Dual-band bandpass filter with stepped-impedance resonators
View Patent ↗A dual-band bandpass filter with stepped-impedance resonators uses only one circuit to generate dual-band effect. It adopts the principle of stepped-impedance resonator, which contains a connecting section and two coupling sections. The impedance and electrical length of the connecting section and coupling sections conforms to a selected condition to generate two passbands at desired frequencies. A multi-layer broadside-coupled parallel lines structure may be applied to increase coupling-amount between the parallel lines so that the dual-band bandpass filters have broader bandwidth and less loss.
1. A dual-band bandpass filter equipped with stepped-impedance resonators for filtering a signal, comprising:
a circuit board;
an input end located on the circuit board for receiving the signal;
an output end located on the circuit board to transmit the filtered signal; and
at least two resonators located on the circuit board, each of the resonators including a connecting section and two coupling sections; the connecting section connecting two coupling sections; one coupling section of the first resonator being coupled with one coupling section of the second resonator and the other coupling section of the first resonator being coupled with the input end or the output end;
wherein the circuit board is a multi-layer circuit board, including at least a first layer, a second layer and a third layer, the resonators being located at least on the second layer, the input end and the output end being located respectively on the first layer and the third layer;
wherein an impedance of the connecting section and the coupling sections satisfies the condition:
R
=
(
tan
π
f
1
2
f
2
)
2
,
wherein f 1 is a first resonance frequency of the resonator, and f 2 is the second resonance frequency of the resonator and wherein each of the connecting sections of the two resonators is located on two of the layers of the circuit board such that the coupling sections of the two resonators are located on two opposite sides of the circuit board.
2. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 1 , wherein the impedance of the connecting section and the coupling section is controllable by adjusting the width and length of the coupling sections and the connecting section.
3. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 1 , wherein the coupling sections are connected to the two ends of the connecting section in a symmetrical fashion.
4. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 1 , wherein the coupling sections and the connecting section are transverse electromagnetic (TEM) or quasi-TEM transmission lines.
5. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 4 , wherein the coupling sections have respectively a long shaft in parallel with a long shaft of the connecting section.
6. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 4 , wherein the coupling sections have respectively a long shaft in normal to a long shaft of the connecting section.
7. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 6 , wherein the two coupling sections are located on the same side of the connecting section.
8. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 6 , wherein the two coupling sections are located on two opposite sides of the connecting section.
9. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 1 , wherein the resonators, and the input end and the output end are located on opposite sides to the circuit board.
10. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 1 , wherein the coupling sections are broadside-coupled or co-plane coupled.
11. A dual-band bandpass filter equipped with stepped-impedance resonators for filtering a signal, comprising:
a circuit board;
an input end located on the circuit board for receiving the signal;
an output end located on the circuit board to transmit the filtered signal; and
at least two resonators located on the circuit board, each of the resonators including a connecting section and two coupling sections; the connecting section connecting two-coupling sections; one coupling section of the first resonator being coupled with one coupling section of the second resonator and the other coupling section of the first resonator being coupled with the input end or the output end;
wherein the circuit board is a multi-layer circuit board including at least a first layer, a second layer and a third layer, one of the two resonators being coupled with the input end on the first layer and being crossed over to the second layer to couple with another resonator, the other resonator being crossed over to the third layer to couple with the output end;
wherein an impedance of the connecting section and the coupling section satisfies the condition:
R
=
(
tan
π
f
1
2
f
2
)
2
,
wherein f 1 is a first resonance frequency of the resonator, and f 2 is the second resonance frequency of the resonator.
12. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 11 , wherein the impedance of the connecting section and the coupling section is controllable by adjusting the width and length of the coupling sections and the connecting section.
13. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 11 , wherein the coupling sections are connected to the two ends of the connecting section in a symmetrical fashion.
14. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 11 , wherein the coupling sections and the connecting section are transverse electromagnetic (TEM) or quasi-TEM transmission lines.
15. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 14 , wherein the coupling sections have respectively a long shaft in parallel with a long shaft of the connecting section.
16. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 14 , wherein the coupling sections have respectively a long shaft in normal to a long shaft of the connecting section.
17. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 16 , wherein the two coupling sections are located on the same side of the connecting section.
18. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 16 , wherein the two coupling sections are located on two opposite sides of the connecting section.
19. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 11 , wherein the resonators, and the input end and the output end are located on opposite sides to the circuit board.
20. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 11 , wherein each of the connecting sections of the two resonators is located on two sides of the circuit board such that the coupling sections of the two resonators are located on two opposite sides of the circuit board.
21. The dual-band bandpass filter equipped with stepped-impedance resonators of claim 11 , wherein the coupling sections are broadside-coupled or co-plane coupled.