WO2010044502A1

WO2010044502A1 - Dual band pass filter

Info

Publication number: WO2010044502A1
Application number: PCT/KR2008/006281
Authority: WO
Inventors: Chung-Seok Lee; Jong-Soo Ha; Hee-Seok Song; Young-Ki Kim; Soon-Young An; Jin-Wuk Seo; Jung-Woo Kang
Original assignee: Samyoung Electronics Co., Ltd.
Priority date: 2008-10-16
Filing date: 2008-10-23
Publication date: 2010-04-22
Also published as: KR20100042299A

Abstract

A dual band pass filter is disclosed. The dual band pass filter includes matching circuit matching impedance of signal inputted from antenna port through matching between serial inductor and parallel capacitor, BPF passing VHF band signal and outputting VHF band signal to VHF port, and HPF passing UHF band signal and outputting UHF band signal to UHF port. The matching circuit, BPF, and HPF have plural laminated layers. Circuits are laminated so that small sized dual band pass filter is designed. Since fundamental resonant frequency and first harmonic frequency of resonator is very large, dual band pass filter of wide pass band having wide upper stopband property is manufactured. Since circuits are laminated to miniaturize filter, small filter is designed. Since difference between fundamental resonant frequency and first harmonic frequency of resonator is very large, duplexer of broad pass band having wide upper stopband property is manufactured.

Description

DUAL BAND PASS FILTER

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a double band pass filter and, more particularly to a dual band pass filter including a matching circuit for impedance matching, a band pass filter (BPF) to pass a very high frequency (VHF) signal, and a high pass filter (HFP) to pass an ultra high frequency signal .

2. Description of the Related Art

A general band pass filter circuit consisting of lumped elements includes a T-type band pass filter circuit as illustrated in FIG. 1 and a π-type band pass filter circuit as illustrated in FIG. 2.

Each of the band pass filter circuits in FIGS. 1 and 2 is constructed by combining a resistor 110 of a prototype low pass filter circuit with networks of a serial resonator 140 and parallel resonators 150 each of which includes inductors 120 and capacitors 130. In the band pass filters as illustrated in FIGS. 1 and 2, there are several difficulties in designing a filter such that unique parameters of the respective lumped elements are determined when the respective prototype lumped elements are arranged in the form of resonators using a frequency conversion function, characteristics of the filters are suddenly changed by a minute change of the parameters, and it is hard to implement the serial resonators 140 and the parallel resonators 150 simultaneously.

Thus, the band pass filter is practically implemented by only one type of a resonator using an inverter with emittance conversion characteristics.

That is, there is an existing band pass filter having J- inverters 200 (admittance inverter 210) as illustrated in FIG. 3 or K-inverters 220 (impedance inverter 230) as illustrated in FIG. 4.

In order to combine the networks of the serial resonators 140 and the parallel resonators 150 as illustrated in FIGS. 1 and 2 with each other, a phase of voltage must be the same as that of current when applying AC voltage 100. However, since, in the band pass filter, the parameters of lumped elements are already determined and the characteristic of the filter is changed due to a minute change of the parameters of the lumped elements, the band pass filter must be implemented by an inverter of only one type having the emittance conversion characteristics of the serial resonators 140 and the parallel resonators 150 as illustrated in FIGS. 3 and 4.

On the other hand, in the practice of implementing a band pass filter consisting of the lumped elements, resonators and inverters of the band pass filter must be implemented using a distributed constant circuit such as a transmission line. In other words, the resonators using a transmission line can implement a serial resonance circuit using a λ/2 transmission line with a short end or a parallel resonance circuit using a λ/4 transmission line with a short end and a λ/2 transmission line with an open end.

However, the above-mentioned band pass filter has the following disadvantages.

First, when the λ/2 and λ/4 resonators are applied to a single sided circuit and a double sided circuit, it is difficult to design a small filter because of a length of the transmission line. That is, there are restrictions such that the λ/2 resonator must be λ/2 in length and the λ/4 resonator must be λ/4 in length. Thus, since the resonators increase in size, it is technically difficult to design a small filter.

