Frequency and bandwidth tunable microwave filter
View Patent ↗An RF bandpass filter includes a cascaded series of a first subfilter and a second subfilter. Each subfilter includes a respective inverter, voltage-controlled capacitor and inductor. A first selected one of the first subfilter and the second subfilter is a pseudo low pass filter and a second selected one of the first subfilter and the second subfilter is a pseudo high pass filter. The RF bandpass filter is configured to separately control a bandwidth and center frequency of output RF energy. The bandwidth may be controlled to be substantially fixed over a significant substantial range. The center frequency and bandwidth are controlled by adjusting a voltage input to one or more of the voltage-controlled capacitors.
1. A radio frequency (RF) bandpass filter, the filter comprising:
a cascaded series of a first subfilter and a second subfilter, the first subfilter comprising a first input port, a first output port, a first inverter, a first voltage-controlled capacitor and a first inductor, a proximal terminal of the first inverter being coupled with the first input port, the first voltage-controlled capacitor and the first inductor being connected in parallel between a distal terminal of the first inverter and ground; the second subfilter comprising a second input port, a second output port, a second inverter, a second voltage-controlled capacitor and a second inductor, a proximal terminal of the second inverter being coupled with the second input port, the second voltage-controlled capacitor and the second inductor being connected in parallel between a distal terminal of the second inverter and the second output port, an input terminal of the second inverter being coupled with the second input port; wherein:
a first selected one of the first subfilter and the second subfilter comprises a pseudo low pass filter and a second selected one of the first subfilter and the second subfilter comprises a pseudo high pass filter; and
the RF bandpass filter is configured to output RF energy and to separately control a bandwidth and a center frequency of the RF energy, the center frequency being tunable by adjusting a voltage input to one or both of the first voltage-controlled capacitor and the second voltage-controlled capacitor.
2. The filter of claim 1 , wherein each of the first inductor and the second inductor have a respective self resonant frequency and one or both of the first inductor and the second inductor operate at a frequency substantially below the respective self resonant frequency.
3. The filter of claim 1 , wherein the filter is configured to control the bandwidth at a substantially fixed bandwidth W over a center frequency tuning range.
4. The filter of claim 3 , wherein the center frequency is tuned and the substantially fixed bandwidth W is controlled, by adjusting a respective voltage input of each of the first voltage-controlled capacitor and the second voltage-controlled capacitor.
5. The filter of claim 4 , wherein the center frequency tuning range is from 85% to 115% of a nominal center frequency.
6. The filter of claim 5 , wherein the nominal center frequency is greater than 500 MHz.
7. The filter of claim 1 , wherein at least a first selected one of the first inverter and the second inverter includes a capacitive inverter.
8. The filter of claim 1 , wherein at least a first selected one of the first inverter and the second inverter includes an inductor.
9. The filter of claim 1 , wherein one or both of the first voltage-controlled capacitor and the second voltage-controlled capacitor is selected from the group consisting of: a varactor, a ferroelectric material, or a microelectromechanical system (MEMS) capacitor.
10. A multiplexer comprising:
at least two radio frequency (RF) bandpass filters, wherein:
the multiplexer is configured to channelize an input RF band of electromagnetic energy into a set of output channels by way of the RF bandpass filters, each output channel configured to output RF energy at a respective wavelength λ i ; and
at least one of the RF bandpass filters comprises:
a cascaded series of a first subfilter and a second subfilter, the first subfilter comprising a first input port, a first output port, a first inverter, a first voltage-controlled capacitor and a first inductor, a proximal terminal of the first inverter being coupled with the first input port, the first voltage-controlled capacitor and the first inductor being connected in parallel between a distal terminal of the first inverter and ground; the second subfilter comprising a second input port, a second output port, a second inverter, a second voltage-controlled capacitor and a second inductor, a proximal terminal of the second inverter being coupled with the second input port, the second voltage-controlled capacitor and the second inductor being connected in parallel between a distal terminal of the second inverter and the second output port, an input terminal of the second inverter being coupled with the second input port; wherein:
a first selected one of the first subfilter and the second subfilter comprises a pseudo low pass filter and a second selected one of the first subfilter and the second subfilter comprises a pseudo high pass filter; and
the RF bandpass filter is configured to output RF energy and to separately control a bandwidth and a center frequency of the RF energy, the center frequency being tunable by adjusting a voltage input to one or both of the first voltage-controlled capacitor and the second voltage-controlled capacitor.
11. The multiplexor of claim 10 , wherein each of the first inductor and the second inductor have a respective self resonant frequency and one or both of the first inductor and the second inductor operate at a frequency substantially below the respective self resonant frequency.
12. The multiplexor of claim 10 , wherein at least one of the RF bandpass filters is configured to control the bandwidth at a substantially fixed bandwidth W over a center frequency tuning range.
13. The multiplexor of claim 12 , wherein the center frequency is tuned and the substantially fixed bandwidth W is controlled, by adjusting a respective voltage input of each of the first voltage-controlled capacitor and the second voltage-controlled capacitor.
14. The multiplexor of claim 13 , wherein the center frequency tuning range is from 85% to 115% of a nominal center frequency.
15. The multiplexor of claim 14 , wherein the nominal center frequency is greater than 500 MHz.
16. The multiplexor of claim 10 , wherein at least a first selected one of the first inverter and the second inverter includes a capacitive inverter.
17. The multiplexor of claim 10 , wherein at least a first selected one of the first inverter and the second inverter includes an inductor.
18. The multiplexor of claim 10 , wherein the one or both of the first voltage-controlled capacitor and the second voltage-controlled capacitor is selected from the group consisting of: a varactor, a ferroelectric material, or a microelectromechanical system (MEMS) capacitor.