Re: band pass filter in ADS
can any1 tell me how to find the number of elements in the filter?
my frequencies are 2.10ghz-2.0ghz
passband return loss <20 db
rejection =25 db @2400 mhz
Your specifications are odd, for several reasons.
Firstly, I suspect you mean
passband return loss >20 dB
or
passband return loss ≧ 20 dB
since what you stated means an SWR of 1.01:1 (return loss 46 dB) would be unacceptable, whereas a SWR of 3:1 (return loss 6 dB) would be OK. I doubt that is what you mean.
Secondly you have put no upper limit on the passband attenuation. Is 20 dB attenuation in the passband acceptable to you? Perhaps you can tolerate 24 dB attenuation in the passband, though I suspect you can't.
Thirdly you specified a rejection of 25 db @2400 mhz. I suspect you mean MHz, not mhz.
Fourthly you have not specified any rejection on the lower frequency side, so your specification indicates a low pass filter, not a band-pass filter.
Neither have you specified any frequencies over which the rejection must exist. You might want it to reject from DC up to your passband, but perhaps it does not matter what the attenuation is at very low frequncies.
You have not specified any range of rejection on the high side. In practice, you are not going to be able to make a filter that has an attenuation of at least 25 dB from 2400 MHz to light. But perhaps you need 25 dB from 2.4 to 10.0 GHz, or perhaps you don't care about anything above 6 GHz.
You say your frequencies are 2.10ghz-2.0ghz. This should be written as GHz, not ghz, but its normal to put the lower frequency first, then the upper frequency. I suspect you mean 2.0 to 2.1 GHz.
You have not specified any passband ripple. That may or may not be important.
You have not specified any impedance value for this. I assume it will be 50 Ω, but you have not stated it.
You have not specified any power handling capability. Does it have to take 1 MW ?
Before worrying what order the filter is, what type of response it has, you need to get clear in your own head exactly what specifications you are trying to meet. Otherwise, if you simulate or build this, how on earth are you going to know if it meets the specification or not?
Dave