Second, in view of frequency characteristics of the resonator, there is a technical restriction that resonance is generated at a desired reference frequency f and (2n+l) times the reference frequency, for example, 3f, 5f, etc. In a case of designing a filter using the frequency characteristics of a resonator, a designer feels difficulty of forming a diplexer having broad pass band because of harmonic pass band occurring at integer times a desired pass band. Thus, performance of overall circuit deteriorates.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an aspect of the present invention to provide a diplexer of a broad pass band with a wide upper stop band by laminating circuits to miniaturize a filter and by increasing a difference between a fundamental resonant frequency and a first order harmonic resonant frequency.

It is another aspect of the present invention to provide a very small dual band pass filter applicable to a digital video broadcasting-terrestrial/handheld (DVH) device as a European digital-TV broadcasting standard and to provide a very small dual band pass filter to which low temperature co- fired ceramic (LTCC) technology is applied to a small and light communication terminal. In accordance with an aspect of the present invention,

the above and other objects may be accomplished by the

provision of a dual band pass filter including: a matching

circuit matching impedance of a signal inputted from an

antenna port through matching between a serial inductor and a

parallel capacitor; a band pass filter (BPF) passing a VHF

band signal and outputting the VHF band signal to a VHF port;

and a high pass filter (HPF) passing a UHF band signal and

outputting the UHF band signal to a UHF port; wherein the

matching circuit, the BPF, and the HPF have structures in

which a plurality of layers are laminated; wherein, the

matching circuit, a first inductor (50βd) on a certain layer

receives a signal through the antenna port, the first inductor

50βd and second inductors (507b, 508b, 509b, 510b, 511b, 512a,

and 513a) which are laminated on certain layers and are

electrically connected to each other, form a matching line,

and the first inductor (50βd) and the second inductors (507b,

508b, 509b, 510b, 511b, 512a, and 513a) make an impedance matching with a first capacitor (518a) on a certain layer; wherein, in the BPF, second capacitors (515a and 517b) , which are laminated on certain layers and are electrically connected to each other, receive a signal transmitted from the matching circuit to the BPF, third inductors (506e, 507c, 508c, and 509c) , which are laminated on certain layers and are electrically connected to each other, form a resonant line of the BPF, the third inductors (506e, 507c, 508c, and 509c) make resonance with third capacitors 518b and 518c which are laminated on certain layers and are electrically connected to each other, and fourth capacitors (515b and 517c), which are laminated on certain layers and are electrically connected to each other, output a signal passed through the BPF to the VHF port; and wherein, in the HPF, fifth capacitors (505a and 506a) , which are laminated on certain layers and are electrically connected to each other, receive a signal transmitted from the matching circuit to the HPF, fourth inductors (507a, 508a, 510a, and 511a) , which are laminated on certain layers and are electrically connected to each other, form a resonance line of the HPF, the fourth inductors (507a, 508a, 509a, 510a, and 511a) make resonance with the fifth capacitors (505a and 50βa) sixth capacitors (503 and 505c) , and seventh capacitors (504 and 50βc) which are

laminated on certain layers and are electrically connected to

each other, and the seventh capacitors (504 and 50βc) output

a signal passed through the HPF to the UHF port.

Moreover, in the BPF, fifth inductors (506f, 507d, 508d,

and 509d) , which are laminated on certain layers and are

electrically connected to each other, adjust a pass bandwidth.

In the BPF, eight capacitors (514a, 515a, and 515b) ,

which are laminated on certain layers and are electrically

connected to each other, generate a notch of the BPF, and the

BPF further comprises a ninth capacitor (517a) on a certain

layer connected to an output end of the BPF.

In the HPF, tenth capacitors (505b and 506b) , which are laminated on certain layers and are electrically connected to each other, adjust an interval between poles of return loss.

According to the present invention, since circuits are

laminated to miniaturize a size of a filter, a small sized

filter can be designed. Since a difference between a

fundamental resonant frequency and a first harmonic frequency

of a resonator is very large, a diplexer of a broad pass band

having a wide upper stopband property can be manufactured.

In particular, according to the present invention, a band pass filter can be applied to a DVB-T/H as a European digital TV broadcasting standard. Moreover, low temperature co-fired ceramics (LTCC) are applied to a very small sized band pass filter to suit to a small and light communication terminal .

