I'm building a circuit using a SI4362 receiver, which has a differential input. There is an application note from SiLabs AN643 which describes both how to match the impedance of the antenna to the LNA, AND how to provide a single ended to differential input function.
Unfortunately I barely understand RF (which probably means I shouldn't be undertaking this project, but hey, that's what hobbies are for).
For an antenna, I was thinking of using either the ANT-315-HETH or ANT-433-HETH, because I want to easily be able to switch my board from one frequency to another (both antennas are the exact same size).
Here's where I get confused: I believe the antenna is double ended, so I think there is no need to ground one end of it. In AN643, Fig 1 and 2 show how to build a circuit for a grounded antenna. I suppose I could just ground the antenna in my circuit, but if it's unnecessary, I'd rather not -- it means tying a potentially noisy ground to the antenna path, or routing a separate ground.
So my questions:
1. Can I follow Fig 1 or 2 of AN643, but instead of using ground in the antenna path, just connect all those points together?
2. If the answer to #1 is yes, then is it still true that the 4 element match network (figure 2) is better than the 3 element match network? It seems to me that a symmetric circuit would be better.
3. Again, if the answer to #1 is yes, then should the values of CR1 and CR2 be different (from fig 1)? On pages 9-10 they list the equations for assigning Ctotal between CR1 and CR2, but again my intuition says a symmetric circuit (one where CR1=CR2) would work better. I'm wondering if the asymmetric assignment only makes sense when tying one side to ground, or if it is always the correct design?
4. Or... maybe I'll use a splatch antenna (ANT-315-SP/ANT-433-SP). How do I decide which antenna is better for my purpose? I'm making a TPMS receiver; distance isn't far (maybe 10ft) but there are a lot of metal obstacles. Need to receive both forward and back (though more in the forward direction), and side to side.
Thanks for any help!
Unfortunately I barely understand RF (which probably means I shouldn't be undertaking this project, but hey, that's what hobbies are for).
For an antenna, I was thinking of using either the ANT-315-HETH or ANT-433-HETH, because I want to easily be able to switch my board from one frequency to another (both antennas are the exact same size).
Here's where I get confused: I believe the antenna is double ended, so I think there is no need to ground one end of it. In AN643, Fig 1 and 2 show how to build a circuit for a grounded antenna. I suppose I could just ground the antenna in my circuit, but if it's unnecessary, I'd rather not -- it means tying a potentially noisy ground to the antenna path, or routing a separate ground.
So my questions:
1. Can I follow Fig 1 or 2 of AN643, but instead of using ground in the antenna path, just connect all those points together?
2. If the answer to #1 is yes, then is it still true that the 4 element match network (figure 2) is better than the 3 element match network? It seems to me that a symmetric circuit would be better.
3. Again, if the answer to #1 is yes, then should the values of CR1 and CR2 be different (from fig 1)? On pages 9-10 they list the equations for assigning Ctotal between CR1 and CR2, but again my intuition says a symmetric circuit (one where CR1=CR2) would work better. I'm wondering if the asymmetric assignment only makes sense when tying one side to ground, or if it is always the correct design?
4. Or... maybe I'll use a splatch antenna (ANT-315-SP/ANT-433-SP). How do I decide which antenna is better for my purpose? I'm making a TPMS receiver; distance isn't far (maybe 10ft) but there are a lot of metal obstacles. Need to receive both forward and back (though more in the forward direction), and side to side.
Thanks for any help!