シグマアンテナは，小暮裕明，JG1UNE　によって考案された，コンパクト２エレメント・ビームです． ギリシャ文字のシグマの形にすることで，ほぼ性能を損なわずに小型化しています．
コンパクト・アンテナブック (ダイナミックハムシリーズ７) (CQ出版社)などで紹介され，ARRLの QST誌にも載ったことで世界的にもひろく試されています．Peter Dodd, G3LDO からは，解析の結果， 種々の折曲げエレメント・アンテナの内で最もよい成績との評価を得ました．
Peter Schmidt, DL9JFT による，ワイヤーで軽量化したバージョンは こちらから．

参考文献：
『14MHz”ダブル-D”アンテナ 』，CQ ham radio，1997．4，p.118-122 ，CQ出版社
"Wire Beam Antenna and the Evolution of the Double-D", Peter Dodd G3LDO, QST, Oct. 1984

A full-size beam antenna is great - if you have the space for one. Many of us, however, live in apartments and just don't have that space. These figures show my experiments with a miniaturized beam antenna in a Sigma configuration. My antenna is mounted at the top of a tower, about 15 m above the building roof.
The Sigma beam is a compact antenna shaped like the Greek letter sigma; it is a V beam with the element ends to reduce its size. Be sure to flatten the tube joints (after assembly!) to keep the element ends from rotating.
An SWR plot of my Sigma beam compares well with that of a full-size, two-element V-beam. The two curves are nearly identical, with the SWR less than 1.7:1 from 28 to 29 MHz. The folded element ends seem to have little effect on the antenna impedance. The V antenna has slight gain over a dipole, and I feel that the Sigma beam provides the performance of a V beam in a very compact package.
The antenna weight can be reduced, and construction simplified, if we use straight bamboo or fiberglass spreaders to support wire elements.
There's no need to give up DXing because you live in an apartment.
Try a Sigma beam!

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