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit of an existing T-type band pass filter consisting of lumped elements/ FIG. 2 is a circuit of an existing π-type band pass filter consisting of lumped elements;

FIG. 3 is a circuit of an existing band pass filter consisting of J-inverters (admittance inverters);

FIG. 4 is a circuit of an existing band pass filter consisting of K-inverters (impedance inverters);

FIG. 5 is a block diagram illustrating a dual band pass filter according to an embodiment of the present invention;

FIG. 6 is a circuit diagram of the dual band pass filter according to the embodiment of the present invention;

FIG. 7 is a partially enlarged view of a transmission line (TL) used in the circuit of FIG. 6;

FIG. 8 is a perspective view of the dual band pass filter according to the embodiment of the present invention;

FIG. 9 is an exploded perspective view of the dual band pass filter according to the embodiment of the present invention;

FIGS. 10 to 29 are views illustrating respective layers of the dual band pass filter according to the embodiment of the present invention; and

FIG. 30 is a graph illustrating frequency characteristics of the dual band pass filter according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various other objects, features, and attendant advantages of the present invention will be more fully appreciated from the following detailed description when considered in connection with the accompanying drawings in which like reference characters designate like or corresponding parts throughout the several views. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to accompanying drawings. FIG. 5 is a block diagram illustrating a dual band pass filter according to an embodiment of the present invention.

A dual band pass filter according to the embodiment of the present invention includes a matching circuit 340 for impedance matching in an antenna port 310, a band pass filter (BPF) 350 passing a VHF signal to a VHF port 320, and a high pass filter (HPF) 360 passing a UHF signal to a UHF port 330.

In the dual band pass filter according to the embodiment of the present invention, the antenna port 310 forms the matching circuit 340 with a serial inductor and a parallel capacitor for the optimization of impedance matching. A BPF having high frequency selectivity is designed for the VHF band and an HPF is designed for low loss in the UHF band. The respective ports 310, 320, and 330 are treated by side printing. FIG. 6 is a circuit diagram of the dual band pass filter according to the embodiment of the present invention, and FIG. 7 is a partial enlarged view of a transmission line (TL) used in the circuit of FIG. 6.

The TL represents a line through which an electromagnetic wave travels and may be a microstrip or a stripline. As illustrated, TIl to TLβ 401, 402, 403, 404, 405, and 406 are inductors, in which inductor devices are implemented on a plane. In more detail, as illustrated in FIG. 7, the inductors have a stripline configuration 440 in which an inductor is sandwiched by ground plates (GND) 441. Cl to C8 are capacitors, in which capacitor devices are implemented on a plane. Zl is impedance at the antenna port 310, Z2 is impedance at the VHF port 320, and Z3 is impedance at the UHF port 330.

Hereinafter, functions of the respective inductors and capacitors which are illustrated in the drawings will be described.

TLl 401 is to optimize the impedance matching condition at the antenna port 310 with the inductance component of the matching circuit 340. TL2 402 and TL3 403 are resonant lines of the BPF 350 and determine a frequency position of a signal- passing band. TL4 404 is for the inductance coupling of the BPF 350 and adjusts a pass bandwidth. TL5 405 and TLβ 406 are resonant lines of the HPF 360 and determine a frequency position of a signal-passing band.

Cl 411 optimizes impedance matching condition at the antenna port 310 with the capacitance component of the matching circuit 340. C2 412 is for input coupling of the BPF 350 and has influence on an insertion loss condition of the BPF 350. C3 413 and C4 414 are loading capacitors of the BPF resonator, determine a frequency position of a signal-passing band, and control a harmonic component. C5 415 is an output coupling of the BPF 350 and has influence on the insertion loss condition of the BPF 350. C6 416 is an input coupling of the HPF 360 and has influence on the insertion loss condition of the HPF 360. C7 417 is for capacitance coupling of the HPF 360 and adjusts an interval between poles of return loss. C8 418 is for an output coupling of the HPF 360 and has influence on the insertion loss condition of the HPF 360. C9 419 is for coupling of the BPF 350, generates a notch of the BPF 350, and has influence on attenuation condition. ClO 420 is positioned at an output end of the BPF 350 to be grounded and has influence on the attenuation condition. A resonator employed in the dual band pass filter according to the embodiment of the present invention is connected to an inductor and a capacitor in serial or parallel to resonate. Since the inductor and the capacitor are laminated in the resonator and the resonator is a stepped impedance resonator, the resonator has bandstop characteristics . Resonant frequency at the BHF band is generated by which T12 402 and C3 413 and T13 403 and C4 414 resonate respectively. Resonant frequency at the UHF band is generated by TL5 405 and Cβ 416 and TL6 and C8 418 resonate respectively. The detailed description for the same will be carried out with reference to FIG. 30 later.

