WO1999018629A2

WO1999018629A2 - Microwave filter and method for fabricating microstrip band pass filter

Info

Publication number: WO1999018629A2
Application number: PCT/KR1998/000303
Authority: WO
Inventors: Soon Kil Chung; Jang Hwan Bae; Kwang Hee Cha; Alexandre Zakharov
Original assignee: World Peace Inst Of Technology; Jang Hwan Bae; Kwang Hee Cha; Soon Kil Chung; Alexandre Zakharov
Priority date: 1997-10-04
Filing date: 1998-10-01
Publication date: 1999-04-15
Also published as: JP2002532916A; WO1999018629A3

Abstract

A microwave filter which is used for implementing a band filtering with respect to a microwave signal of a predetermined band for various portable mobile communication products including a cellular phone, a GPS (Global Positioning System), and a PCS (Personal Communication System). The filter is capable of fabricating a compact size and light band pass filter by forming a microstrip resonator using a known semiconductor process such as a photolithography, an etching process, etc. after a conductive metallic layer such as Cr, Cu, etc. is deposited on a dielectric substrate of a high dielectric rate using a ceramic dielectric such as BaTi4O9, ZnO. The microwave filter includes a groove (150, 160) formed in a center portion of an opposite surface of a pair of microstrip resonators (130, 140) opened to each other and arranged to face each other for thereby filtering only a predetermined band frequency.

Description

MICROWAVE FILTER AND METHOD FOR FABRICATING

MICROSTRIP BAND PASS FILTER

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to a microwave filter and a method for fabricating a microstrip band pass filter, and in particular, to an improved microwave filter and a method for fabricating a microstrip band pass filter which are capable of implementing a compact size and lightness of a filter by using a ceramic dielectric such as BaTi₄Oc,, ZnO, depositing a conductive metallic layer such as Cr, Cu, etc. on the dielectric substrate of a high dielectric rate and foirning a microstrip type resonator using a semiconductor process such as a photolithography process and an etching process.

2. Description of the Conventional Art

In an advanced information society, an information communication field is greatly developed. Therefore, the development in the field of an information communication section is widely conducted.

In particular, in the field of the information communication section, a mobile communication field has a wide range of markets. In addition, the research and development thereof is rapidly advanced. Therefore, in the world, the mobile communication field receives big attention from people, and the demand therefor is increased.

As the parts of a RF (Radio frequency) for a system of a mobile communication device, there are known a power amplifier, a voltage control oscillator, a temperature compensation crystal oscillator, a high frequency filter, Among the above-described parts, a material of a high frequency filter having a high dielectric rate and a temperature characteristic was developed in 1980 based on the high frequency filter using a dielectric resonator. Currently, the products by Motorola, Murata Co. and Machcita of Japan are widely used. As the products of a mobile communication becomes compact-sized and light, the ceramic dielectric having a high dielectric rate and a low loss is developed, and as a part fabrication technique is advanced, the volume and weight of the high frequency filter becomes small.

Actually, Murata company of Japan fabricates a resonator having a high dielectric rate and a small-sized filter based on an advanced circuit design technique.

Generally, since the length of the high frequency dielectric resonator is reversely proportional to square root of the dielectric ratio, in order to πj±rumize the filter, a material having a high dielectric rate should be used. In order to implement an excellent filter characteristic, a material having a high Q value and a less change in temperature is necessary. The microwave filter is fabricated using a microstrip line and is small and light, so that the demand for the use of the same is increased at low price.

The microwave filter is a 2-port circuit used for controlling a frequency response of a microwave frequency response based on the decreased in a transmission and a stop band width of a band pass frequency.

As a typical microwave filter, there are known a low pass filter, a high pass filter, a band pass filter, and a band stop filter.

The application of the above-described microwave filter is used for a microwave communication, a radar or test system or a measuring system. The planar type transmission line is a passive device in the design of a microwave circuit, and the microstrip line which is one of the mist important structures is applicable for the passive device, so that it is widely used for a microwave integrated circuits design. The initial planar type transmission line was developed by R.M. Barrett in a type of a planar type coaxial line which was similar to the strip line used for a power distribution circuit of an antenna system in the second world war.

The above-described technique was disclosed by H. Howe. Jr. At the time, H. Wheeler fabricated the planar type transmission line using a planar identical planar strip in 1936.

However, until 1950, the planar type transmission line was not widely fabricated.

The theoretical study on the characteristic of the strip line was performed by S. Chob, etc. Thereafter, a combiner, a hybrid, a filter, an antenna and other parts were formed of the strip line.

The microstrip line was developed by ITT (International Telephone and Telegraph corporation) in 1952.

The initial version of the microstrip line was relatively thick, so that it was not actually used.

In the 1960s, as the substrate was made thinner, the microstrip line was widely used.

The microwave filter theory was started by Mason, Sykes, Darlington, Fano, Lawson and Richard before the second world war, and in the end of the 1930s, the image parameter method was adapted to the design of the microwave filter. Recently, the filter design is implemented based on the insertion loss method depending on the circuit combining technique.

In addition, in 1948, R. I. Richard disclosed a method that the filter using a distributed transmission line was combined with the distribution device filter theory for thereby establishing an important concept for the design of the microwave filter.

A method used for converting the integrated circuit into a transmission line unit and separating the devices of a filter using a transmission line portion was disclosed by K. Kuroda based on four equations. As the kinds of the microstrip filter, there are known a commensulator line filter, a step type impedance filter, a combined line filter, a filter using a combined resonator, a filter using a capacitance combined resonator, a common filter for a direct combining wave guide, a hairpin filter, an interdigital filter, a hybrid filter, etc.

Figure 1 illustrates a microstrip band pass filter which is a conventional microwave filter. The construction of the same will be explained with reference to Figure 1.

In the drawings, reference numeral 11 represents a dielectric substrate. The lower surface of the dielectric substrate 11 is connected with a ground, and the upper surface of the same is electromagnetically opened.

A plurality of microstrip resonators 12 having an inductance component are horizontally arranged on the upper surface of the dielectric substrate 11.

The microstrip resonators 12 are connected with a connection unit 13 having a capacitance component, and the microstrip resonators 12 at both sides are connected with an input terminal 14 and an output teirninal 15.

In the microstrip band pass filter which is a conventional microwave filter, a microwave frequency signal to be filtered based on the band filtering is inputted into the input terminal 14.

The inductance component of the microstrip resonator 12 and the capacitance component of the connection unit 13 are resonated for thereby filtering the signals of a predeteπnined frequency based on the band pass filtering.

Namely, The wide band pass filtering is implemented by the microstrip resonators 12 which are openly arranged.

