Wire Moxon Rectangles for 40-10 Meters

L. B. Cebik, W4RNL

Since a posting on QRP-L, the Moxon rectangle has drawn considerable attention. A full analysis of the antenna appears in the Spring, 1995, issue of Communications Quarterly. Basically, the Moxon rectangle is a wire antenna that can be fix-mounted or rotated. It is directional with about the gain of a 2- element Yagi (6 dBi in free space) and has an outstanding front-to-back ratio (greater than 30 dB in free space), with a very broad frontal lobe (-3dB beamwidth = 70 degrees, usable beamwidth = nearly 180 degrees forward). The basic outline of the antenna appears in Figure 1.

Since the article and the posting appeared, I have heard of successful constructions of Moxon's, one for a Field Day Novice station. I have also had two types of requests. One has asked for dimensions for other bands. The other inquiry wondered if the feedpoint impedance might be brought closer to 50 ohms. The original design showed a feedpoint impedance close to 80 ohms.

I remodeled the antenna with good results on both counts. Table 1 provides dimensions for the Moxon rectangle for 40 through 10 meters. The dimensions are not perfect simple scalings, because the length-to-wire- diameter ratio changes for each ham band.

Table 1. Moxon Dimensions for 40 - 10 Meters

Design Dimension (feet) Band Frequency(MHz) A B C D E 10 28.50 12.44 1.94 0.41 4.76 2.41 12 24.94 14.22 2.22 0.46 5.44 2.76 15 21.20 16.72 2.63 0.52 6.40 3.25 17 18.12 19.56 3.10 0.59 7.49 3.80 20 14.17 25.00 4.00 0.72 9.57 4.85 30 10.12 35.00 5.60 1.00 13.40 6.80 40 7.15 49.56 8.01 1.33 18.97 9.63

Note: all models composed of #14 copper wire. All of the antennas exhibit feedpoint impedances between about 56 and 58 ohms, a close match to the standard amateur 50-ohm coaxial cable. Free space gain and front-to-back ratio are consistent for all the models, averaging 5.8 dBi and greater than 32 dB in free space, respectively, at the design frequency, centered in each band. Figure 2 shows a typical free space azimuth pattern for the antenna.

All of the models use #14 copper wire, although the various factors that contribute to the Moxon pattern tend to cancel out as wire size increases. Hence, a tubing model will have dimensions close to those for a thin wire model. However, it will exhibit a broader SWR bandwidth. The models were constructed on EZNEC Pro, a NEC-4 implementation by W7EL. At heights below 1/2 wavelength, the front-to-back ratio will deteriorate somewhat, but usable values can be obtained. Figure 3 shows the azimuth pattern of a Moxon Rectangle at the elevation of maximum radiation, with a height of a half wavelength above real, medium ground. The pattern (especially front-to-back ratio) improves toward free space values as the antenna is further elevated. Elevation angle of maximum radiation is the same as a 2-element Yagi at the same height, for example 25?at 1/2 wl up, 14?at 1 wl up. etc.

The bandwidth for 2:1 SWR is only about 100 kHz on 40 with #14 wire. Above 40, the 2:1 SWR bandwidth covers the entire amateur band. For 30 and up, the front- to-back ratio is better than 15 dB across the band.

The original article showed one construction technique for 10 meters. Many others are possible, whether the material is wire or aluminum tubing. I shall leave the exact methods to the reader's ingenuity.

A Hybrid Wire Moxon-Yagi for 20-10 Meters

Although the Moxon rectangle does not lend itself readily to nesting in a single plane without careful trapping (as described in Moxon's account in his classic HF Antennas for All Locations), ingenuity has produced some interesting variants for multi-band use. Dennis Schaefer, W5RZ, has designed a hybrid Moxon based on the 20-meter wire dimensions shown above. Inside the rectangle, he added elements for 10 and 15 meter operation. The 15-meter element is a reflector, but the 10-meter element turns out to be a director, reversing the antenna pattern. The dimensions are sketched in Figure 4.

The design frequency performance for each band is summarized in Table 2. All values are based on free-space models.

Table 2. Modeled Tri-band Performance of the W5RZ Hybrid Frequency Gain (dBi) F-B (dB) Feedpoint Impedance 14.15 5.8 34.0 60 - j 2 21.2 6.4 9.7 180 + j 935 28.4 5.8(rev) 6.9 2100 + j3060

The antenna is designed to be fed with parallel transmission line and to be matched by a balanced antenna tuning unit. Free-space modeling of the antenna design shows that on 15 meters, the drive provides a double-humped current distribution, with a high reflector current on the 15-meter element. Current on the 10-meter element and the 20-meter reflector is low. On 10-meters, the current distribution is typical of a 1-wl element, with high director current on the 10-meter element.