FIG. 8 is a perspective view of the dual band pass filter 500 according to the embodiment of the present invention, and FIG. 9 is an exploded perspective view of the dual band pass filter 500 according to the embodiment of the present invention.

In the dual band pass filter according to the embodiment of the present invention, a total of 20 layers are laminated TLs and the respective layers are connected to each other through a via-hole 530. A wide area is required to achieve high inductance and capacitance. However, according to the dual band pass filter 500 of this embodiment of the present invention, a pattern is formed in the form of a laminated structure so that desired parameters may be achieved by a small sized filter 500. Since the dual band pass filter 500 according to the embodiment of the present invention has a size of 3.2 mm * 2.5 mm * 1.0 mm (L * W * T) , a very small sized laminated dual band pass filter 500 may be manufactured.

In the dual band pass filter according to the embodiment of the present invention, various laminating technologies may be applied to manufacture a filter. Particularly, the dual band pass filter may be applied to a filter using a multilayer printed circuit board (PCB) , a filter using low temperature co-fired ceramic (LTCC) technology, and other laminated structure using other materials. Moreover, the dual band pass filter is employed in an RF module using the laminating technology so that the RF module may be designed.

Meanwhile, the LTCC technology is a technique of manufacturing a multi-layer laminated semiconductor device using a ceramic dielectric with a thick layer (thickness: tens to hundreds of micrometers) , manufactured by tape casting and a conductive metal paste for implementing several circuit devices .

In more detail, FIG. 9 shows a connection between respective layers used in the dual band pass filter according to the embodiment of the present invention. The respective layers are electrically connected to each other through coupling and a via-hole 530. On the other hand, the via-hole 530 is made by making a hole in a dielectric material and filling the hole with metal to transmit an electric signal. Some of the layers are electrically connected to each other through the via-hole 530 and others are connected to each other by the coupling. In this embodiment, inductance components are connected to each other through the via-hole 530 while capacitance components are connected to each other through the coupling.

The inductance components are connected to each other through the via-hole 530 to obtain a high inductance and to reduce a size. When the inductance components are implemented in a plane, an area where the inductance components are implemented is wide and a size of a product increases. Thus, the present invention is made to overcome this problem. For example, seventh to eleventh layers 507, 508, 509, 510, and 511 have the same structure as those of the inductance components of TL5 405 to TLβ 406 in FIG. 6. When the structure is implemented in a plane, it needs a wide area and a size of a product increases. Since a distance between the respective layers is very short as long as 30 micrometers when the layers are laminated according to the embodiment of the present invention, a desired small size of an inductance may be obtained when the layers are connected to each other through the via-hole 530.

Moreover, in the dual band pass filter 500 according to the embodiment of the present invention, the layers are connected in a laminated structure so that the capacitance components are connected to each other through the coupling. Like, the connection between the inductance components through the via-hole 530, the capacitance components are connected to each other through the coupling so that the capacitance increases and a size of the filter is reduced. For example, in order to obtain the capacitances, namely, C8 418 in FIG. 6, a capacitor is implemented on a fourth layer 504 and a sixth layer 506 in the laminated form such that capacitors with the same structure are patterned on the upper and lower layers. Therefore, the laminated structure of multiple layers is formed to obtain the capacitance of C8 418 so that an area of a pattern implemented in a plane is reduced by a half and a size of a product is reduced. FIGS. 10 to 29 are pattern views illustrating respective layers of the dual band pass filter 500 according to the embodiment of the present invention.

