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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

3 D Corner Reflector Antenna as an efficient feed for offset parabolic antennas for 5.8 GHz

3D角反射天线作馈源的 5.8GHz 偏馈抛物面天线 Dragoslav Dobrii, YU1AW Abstract 摘要 In this article I present a modification of 3D corner reflector antenna in order to adjust it for the use as a feed for SAT TV offset parabolic antennas on 6 cm Ham band or WLAN frequencies of 5.8 GHz. 本文介绍用改进型3D角反射天线, 为6厘米业余无线电通信频段STA卫星电视 或WLAN频段5.8GHz频道的偏馈抛物面天线作馈源. Introduction 引言 The problems that occur while illuminating shallow offset parabolas, in addition to those related to the efficient use of parabolic generally, are additionally aggravated by the specific geometry of the parabolic mirror itself. Feed positioning in the way that its phase center exactly coincides with the focus of the offset parabola and its direction so that the radiation maximum falls in the geometric center of the elliptic reflector surface are not intuitive at all, as in classic parabolic antennas. Therefore, there are a many confusions and wrongly positioned feeds that don't correctly illuminate offset a parabolic dish, decreasing its efficacy and gain. 这个问题时常存在于浅照射的偏馈抛物面天线上, 除了和抛物面天线的效率 有关之外,抛物线反射面本身的具体几何形状又使之更加严重.馈源用这样的 方式定位——其相位中心准确位于偏馈抛物线反射器的焦点,方向也要准确, 这样辐射最大值才能落在椭圆形反射面的几何中心,这样一点也不直观,正如 标准的抛物面天线.因此,有许多混乱和错误放置馈源的方式,不能正确照射 抛物柱面反射器,降低了其效率和增益. Classic and offset parabola 标准的和偏置的抛物面 A parabolic surface or paraboloid is formed by rotation of parabolic curve around its axis of symmetry. The specificity of the surface gained in this way is that when the beam of rays parallel to its axis of rotation falls on it, the beam is reflected so that all the rays meet in one point, known as the focus, in the same way that optical lenses focus light rays in their focus. 抛物线的表面或曰抛物面,是由抛物线围绕其对称轴旋转而成,其特点是, 和抛物线对称轴平行的射线波束被抛物面所反射,所有的电波都在同一点汇聚,

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September,2009

3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

我们把这点叫做焦点. When the piece of a (mathematically infinite) surface of paraboloid is cut off, a parabolic reflector or mirror is gained. Cutting off (cropping) can be carried out in many ways, but all of them can be classified in two groups: those whose surface of cropping is perpendicular on the axis of symmetry, and those whose surface of cropping are not perpendicular. When the plane that cuts off paraboloid is perpendicular on the axis of symmetry, a round segment of paraboloid is gained, whose focus is in the center, i.e. on the axis of symmetry on certain distance from geometric center of the surface, depending on the position of the cropping plane. Usually, the distance of the cropping plane is smaller than the equivalent focus and therefore in majority of dishes focus resides outside of the opening of the dish. The segment gained in this way is classic parabolic antenna. 截取一个(无限大的)抛物面的某一部分,就得到了一个抛物面反射器或 曰抛物面镜.切割方法有多种,但基本分为 2 类:一类切割面是垂直于对称轴 的,另一类是不垂直的.当抛物面切割面垂直于对称轴,就得到一个圆形的抛 物面,它的焦点位于正中央,即对称轴上距离抛物面几何中心一定距离的地方, (取决于截取平面的位置). 通常截面(到抛物面几何中心)的距离比等效焦点(到抛物面几何中心) 的距离要小,因此大多数焦点位于抛物面口径面的外面.用这种方法得到的截 面就是标准的抛物面天线. All paraboloid segments gained in this way have one parameter by which they may be grouped regarding characteristics. That is the ratio between focal distance from center (F) and diameter of the segment of parabolic surface (D). All parabolic antennas that have equal ratio F/D may be illuminated by the same feed regardless its diameter, i.e. whether they are large or small, because their all other geometric dimensions are proportional, too. The ratio F/D is also crucial in determining the characteristics of the feed that will illuminate the dish. The reason for this is that ratio F/D determines the angle the edges of the parabola are seen from the focus. The smaller the ratio F/D, the deeper the dish is and this angle is greater, and vice versa, the greater the F/D ratio, the shallower the dish is and the angle are smaller. Since feed needs to be constructed in the way that it radiates only in the direction of the parabola, and that in all other directions it radiates as little as possible, this means that the ratio F/D, also determines the optimal radiation diagram of the feed. Hence, every F/D has its optimal feed, regardless all other dimensions! Therefore, when the optimal feed for a parabola is determined, the only thing that matters is its F/D! 所有用这种方法获得的抛物面有一个特性(并以此特性分类),即焦距(F) 和抛物面口径面的直径(D)的比值,所有的F/D比率相同的抛物面天线,不管 其直径是否相同,都可以使用相同的馈源.也就是说,不管它们的大小,因为 它们其它的几何尺寸也是成比例的.在决定典型照射馈源时,F/D的比率也是决 定性因素. 原因就是F/D的比率限定了抛物线焦点到边缘的角度. 口径面深的F/D 比率小,角度就大.反之亦然,浅的口径面,F/D比率大,角度就小.因为馈源 必须向抛物面四周方向辐射,而其它方向照射要尽可能小,这就意味着F/D的比 率也决定了馈源的最佳辐射方向图.因此,每一个F/D都有自己的最佳馈源,无 论其它的尺寸如何.为此,当抛物面的最佳馈源确定之后,唯一一件重要的事