This is just one possible direction of exoanding the capabilities of the Moxon Rectangle, and the future is likely to see additional examples of antenna design ingenuity, using the rectangle as the foundation.

Conclusion

The standard of comparison for the Moxon is the 2-element Yagi. While a Yagi has marginally more gain, the Moxon's front-to-back ratio is very much superior. It will likely improve your ears much more than it will diminish your voice. And, as the old but true saying goes, if you can't hear 'em, you can't work 'em.

First printed in QRPp, December, 1995. Updated and enlarged 6-10-99. ?L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author. 40-10m 由金属线制成的 Moxon 长方形定向天线 L. B. Cebik,W4RNL

自从在 QRP-L上的一个公告之后， Moxon 长方形天线引起了极大的关注。天线的全文分析是在1995年春,每季通信议题刊登的。Moxon天线的基本形式是一个线状的长方形天线，可是固定或转向安装使用。它有 2个元件 Yagi(自由空间的 6 dBi) 的增益，而且有一个杰出的前後比 ( 自由空间大于30个分贝),有一个非常宽广的正向指向性.(-3db 带宽=70度, 可使用的波束宽度 = 将近180度向前的功率)天线的基本结构图，在图 1 。

因为文章和布告出现,我已经听说 Moxon's天险的成功设计,户外运动日已经新手的首选。这里，我有两个问题。一是能否有其他波段的设计。另一个是如何使得馈电点阻抗较接近50 欧。因为，最初的设计馈电点阻抗约为80欧。

我有两个改造好的天线统计结果。表 1为 Moxon 长方形天线为 40 到10 米的结构尺寸统计不是完美的简单计数, 因为长度-线- 每个业馀家要考虑到线材直径比率带来的变化。

表 1. Moxon 大小为 40- 10m

频带设计频率(MHz)尺寸(feet) A B C D E 10 28.50 12.44 1.94 0.41 2.41 4.76 12 24.94 14.22 2.22 0.46 2.76 5.44 15 21.20 16.72 2.63 0.52 3.25 6.40 17 18.12 19.56 3.10 0.59 3.80 7.49 20 14.17 25.00 4.00 0.72 4.85 9.57 30 10.12 35.00 5.60 1.00 6.80 13.40 40 7.15 49.56 8.01 1.33 9.63 18.97 注意: 所有的模型 #14个铜线组成。所有的天线馈电点阻抗都在56到58欧之间,可以与标准的50个欧电缆匹配。在设计频率和带宽里，自由空间增益和前後比对所有的模型是一致的, 平均 5.8 dBi ，前后比自由空间为32分贝。图 2 为天线一个典型的自由空间中的方位图。

所有的模型都使用 #14个铜线, 虽然对 Moxon 图案会因各种不同的因数容易改变，但只要按规定尺寸制作增减就可以。

设计表 2 中概述。所有的数值以自由空间模型为基础。

表 2. 做模型了 W5RZ 拼合的 Tri- 能带绩效频率得到 (dBi)F- B(分贝)Feedpoint 阻抗 14.15 5.8 34.0 60-j2 21.2 6.4 9.7 180+j935 28.4 5.8 16.9 2100+j3060 天线被设计与平行传送线一起送到一个被平衡的天线调谐单元匹配。天线设计的自由空间靠模切在 15 公尺上，磁盘提供加倍- 有肉峰的目前分配, 由于一高反射器目前的在 15个仪表的元件上。目前的通 10个仪表的元件和 20个仪表的反射器是最低值。在 10 仪表上，目前的分配一个 1 wl 的元件是典型的,藉由目前的在 10个仪表的元件上的高导向体。这只是一个可能的 exoanding 的方向 Moxon 长方形的能力，而且未来可能天线设计智巧的附加例子,使用长方形如基础。结论比较的标准为 Moxon 是 2个元件的 Yagi 。当 Yagi 边缘地多有增益的时候,Moxon's 的前後比非常上好。它更加多将会或许改听觉，相比较它将会噪声较小。

在 QRPp ， 1995 年十二月首次印刷。 6-10-99 由?L. B. Cebik，W4RNL修改出版。数据可以个人使用，但是不经作者的许可，任何其他的媒介不得引用, 再版。