In this embodiment of the present invention, seventeen layers are laminated in the dual band pass filter 500 and the respective layers are electrically connected to each other through the via-hole 530. Hereinafter, the respective layers will be described.

In this embodiment of the present invention, twenty layers are laminated in the dual band pass filter 500 and a circular point of each of the respective layers indicates the via-hole 530. The respective layers are electrically connected to each other through the via-hole 530. Hereinafter, the respective layers will be described. FIG. 10 shows a first layer 501 that is a marking pattern to recognize a direction of a port.

FIG. 11 shows a second layer 502 that is a GND pattern breaking an external signal transmitted to an upper ground plane and serving as a ground. FIG. 12 shows a third layer 503 that is an output coupling pattern which serves as the capacitor C8 418 in FIG. 6. FIG. 13 shows a fourth layer 504 that is an output coupling pattern of the HPF 360 like the third layer 503, serves as the capacitor C8 418 in FIG. 6, and is connected to the UHF port 330. FIG. 14 shows a fifth layer 505 where input/output couplings of the HPF 360 are carried out and in which a five- first capacitor 505a serves as the capacitor C6 416 of FIG. 6 through which a signal transmitted from the matching circuit 340 is input into the HPF 360. A five-second capacitor 505b serves as the capacitor C7

417 in FIG. 6 and is a coupling pattern of a filter.

A five-third capacitor 505c serves as the capacitor C8

418 in FIG. 6 and is coupled with the capacitor of the fourth layer 504 and the capacitor of the sixth layer 506 in the same pattern.

FIG. 15 shows a sixth layer 506 in which a six-first capacitor 506a serves as the capacitor of C6 416 in FIG. 6 and is coupled with the five-first capacitor 505a of the fifth layer in the same pattern. A six-second capacitor 506b serves as the capacitor C7 417 in FIG. 6 and is coupled with the five-second capacitor 505b of the fifth layer in the same pattern. Moreover, the six-second capacitor 50βb is a coupling pattern of the HPF 360.

A six-third capacitor 506c serves as the capacitor C8 418 in FIG. 6 and is coupled with the five-third capacitor 505c in the same pattern. The six-third capacitor 506c is a portion through which a signal is output to the UHF port 330.

A six-first inductor 506d serves as the inductor TLl 401 in FIG. 6 and is a portion through which a signal is input from the antenna port 310. Moreover, the six-first inductor 506d is a matching line for the impedance matching. A six-second inductor 506e serves as the inductors TL2 402 and TL3 403 in FIG. 6 wherein TL2 402 and TL3403 are resonator lines of the BPF 350.

A six-third inductor 506f serves as the inductor TL4 404 in FIG. 6 that is for the inductance coupling. FIG. 16 shows a seventh layer 507 in which a seven-first inductor 507a serves as the inductors TL5 405 and TL6 406 in FIG. 6 and is a resonator line of the HPF 360.

A seven-second inductor 507b serves as the inductor TLl

401 in FIG. 6 and is a matching line for the impedance matching.

A seven-third inductor 507c serves as the inductors TL2

402 and TL3 403 in FIG. 6, which are resonator lines of the BPF 350 .

A seven-fourth inductor 507d serves as the inductor TL4 404 in FIG. 4, which is for the inductance coupling.

FIG. 17 shows an eighth layer 508 in which an eight-first inductor 508a serves as the inductors TL5 405 and TL6 406 in FIG. 6 and are resonator lines of the HPF 350.

An eight-second inductor 508b serves as the inductor TLl

401 in FIG. 6 and is a matching line for the impedance matching. An eight-third inductor 508c serves as the inductors TL2

402 and TL3 403 in FIG. 6, which are resonator lines of the BPF 350.

An eight-fourth inductor 508d serves as the inductor TL4 404 in FIG. 6, which is for the inductance coupling. FIG. 18 shows a ninth layer 509 in which a nine-first inductor 509a serves as the inductors TL5 405 and TLβ 406 in FIG. 6 and are resonator lines of the HPF 360.

A nine-second inductor 509b serves as the inductor TLl

401 and is a matching line for the impedance matching. A nine-third inductor 509c serves as the inductors TL2

402 and TL3 403 in FIG. 6 and is a resonator line of the BPF 350. A nine-fourth inductor 509d serves as the inductor TL4 404, is for the inductance coupling, and is grounded to GND.