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

情就是它的F/D! When the plane that cuts the paraboloid is not perpendicular to the axis, elliptic segment of paraboloid is gained, whose focus is not in the geometric center of the parabolic surface, but is more or less shifted towards periphery, depending on the cut angle. The offset parabolic antenna is gained in this way. Because the cropping angle can be any one, the focus positions can also be in different places in relation to geometric center of gained parabolic surface. However, besides this difference in parameters, F/D still remains the only factor that determines the characteristics of the optimal feed for given offset parabola. 当抛物面切割面不垂直于轴线, 就得到椭圆形的截面, 它的焦点不在抛物面 的几何中心,差不多移到边缘附近,随切割角度而定.偏馈抛物面天线就是这 样得到的.因为切片可以是任意角度,焦点的位置也就在不同的地方,与抛物 面几何中心有关.不管怎样,除了这个不同的特点以外,F/D依然是决定偏馈抛 物面的最佳馈源的唯一要素.

Fig. 1. Offset parabola geometry

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September,2009

3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

图1 :偏馈抛物面几何关系 In the case of an arbitrarily chosen segment of paraboloid, the problem is in determining F/D ratio. Without going in some specificities and possible exhibitions of different manufacturers of offset dishes, generally it can be said that the focal distance F is approximately equal to the distance between focus (in SAT TV antenna: from the opening of the converter waveguide) and parabola's geometric centre. For diameter D the smaller axis of the ellipse, i.e. the antenna's wideness, is taken. In offset parabolic antennas F/D is usually two times greater than in classic ones. 如何选择抛物面的截面,取决于F/D的比率.一般来说,焦距F约等于焦点 (在卫星电视天线是波导变换器开口处)和抛物线的几何中心之间的距离.至 于D,如果口径面是椭圆形就取其短轴,也就是天线的宽度.通常偏馈抛物面天 线的F / D是标准抛物面天线的2倍.