The band pass filtered signals are outputted through the output terminal 15 based on the microstrip resonators 12.

The signals of frequency which are not in the range of the pass band are reflected by the microstrip resonator 12 and are not outputted through the output terminal 15.

In the conventional art, in order to implement the band filtering with respect to a microwave frequency of a desired frequency, since a plurality of microstrip resonators 12 having an inductance component and a plurality of connection units 13 having a capacitance component are used, the size of the same is increased, and it is impossible to a compact size product using the microstrip band pass filter which is a microwave filter.

In addition, Figure 2 illustrates another example of the band pass filter which is a conventional microwave filter. The construction of the same will be explained with reference to Figure 2.

In the drawings, reference numeral 21 represents a dielectric substrate. An input microstrip resonator 22 and an output microstrip resonator 23 are provided at both sides of the dielectric substrate 21, and an intermediate microstrip resonator 24 is provided between the input microstrip resonator 22 and the output microstrip resonator 23.

In addition, the input terminal 23 and the output terminal 26 are connected with the input microstrip resonator 22 and the output microstrip resonator 23, respectively.

In the thusly constituted conventional microstrip band pass filter which is a conventional microwave filter, a microwave frequency signal of a predetermined frequency to be processed based on a band filtering is inputted into the input microstrip resonator 22 through the input terminal 25.

The microwave signal of a frequency selected among the inputted microwave frequency signals is sequentially transferred through the intermediate microstrip resonator 24 and the output microstrip resonator 23 in the input microstrip resonator 22. In addition, a signal of a predetermined frequency is band-filtered, and the thusly band-filtered microwave frequency signal is outputted to the output terminal 26.

In the conventional art, it is not needed to decrease the number of microstrip resonators, and to form a connection unit between the microstrip resonators.

However, in order to implement a band filtering based on a high selectivity for a desired microwave using a microstrip band pass filter which is a microwave filter, the distances between the input microstrip resonator 22, the intermediate microstrip resonator 24, and the output microstrip resonator 23 should be increased. Therefore, it is impossible to decrease the size of the band pass filter.

In addition, in the microwave filter, a plurality of band pass filters are arranged on the dielectric substrate in serial or in parallel except for the band pass filter for thereby fabricating a planar type duplex filter.

As shown in Figure 3, the above-described planar type duplex filter will be explained based the USP Serial No.5, 151,670 as an example of the same.

The duplex filter is formed of microstrip resonators 41 and 43 which are exposed in the air and includes two band pass filters 38 and 39 operated in different frequency bands and uses a common combined line 42 disposed in one housing 40.

In more detail, the above-described duplex filter includes a housing 40, a common combined line 42 electrically with the housing 40, a plurality of first resonators 41 disposed in the housing 40 and operated in a first frequency band, one of which is connected with the common combined line 42, a planar plate 44 disposed in the housing and electrically connected with the housing 40, a second resonator 53 disposed in the housing 40, operated in a second frequency band higher than the first frequency band, having a first end portion disposed on the planar plate 44 and electrically connected with the planar plate 44 based on the first end portion at a portion where the planar plate is spaced apart by 1/4 wavelength of the second frequency from the common combined line 42, and an energy combining unit(not shown). However, the thusly constituted duplex filter has a complicated structure, and the size of the product is large, and the distance between products is wide, so that the size of the duplex filter is increased, and the fabrication cost of the product is high.

Figure 4 illustrates another example of the planar type duplex filter which is a conventional microwave frequency filter. In Figure 2, reference character "s" represents a dielectric substrate one surface of which is connected with a ground, and on the other surface of which, a plurality of conductive microstrips are arranged for thereby electrically combining the resonators.

A first output teπninal of a duplex filter is formed at one end of the microstrip 60 among the microstrips, and one end of the microstrip 61 is connected with a first variable capacity diode 65, and one end of the microstrip 62 operates as an input terminal of the duplex filter.

A second output teπriinal of a duplex filter is formed at one end of the microstrip 64, and one end of the microstrip 63 is connected with a second variable capacity diode 66, and the other ends of the microstrips 60, 62, 64 are connected with a ground, respectively, and the other ends of the microstrips 61 and 63 are opened.

The length of the microstrip 62 is the same as 1/4 wavelength of the center frequency of the input signal, and the lengths of the microstrips 60 and 61 are shorter than the length of the microstrip 62, and the lengths of the microstrips 63 and 64 are longer than the microstrip 62.

In the thusly constituted duplex filter, a variable voltage is applied to the variable capacity diodes 65 and 66. In the duplex filter as shown in Figure

4, the electrical signal inputted into the duplex filter through the input terminal 70 of the duplex is filtered by each microstrip resonator having different pass bands and outputted through the output terminals of the duplex.

However, since the duplex filter has an adjacent band pass near the center frequency, the frequency characteristics such as band width or a frequency selectivity are not good. Since the dielectric resonator of a column shape is formed on the dielectric substrate based on a method that the ceramic dielectric bulk is directly cut or pasted using a predetermined apparatus, the method for fabricating the microwave band pass filter is generally used. However, the column-shaped microwave filter fabricated based on the mechanical forming process has a limit for decreasing the distance between the resonators and the length of the resonator due to its coherent limit, so that it is impossible to fabricate a small size and light filter.

Therefore, the size of the substrate used for a single device is big, and an expensive dielectric substrate is used. Therefore, the fabrication cost is increased. As the size of the filter is large, it is impossible to directly connect with a surrounding device and implement an integration between the devices.

However, the problems of the compact and light filter and integration between the devices may be overcome by forming a microstrip line type resonator on the dielectric substrate through the conventional semiconductor processes such as a deposition process, a photolithography process, and an etching process after the dielectric substrate of the planar type is fabricated.

In particular, the microstrip line has an advantage in that it is possible to easily connect and fabricate the passive device, so that it is applicable for the microwave integrated circuit design.

In addition, when forming a substrate using a ceramic dielectric having a high dielectric rate, since it is possible to decrease the distance between patterns formed on the dielectric substrate by decreasing the strength of the magnetic field between the microstrips, a compact and light filter is implemented, so that the size of the dielectric substrate is decreased per device, and the fabrication cost of the filter is decreased.

In order to fabricate the dielectric substrate for a microwave filter, the material having a high dielectric rate is preferably used; however, the complex perovskite such as Ba(Mgι_/3Nb_2/3)O₃, BaMgO used for fabricating the dielectric substrate having a high dielectric rate is so expensive, so that there are many problems for actually using the above-described materials.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a microwave filter and a method for fabricating a microstrip band pass filter which overcomes the aforementioned problems encountered in the conventional art.

