What gives an antenna its characteristics?

When an antenna has a range of 902-928, what gives it those properties? I opened an antenna and only saw metal. Is it the thickness of the metal? Or the shape the metal was cut into? There was no resistor or anything inside. However I opened another one and it had a different shape and one resistor soldered inside. Any ideas?

Thanks

Shape. Dimensions. Impedance. Material.

Where does it get its impedance from? I can tell that the material is made of aluminum. Is there a free software I could use to design an antenna?

Thank you

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Where does it get its impedance from? I can tell that the material is made of aluminum. Is there a free software I could use to design an antenna?

Thank you

kirr45 said:

When an antenna has a range of 902-928, what gives it those properties? I opened an antenna and only saw metal. Is it the thickness of the metal? Or the shape the metal was cut into? There was no resistor or anything inside. However I opened another one and it had a different shape and one resistor soldered inside. Any ideas?

Thanks

Click to expand...

Stricly speaking, if an antenna has a frequency coverage of 902-928 MHz, then that needs clarification on what parameter(s) are met over that. Such as the gain is above X dB over that range, the VSWR is less than Y over that range.

Resistors in an antenna would usually be a bad idea. The absorb power and turn it into heat. That is the last thing you generally want in an antenna, as you want to radiate the power that the antenna receives at its input terminal, or output the power it receives on the elments(s). (An antenna can be used for transmitting or receiving. Within limits, a good transmitting antenna is a good receiving one).

The type of metal (copper better than alluminium, silver better than both, brass quite poor), as well as the size, shape and design. If it's in an enclosure, the type and size of the enclosure. Basically just about anything can effect an antenna's properties. The skill in designing an antenna is knowing what effects the properties, and how to put that to best use.

Dave

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kirr45 said:

Where does it get its impedance from? I can tell that the material is made of aluminum. Is there a free software I could use to design an antenna?

Thank you

Click to expand...

Before using any software, you need to read about antenna design. If you don't know the basics (and it is clear you don't), then no software is going to be much use to you.

Amateur radio books are a good place to learn the basics of antenna theory, but to really understand antennas, you need an excellent knowledge of maths and engineering.

Once you do know something about antenna theory, then MMANA-GAL is quite useful, and it is free.

In another thread, when someone asked for free software, people replied with software like antenna magus, CST and HFSS. Hopefully they can not do that!

Dave

Allow me to add to Dave's excellent summary by mentioning 4NEC2 (a Win32 application) - a free front-end for NEC2 code, and also xnec2c which is linux GUI orientated, and finally nec2c which is a terminal linux application. All freeware.