Compact two-element antenna for the range 20 m
One English shortwave developed a compact two-element antenna, dubbed. "Zygi-beam". Each element of the antenna (see Fig. 1) made in the form of a rectangle, the sum of the lengths of the sides of which are approximately equal to L/2, and the ratio of large parties to small - two. The middle of the large sides are open. The antenna elements are arranged in one plane and have an active power. The elements are made from lengths of aluminum tubing with outer diameters of 13 and 6 mm Segments of thin tubes bent in the form of the letter P and ends with a length of about 160 mm, and is inserted into the thick tubes.
The antenna elements is fixed on the plates the size H mm made of steel and Plexiglas (see Fig. 2). To the steel plates attached to the ends of the tubes to which the power is connected, and to the plates of Plexiglas - the free ends of the tubes under high voltage.
A segment of the transmission line, connecting elements formed from ribbon cable length 2185 mm with a characteristic impedance of 300 Ohms.
The elements of the antenna at the resonant frequency shown in Fig.1, is produced when disconnected the ribbon cable moving thin tubes inside thick. Moving tubes of 2.5 mm leads to a change in resonant frequency of approximately 100 kHz. The setting of each item should be made from both sides in order to preserve the symmetry of the structure. The value of SWR is properly tuned antenna at the frequency of 14.2 MHz should not exceed 1.1. Reduce the CWS can be achieved by adjustment of the element A. From tuning element B depends mainly power ratio of radiated in the forward and reverse directions.
The input impedance of the antenna is 42 Ohms, allowing you to use its power cable with a characteristic impedance of 50 Ohms. If you use 75 Ohm cable for matching the antenna with feeder was used transformer, mounted near the input terminals of the antenna. with the transformation ratio of the resistances 1.6.
The beam width at the half-power level is approximately 70° with respect to capacity, emitted in forward and reverse directions about 8-10 dB. Antenna gain is estimated by the author, is more than 4 dB. The antenna emits energy primarily at small angles to the horizontal, the height of the installation has little effect on performance.
Publication: N. Bolshakov, rf.atnn.ru