The optimal feed 最佳馈源 The optimal feed for some given parabola has to fulfill several important characteristics: 抛物面天线的最佳馈源必须具备以下重要特征: 1. The radiation angle of the main beam, between the points in which the radiated power is -10dB in relation to the maximal value, has to match the subtended angle. In fact, that is the angle with the angular point in focus and with the arms of the angles that touch the edges of parabolic reflector. The feed radiation angle both in horizontal and in vertical plane has to be the same, regardless the elipticity (貌似elipticity 这个词拼错了,应该是ellipticity吧——译者注)of offset parabola. 1,主束的方向角,在增益为-10dB(相对于最大值)的两点之间的角度, 必须与张角相配.实际上,张角的角顶在焦点上,角的边线连接抛物面边沿. 馈源的方向角在水平和垂直都应当相同.而不管偏馈抛物面的椭圆率如何. 2. The phase center of the feed has to be well defined and stable with changes of frequencies within the working range. The change of the phase within the whole angle of illumination has to be as small as possible. 2,在其工作范围内更换工作频率时,馈源的相位中心必须精准,稳定.整 个辐射角度的相位变化必须尽可能地小. 3. The feed characteristics must not change much in the presence of the parabolic reflector and carrier structure. 3,在抛物面反射器和托架前面,馈源的特性参数不能有太大的变化. 4. Feed radiation diagram has to be very clean, i.e. with low side lobes and rear lobes. 4,馈源方向图必须非常干净,即,旁瓣和后瓣应非常低. 5. Feed structure has to encroach as little as possible in focal cones, i.e. in the space between focus and the antenna surface. Therefore, it is good when the feed phase center is on the front edge or directly in front of the feed antenna structure toward reflector. 5,馈源结构必须尽可能地少地伸进焦点椎体中,即,焦点和天线表面之间 的空间.为此,馈源相位中心最好在前沿,或直接在馈源天线指向反射器方向 的前面.

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

It is not easy at all to accomplish all these demands. Efficiency and gain of a parabolic antenna directly depend on the degree of accomplishing of these demands. Therefore, in practice, it is common to make a good feed first and then, according to it, choose or make parabolic reflector with F/D that fits the best. However, if you want to use the cheap production of SAT TV offset parabolas for the work on 13cm Ham band or WLAN frequencies; you have to try to construct the feed that matches existing parabolas. SAT TV antennas usually have F/D in range from 0.7 to 0.9. For efficient illumination, a feed with a clean diagram that has equal width of the main beam in both planes and gain of about 12-14 dBi is needed. This fact excludes some antennas as efficient feeds for SAT TV offset parabolas. Among them is, for example, the coffee can (simple open waveguide) that has gain of about 6-7 dBi and is very inefficient as feed for offset parabolas. It is acceptable only for parabolas that have F/D less than about 0.5. The bi-quad is a somewhat better, with its gain of about 10 dBi, and its optimal version with evened diagrams in both planes and gain of 11 dBi is even better. The addition of director element in 2 element bi-quad feeds gave high values of efficiency of illumination of offset parabolas. However, an additional problem is the range of 5.8 GHz where building the bi-quad antenna represents big problem because of very small tolerances and high precision that needs to be achieved. 达到这些要求并不容易.抛物面天线的效率和增益完全取决于实现这些要 求的程度.为此,在实践中,一般制作一个好的馈源,毫无例外的是,首先要 选择或制作一个F/D值最大程度的适合馈源的抛物面反射器.无论如何,如果你 想用一个低制作成本的卫星电视偏馈抛物面天线,工作于13厘米的业余无线电 频段或者WLAN波段,你必须制作一个与现有抛物面反射器相配的馈源.卫星电 视天线的F/D一般为0.7-0.9 .为了高效率照射,馈源必须有干净的方向图,主 束在水平面和垂直面要等宽,还要有12-14dB的增益.这实际就排除了一些天线 做为卫星电视偏馈抛物面天线的馈源,它们是,例如,咖啡筒(简单的开口波 导)有大约6-7dBi的增益,做偏馈抛物面天线的馈源很不称职.可以接受它的 只有F/D小于0.5的抛物面反射器.菱形天线稍微好一些,大约有10dBi的增益, 其最佳版本的水平和垂直方向增益都达到大约11dBi甚至更高.叠加双菱馈源天 线增加的引向器给了偏馈抛物面天线更高的照射效率.不过,在5.8GHz的频段 又有另外的问题,制作菱形天线出现大麻烦,需要达到非常高的精确度和非常 小的误差.