It is another object of the present invention to provide a microwave filter which is used for implementing a band filtering with respect to a microwave signal of a predetermined band for various portable mobile communication products including a cellular phone, a GPS (Global Positioning System), a PCS(Personal Communication System), and ASIC

It is another object of the present invention to provide a method for fabricating a microstrip band pass filter which is capable of fabricating a compact size and light band pass filter by forming a microstrip resonator using a known semiconductor process such as a photolithography, an etching process, etc. after a conductive metallic layer such as Cr, Cu, etc. is deposited on a dielectric substrate of a high dielectric rate using a ceramic dielectric such as BaTi₄O₉, ZnO. In order to achieve the above objects, there is provided a microwave filter comprising a groove formed in a center portion of an opposite surface of a pair of microstrip resonators opened to each other and arranged to face each other for thereby filtering only a predetermined band frequency.

In order to achieve the above objects, there is provided a method for fabricating a microwave filter and a microstrip band pass filter which includes the steps of mixing BaTi4O9 with Cr2O3 or A12O3 and preparing a dielectric substrate, rinsing the dielectric substrate based on a chemical process, depositing a conductive metallic layer on the dielectric substrate, defining a microstrip region using a photomask and etching the conductive metallic layer, and cutting the dielectric substrate to the size of a device and forming a predetermined shape of the same. Additional advantages, objects and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not jirnitative of the present invention, and wherein:

Figure 1 is a plan view illustrating a band pass filter which is a conventional microwave filter;

Figure 2 is a plan view illustrating another band pass filter which is a conventional microwave filter; Figure 3 is a plan view illustrating a planar type duplex filter which is a conventional microwave filter;

Figure 4 is a plan view iUustrating another planar type duplex filter which is a conventional microwave filter;

Figures 5A and 5B are perspective and plan views iUustrating a band pass filter which is a microwave filter according to an embodiment of the present invention;

Figure 6 is a plan view iUustrating a horizontal groove of a band pass filter which is a microwave filter according to another embodiment of the present invention;

Figure 7 is a plan view iUustrating a horizontal groove of a band pass filter which is a microwave filter according to another embodiment of the present invention;

Figure 8 is a plan view iUustrating another embodiment of the present invention of a band pass filter which is a microwave filter according to the present invention;

Figures 9A and 9B are views for explaining the operational characteristic of a band pass filter according to the present invention;

Figures 10A and 10B are plan and perspective views iUustrating a planar type duplex filter which is a microwave filter according to an embodiment of the present invention;

Figures 11A and 11B are plan and perspective views illustrating a planar type duplex filter which is a microwave filter according to an embodiment of the present invention;

Figures 12A, 12B and 12C are plan views iUustrating a horizontal groove of a planar type duplex filter which is a microwave filter according to another embodiment of the present invention;

Figure 13 is a plan view iUustrating a transmitter and receiver band pass filter in which an upper portion of a transmitter microstrip resonator and an upper portion of a receiver microstrip resonator are opposite in paraUel in a planar type duplex filter which is a microwave filter according to the present invention; Figure 14 is a plan view iUustrating a plan view iUustrating a transmitter and receiver band pass filter in which a lateral side of a transmitter microstrip resonator and a lateral side of a receiver microstrip resonator are opposite in serial in a planar type duplex filter which is a microwave filter according to the present invention; Figure 15 is a view illustrating different connection positions of an input/ output terminal in a planar type duplex filter which is a microwave filter according to the present invention;

Figure 16 is a flow chart iUustrating a fabrication process of a dielectric substrate used for a microstrip band pass filter according to the present invention; and

Figure 17 is a flow chart illustrating a fabrication process of a microstrip band pass filter according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention wiU be explained with reference to the accompanying drawings.

Figures 5A and 5B are perspective and plan views iUustrating a band pass filter which is a microwave filter according to an embodiment of the present invention. The construction of the same will be explained. In the drawings, reference numeral 100 represents a dielectric substrate the lower surface of which is connected with a ground, and the upper surface of which is electromagneticaUy opened.

In addition, reference numerals 110 and 120 represent an input terminal and an output terminal formed in one side and the other side of the dielectric substrate 100.

Reference numerals 130 and 140 represent an input microstrip resonator and an output microstrip resonator opened on the upper surface of the dielectric substrate 100 and longitudinally arranged thereon.

The input microstrip resonator 130 and the output microstrip resonator 140 are connected with an input terminal 110 and an output terminal 120, respectively, and traversing grooves 150 and 160 are formed at an intermediate portion between the microstrip resonators 130 and 140. The traversing grooves 150 and 160 may be formed in various shapes.

For example, as shown in Figure 5A, the traversing grooves may be formed in rectangular, and the same mat be formed in a semi-longitudinal shape in which an inner portion is rounded as shown in Figure 6, and the same may be formed in a ladder shape in which an outer portion is wide, and an inner side is narrow as shown in Figure 7.

In addition to that, the traversing grooves 150 and 160 may be formed in various shapes.

Figure 8 illustrates a plan view iUustrating another embodiment of the band pass filter which is a microwave filter according to the present invention. The construction of the same wiU be explained with reference to Figure 8.

A pluraUty of intermediate microstrip resonators 170 are provided between the input microstrip resonator 130 and the output microstrip resonator 140 connected with the input terminal 110 and the output terminal 120.

A traversing groove 180 is formed at both sides of the intermediate microstrip resonator 150.

In the thusly constituted microstrip band pass filter which is a microwave filter according to the present invention, when a microwave signal of a predetermined frequency is inputted into the input terminal 110, the thusly inputted microwave signal is band-filtered by the microstrip resonators 130,

140 and 170 and is outputted to the output terminal 120.

At this time, the signals having a frequency except for the bands set to the microstrip resonators 130, 140 and 170 and the traversing grooves 150, 160 and 180 are reflected by the microstrip resonators 130, 140 and 170 and are not outputted to the output terminal 120.

The sizes of the traversing grooves 150, 160 and 180 are controUed between 0.05-0.25, so that it is possible to increase the selectivity of the frequency below about 3%. In addition, the characteristics of the microstrip band pass filter may vary in accordance with the size and shape of the microstrip resonators 130, 140 and 170 and the traversing grooves 150, 160 and 180 formed in the microstrip resonators 130, 140 and 170. In the present invention, the microwave signals of a desired frequency is filtered by varying the size and shapes of the microstrip resonators 130, 140 and 170 and the traversing grooves 150, 160 and 180.

When designing the microstrip band pass filter according to the present invention, the most important variables are impedance and valid dielectric rate of the microstrip resonators.

The impedance and vaUd dielectric rate of the microstrip resonators

130, 140 and 170 are determined by the dielectric rate of the dielectric substrate 100 and the width and thickness of the microstrip resonators 130,

140 and 170 of the microstrip band pass filter based on the foUowing Equations 1 and 2.