FIG. 19 shows a tenth layer 510 in which a ten-first inductor 510a serves as the inductors TL5 405 and TLβ 406 in FIG. 6 and are resonator lines of the HPF 360.

A ten-second inductor 510b serves as the inductor TLl 401 in FIG. 6 and is a matching line for the impedance matching.

FIG. 20 shows an eleventh layer 511 in which an eleven- first inductor 511a serves as the inductors TL5 405 and TL6 406 in FIG. 6, is a resonator line, and is grounded to a nineteenth layer 510 through GND.

An eleven-second inductor 511b serves as the inductor TLl 401 in FIG. 6 and is a matching line for the impedance matching. FIG. 21 shows a twelfth layer 512 in which a twelve-first inductor 512a serves as the inductor TL 1 401 in FIG. 6 and is a matching line for the impedance matching.

FIG. 22 shows a thirteenth layer 513 in which a thirteen- first inductor 513a serves as the inductor TLl 401 in FIG. 6 and is a matching line for the impedance matching.

FIG. 23 shows a fourteenth layer 514 in which a fourteen- first capacitor 514a serves as the capacitor C6 419 in FIG. 6 and is a coupling pattern of the BPF 350.

FIG. 24 shows a fifteenth layer 515 in which a fifteen- first capacitor 515a serves as the capacitor of C2 412 in FIG. 6. The fifteen-first capacitor 515a is a portion through which a signal is input from the matching circuit 340 to the BPF 350 and is coupled with the capacitor 514a of the fourteenth layer.

A fifteen-second capacitor 515b serves as the capacitor of C5 414 in FIG. 6, is a portion through a signal is output to the VHF port 320, and is coupled with the capacitor 514a of the fourteenth layer.

FIG. 25 shows a sixteenth layer 516 in which a sixteen- first capacitor 51βa serves as the capacitor of C2 412 in FIG. 6. The sixteen-first capacitor 516a is a coupling pattern of an input signal.

A sixteen-second capacitor 516b serves as the capacitor C5 415 in FIG. 6 that is a coupling pattern of an output signal.

FIG. 26 shows a seventeenth layer 517 in which a seventeen-first capacitor 517a serves as the capacitor ClO 420 in FIG. 6.

A seventeen-second capacitor 517b serves as the capacitor C2 412 in FIG, 6 through which a signal is input from the matching circuit 340 to the BPF 350.

A seventeen-third capacitor 517c serves as the capacitor C5 415 in FIG. 6 through which a signal is output to the VHF port 320.

FIG. 27 shows an eighteenth capacitor 518 in which an eighteen-first capacitor 518a serves as the capacitor Cl 411 in FIG. 6 to be the matching circuit 340 for the impedance matching. An eighteen-second capacitor 518b serves as the capacitor C3 413 in FIG. 6 to be a loading capacitor of a resonator of the BPF 350.

An eighteen-third capacitor 518c serves as the capacitor C4 414 in FIG. 6 to be a loading capacitor of a resonator of the BPF 350.

FIG. 28 shows a nineteenth layer 519 that is a GND pattern breaking an external signal and serving as a ground.

FIG. 29 shows a twentieth layer 520 which is mounted on a

PCB or a module and through which a signal is input and output. The dual band pass filter according to the embodiment of the present invention includes a matching circuit for impedance matching a signal input from the antenna port by matching the serial inductor and the parallel capacitor, the BPF passing a signal at VHF band and outputting the signal to the VHF port, and HPF passing a signal at UHF band and outputting the signal to the UHF port. The matching circuit, the BPF, and the HPF have a structure in which plural layers are laminated.

First, the matching circuit receives a signal by which the six-first inductor 506d receives the signal through the antenna port 310. The six-first inductor 506d, the seven-second inductor 507b, the eight-second inductor 508b, the nine-second inductor 509b, the ten-second inductor 510b, the eleven-second inductor 511b, the twelve-first inductor 512a, and the thirteen-first inductor 513a, which have a laminated structure for the matching the signal received from the antenna port and are connected to each other through the via-hole, form a matching line.