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 2. Offset parabola efficiency with 31 and 44 mm diameter coffee can feed at 5.8 GHz frequency. 图2:直径31和44mm的咖啡筒做馈源用于5.8GHz频段时,偏馈抛物面天线的效

率

3D corner reflector antennas, and especially the shortened version, are good candidates for feed, but the problem is that it has very unequal diagram – in horizontal plane it is much wider than in vertical plane. By diminution of the antenna to 1.7 wavelengths, to decrease the gain to needed 13 dBi, this unevenness is further increased. Therefore, I modified this antenna in order to get more even diagram, which will be discussed in this article. I achieved, although not perfect, yet a very simple and reliable feed for 5.8 GHz range with acceptable efficiency. 3D角反射器天线,尤其是短的类型,是非常好的馈源选择.问题是它的方 向图不均衡——水平方向图比垂直方向图宽许多,把天线缩短到1.7波长,降低 增益到需要的13dBi,这种不均衡就更加严重.因此,改进这种天线以获得更加 均衡的方向图,是本文将讨论的问题.我获得了一个虽然不很完善,但是简单 而可靠的,具有可以接受的效率的5.8GHz波段的馈源. For those who will, while reading this, say they tried Coffee can, biquad, 3D corner or any other randomly chosen antenna as feed for offset parabola and that 'it works', I will only say that any antenna or piece of wire put approximately in focus of the offset parabola has to work by the laws of physics! So, it is not the question 'does it work?' The question is 'how it works?' in relation to how it could and should work! I presented some diagrams of efficiency of a coffee can with different diameters as feeds for parabolas with different F/D and it is very clear how efficiently they work with offset dishes whose F/D is in the range 0.7-0.9 (colored range). It is clear that offset parabola with a coffee can whose diameter is 0.6 wave lengths, i.e.

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September,2009

3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

about 31 mm, has efficiency of about 25%, that consequently decreases the gain of antenna for 6 dBi in relation to theoretic value, and that is exactly how much it would be gained with two times smaller, efficiently illuminated offset parabola! Even a coffee can with diameter of 0.86 wavelengths, or 44 mm doesn't work brilliantly. It gives about 4 dB loss of gain of antenna in relation to theoretic value with an efficiency of 100%. Greater diameters of coffee can have problem with appearance of higher modes of EM waves and consequently very problematic diagram and phase center, so they are not recommended. 看到这里人们会说,他们采用咖啡筒,菱形,3D角或者任何其它,随便找 一个天线做偏馈抛物面天线的馈源,都能工作.我要说,按照物理定律,任何 天线或者哪怕是一段铜线,放在偏馈抛物面天线焦点附近都能工作!那么,问 题不是"它能不能工作?"而是"它怎样工作?"就是说,它能够怎样和必须 怎样工作!我提供一些不同直径的咖啡罐做不同F/D的抛物面的馈源的效率图 表,可以清楚的看出,当偏馈抛物面天线的F/D在0.7-0.9范围(彩色范围)时, 它们的工作效率如何.很显然,偏馈抛物面天线用直径0.6波长(大约31mm)的 咖啡罐馈源,效率大约是25%.比理论值减少了6dBi的天线增益,准确的说,这 是二分之一的偏馈抛物面天线的照射强度.即使咖啡罐的直径是0.86波长 (44mm)也不能很好工作.它损失了大约4dBi的天线增益,理论上说就是100% 的效率.更大直径的咖啡罐出现了更高形式的EM波,因此方向图和中心相位也 非常成问题的,它们不被推荐. The addition of conic funnet (这里的funnet疑似funnel——译者注)can partially improve the situation, but such horn antennas have uneven diagrams in vertical and horizontal planes, which is very undesirable for antennas that pretend to be good and efficient feed for dish. 加上圆锥形漏斗可以部分改善这一状况,但是这样的喇叭天线的水平和垂 直方向图是不平衡的,这对于一个很好的,高效的抛物面馈源来说是个很大的 麻烦. A 3D corner reflector antenna, with dimensions of 1.7 wavelengths, still has too narrow a vertical diagram and is suitable only for very shallow offset parabolas, with F/D of about 1 and more. 一个尺寸为1.7波长的3D角反射器天线,垂直方向图非常狭窄,只适合很浅 的偏馈抛物面天线,其F/D大约1或者更多.

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Offset parabola efficiency with 3D corner reflector antenna of 1.7 wavelength feed at 5.8 GHz frequency. 图3: 1.7波长的3D角反射器天线做馈源时,5.8GHz频段偏馈抛物面天线的效率

Fig. 3.

