In the manufacture KB antenna can win the strengthening
In the manufacture LW antenna can win in gain, if a normal frame antenna double square to convert to rectangular, as shown in Fig. 1.
Active, or radiating, are the vertical sides of the antenna. To increase the efficiency of their benefits from dural tubes with a diameter of 10-20 mm Horizontal side - reactive complement the perimeter of the rectangle to the resonant length and made from conventional antenna cord. The upper side is broken exactly in the middle Marinova insulator to the distribution of the current frame is not dependent on the connection points of the feeder, changing to align the antenna with any cable. The input impedance of the scope varies from 30-40 ohms (the feeder is attached in the corner of the frame) to several thousand ohms in the center of the horizontal side. The feeder is placed along the conductor antenna and discharged at a right angle in any direction from the middle of the vertical sides, i.e. at the point antinodes current. For complete balancing preferably a braided cable at that point to connect with the wire antenna.
The radiation characteristics of the "Rectangle" is approaching-phase two-element antenna (gain of about 2-3 dB), but has a relatively narrow band of operating frequencies - 2% for 20 m band. In Fig. 2 presents the comparison of the directivity in the horizontal plane of the frame of the double square with vertical polarization 1 and described antenna 2. Parasitic petals are virtually absent due to the small distances between the reactive side of the frame.
Due to the small height of the Rectangle appears to be very convenient for ranges of 40, 80 m. it must be Set so that there was no shading of the objects. The distance from the bottom wire to the roof may be several tens of centimeters. To obtain unidirectional charts you can use the same frame that is configured as a reflector or Director, at the distance of 0.05 to 0.15 l from the first. In the case where the antenna height is critical, "Rectangle" can be used with success on the higher frequency bands in the composition of the multi-element directional antennas. The properties of such a three-element system similar characteristics up antenna type Yagi-UDA are presented. Calculator for calculation of antenna elements (RA3TOX) Enter the frequency (MHz) Vertical side (short) = (cm) Horizontal side (long) = (cm)
Author: Yu Medanic (UB5UG), Kyiv; Publication: N. Bolshakov, rf.atnn.ru