[Equation 1]

Z = . f ln (-^ + 0.25 f ) (^ < 1)

2 π V ε EFF ^{w h h}

= , ^η [^ + 1.393 + 0.667 x In ( + 1.444)] ' (ηr ≥ D

V ε EFF " ^{n n}

[Equation 2]

where Z represents impedance, ε _EFF represents a vaUd dielectric rate,

W represents the widths of microstrips 130, 140 and 170, h represents the thickness of microstrips 130, 140 and 170, ε represents a dielectric rate of the dielectric substrate 100, and ) represents 120 π Ω.

The impedance Z and the vaUd dielectric rate ( ε _EFF ) are computed based on the Equations 1 and 2, and the lengths (L) of the microstrip resonators 130, 140 and 170 are computed using the Equation 3 based on the resonant frequency to be filtered.

[Equation 3]

L = C

2 F₀ ^r EFF

where C represents 3 X 10 mm/ sec, and Fo represents a resonant frequency.

In the equation 3 of the present invention, the specs of the microstrip resonant 130, 140 and 170 are determined for thereby forming the traversing grooves 150, 160 and 180 in the microstrip resonators 130 and 150.

Therefore, it is possible to significantly decrease the size of the microstrip band pass filter by forming the traversing grooves 150, 160 and 180 in the microstrip resonators 130, 140 and 170.

The principles that the signals flow from the microstrip resonators 130, 140 and 170 to the neighboring microstrip resonators 130, 140 and 170 will be explained. First, as shown in Figure 9, the impedance (Zm) in the microstrip resonators 130, 140 and 170 and the impedances (Z02) in the interval in which the impedance traversing grooves 150, 160 and 180 are formed are computed.

Next, the lengths (Li) of the microstrip resonators 130, 140 and 170 and the lengths (L2) in the intervals in which the traversing grooves 150, 160 and 180 are formed are computed, and then the ratio (m) of the impedance and the ratio (q) of the length are computed based on the Equations 4 and 5.

[Equation 4]

m = - Z^ —(j2

[Equation 5] ₂

The ratio (m) of the impedance and the ratio (q) of the length computed based on the Equations 4 and 5 is inserted into Equation 6 for thereby computing the resonant frequency [ω).

[Equation 6]

Since the resonant frequency of the microstrip resonators 130, 140 and 170 may be computed based on the Equation 6, it is easily design the microstrip band filter which is a microwave filter which is capable of band-filtering the microwave signal.

In addition, the resonant frequencies of the microstrip resonators 130, 140 and 170 are affected by the resonant frequencies of the microstrip resonators 130, 140 and 170 of the eariier circuit.

The ratio R of the resonant frequency is generaUy 2. Namely, the frequencies of the microstrip resonators 130, 140 and 170 uses two times the frequencies of the microstrip resonators 130, 140 and 170 of the eariier circuit. The resonant frequency (F₀) of the microstrip resonator 130 of the first circuit is computed based on the following equation 7.

[Equation 7]

<" oι _r

2 [ (L, - L₂)v ε EFFi + L2 e EFF2 ]

In addition, the following Equation 8 is obtained for computing the resonant frequency (F02) of the microstrip resonator 140 or the microstrip resonator 170 of the second circuit based on the Equation 7.

[Equation 8]

F₀₂ = R x F₀

In the above-described methods, the widths, lengths and thicknesses of the microstrip resonators 130, 140 and 150 are determined, and the impedance and vaUd dielectric rate are inserted therein for thereby using the values for fabricating the band pass filter which is a microwave filter. In addition, the planar type duplex filter is formed of a band pass filter, the values are used for the same.

The planar type duplex filter according to the present invention wiU be explained with reference to Figures 10 through 15.

Figures 10A and 10B are plan and perspective views illustrating a planar type duplex filter which is a microwave filter according to the present invention. The construction of the same wiU be explained with reference to Figures 10A and 10B.

In the drawings, reference numeral 210 represents a dielectric substrate in which a lower surface of the same is connected with a ground, and a lower surface of the same is opened. At this time, a plurality of electrodes may be formed on the grounded lower surface for a connection with an external circuit.

The microstrip duplex filter which is a microwave filter is formed of the resonators which are arranged in paraUel and are electromagnetically connected. In the drawings, reference numeral 220 represents receiver microstrip resonators opened on the upper surface of the dielectric substrate 210 and arranged in paraUel.

In addition, reference numeral 230 represents a transmitter microstrip resonator opened at a predetermined space from the receiver microstrip resonator 220 on the upper surface of the dielectric substrate 210 and arranged in the same direction as the receiver microstrip resonator 220.

Reference numerals 240 and 250 represent a receiver input/ output terminal and a transmitter input/ output terminal connected with the microstrip resonators 220 and 230 formed on the upper surface of the dielectric substrate 210 for receiving/ transmitting an electrical signal.

The receiver microstrip resonator 220 includes a first receiver microstrip resonator 220a and a second receiver microstrip resonator 220b opened on the upper surface of the dielectric substrate, arranged in one direction, and forming an electromagnetic connection. The above- described constructions and the receiver input/ output terminal 240 for transmitting an electrical signal from the receiver microstrip resonator 220 to an external circuit form a receiver band pass filter (Rx).

In addition, the transmitter microstrip resonator 230 includes a first transmitter microstrip resonator 230a and a second transmitter microstrip resonator 230b opened on the upper surface of the dielectric substrate, arranged in parallel in the same direction as the receiver microstrip resonator

220 at a predeterrriined space from the receiver microstrip resonator 220.

In addition, the above-described construction and the transmitter input/ output terminal 250 for transmitting an electrical signal from an external circuit to the transmitter microstrip resonator 230 form a transmitter band pass filter (Tx).

Preferably, the lengths of the microstrip resonators 220 and 230 are identical and are formed of end portions, and are arranged not to be mismatched in their lengthy directions.

In particular, a traversing groove 260 which operates for the same role as the band pass filter is formed at an intermediate portion of the upper units 222 and 232 opposite to the microstrip resonators 220 and 230, so that the signals having a frequency in the band set for the microstrip resonator and the traversing groove 260 among the microwave signals inputted into the microstrip band pass filter are passed.

At this time, the band frequency is set by controlling the size and shape of the traversing groove 260, and it is possible to decrease the size of the microstrip resonator and significantly decrease the selectivity of the frequency.

