I need to know abt biasing ckt for varactor and PIN diodes to be used in reconfigurable microstrip filter. I have seen ckt given in datasheet. It seems it is having more inductor and capacitors and its difficult to mount on Microstrip filter. How can we do it? Can we take any simple RF inductor, blocking capacitor and resisitor and connect them in series and use as a biasing ckt for reconfigurable filter.
Designing ckt means which values should we take? Any approx value can we consider for it?
Hello,
PIN diode is the best option for mention circuit. PIN diode is used in the path of input RF signal and connected such that its cathode will be towards input and anode towards antenna (output). During ON period, diode is ON by applying forward biasing and during OFF period diode has to be reversed bias. During forward bias, diode resistance is zero and RF reach to antenna through diode and during reverse bias OFF, diode will block the RF reaching to antenna.
Use blocking capacitors to avoid DC reaching to antenna or source as well as blocking inductor to avoid the RF flow towards DC source. Paper is attached for help.
Thanks,
You can't give one answer to such a general question.
Is your filter low-pass or bandpass? What do you want to change: cut-off frequencies, bandwidth or response type? In what frequency range do you work - 1-5, 5-10, >10 GHz? Etc.
For a band-pass type on a multi-layer circuit board one possibility is to connect to pin diodes via lines quarter wavelength long at the centre frequency located on a lower layer.
Another possibility, depending on frequency, response type and circuit configuration, is to drive directly with the collector or drain of a high frequency transistor.
I agree with recommendation above to use pin rather than varactor diodes from a distortion point of view if the pin diodes are used as on/off switches. Varactor diodes used to continuously tune a band-pass filter can cause serious intermodulation problems.
With more information re your problem I could perhaps give a more meaningful answer. You should also clarify the role of the filter in your antenna. Your title says reconfigueable antenna, your text only refers to microstrip filter.
Thanks Pieter Willem Van der Walt Denis Jaisson
for answer. now I am clarifying that I am designing BANDPASS Microstrip Filter for Wimax 2.4 and 5 GHz frequency band.I am going for single layer PCB.
I am trying to tune frequency continuously. How to decide biasing circuit for that. DO I need to consider all biasing component in simulation CST? I am just keeping varible Capacitor in CST.
I was asking PIN diode for Switching or tuning small range.
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