I figure that I need to create a Band Pass Filter as the matching network that has a 300 MHz center and bandwidth of 100MHz, i.e. cutoff frequencies at 200 & 400 MHz.
Hello, infinite_gbps
As i can see you have used ideal L and C in you matching network - so you get very narrow bandwidth.
If you use real, for example, Murata's elements, i guess the plot will be different.
You are doing something wrong in your analysis of this matching network. You should get a >20dB return loss bandwidth of nearly 200MHz with this network.
edit: see post #7 for a possible reason you are seeing a narrow bandwidth with this network.
A 100MHz bw is 250 to 350MHz so are you really asking for a 200MHz bw?
G0HZU said:The current network should give <0.25dB insertion loss over 200-400MHz with reasonable quality SMD parts. The loss will be slightly less with better quality parts.
G0HZU said:In reality I suspect the (60.95, -45.75) Ohm source itself will show a different impedance across 200-400MHz and this will complicate the matching network.
Perhaps IG should remeasure the source impedance to see how it changes across 200-400MHz and this will reduce the possibility of disappointment when testing the network on the real hardware. i.e. does the source on its own still look like 60.95, -45.75 across 200-400MHz. I suspect it will not.
Can you post up the s parameters of the source over 200-400MHz?
I suspect a more complex network will be required as the source may have a very different impedance across 200-400MHz.
I didn't expect a .25 dB insertion loss, but you are right, the shown return loss graphic doesn't fit the shown source impedance and matching network. It's showing a kind of high Q
resonator.
The S11 file for your source shows the impedance changes a lot over the 200-400MHz range. This will make it much harder to match with a decent bandwidth.
Can I ask what the source consists of? The S11 file looks like the response from a narrowband filter. This is why you only see a narrow bandwidth match.
Is the network after the switch a narrow RF filter or duplexer? i.e. does your system look like antenna + duplexer/filter + switch + (new matching network) + LNA?
The reason I think your source looks like a filter is because the reflection coefficient swings around the smith chart a lot either side of 300MHz.
If you plot the return loss of the source you will see it is very poor immediately either side of 300MHz. This is a similar response to a narrowband 300MHz filter.
It will be difficult to match this without having the following problems:
The network produced to give a good broadband match will be quite complex and will probably be very sensitive to component tolerance.
The network will probably end up with an undesirable insertion loss at 300MHz (ahead of your LNA)
Are you expecting to receive signals over 200-400MHz with your LNA?
It states that (in the "Low-Q or Wideband Matching Networks" on page 69) that one needs fairly broad range of frequencies matched that one can simply use two L sections. They would be series connected rather than using back to back configurations of Pi or T networks.
Agree with this? Not sure what he is talking about as be goes on.
The statement has been effectively disproved by the tabulated S11. I don't expect, that a wideband impedance matching can be achieved with this higly resonant source impedance. As a simple example, consider a series LC circuit. It could be only compensated by a negative inductance and capacitance, which both doesn't exist.I had a source that has a 60.95-j45.75 impedance.
Also can you elaborate on what you meant by saying "fairly basic source and load matching task"? I thought broadband matching meant that you have frequencies that saw different impedances. Are the differences so huge that make it impractical?
McLean [3] has described the fundamental theoretical limit for the minimum Q-value of a small antenna. If the antenna can be placed inside a sphere of radius a, the minimum Qvalue-value for a loss-less antenna is
Qmin = 1/(ka)³
where k = 2pi/λ
This expresses the absolute minimum Q value the antenna can take. Unfortunately, the theory does not tell us how to implement a minimum Q antenna. The antenna Q can of cause be reduced by introducing loss (a resistor) in addition to the radiation resistance, but this would reduce the antenna efficiency, see below.
J.S.McLean: A re-examination of the fundamental limits on the radiation Q of electrically small antennas, IEEE Trans Antennas Propagat, vol 44, pp672-675, May 1996
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?