antenna issue
I am a newbee in antenna design and stuff. I have been working on a
2.4G rf module. I have some basic questions about the usage of antenna
with this module.
1 > What is relation ship between the gain of an antenna and the distance it can cover. I mean, if I use a antenna with 5 dbi gain, and pump about 20 dBm of power at 2.442 ghz, what distance can I cover(indoor and outdoor) ?
2 > The antenna claims to have the following parameters
Gain : 5 dbi
VSWR : <= 2.0
Polorisation : Vertical
Input impedance : 50 ohm
cable length : 60mm with Murata connector
The radiation pattern and other graphs I have are attached.
I feel that this is quite not possible, Am I correct ?
3 > My electronics stack is like this
Bottom layer : Circuit and PCB : 5 mm thick
Middle layer : Lithium battery : 5 mm thick (35mm x 24mm)
Top layer : Antenna : 30mm x 20mm x 1mm
Enclosure is Rapid Prototype plastic
The gap between each layer is less than 1 mm.
Will this stack cause any problem to the RF performance?
Please help!
Regards
Prithvi
Link Budget example (you shall know the RX sensitivity):
RX_inp_level[dBm] = TX_Power[dBm] + TX_Ant_Gain[dB] ? Free_Space_Path_Loss[dB] ? Total_Cable_loss[dB]+ Rx_Ant_Gain[dB] -Fade_Margin[dB]
where:
Free_Space_Path_Loss[dB] = 27.6 ? 20*LOG[Frequency[MHz]] ? 20*LOG[Distance[m]]
Antenna pattern and VSWR that you provided looks realistic.
The PCB stack should be fine for your antenna, assuming is a monopole.
Hello vfone,
Thankyou for the reply.
What are the typical ranges of the cable losses and fade margins ?
Does the gain of the antenna depend on the environment in which the antenna is?I mean does the gain change if the antenna is in an indoor space?
I am using a RF connector, so should I include any interface loss.
The observation I have made while testing my system is the when I test it in an open field then the performance is good but if I test it in closed space, the performance degrades rapidly. I know that this is because of multipath effect, but is there any way in which my antenna design can help me in this?
Please let me know!
Regards
Prithvi
You can use in your case a fade margin approximately of 20dB, and probably adding another 10dB for indoor people moving around.
Omnidirectional antenna (with low gain) cannot help to much for indoor propagation, where absorption, penetration and reflection depends by the construction materials used.