Since the operation of the microstrip band pass filter having the traversing groove is the same as the eariier embodiment of the present invention, the description thereof is omitted. At this time, in the duplex filter, the transmitting and receiving operation frequencies are determined. In addition, the lengths and widths of the transmitter and receiver microstrip resonators and the width and length of the traversing groove are determined based on the operational frequency. This determination is implemented based on the equation used for the microstrip band pass filter which is a microwave filter. In the drawings, reference numeral 270 represents a common input/ output terminal for commonly inputting and outputting an electrical signal inputted into or outputted from an antenna into two microstrip resonators, and reference numerals 280 and 290 represent a receiver shunting line 280 and a transmitter shunting line 290 through which an electrical signals inputted from the common input/ output terminal 270 and outputted to the common input/ output terminal 270 forming a T-shape junction portion with the common input/ output terminal 270 is inputted into or outputted from the receiver microstrip resonator 220 and the transmitter microstrip resonator 230. The operational principle of the planar duplex filter which is a microwave filter according to the present invention will be explained with reference to figure 10.

The planar type duplex filter according to the present invention has two operational modes of a transrnitting mode and a receiving mode. Each operational mode has its own band frequency.

When the planar type duplex filter operates in the receiving mode, the input signal (FR) of the receiving mode inputted from the antenna (ANT) is inputted into the common input/output terminal 270. The input signal in the pass band of the input signal (FR) of the receiving mode passes through the receiver microstrip band pass filter (Rx) forming of the receiver microstrip resonator 220 through the receiver shunting line 280 of the T-shape junction portion and is inputted into the receiver input/ output terminal 240.

At this time, the length of the transmitter shunting line 290 is deterrnined by the value which is capable of removing the shunting influence with respect to the receiver band pass filter (Rx) of the transmitter band pass filter (Tx) which represents an operational loss of the filter when being operated together with the transmitter band pass filter (Tx) when the receiver band pass filter (Rx) is operated based on the input signal (FR) of the receiving mode. Therefore, the input signal of the receiving mode passes through only the receiver shunting line 280 of the T-shaped junction portion.

When the planar type duplex filter is operated in the receiving mode, the input signal (F_R) of the transirutting mode is passes through the transmitter microstrip band pass filter rTx) formed of the transmitter microstrip resonator 230 and is inputted into the common input/ output terminal 270 through the transmitter shunting line 290 of the T-shape junction portion.

At this time, the length of the receiver shunting line 280 is determined for removing the shunting influence with respect to the transmitter band pass filter (Tx) of the receiver band pass filter (Rx), so that the input signal of the pass band of the transrrnτ±ing mode is not inputted into the receiver shunting line 280 and passes through only the transmitter shunting

Une 290 of the T-shape junction portion.

Namely, when the band pass filters (Rχ)(Tχ) are operated with a common load (ANT), the shunting influence affects the frequency characteristic of the duplex filter. This problem may be minixnized by properly controlling the lengths of the shunting lines 280 and 290 of the T-shape junction portion.

In more detaU, the length (IR) of the receiving shunting line is deteπnined to have a mirjimum shunting effect with respect to the transmitter band pass filter (Tx) when the receiver band pass filter (Rx) is operated in the pass band of the input signal (FT) of the transmitting mode based on the following equation.

[Equation 9]

where I_R represents the length of the receiver shunting hne 280, c represents the speed of fight in vacuum,

Z_R represents a wave resistance of the receiver shunting line 280,

F_T represents the transmitting frequency,

X_R(F_T) represents an imaginary number of the wave resistances of the common input/ output terminal 270 of the receiver band pass filter (Rx) of the receiving frequency (FT) and ε _R,_etf represents the receiver shunting line 280. The receiver shunting line 280 determines the input resistance of the receiver band pass filter (Rx) of the T-shape junction. If the length (I_R) of the receiver shunting line is determined based on the equation 1, the input resistance of the receiver band pass filter (Rx) of the transmitting frequency (F_T) is greatly increased, so that the shunting effects with respect to the transmitter band pass filter (Tx) in the transrmtting frequency (F_τ) is restricted. At this time, the transmitter band pass filter (Tx) has an effect that it is operated in the normal mode.

The length (lτ) of the transmitter shunting line is determined so that the transmitter band pass filter (Tx) minimums the shunting effects with respect to the receiver band pass filter (Rx) in the pass band of the input signal (F_R) of the receiving mode based on the foUowing equation.

[Equation 10]

where Iτ represents the length of the transmitter shunting line 290,

Z_τ represents a wave resistance of the transmitter shunting line 290, F_R represents the receiving frequency,

X_T(F_R) represents an imaginary number of the wave resistances of the common input/ output terminal 270 of the receiving frequency (FR) and the transmitter shunting line 290, and ε τ,_eff represents a valid dielectric rate of the transmitter shunting hne 290.

Figure 11 illustrates another embodiment of the planar type duplex which is a microwave filter according to the present invention. As shown in Figure 11, the planar duplex filter includes a plurahty of intermediate microstrip [ resonators 300 between a pair of external microstrip resonators 220 and 230 of the microstrip band pass filter formed on the upper surface of the dielectric substrate. Preferably, a traversing groove 261 is formed to be opposite to the traversing groove 260 formed on the external microstrip resonators 220 and 230 at both sides of the intermediate microstrip resonator 300.

As shown in Figures 10 and 11, the traversing groove of the microstrip resonator may be formed in various shapes line the traversing groove formed in the microstrip band pass Alter which is a microwave filter as shown in Figure 7.

The traversing groove as shown in Figure 12 may be formed in a shape such as a semi-elongated shape in which an inner portion is rounded or a ladder shape in which an outer portion is wider and an inner portion is narrower. In addition, the traversing groove of the transmitter microstrip resonator and the traversing groove of the receiver microstrip resonator may be differently formed.

In addition, when two band pass filter in which the planar duplex filter is formed on one substrate are prepared, and the system is operated with one common rod, for example, antenna(ANT), the frequency characteristic such as a frequency response or a VSWR are degraded for the reason that an electromagnetic parasitic interference effect occurs between the shunting influence and the band pass filter when the system is operated with respect to the common rod. In order to decrease the electromagnetic parasitic interference effects between the band pass filters in the planar duplex filter which is a microwave filter, it is necessary to properly arrange the band pass filters.

As shown in Figure 13, if the upper portion 232 of the transmitter microstrip resonator 230 and the upper portion 222 of the receiver microstrip resonator 220 are arranged to be opposite to each other, a relatively large electromagnetic interference occurs between the band pass filters.

This interference occurs due to a magnetic reason. When the distance (1) between the band pass filters is increased, the operational loss of the band pass filter is graduaUy decreased.

