Help me design a 30x40mm antenna

[HeiFelix]

Small Antenna

I begin to design a antenna which must fit in size at 30X40mm on 315MHZ.
Is a coil of wire antenna always better than a PCB trace antenna, if I do not care the manufacture difficulty?
Should the wire be as long as near the wavelength/4=2.4m?
should the coil be flattened?
To catch more area and the wire length, the coil should be retangle. Is result better than a circular core?
If I use 0.5mm(diameter) wire to reach the length of 2.4m in 30X40mm area, How much gain will i get?

Help me!

 

[vfone]

Re: Small Antenna

Yes, an air-coil wire antenna is better than a PCB antenna assuming that you are using an usual FR4 material. This due to higher loss. You can try to use a wire length of lambda/8.
Theoretically the circularly coil give the best radiated resistance. You can flattened the coil and measure what gain you get, before and after.
Below is an empirical formula to calculate the gain:
G = 11.8 + 10 * log {(C/L)^2 * N * d} [dBi]
Where C is circumference, N is nr of turns, d distance between turns, and L is the wavelength.
regards

 

[unine]

Re: Small Antenna

@HeiFelix

Have you already realized the antenna (coil and/or PCB)? Have you already measured the gain?
If so, can you give some informations (dimension, ev. images)?

Thanks

 

[ali]

Small Antenna

and another thing about coil antenna is the larg amounts of reactance of the coil . you use a shunt capacitor to disapear it, and another important thing is this kinds of antenna have very narrow bandwidth

 

[mozee]

Re: Small Antenna

...and really detunes when close to metal objects