‰  NOW 40 WPM  ‰  TEXT IS FROM SEPTEMBER 2013 QST  PAGE 39‰
HOWEVER, BASED UPON COMPUTER MODELING USING A HYBRID MODEL TO REPRESENT THE
PRACTICAL GROUND ITS GAIN IS ESTIMATED TO BE BETWEEN 7 AND 8 DBI.  THE
HORIZONTAL AND VERTICAL HALF POWER BEAM WIDTHS ARE 90 AND 35 RESPECTIVELY,
WITH A VERTICAL BEAM ELEVATION OF 20.  MODELING HAS ALSO PREDICTED THAT THE
ANTENNA CHARACTERISTICS VARY ONLY SLIGHTLY ACROSS THE OPERATING BANDWIDTH
OF 0R45 MHZ AT 21 MHZ.  THE DIRECTIONAL PROPERTIES OF THE ANTENNA ACCORDED
WELL WITH COMPUTER MODELING, POTENTIALLY

SET OF DRIVE CURRENTS, PROVIDES A BASIS FOR COMPARISON SEE FIGURE 12.  IT
SHOWS THAT THE FORWARD GAIN SHOULD BE 7R32 DB, THE HIGHEST ATTAINABLE VALUE
ON THIS PRACTICAL GROUND.  THE BEHAVIOR IN THE REAR SECTION IS DETERMINED
BY THE DEGREE OF CANCELATION OF THE FIELDS FROM THE FOUR ELEMENTS.  IT IS
HERE THAT SMALL DIFFERENCES BETWEEN THE FIELD COMPONENTS BECOME APPARENT
AND REFLECT IMPERFECTIONS IN THE ARRAY AND ITS FEED SYSTEM THAT CAUSE
ERRORS IN THE DRIVE CURRENTS.  FIGURE 13 REPRESENTS THE SUPERIMPOSED DATA
ON RECTILINEAR AXES TO AID COMPARISON.  THERE IS SIGNIFICANT AND CONSISTENT
DETAIL IN THE REAR SECTOR.  THE OVERALL IMPRESSION IS OF SIMILARITY IN THE
MAIN LOBES FOR THE FOUR BEAM HEADINGS.  THE ACTUAL DRIVE CURRENTS WERE
INSERTED INTO THE SIMULATION AND THE PREDICTED GAIN VALUES COME CLOSE TO
THE MAXIMUM ATTAINABLE ON THE HYBRID GROUND, COMPARE FIGURES 12 AND 14.
THE OBSERVED FRONT TO BACK RATIOS WERE AT LEAST 20 DB ON THIS GROUND AND
FIGURE 12 SUGGESTS THAT AN IMPROVEMENT BY 3 TO 4 DB MIGHT BE ACHIEVABLE.
ALTHOUGH APPRECIABLE, IT IS QUESTIONABLE IF THIS IMPROVEMENT WOULD HAVE
PRACTICAL VALUE SINCE THE RATIO WAS ALREADY 20 DB.  IT IS INTERESTING TO

FOUR DIRECTIONS, AGAIN ON THE HYBRID GROUND.  THE NORMALIZED CURRENTS WHICH
SOMETIMES DEVIATED FROM THE INTENDED VALUES ARE LISTED IN TABLE 7, THE
REASONS FOR THIS WILL BE DISCUSSED LATER.  THE MODELED POLAR PATTERNS USING
THE ACTUAL DRIVE CURRENTS ARE SHOWN IN FIGURE 13 THIS AND THE FOLLOWING
FIGURES CAN BE FOUND AT WWW. ARRL.  ORG QST IN DEPTH.  THERE IS GOOD
AGREEMENT BETWEEN THESE AND THOSE THAT WERE MEASURED.  THE FRONT TO BACK
RATIOS SPAN THE RANGE FROM 20R6 TO 14R7 DB AND ARE SOMEWHAT SMALLER AND
LESS CONSISTENT THAN THOSE MEASURED.  THE BEAM WIDTHS ARE IN VERY GOOD
AGREEMENT WITH THE MEASUREMENTS.  PREDICTED, BUT NOT MEASURED, ARE THE
FORWARD GAINS.  THESE ARE VERY SIMILAR FOR THE FOUR DIRECTIONS, RANGING
BETWEEN 7R00 AND 7R36 DBI AS SHOWN IN FIGURE 14.  THE SIMULATION ALSO
PROVIDES THE ELEVATION OF THE MAIN LOBE ABOVE THE HORIZON.  ALTHOUGH THE
ONLY PATTERN PRESENTED HERE, FIGURE 15, IS FOR THE NE DIRECTION, THE PEAK
ELEVATION IS CLOSE TO 20 FOR ALL BEAM HEADINGS, WITH A HALF POWER VERTICAL
BEAM WIDTH OF 35.  A VERY USEFUL INDICATION OF THE INSENSITIVITY TO
FREQUENCY ACROSS THE 21 MHZ BAND IS PROVIDED BY THE TWO NE POLAR PATTERNS
IN FIGURE 16.  THIS 2 CHANGE OF FREQUENCY CAUSED A CHANGE OF ONLY 0R5 DB IN
THE FRONT TO BACK RATIO AND A NEGLIGIBLE CHANGE IN GAIN OF ONLY 0R05 DB.
DISCUSSION THE ANTENNAS BEHAVIOR ON THE HYBRID GROUND, BUT WITH A PERFECT
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