At this time, in order to duUy decrease the operational loss of the band pass filter by decreasing the electromagnetic interference, the distance (1) between the band pass filters should be fuUy increased. This distance increase represents an increase of the size of the duplex filter. In addition, in the planar type duplex filter, in order to mmimize the shunting effects and the electromagnetic interference effects, the lateral portion 132 of the transmitter microstrip resonator 230 and the lateral portion 221 of the receiver microstrip resonator 220 are preferably arranged to be opposite in the band pass filters.

In this case, the electromagnetic interference between the band pass filters becomes electronic, in more detail, capacitive, so that when the distance between the band pass filter is increased, the operational loss of the band pass filter is significantly decreased.

According the experiment conducted by the inventor of this invention, in the duplex filter as shown in Figure 14, when the distance (1) between the band pass filters was 2mm, the parasitic interference occurring between the filters, namely, the loss (L) of the band pass filter was about 20dB, namely, it was fuUy decreased. In addition, in the duplex filter as shown in Figure 13, in order to decrease the loss of the band pass filter to about 20dB, the distance between the band pass filters should be 9mm, namely, the same should be more widened compared to the filters as shown in Figure 14.

Therefore, when fabricating a small size planar type duplex filter, in the band pass filters of the duplex filters, both end portions 221 and 231 of the microstrip resonators are preferably arranged in series to be opposite. Figure 15 iUustrates other connection points of the input/ output terminal 240 and 250 with respect to the microstrip resonators 220 and 230 of the band pass filter in the planar duplex filter. Here, the operational frequency range of the duplex filter is a detuning frequency (F0 + F1) with respect to the center of the center frequency (Fo) of the band pass filter.

In Figure 15, the numbers of the connection points of the input/ output terminal are given 1 to 5 in the sequence from the end portions 221 and 231 of the resonators 220 and 230 to the center portion of the same.

If the connection points of the input/ output terminals 240 and 250 are at the point of 1, which is the farest from the center line of the resonators 220 and 230, in the filter response curve indicating the operational frequency-to-filter operational loss of the filter, the filter loss is highest in the center frequency (F₀), and the filter loss is smaUest in the detuning frequency (Fo± Fi) for thereby forming a parabolic curve.

In addition, the connection point of the input/ output terminals 240 and 250 becomes near the center line, namely, is at the point of 2, the filter response curve is formed like a parabolic curve and has a less loss compared to the case of the point of 1.

In addition, if the connection point of the input/ output terminals 240 and 250 becomes more near the center line, namely, the point of 3, the filter loss at the center frequency is increased more than the case of 2; however, in the boundary (Fo± ΔF), the filter loss is more decreased compared to the case of the point of 2. Therefore, in the filter response curve, the curve becomes near straight line in the pass band compared to the point of 2. Therefore, the case that the connection point of the input/ output terminal is 3 has less operational loss of the filter compared to the case that the connection point of the input/ output terminal is 2. Here, ΔF represents the difference (FWHM/2) between the frequency and the center frequency when the output power is -3dB with respect to the output power of the filter in the case of the center frequency.

If the connection point of the input/ output terminals 240 and 250 is at the point of 4, the loss at the boundary (Fo± ΔF) of the pass band of the filter is more decreased compared to the filter loss at the center frequency, so that two minimurn points are obtained at both sides with respect to the center frequency in response curve.

The minimum points of the filter response curve are controUable in accordance with the connection point of the input/ output terminals 240 and 250. The loss at the boundary (Fo+ ΔF) of the pass band of the filter is more increased compared to the point of 3. Therefore, the operational loss of the filter becomes more sensitive to the operational frequency for thereby increasing the selectivity of the filter.

However, the connection point of the input/ output terminals 240 and

250 becomes near the point of 5, which indicates more adjacent compared to the neighboring end portion of the traversing groove 160, the selectivity of the filter is more increased; however, the filter losses in the pass band becomes too large.

As a result, the connection point of the input/ output terminals 240 and 250 has a high filter frequency selectivity because the filter operational loss is sUghtly increased more than or becomes equal to the loss at the boundary (Fo ± ΔF) of the pass band of the filter for thereby having a high filter frequency selectivity and a low filter operational loss like the point between the points of 3 and 4.

At this time, the connection point of the input/ output terminals 240 and 250 may become any point where is symmetrical with respect to the center hne of the resonator.

According to the experiment conducted by the inventor of this invention, the length of the resonator of the band pass filter was 11mm, and the length of the input/ output terminal was 1mm, and the width of the same was 0.5mm. In the case of the receiver band pass filter (Rx), the connection points 1 and 4 are formed at 1.2mm, 1.0mm, 0.8mm and 0.6mm from the neighboring end portions of the traversing groove formed in the microstrip resonator, and then the filter response curve was checked. As a result of the checking, when the connection point is at 4, namely, the connection point of the input/ output terminal is at a point spaced apart by 0.6mm from the neighboring end portion of the traversing groove formed in the microstrip resonator, the highest frequency selectivity and lowest filter operational loss were obtained.

In addition, in the case of the transmitter band pass filter (Tx), the connection points 1 through 4 of the input/ output terminal were defined at 1.0mm, 0.8mm, 0.6mm, 0.4mm from the neighboring end portions of the traversing groove formed in the microstrip resonator, and then the filter response curve was measured. When the connection point of the input/ output terminal was at the point of 4, namely, when the point was spaced apart by 0.4mm from the neighboring end portion of the traversing groove formed in the connection microstrip resonator, the highest frequency selectivity and the lowest filter operational loss were obtained.

If the filter loss at the center frequency (Fo) was larger than the loss at the boundary (Fo± ΔF) of the pass bans of the filter, the VSWR at the center frequency was increased. In this case, the connection point of the input/ output terminal is controUed so that the VSWR does not exceed 2.

The above-described explanations correspond to the filter response curve based on the connection point of the input/ output terminals. ActuaUy, in the case of the duplex filter, the connection point of the input/ output terminal is determined in accordance with the variation of the filter response curve, the material of the band pass filter, the size and shape of the traversing groove.

Figure 16 is a view Ulustrating a fabrication process of a microstrip band pass filter according to the present invention, and Figure 17 is a flow chart iUustrating a fabrication process of a dielectric substrate using a ceramic dielectric monocrystal according to the present invention.

In particular, Figure 16 iUustrates a detaUed process for fabricating the dielectric substrate having a preferred characteristic. In this process, BaTiO₄Og and ZnO(or Cr₂O₃ or AI2O3) are selected and mixed in order for the substrate to have a dielectric rate ( ε r=35~92) of about 35-92, and then a substrate 810 as shown in Figure 17A is fabricated through the dry, milling, selection, and sintering processed. At this time, Cr₂O3 or AI2O3 may be used instead of ZnO.