Truncated 3D corner reflector feed for 5.8 GHz 用于5.8GHz的削顶3D角反射器馈源 As shown in the picture above, 3D corner reflector antenna has relatively good efficiency when it is illuminating dishes whose F/D is 0.9 and higher. The reason for this is its very narrow vertical radiation angle. That is, the vertical radiation angle is too narrow for the illumination of SAT TV offset parabolas, and horizontal is too wide, as shown in the figures. It is obvious that 3D corner reflector antenna could be also adjusted for offset parabolas with a lower F/D if the diagram could be widen in vertical plane and narrowed in horizontal plane so that they are approximately equal to each other and at the same time retain all other good characteristics of this antenna. Since widening and narrowing of the diagram is possible only by modifying of the geometry of reflector, the change of dimensions and shape of the reflector was the course I took. However, the change of geometry on this geometrically symmetrical reflector carried the danger of loosing some of the basic characteristics of geometric optics, by whose principles this antenna functions. That would immediately mean the complete change of the most of the essential and valuable characteristics of the

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September,2009

3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

antenna, too. 正如上图所示,3D角反射器天线在抛物面F/D为0.9或更高时有很高的效率. 原因是它的垂直方向角非常狭窄,换句话说,对于偏馈卫星电视抛物面天线来 说,垂直方向角太狭窄了,而水平方向角又太宽了,如图所示.显然,3D角反 射器天线也必须调整才能用于低F/D的偏馈抛物面,如果它的垂直方向图必须 宽,水平方向图必须窄,那么垂直和水平两者之间必须大体平衡,而同时要保 持天线的其它所有良好特性.因为加宽和缩窄方向图可能只需改变反射器的几 何结构,那么改变反射器的尺寸和形状就是我做的另一道菜.无论如何,这个 对称几何反射器形体的改变,可能会带来这个天线赖以运作的基本几何特性不 稳定的危险.这也就意味着完全改变了天线的大部分实质性的宝贵的特性. By small changes, actually by gradually removing the parts of the reflector responsible for vertical radiation beam narrowing, I succeeded in progressively widening the vertical diagram. At the same time, in order to narrow the horizontal radiation diagram, I increased the length of the sides of the reflector. With constant monitoring of the achieved results, I made the radiation diagram angles in both planes approximately equal, which is needed for efficient illumination of parabolas whose F/D is about 0.7-0.9. In the end, the result was the optimal diagram for the use with SAT TV offset parabolas. The input impedance of the antenna, the wideness of the frequency working range and purity of the diagram of the antenna remained practically unchanged. 通过小的改变,实际上是通过逐渐除去反射器造成垂直辐射波束狭窄的那 部分,我成功地逐步加宽了垂直方向图,同时,为了缩窄水平方向图,我增加 了反射器的边长.我边改造边监测改善的结果,我得到了适合F/D大约0.7-0.9 的抛物面反射器需要的水平和垂直均衡的方向角,最终得到了用于偏馈卫星电 视抛物面反射器天线的最佳方向图.天线的输入阻抗,工作频率的带宽和纯正 的方向图几乎保持不变. The vertical diagram, of the main beam in addition to widening, became much cleaner, which additionally improved the characteristics of the feed. The gain of the feed antenna is practically unchangeable (about 14.8 dBi), and input SWR is below 1.5:1 in the whole working range. 垂直方向图(除主束加宽之外)变得非常干净,改善了馈源的特性,在整 个工作频段, 馈源天线增益没有改变 (大约14.8dBi) 输入驻波比低于1.5: . , 1

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 4. Comparative diagrams for shortened 3D corner reflector antenna of 2 wavelengths and truncated 3D corner reflector feed 图4: 2波长缩短3D角反射器天线和削顶3D角反射器馈源方向图比较

Fig. 5. Truncated 3D Corner Reflector Feed gain 图5:削顶3D角反射器馈源的增益

Fig. 6. 3D radiation diagram of Truncated 3D Corner Reflector Feed 图6:削顶3D角反射器馈源的立体方向图

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 7. Truncated 3D Corner Reflector Feed input matching 图7:削顶3D角反射器馈源的输入匹配

Fig. 8.

