The G-Unit
Text books have explained colinear and log periodic designs thoroughly in the past, but none to date have covered Matchmaster's patented G-Unit design. This may be because of the theory's complexity, however, some aspects can be simply explained.
As a bare unit, the G-Unit has a directivity in the direction 'Z' (as shown in FIG. 1.). Each G-Unit is designed specifically for a group of two or more frequencies, and each type is characterised by two dimensions, being; the front dipole - 'F' and the rear dipole - 'R'.
Let us consider the capital city frequencies, channels 7, 9, 10 & Ch.2. The higher frequencies (7 & 9) are approximately three times higher than channel 2. In the G-Unit design, 'R' is three times longer than 'F'. This relationship is important because 'F' is approximately half a wavelength long at channels 7 to 9, and 'R' is approximately 3 x half a wavelength at channels 7 to 9. Both front (F) and rear (R) dipoles are working at these frequencies.
The rear dipole also acts as a half wave dipole for channel 2. The result is a much higher gain in a more compact design.
There are several properties of the G-Unit that explain it's performance. The principle incorporates a colinear array enabling a high front to back ratio, bandwidth and impedance matching properties.
Sections A & B constitute a colinear array. C & D may be included, as they are almost colinear with A & B outer sections. The colinear operation gives considerable gain, narrow main lobes and none or negligable side lobes.
The input impedance of the G-Unit (capital city model) is 315 ohms at 190 MHz, near perfect matching for a wideband antenna. At the frequencies of Ch, 7 & 9, the standing wave ratio is increased to about 1.5, remarkably better than the tolerated maximum value of 2, for good quality TV reception. The bandwidth and matching properties of the G-Unit are mainly achieved due to the transmission line stub effects. Briefly explained, sections A & B act as short circuited 1/4 wave stubs, and sections C & Doperate like 3/4 wave stubs.
