Small size cross-coupled trisection filter

Details Small size cross-coupled trisection filter Small size cross-coupled trisection filter

2001-06-20

2003-08-19

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Coupling networks

Wave filters including long line elements

C333S219000, C333S185000

Reexamination Certificate

active

06608538

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cross-coupled trisection filter, with inductance and capacitance devices, thereby reducing its physical size and increasing the production yield.
2. Description of Related Art
According to the filter design specification, if the degree of the resonator is increased, the selectivity of the frequency band is increased. However, this is accompanied with bandpass attenuation C and an increase in physical size. Refer to
FIG. 1
for a prototype of a cascade trisection bandpass filter. As shown in
FIG. 1
, any cascade trisection bandpass filter generally provides asymmetric frequency response. Conventional bandpass filters with asymmetric response are further described in “Microstrip Cross-coupled trisection bandpass filters with asymmetric frequency characters” by J. -S. Hong and M. J. Lancaster, as shown in
FIG. 2
a
, and in “Microstrip Cascade Trisection Filter” by Chu-Chen Yang and Chin-Yang Chang, as shown in
FIG. 2
b
. The resonators R
1
a
, R
2
a
, and R
3
a
in
FIG. 2
a
are construed on a substrate sun, wherein the resonator R
1
a
has an input port IN and the resonator R
3
a
has an output port OUT. The resonators R
1
b
, R
2
b
, R
3
b
, R
4
b
, and R
5
b
in
FIG. 2
b
are construed on a substrate (not shown), wherein the resonator R
5
a
has an input port P
1
and the resonator R
3
a
has an output port P
2
. As shown in
FIG. 2
a
, the 3-pole filter structure is composed of three &lgr;/2-line open-loop resonators R
1
a
, R
2
a
, R
3
a
on one side of the dielectric substrate SUB with a ground plane on the other side. The cross coupling between resonators R
1
a
and R
3
a
exists because of their proximity. An attenuation pole of finite frequency exists on the high side of the pass band due to the cross-coupling. As shown in
FIG. 2
b
, the 5-pole filter with two &lgr;/2-line open-loop resonators and three hairpin resonators has mixed (electric and magnetic) couplings between resonators R
1
b
and R
2
b
and between resonators R
2
b
and R
3
b
, the mixed couplings between resonators R
3
b
and R
4
b
and between resonators R
4
b
and R
5
b
. The lower attenuation pole is due to the nonadjacent magnetic coupling between resonators R
1
b
and R
3
b
, and the upper attenuation pole is due to the nonadjacent electric coupling between resonators R
3
b
and R
5
b
. Thus, both
FIGS. 2
a
and
2
b
can achieve a higher selectivity without increasing the degree of poles, i.e. the number of resonators. However, such a structure exhibits increased size and easily suffers spurious effect on odd frequencies of the band pass (see the appendix A), so the required level of filtration is not achieved.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a filtering structure, which adds a serial capacitance device into each resonator of the filter in
FIG. 1
to reduce the filter size.
Another object of the invention is to provide a small size cross-coupled trisection filtering structure, which uses the semi-lumped LC resonator to avoid the spurious effect and also keep the attenuation pole on the high frequency during the band pass.
Another object of the invention is to provide a small size cross-coupled trisection filtering structure, which only couples to the high impedance transmission portion of the resonators, thereby fitting a multilayer and easily adjusting the frequency of an attenuation pole by changing the high impedance transmission distance of the first and third poles without changing the bandpass characteristics.
The invention provides a small size cross-coupled trisection filter structure, including a first resonance unit; a second resonance unit; and a third resonance unit. Each of the units includes an inductance device, e.g. a transmission line, and a capacitance device, e.g. a capacitor, wherein the high impedance transmission portions of two of the units are coplanar and one has an input while the other has an output.


REFERENCES:
patent: 5382925 (1995-01-01), Hayashi et al.
patent: 6208226 (2001-03-01), Chen et al.
patent: 6294967 (2001-09-01), Hirai et al.
patent: 6323745 (2001-11-01), Toncich
patent: 6504451 (2003-01-01), Yamaguchi
Yang et al, IEEE Microwave and Guided Wave Letters, vol. 9, No. 7, pp. 271-273 (1999).
Hong et al, IEE Proc-Microw Antennas Propag., vol. 146, No. 1, pp. 84-90 (1999).

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