Input impedance of Truncated 3D Corner Reflector Feed 图8:削顶3D角反射器馈源的输入阻抗

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 9. Main beam of Truncated 3D Corner Reflector Feed 图9:削顶3D角反射器馈源的主波束

Fig. 10. Horizontal and vertical diagram of Truncated 3D Corner Reflector Feed 图10:削顶3D角反射器馈源的水平和垂直方向图

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 11. Elements current and back lobes of Truncated 3D Corner Reflector Feed 图11:削顶3D角反射器馈源的振子电流和后瓣

Fig. 12. End view and side view of Truncated 3D Corner Reflector Feed 图12:削顶3D角反射器馈源的端视图和侧视图

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 13. Cut dimensions and bending lines for reflector of Truncated 3D Corner Reflector Feed 图13:削顶3D角反射器馈源的反射器的剪裁尺寸和弯折线

Mechanical construction of the antenna 天线的机械结构 The radiator and director are made out of two pieces of copper wire, diameter 1.6 mm and total length of 37.9 mm for radiator and 33.4 mm for director, measured from the reflector surface! The reflector surface may be only made out of copper, aluminum or brass tin. The reflector is cut off according to given dimensions and folded at a 90 deg. angle according to dashed lines. The backside can be soldered at the junction if the reflector is made out of copper or brass and in that case the overlapping field is not necessary. The backside can also be fixed by screwing or pop-riveting in very densely overlapping fields. Overlapping fields must always be on the backside of the reflector. I also tried a feed antenna whose bottom reflector surface was left unshortened for better mechanical stiffness. The impact of this additional surface is very small, although it slightly narrows the vertical diagram and consequently slightly

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

spoils efficiency. 引向振子和有源振子是两段铜线做成,直径1.6mm,有源振子全长37.9mm, 引向振子全长33.4mm,都是从反射器表面算起!反射器表面只能用铜,铝或者 黄铜材料制作.反射器要按照给出的尺寸剪裁,依据所示虚线弯折90度.如果 反射器是用铜或黄铜制作的,背部可以焊接在一起,这种情况下不一定要层叠 搭接.背部也可以用螺栓或拉丁非常紧密地搭接.搭接必须在反射器后面.我 曾经试制一个馈源,为了提高机械强度,把它的底部截短了,这对它的影响很 小,虽然因为缩窄了垂直方向图而导致轻微的效率损失.

Fig. 14. Elements dimension of Truncated 3D Corner Reflector Feed 图14:削顶3D角反射器馈源的振子尺寸

Protection from atmospheric action 防护大气侵蚀作用 It is the best that this protection is done while the metal is still light and without corrosion and antenna is covered by thin layer of varnish. Before that, the upper opened part of the connector is protected with a thin layer of polyethylene, using the pistol that melts polyethylene bars and deposits liquid plastic on the desired surface. The layer of polyethylene should be waterproof, but as thin as possible! So, it is wrong to put large amounts of plastic in thick layer to the connection, because it's useless and serves only to worsen impedance matching! Also, the use of silicone is strictly forbidden because of its chemical aggressiveness and great losses at higher frequencies! 最好在金属线还是光亮的,没有被腐蚀之前就在天线表面涂上一层薄薄的 清漆,在此之前,接头上部裸露的部分要用聚乙烯保护起来,用热熔枪融化聚 乙烯棒涂在该处.聚乙烯层必须是不透水的,但是要尽可能的薄!在接点处堆