The inductors 50βd, 507b, 508b, 509b, 510b, 511b, 512a, and 513a of the matching line connected to each other through the via-hole make the impedance matching with the eighteen- first capacitor 518a.

Second, in the BPF, the fifteen-first capacitor 515a and the seventeen-second capacitor 518b having a laminated structure receive a signal transmitted from the matching circuit 340 to the BPF 350, and the fifteen-first capacitor 515a and the seventeen-second capacitor 517b form an input coupling of the BPF with the sixteen-first capacitor 516a.

The six-second inductor 506e, the seven-third inductor 507c, the eight-third inductor 508c, and the nine-third inductor 509c, which have a laminated structure and are connected to each other through the via-hole, form a resonant line of the BPF.

The inductors 50βe, 507c, 508c, and 509c of the resonant line of the BPF, connected to each other through the via-hole, make resonance with the eighteen-second capacitor 518b and the eighteen-third capacitor 518c. The fifteen-second capacitor 515b and the seventeen-third capacitor, having a laminated structure, output a signal passing through the BPF to the VHF port 320, and the fifteen- second capacitor 515b and the seventeen-third capacitor 517c make an output coupling of the BPF with the sixteen-second capacitor 516b.

Moreover, in the BPF, the six-third inductor 506f, the seven-fourth inductor 507d, the eight-fourth inductor 508d, and the nine-third inductor 509d, having a laminated structure and connected to each other through the via-hole, form the inductance coupling to adjust the pass bandwidth and are grounded to the GND 519. In the BPF, the fourteen-first capacitor 514a and the fifteen-first capacitor 515a make the capacitance coupling with the fifteen-second capacitor 515b to generate notch of the BPF 350 and to have influence on the attenuation condition, and the seventeen-first capacitor 517a is positioned at the output end of the BPF 350 to be grounded to the GND 519 and has influence on the attenuation condition.

Third, in the HPF, the five-first capacitor 505a and the six-first capacitor 506a having a laminated structure receive a signal transmitted from the matching circuit 340 to the HPF 360, and the five-first capacitor 505a and the six-first capacitor 506a make an input coupling of the HPF 360.

The seven-first inductor 507a, the eight-first inductor 508a, the nine-first inductor 509a, the ten-first inductor 510a, and the eleven-first inductor 511a, having a laminated structure and connected to each other through the via-hole, form a resonant line of the HPF 360 and are grounded to the GND 519. The inductors 50a, 508a, 509a, 510a, and 511a of the resonant line of the HPF 360, which are connected to each other through the via-hole, make resonance with the five-first capacitor 505a, the six-first capacitor 506a, the capacitors on the third layer 503 and the fourth layer 504, the five- third capacitor 505c, and the six-third capacitor 506c.

The capacitor on the fourth layer 504 and the six-third capacitor 506c, having the laminated structure, output the signal passing through the HPF 360 to the UHF port 330. The capacitors on the third layer 503 and the fourth layer 504, the five-third capacitor 505c, and the six-third capacitor 506c make the output coupling of the HPF 360.

Moreover, in the HPF, the five-second capacitor 505b and the six-second capacitor 506b, having the laminated structure, make the capacitance coupling and adjust the interval between poles of the return loss.

As described above, although the embodiment of the present invention is described by taking the dual band pass filter having a structure in which twenty layers are laminated, the dual band pass filter needs various capacitances and inductances in accordance with a desired frequency range. It is appreciated to those skilled in the art that the dual band pass filter according to the embodiment of the present invention may be designed to have layers more or less than twenty.

FIG. 30 is a graph illustrating frequency characteristics of the dual band pass filter 500 according to the embodiment of the present invention.

In FIG. 30, S (3, 1) indicates that a signal is input through the antenna port 310 and is output to the UHF port 330, S (2, 1) indicates that a signal is input through the antenna port 310 and is output to the VHF port 320, and S (1, 1) indicates a return loss in which a signal input through the antenna port 310 is returned and loss is generated. The vertical axis represents loss of signals in the unit of dB in which the loss increases as going down the graph and whose frequency is not passed.