Each process for fabricating the dielectric substrate according to the present invention wfll be explained with reference to Figure 16. First, BaTiO Og and ZnO are mixed at a ratio of 94wt% : 6wt% (600) and then a mixture is inserted into a dryer and is dried at a temperature of 100-110 °C for 2 hours (610).

At this time, the ratio of BaTϊO O₉ and ZnO may be controUed to have a desired dielectric rate. At this time, if necessary, the weight of the mixture is measured.

Next, the mixture obtained by mixing the source materials and distilled water are milhng-processed for about 3-10 hours using a baU-milling machine (620), and the powder of 15~20μm is filtered therefrom using a sieve (630). This powder is dried at a temperature of 100-110 °C for about 2 hours (640). The thusly processed dielectric powder is sintered at a temperature of

1150 °C under normal pressure for 4-6 hours (650), and then the resultant mixture is mixed with the distiUed water and is miUing-processed for 25-30 hours (660).

The dielectric powder of 15~20μm is filtered using the sieve (670) and dried in the dryer at a temperature of 100-110 °C for 2 hours (680), and the thusly dried powder and paraffin (3~4wt%) are inserted into an alumina furnace and mixed therein and dried at a temperature of 110 TJ for 2 hours (690).

The mixture formed in the steps 600 through 690 is formed to a desired shape under pressure of 50~60Mpa (700) and is sintered in the furnace at a temperature of 1320-1350 "C for 2 hours (710) for thereby forming a dielectric substrate 810 through a mechanical process (720) such as a grinding and pohshing process.

The characteristics such as a dielectric rate and temperature of the thusly fabricated dielectric substrate are measured (730) for thereby checking whether the dielectric substrate has a desired characteristic.

Figure 17B iUustrates the substrate rinsing process which is used for removing pollutants from the dielectric substrate.

The dielectric substrate 810 is boiled in dimethylformamid for about 30 minutes and then is rinsed in flowing water for 10 minutes. Thereafter, the dielectric substrate 810 is rinsed in the solution of KMnO4 150g/l(H2O : H3PO4 = 1:3 for 10 minutes.

Figure 17C illustrates the process in which the conductive metallic layer formed of a Cr layer 820 and a Cu layer 830 is deposited on the dielectric substrate 810 using an electron beam deposition process.

This process will be explained in detaU.

First, the dielectric substrate 810 is heated to a temperature of about

573 ° K, and then the Cr layer 820 and the Cu layer are sequentiaUy deposited on the dielectric substrate 810 using a vacuum deposition device. At this time, the dielectric substrate 801 is spaced apart by about 120mm from the evaporator.

The Cr layer 802 is used for easily implementing a junction between the dielectric substrate 810 and the Cu layer 830. At this time, the power is

P=4kV, the current is 1=150mA, and the surface resistance of the Cr layer 820 is 120.0 ~ 130 i2 (in the present invention, it corresponds to a thickness of

500-2000 A).

GeneraUy, the thickness of the Cr-layer is reverse proportional to the surface resistance. If the surface resistance is smaU, the performance of the microstrip resonator is decreased. On the contrary, if the surface resistance is large, an adhesion force on the substrate 810 is decreased.

Therefore, in order to maximize the performance of the filter, the thickness of the Cr-layer 820 is preferably formed to 120 Ω ~ 13013

In addition, the copper layer 830 is deposited to a thickness of 8 ~ 10 m for the reason that if the thickness of the copper layer 830 is below 8μm , the performance of the microstrip resonator is decreased. If the thickness of the copper layer 830 is over lOμm , the performance of the microstrip resonator is not increased. Therefore, in the present invention, it is possible to implement a compact and Ught filter based on the thickness of copper layer of 8~ 10μm. Figures 17E through 17F illustrate the photoUthograpgy process and the etching process. In these processes, a positive photoresist 840 is formed on the copper layer 830 to a thickness of lμm using a centrifugal separator based with a spin being apphed thereto and then is dried at a temperature of 95 TJ for about 10 minutes by infrared ray. Next, the positive photoresist 840 is exposed for about 30 seconds through a circuit-printed photomask 850 using a hght exposing apparatus having an infrared lamp, and then the positive photoresist 840 is processed in a developing solution (0.5% KOH) as shown in Figure 17D. Thereafter, the position photoresist 840 is heat-treated in the infrared ray apparatus at a temperature of 120 TJ for about 10 minutes, and a predetermined portion of the same is selectively etched using a selective etchant as shown in Figure

17E.

At this time, the etchant for Cr is formed of a Cr anhydrite of 200g, a sulfuric acid of 26ml, NaCl of 5g, and water of 1 l(solid). The etchant for copper is formed of a potassium ferricyanide, a caustic potash, and water of 1 l(solid).

After the etching process is performed, as shown in Figure 16F, the photoresist layer 840 is removed using

and then the substrate is cut to the size of each device using a cutting machine containing a diamond for thereby fabricating a microstrip band pass filter according to the present invention.

Therefore, the traversing groove is formed in the microstrip resonator of the band pass filter which is a microwave filter according to the present invention for thereby forming a microstrip band pass filter. In the present invention, since it is possible to fabricate a smaller and Ughter microstrip band pass filter compared to the conventional art, the microstrip band pass filter according to the present invention is used for a small and hght communication device. In addition, the planar type duplex filter which is fabricated according to another ernbodirnent of the present invention is used for the transmitter and receiver microstrip band pas filter formed of a microstrip resonator in which a traversing groove is formed on the dielectric substrate one of which is connected with a ground and a plurality of input/ output terminals, so that the mobUe communication units may be made compact-sized and hghter. In addition, the thusly fabricated filter is easily integrated with other microwave device for thereby implementing a high integration.

In addition, in the above-described planar type duplex filter, the band pass filters are arranged so that it is capable of mimrni-άng the electromagnetic interference between the band pass filters for thereby enhancing the frequency characteristics. In addition, the operational loss of the filter and the selectivity of the frequency are fuUy decreased by optimizing the connection points between the input/ output terminals and the microstrip resonator.

The microwave band pass filter according to the present invention may be used for a major element for a mobUe communication and a satellite communication transmitting and receiving system which is capable of minimizing the loss of the information in the region of microwave frequency over a few GHz and processing the signals at high speed. The microwave filter according to the present invention is capable of minimizing the line width of the circuit pattern by using the semiconductor processes and decreasing the length of the dielectric resonator and the distances between the circuit patterns by using a dielectric monocrystal substrate having a high dielectric rate, so that it is possible to fabricate a microwave part which is Ught and compact based on the lightness and high integration of the device for thereby decreasing the fabrication cost of the product.