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

积大量的厚厚的塑料制品是错误的,因为它不仅无用还会破坏天线的阻抗匹配! 同样,严禁使用硅有机树脂,因为它具有腐蚀性,还会使高频大量损失! Placing the feed in the focus of the offset parabola 在偏馈抛物面天线放置馈源 The analysis of the phase center of truncated 3D corner feed revealed that it is positioned 1.63 wavelengths or 83 mm in front of the reflector measured from the apex along a large diagonal that is 45 degrees in relation to all three reflector surfaces, i.e. in direction of the maximal radiance. That point (that is in the figure given as coordinate center) must be placed in the focus point of the parabola as precisely as possible! The direction of maximal radiation of the main beam must be directed into the geometrical center of the elliptic surface of the parabola. 分析报告显示,削顶3D角反射器馈源的相位中心,位于反射器前面从顶点 到1.63波长(83mm)的位置,沿着一个与3个反射面都是45°的大对角线(即最 大距离)的方向.这点(这里被赋予坐标中心的角色)必须精确的置于抛物线 焦点上!主束的最大辐射方向必须指向抛物线椭圆表面的中心. When SAT TV offset parabolas are used, focus is determinate by the position of the SAT TV converter. The focus of the parabola, practically, is in the entrance in the waveguide of the converter. By measuring the distances between the entrance of the converter and at least 3 fixed points at the edges of the parabola, one should keep the information about the position of the focus, so that it could be precisely determined and restored when the SAT TV converter and original carrier are taken off or adjusted in order to be able to carry a different feed. This is very important because it is very often the case that, after the correction of the feed carrier, the position of the parabola's focus is lost and it cannot be restored if there is no information, i.e. space coordinates in relation to the parabolic surface. 当使用卫星电视偏馈抛物面天线时,焦点限定在卫星电视变频器的位置. 抛物线的焦点实际上在变频器波导入口处.测量波导入口和抛物面边缘上至少3 个定点的距离,就知道了焦点的位置.要保存好焦点位置的数据,这样,当我 们为了使用不同的馈源,拿掉或者调整了卫星电视变频器和原来的托架之后, 就能准确的确定和还原它们.这点非常重要,因为这是经常的事.更换了馈源 托架之后,如果没有相关资料,即,抛物面空间座标,找不到抛物面焦点的位 置,就无法复原.

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 15. Phase center position of Truncated 3D Corner Reflector Feed and its location in relation to parabola focus 图15:削顶3D角反射器馈源的相位中心和相对于抛物面焦点的位置 Results with an offset parabola 用于偏馈抛物面天线的效果 We achieved very good results by analysis of truncated 3D corner feed with rectangle shaped offset parabola, with dimensions 100x110 cm and F/D=0.8. We confirmed very high efficiency on the basis of achieved gain of the parabolic antenna in relation to theoretic value. The calculation of the efficiency of illumination of parabola from its gain gave the value of about 57%, which relatively well coincides with calculations of efficiency derived from the shape of the feed diagram given in Figure 17. An elliptical parabola with the same dimensions would have smaller gain by about 1 dB in relation to this analyzed rectangular, with the same efficiency, because of smaller geometric surface of the elliptic parabola. 通过分析削顶3D角反射器馈源用于尺寸100×110cm,F/D=0.8的长方形偏馈 抛物面反射器,我们得到很好的结果.我们确认,在达到偏馈抛物面天线理论 增益的基础上,抛物面天线获得非常高的效率.计算得知,抛物面的照射效率 大约是57%,这与图17馈源方向图显示的结果完全一致.一个同样尺寸,同样 效率的椭圆形抛物线反射器,比这个长方形反射器低大约1dB的增益,这是由于 椭圆形抛物面几何表面小一些. Another confirmation that this is a very good feed is the purity of achieved radiation diagram of parabola. First side lobes are suppressed 20 dB, and F/B is more than 30 dB. Maximal gain of the antenna is achieved when the phase center of the feed is exactly in the focus of parabola and when the large diagonal of truncated 3d corner feed, i.e. maximum of radiation diagram of the main beam, is directional into the geometric center of parabolic surface that is in the crosshair of large and small axis of

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

ellipse. The input impedance of the feed remained practically unchanged when placed in focus of parabola, which was expected from this antenna that is known by its low Q factor. 另一点被证实的是,这是一个方向图纯净完美的,非常好的抛物面天线的馈 源.第一副瓣抑制为20dB,前后比大于30dB.当馈源的相位中心准确位于抛物 面中心时,当削顶3D角反射器馈源的长对角线,即主束的最大方向图指向抛物 面口径面几何中心也就是椭圆形的长轴和短轴交点时,天线获得最高的增益. 位于抛物面焦点时,馈源的输入阻抗几乎保持不变,对这个以低Q因素闻名的天 线来说,这些正是我们所期待的.

