Practical_Antenna_Handbook_0071639586
548 P a r t V I I : T u n i n g , T r o u b l e s h o o t i n g , a n d D e s i g n A i d Figure 25.2 Example of a single wire laid out on x,y,z coordinate system. user will learn how to quickly specify wires and their positions in model space, select an appropriate number of segments for each wire, and position sources within segments. Tip When modeling antenna elements, such as dipoles, that are fed in the center, use an odd number of segments for the wire. This allows placement of the source or feedpoint in the exact center of the middle segment, thus duplicating the actual antenna very closely.
C h a p t e r 2 5 : A n t e n n a M o d e l i n g S o f t w a r e 549 A Typical NEC-Â2 GUI Roy Lewallen, W7EL, produces the EZNEC family of software for Windows PCs. The software extends Roy’s earlier work on DOS versions of EZNEC but is still based on the NEC-Â2 engine. (A professional version based on the NEC-Â4 engine is available for those who obtain the required government license.) Figure 25.3A shows the opening screen in EZNEC+ ver 5.0 for a typical antenna project (in this case, an 80-Âm bent dipole). Visible in this window are file name, frequency, free-Âspace wavelength (in meters), number of wires and segments, number of sources, number of loads, transmission lines, ground type, wire loss, the units employed (meters, feet, etc.), plot type (azimuth, elevation), elevation angle, step size, a reference level, and an alternate Z 0 for the SWR plot (to conveniently handle both 50-Â and 75-ÂΩ system impedances). Command buttons to the left of the main window include Open, Save As, Ant[enna] Notes, Currents, Src [Source] Dat[a], Load Dat[a], F[ar]Field] Tab[le], N[ear]F[ield] Tab[le], SWR, View Ant[enna], and F[ar]F[ield] Plot. The “FF Plot” button graphs the far Figure 25.3A EZNEC+ ver. 5 opening screen.
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548 P a r t V I I : T u n i n g , T r o u b l e s h o o t i n g , a n d D e s i g n A i d<br />
Figure 25.2 Example of a single wire laid out on x,y,z coordinate system.<br />
user will learn how to quickly specify wires and their positions in model space, select<br />
an appropriate number of segments for each wire, and position sources within segments.<br />
Tip When modeling antenna elements, such as dipoles, that are fed in the center, use an odd<br />
number of segments for the wire. This allows placement of the source or feedpoint in the<br />
exact center of the middle segment, thus duplicating the actual antenna very closely.
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