Antenna Reference / Loop Antenna Question
Antenna Reference / Loop Antenna Question
(OP)
Hi guys. As a general question, I was wondering if anyone had located and good antenna theory/design references on the web. I've done a lot of googling, but *good* stuff can sometime be difficult to find.
On a more specific note, does anyone know why you would connect the feed line to a loop antenna mid-loop rather than at the gap?
i.e.:
|-*---|
|
|-* --|
Where the *'s are the feed line connection points.
Is this an effort at impedance matching? The coaxial feed line is connected directly to the antenna with no line balancing methods in place. The antenna is supposedly designed for the 400 MHz range.
On a more specific note, does anyone know why you would connect the feed line to a loop antenna mid-loop rather than at the gap?
i.e.:
|-*---|
|
|-* --|
Where the *'s are the feed line connection points.
Is this an effort at impedance matching? The coaxial feed line is connected directly to the antenna with no line balancing methods in place. The antenna is supposedly designed for the 400 MHz range.





RE: Antenna Reference / Loop Antenna Question
RE: Antenna Reference / Loop Antenna Question
This is a bit of a simplification because, in most cases, the two leads need to be spread apart to reach the two points, and this complicates things a bit.
There may also be some reactance that needs tuning out, and thus you'll often see a series capacitor of various constructions.
In addition to the ARRL books, there are also the RSGB antenna books. These are both national ham radio organizations, USA and UK respectively.
RE: Antenna Reference / Loop Antenna Question
It still seems like it would be a good idea to connect the coax through a balun or other balancing method, though. VE1BLL is correct, the leads do need to be spread out in order to reach both sides of the loop and with nothing nothing in place to isolate the coax from the antenna the feed line essentially becomes part of the antenna.
RE: Antenna Reference / Loop Antenna Question
In short - coax cable is more balanced than it might appear.
The currents inside the coax are forced to be equal and opposite by physics. And so long as the coax in the immediate vicinity of the antenna is dressed away at right angles (symmetrically), then there should no reason for significant common mode currents to be imposed on the outside of the shield.
RE: Antenna Reference / Loop Antenna Question
http://www.antennex.com/
Lots of antenna design archives.