度除了天线之外，机壳本体的电界强度也会随时间改变增大，换句话说只要巧妙应用移动终端机壳的电波放射特性，即使小型天线也可以获得预期的效果。

Antenna and the like of the physical length L G can be represented by the following formula: G = 8log (2L / λ) (dBd) (dBd) when the intensity of the received radio wave (the half-wavelength Dipole comparison) indicator. If frequency is here / 20nm mobile terminal antenna into the equalization formula can be obtained-7.7dB (theory) about efficiency, but the efficiency of the mobile terminal is actually only about-1dB.

Figure 3 is the distribution of electric circle around the mobile terminal, if the figure shows the pulse applied to the antenna sector, the electrical sector around the antenna will change with time, e.g., Electric field intensity of the antenna in addition to the right, the main body electrical cabinet will change the boundary strength increases with time, in other words as long as the radio wave radiation characteristics ingenious application of the mobile terminal casing, a small antenna can be obtained even if the desired effect.

一般数位地表波播送使用波长为400~600nmUHF（UltraHighFrequency）的频宽，然而实际上物理特性上限制，使得一般传统移动终端得天线不容易小型化，因此将移动终端机壳的改成抽取或是折叠设计，形成如图4右侧直接激振天线。

Digital broadcasting generally a wavelength of the surface wave 400 ~ 600nmUHF (UltraHighFrequency) bandwidth, but in fact limit the physical characteristics, such antennas generally have a conventional mobile terminal is not easy to compact, the housing of the mobile terminal into or extracted folding design, forming the right side of Figure 4 direct excitation antenna

接着在波暗室内实际测试上述两种天线的水平面内放射pattern，必需注意的是天线的特性极易受到包含人体在内使用环境的影响，因此测试时被测天线必需远离人体，此外电波几乎是从水平方向入射，所以本测试是以水平面内的放射pattern作为讨论对象。

　　图5是各天线在波暗室内测试获得的结果；表1以Dipole天线作比较基准时的等化平均值，由表1的计算结果可知传统Monopole天线与Dipole天线具备-2.5~2.8dB相同程度的平均等化值。

Then, in the actual test wave dark room within the horizontal plane of the two antenna radiation pattern, must be noted that the characteristics of the antenna can easily be affected by the use of the environment, including the human body contains, so the test must be measured antenna away from the body, in addition to radio waves is almost from the horizontal direction of the incident, the test is based on the radiation pattern in the horizontal plane as a subject for discussion.

Figure 5 is the result of the test antenna wave darkroom obtained; etc. Table 1 is an average value of Dipole Antenna for comparing the reference, Table 1 shows the results with conventional Monopole Antenna Dipole antennas have the same degree of -2.5 ~ 2.8dB the average equalization value.

根据上述测试结果进行屋外测试，测试时在两处际野外（Field）作收、送讯试验。波暗室内测试时被测天线远离人体旋转一圈，依此计算天线的平均收讯功率；相较之下屋外测试时则携带被测天线步行约十分钟左右回旋路程，接着再以Dipole天线作比较基准，计算天线的平均收讯功率。根据表1的计算结果显示，两种天线在四个场地的平均收讯功率几乎完全相同，它与上述波暗室内测试结果一致，依此证明只要巧妙应用移动终端机壳的电波放射特性，即使小型天线也可以获得预期的效果。

According to the tests conducted outside the test results when tested in two inter-field (Field) for income, messenger trials. When wave dark room test measured antenna away from the body revolution, and so calculate the average antenna reception power; comparison test is carried outside antenna under test about ten minutes walk from the roundabout, followed with Dipole Antenna for benchmark to calculate the average reception power antenna. According to the results in Table 1 show that both the average reception power of the antenna are almost identical at four sites, which is consistent with the results of the above test wave dark room, and so long as the skillful use of the mobile terminal proof enclosure wave radiation characteristics, even small antenna can obtain the desired effect.

Table 1 Characteristics of the other antenna

Diversity天线的设计

　　移动通讯系统为了抑制衰减（Fading）造成通讯品质恶化，因此通常都采用Diversity天线。上节介绍的两种Diversity天线，主要设计诉求是收讯用途，所以涉及天线的设置场所与天线构造。

　　此处采取在连接移动通讯系统折叠机壳上增设阻抗（Impedance）Z，如此就能够利用一种天线获得多样的放射pattern，这种设计最大优点是可以大幅缩小天线的设置场所与天线结构物的尺寸。

　　图6是Diversity天线的构造，如图所示它是将天线设置在折叠机壳两接地（Ground）中央，两接地之间再铺设信号线与并排连接的阻抗，接着改变阻抗观察放射pattern。根据图7的测试结果显示，Z=Z0（开放）与Z=Z1（容量性）时，放射pattern发生明显改变，Z=Z0 时放射pattern呈侧向8字形，Z=Z1时放射pattern与Z=Z0截然不同，换句话说即使相同天线，随着Z的变化会出现不同的放射现象。

Diversity antenna design

In order to suppress attenuation of a mobile communication system (Fading) resulting in deterioration of communication quality , it is often Diversity antennas are used . Diversity antenna on the introduction of two sections , the main appeal is the recipient uses the design , so the sites involved in the antenna and the antenna structure set .

Here take additional impedance (Impedance) in the mobile communication system connecting the folding chassis Z, so it is possible to use an antenna to get a variety of radiation pattern, the biggest advantage is that this design can significantly reduce the antenna installation location and antenna structures size.

Diversity antenna structure of Figure 6 is , as shown in it is the two antennas are disposed in a folded chassis ground (Ground) and then laying between the center line and the impedance of the two parallel signal ground connection , and then change the impedance observed radiation pattern. According to the test results in Figure 7 show , Z = Z0 ( open ) and Z = Z1 ( capacitive ) , the radiation pattern changed significantly , Z = Z0 when radiation was sideways figure eight pattern , radiation pattern when Z = Z1 and Z = Z0 different, in other words even if the same antenna , with the changes Z will appear different radioactivity .

为了探讨放射pattern的变化原理，因此对机壳施加电流藉此观察电流分布特性，根据图8的测试结果显示，Z=Z0时上下机壳都有同相电流流动，而且与图7的放射pattern一样都是呈侧向8字形，由于Z=Z0时为同相电流，因此电界是以侧向加算；相对的Z=Z1则变成逆相电流，因此电界横向相互抵销，放射pattern整体呈蝶翼状。由此可知只要改变抗Z就能够控制机壳上的电流，并使电流产生的放射pattern发生变化。

In order to explore the principles of radiation pattern changes, so current is applied to the chassis thereby observe the current distribution characteristics, according to the test results in Figure 8 shows, Z = Z0 while the lower cabinet has the same phase current flow, but also the same as in Figure radiation pattern 7 are presented sideways figure eight, because when Z = Z0 phase current, so the electricity sector is the lateral plus count; relative Z = Z1 becomes reverse-phase current, so the lateral offset electricity sector, showed overall radiation pattern Butterfly shape. It can be seen impedance Z can be changed as long as the control current on the chassis, and a current is generated in the radiation pattern is changed. .