As illustrated in the drawing, characteristics of a 2- pole band pass filter having two poles are illustrated sufficiently, and differently from an existing filter such that it is understood that second and third harmonic pass bands of a designed pass band are not represented.

A frequency passing through the BPF 350 and outputted to the VHF port 320 is 174 MHz to 204 MHz while a frequency passing through the HPF 360 and outputted to the UHF port 330 is 470 MHz to 862 MHz.

Meanwhile, as shown in the graph S (1, 1), there are two poles A and B at the VHF band and two poles C and D at the UHF band. The two poles A and B at the VHF band are generated by which the TL2 402 and the C3 413 of FIG. 6 make resonance with the TL3 403 and C4 414. The two poles C and D at the UHF band are generated by which the TL5 405 and the C7 417 of FIG. 6 make resonance with the TL6 406 and the C8 418. Meanwhile, this is a case when the return loss of a signal input into the antenna port 310 is the greatest at the poles A, B, C, and D, and it is understood that the 2-pole band pass filter is generated around the poles. Moreover, an interval between C and D is wider than that between A and B and this means that a range of the frequency passing through the HPF 360 and outputted to the UHF port 330 is wider than that of the frequency passing through the BPF 350 and outputted to the VHF port 320.

As shown in the graph S (2, 1), a notch (E, F) is generated. This is, as described above, because the capacitor C9 419 generates a notch of the BPF 350 and has influence on the attenuation condition. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A dual band pass filter comprising: a matching circuit matching impedance of a signal inputted from an antenna port by matching between a serial inductor and a parallel capacitor; a band pass filter (BPF) passing a VHF band signal and outputting the VHF band signal to a VHF port; and a high pass filter (HPF) passing a UHF band signal and outputting the UHF band signal to a UHF port; wherein the matching circuit, the BPF, and the HPF have structures in which a plurality of layers are laminated; wherein, in the matching circuit, a first inductor (506d) on a certain layer receives a signal through the antenna port, the first inductor 506d and second inductors (507b, 508b, 509b, 510b, 511b, 512a, and 513a) laminated on certain layers to be electrically connected to each other, form a matching line, and the first inductor (50βd) and the second inductors (507b, 508b, 509b, 510b, 511b, 512a, and 513a) make an impedance matching with a first capacitor (518a) on a certain layer; wherein, in the BPF, second capacitors (515a and 517b) laminated on certain layers to be electrically connected to each other, receive a signal transmitted from the matching circuit to the BPF, third inductors (506e, 507c, 508c, and 509c) laminated on certain layers to be electrically connected to each other, form a resonant line of the BPF, the third inductors (506e, 507c, 508c, and 509c) make resonance with third capacitors (518b and 518c) laminated on certain layers to be electrically connected to each other, and fourth capacitors (515b and 517c) laminated on certain layers to be electrically connected to each other, output a signal passed through the BPF to the VHF port; and wherein, in the HPF, fifth capacitors (505a and 506a) laminated on certain layers to be electrically connected to each other, receive a signal transmitted from the matching circuit to the HPF, fourth inductors (507a, 508a, 509a, 510a, and 511a) laminated on certain layers to be electrically connected to each other, form a resonance line of the HPF, the fourth inductors (507a, 508a, 509a, 510a, and 511a) make resonance with the fifth capacitors (505a and 506a) , sixth capacitors (503 and 505c) and seventh capacitors (504 and 506c) laminated on certain layers to be electrically connected to each other, and the seventh capacitors (504 and 506c) output a signal passed through the HPF to the UHF port.

2. The dual band pass filter as set forth in claim 1, wherein, in the BPF, fifth inductors (506f, 507d, 508d, and 509d) laminated on certain layers to be electrically connected to each other, adjust a pass bandwidth.

3. The dual band pass filter as set forth in claim 1 or claim 2, wherein, in the BPF, eight capacitors (514a, 515a, and 515b) laminated on certain layers to be electrically connected to each other, generate a notch of the BPF, and the BPF further comprises a ninth capacitor (517a) on a certain layer connected to an output end of the BPF.

4. The dual band pass filter as set forth in claim 1, wherein, in the HPF, tenth capacitors (505b and 506b) laminated on certain layers to be electrically connected to each other, adjust an interval between poles of return loss.