High-temperature superconductor low-pass filter for...

Details High-temperature superconductor low-pass filter for... High-temperature superconductor low-pass filter for...

2001-09-17

2003-11-25

Young, Brian (Department: 2819)

Wave transmission lines and networks

Automatically controlled systems

With control of equalizer and/or delay network

C333S204000, C333S175000, C505S210000, C505S701000, C505S866000

Reexamination Certificate

active

06653917

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a low-pass filter for a wireless communication system; and, more particularly, to a HTS low-pass filter for suppressing broadband harmonics.
DESCRIPTION OF THE PRIOR ART
Recently, as various wireless communication systems and services are developed intensively, the considerable performance improvement such as small insertion loss, high selectivity, high sensitivity and small size are needed in development of communication components for a cellular phone and a personal communication system. In order to satisfy these demands, the development of materials, design (circuits) and fabrication (processes) technologies are essential for the communication devices.
Since low-pass filter (LPF) is a frequency selective and passive device with low levels of attenuation, LPF is widely used to reject harmonics or spurious signals in a integrated mixer, a voltage controlled oscillator (VCO) and so on. But an open-stub type low-pass filter and a step-impedance type low pass filter have a narrow stopband (about 3 times of cutoff frequency in case of a conventional LPF).
FIGS. 1A and 1B
show an equivalent circuit diagram and a schematic diagram of a conventional microstrip low-pass filter.
FIG. 1A
shows the equivalent circuit diagram of the lumped-element low-pass filter designed through the transformation of impedance level and frequency scale from the prototype low-pass filter (not shown). The lumped-element low-pass filter (or &pgr;-type low-pass filter) includes an inductance L
2
corresponded to the microstrip transmission line, a first shunt capacitance C
1
and a second shunt capacitance C
2
corresponded to the two parallel microstrip open-stubs (in this case: C
1
=C
2
).
Referring to
FIG. 1B
, the conventional microstrip low-pass filter includes a crystalline substrate
180
(hereinafter, referred to as “an MgO substrate”), a signal transmission input port
150
and a signal transmission output port
160
, two parallel stripe lines
170
of a microstrip open-stub type, a microstrip line
140
and a ground plane
190
.
The signal transmission input port
150
and the signal transmission output port
160
are fabricated on both edges of the top face of the MgO substrate
180
. Two parallel microstrip open-stubs
170
between the signal transmission input port
150
and the signal transmission output port
160
are perpendicular to a signal propagation direction. Therefore, the microstrip line
140
is perpendicular to two parallel microstrip open-subs
170
. The groundplane (e.g., Au or Ag film)
190
is coated at the bottom (backside) of the MgO substrate
180
.
In general, there are some problems in the conventional low-pass filter as described above. Since the conventional low-pass filter has a narrow stopband range in frequency domain, an interference occurred by the adjacent wireless communication systems and a noise generated by the communication system itself are quite serious.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a low-pass filter having a high-efficiency broad stopband characteristics, in which attenuation poles and a frequency range of the stopband can be controlled easily.
In accordance with an aspect of the present invention, there is provided a low-pass filter comprising: a circuit pattern having at least one or more units, wherein the circuit pattern includes a coupled line section having a pair of parallel stripe lines and a transmission line section having a pair of parallel straight lines whose two ports of one side are opened and whose two ports of the other side are connected to each other, each port of one side of the pair of the parallel straight lines being connected with each port of one side of the coupled line section.


REFERENCES:
patent: 5258626 (1993-11-01), Suzuki et al.
patent: 5668511 (1997-09-01), Furutani et al.
patent: 5893026 (1999-04-01), Kim
M. H. Kwak et al. Design Of High Temperature Superconducting Low-Pass Filter For Broad-Band Harmonic Rejection, Sep. 17-22, 2000, Applied Superconductivity Conference, Technology For The 21stCentury, Pre-Conference Booklet.

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