Fig. 16. Vertical and horizontal diagrams of offset parabola with Truncated 3D Corner Reflector Feed 图16:使用削顶3D角反射器馈源的偏馈抛物面天线的垂直和水平方向图

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 17. Parabola efficiency with Truncated 3D Corner Reflector Feed in relation to its F/D ratio 图17:使用削顶3D角反射器馈源时抛物面天线对应F/D比率的效率

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 18. 3D diagram of rectangular offset parabola with Truncated 3D Corner Reflector Feed 图18:使用削顶3D角反射器馈源的偏馈抛物面天线的立体方向图

Fig. 19. Practical use of Truncated 3D Corner Reflector Feed with SAT TV offset parabola 图19:削顶3D角反射器馈源实际应用于卫星电视偏馈抛物面反射器

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Fig. 20. Outlook of Truncated 3D Corner Reflector Feed mounted in focus of offset parabola 图20:削顶3D角反射器馈源安装在偏馈抛物面天线焦点的情景 Conclusion 结论 In this article we showed and, by precise computer simulations, confirmed the possibility of using truncated 3D corner reflector feed for efficient illumination SAT TV offset parabolic dish. Pure diagrams of truncated 3D corner reflector feed, with approximately equal width of the main beam in both planes, proved it to be a very simple and efficient feed for offset parabolic antennas whose F/D is 0.7-0.9. As a result we achieved high efficiency, directivity and purity of the diagram SAT TV offset parabolic antenna on 5.8 GHz. 本文以精确的计算机仿真,证实完全可以用3D角反射器天线做卫星电视偏 馈抛物面天线的馈源.削顶3D角反射器馈源的方向图非常纯净,主束宽度在垂 直和水平方向图大体平衡,证明了它作为一个简单而高效的馈源,适合F/D在 0.7-0.9之间的偏馈抛物面天线.这样,我们获得了高效的,方向性强,方向图 纯净的用于5.8GHz频段的卫星电视偏馈抛物面天线.

Fig. 21. 50 km 5.8 GHz link using offset parabola dish and Truncated 3D Corner Reflector Feed 图21:5.8GHz频段用偏馈抛物面天线和削顶3D角反射器馈源连接50公里

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Acknowledgements 鸣谢 I thank the boys from BG Wireless, and especially Spider, for the help on practical realization and verification of this feed. The feed is tentatively projected for 5.8 GHz links in BG Wireless network and so far it has been successfully tested at a distance of about 50 km. 我感谢来自BG无线的男孩子们,特别是蜘蛛,在这种馈源的证明和实践方 面给予的帮助.这个馈源是为5.8GHz做的实验设计,链接在BG无线网,迄今为 止,它是50公里远距离的成功实验.

Literature 参考书目 1. The W1GHZ Online Microwave Antenna Book 2. PHASEPAT v.1.0 and FEEDPATT v.1.0 programs by Paul Wade, W1GHZ 3. A.W. Love, Reflector Antennas, IEEE Press, 1978. 4. John Kraus, Antennas, McGraw Hill, 1956.

BRIEF BIOGRAPHY OF THE AUTHOR 作者简介 Dragoslav Dobrii, YU1AW, is a retired electronic engineer and worked

for 40 years in Radio Television Belgrade on installing, maintaining and servicing radio and television transmitters, microwave links, TV and FM repeaters and antennas. At the end of his career, he mostly worked on various projects for power amplifiers, RF filters and multiplexers, communications systems and VHF and UHF antennas. For over 40 years, Dragan has published articles with different original constructions of power amplifiers, low noise preamplifiers, antennas for HF, VHF, UHF and SHF bands. He has been a licensed Ham radio since 1964. Married and has two grown up children, a son and a daughter.

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3D 角反射天线作馈源的 5.8GHz 偏馈抛物面天线

Dragoslav Dobrii, YU1AW 先生是贝尔格莱德无线电视台一位退休无线 电视工程师,他在电视台做了 40 年无线电发射机,微波线路,电视和调频中继 以及天线的安装,调试,维修工作.在他职业生涯的最后阶段,他主要从事各 种放大器,高频滤波器,多路复用器,通信系统和特高频,超高频天线的规划. 四十年来,Dragan 出版了多版本的 HF,VHF,和 SHF 频段的功率放大器,低噪 音前置放大器的著作.1964 年他获得业余无线电许可证.已婚,一子一女已成 年.

激情无线(lijiqing)翻译

2009 年 9 月

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September,2009

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