Although the preferred embodiments of the present invention have been disclosed for iUustrative purposes, those skilled in the art wiU appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as recited in the accompanying claims.

Claims

What is claimed is:

1. A microwave filter comprising: a groove formed in a center portion of an opposite surface of a pair of microstrip resonators opened to each other and arranged to face each other for thereby filtering only a predetermined band frequency.

2. The filter of claim 1, wherein said microwave filter is a band pass filter.

3. The filter of claim 1, wherein in said microstrip resonator, a resonant frequency is increased by two times.

4. The filter of claim 1, wherein in said microstrip resonator, the resonant frequency is dete╧Çnined based on the foUowing equation:

- tan (q-^^~ ╧ë ) + m tan - -(l ΓÇö q) ╧ë tan -^U - q)╧ë + x = - = 0

⁴ 1 - mx tan (q-y <a ) x tan - - (l - q) ╧ë

where q represents a ratio between the length of the microstrip resonator and the length of the interval in which the traversing groove is formed, ╧ë represents the resonant frequency, m represents a ratio between the impedance of the microstrip resonator and the impedance in the interval in which the traversing groove is formed.

5. The filter of claim 2, wherein said band pass filter includes: a dielectric substrate having its lower surface connected with a ground circuit and its upper surface electromagneticaUy opened; an input terminal and an output terminal formed in one side and the other side of the dielectric substrate, respectively; an input microstrip resonator and an output microstrip resonator which are opened to each other on the upper surface of the dielectric substrate and are arranged to face each other and connected with the input terminal and the output terminal, respectively; and an traversing groove formed at an intermediate portion of the surface in which the input microstrip resonator and the output microstrip resonator are opposite to each other.

6. The filter of claim 5, wherein a plurality of intermediate microstrip resonators are provided between the input microstrip resonator and the output microstrip resonator.

7. The filter of claim 6, wherein a traversing groove is formed at both sides of the intermediate microstrip resonator.

8. The filter of claim 5, wherein said traversing groove is formed in one shape selected from the group comprising a semi-elongated shape in which an inner portion is rounded and a ladder shape in which an outer side is wider and an inner side of narrow.

9. The filter of claim 1, wherein a pair of said microstrip resonators opened to each other and arranged to be opposite to each other and another pair of said microstrip resonators arranged in one direction are arranged in series by a common input terminal to be opposite with respect to the lateral sides of each resonator at a predetermined space for thereby rriin iizing an electromagnetic interference between the band pass filters and filtering only a predetermined band frequency.

10. The filter of claim 9, wherein said microwave filter is a planar type duplex filter.

11. The filter of claim 10, wherein said planar type duplex filter incudes: a dielectric substrate having its lower surface connected with a ground and its upper surface electromagnetically opened; a transmitter band pass filter having a first transmitter microstrip resonator opened on an upper surface of the dielectric surface and arranged in one direction, a second transmitter microstrip resonator, a first transmitter input/ output terminal formed in one side of the dielectric substrate and connected with the first transmitter microstrip resonator, and a second transmitter input/ output terminal formed in the other side of the dielectric substrate and connected with the second transmitter microstrip resonator; a receiver transmitter band pass filter having a first receiver microstrip resonator opened on an upper surface of the dielectric substrate and arranged in paraUel to the transmitter microstrip resonator and spaced therewith at a predetermined distance, a second receiver microstrip resonator, a first receiver input/ output terminal formed in one side of the dielectric substrate and connected with the first receiver microstrip resonator, and a second receiver input/ output terminal formed in the other side of the dielectric substrate and connected with the second receiver microstrip resonator; and an traversing surface formed on a surface between the transmitter microstrip resonator and the receiver microstrip resonator.

12. The filter of claim 11, wherein in said transmitter band pass filter or said receiver band pass filter, the lengths of each of the transmitter microstrip resonators and each of the receiver microstrip resonators are identical, and the center hne of the resonators are on a straight hne, and both ends of the same are opened.

13. The filter of claim 11, wherein said first transmitter input/ output terminal and said first receiver input/ output terminal include: a common input/ output terminal formed in one side of the upper surface of the dielectric substrate for connecting with an external circuit; and a transmitter shunting line for connecting the common input/ output terminal and the first transmitter microstrip resonator, and a receiver shunting hne for connecting the common input/ output terminal and the first receiver microstrip resonator, wherein the lengths of the transmitter shunting line and the receiver shunting line are determined in order to minimize a shunting influence between the transmitter band pass filter and the receiver band pass filter.

14. The filter of claim 11, wherein said first transmitter input/ output terminal and said first receiver input/ output terminal include: a common input/ output terminal formed in one side of the upper surface of the dielectric substrate for connecting with an external circuit; a transmitter shunting line for connecting the common input/ output terminal and the first transmitter microstrip resonator; and a receiver shunting line for correcting the common input/ output terminal and the first receiver microstrip resonator for thereby forming a T-shape junction, wherein the lengths of the transmitter shunting line and the receiver shunting line are determined based on the foUowing equations for thereby minimizing the shunting effects between the transmitter band pass filter and the receiver band pass filter:

where IR represents the length of the receiver shunting hne 280, c represents the speed of hght in vacuum,

ZR represents a wave resistance of the receiver shunting hne 280,

FR represents the transmitting frequency,

XT(FR) represents an imaginary number of the receiving frequency (F_R) of the common input/ output terminal and the transmitter shunting line, and ╬╡ R,_eff represents an effective dielectric rate of the transmitter shunting line, and

10 where IT represents the length of the transmitter shunting line,

ZT represents a wave resistance of the transmitter shunting line 290, FR represents the receiving frequency,

XT(FR) represents an imaginary number of the wave resistances of the common input/ output terminal of the receiving frequency (F_R) and the Z transmitter shunting line, and ╬╡ ╧ä,eff represents a valid dielectric rate of the transmitter shunting hne.

15. The filter of claim 11, wherein more than one intermediate microstrip resonator is provided between the first transmitter microstrip 0 resonator and the second transmitter microstrip resonator and the first receiver microstrip resonator and the second receiver microstrip resonator.

16. The filter of claim 15, wherein said intermediate microstrip resonator includes a traversing groove formed on the surface opposite to another microstrip resonator.

17. The filter of claim 11, wherein said traversing groove formed in the receiver microstrip resonator is formed in one shape selected from the group comprising a semi-elongated shape in which an inner portion is rounded and a ladder shape in which an outer portion is wider and an inner portion is narrow, and said traversing groove formed in the transmitter microstrip resonator is formed in one shape selected from a rectangular shape, a semi-elongated shape in which an inner portion is rounded, and a ladder shape in which an outer portion is wider and an inner portion is narrow, with the shape of the traversing groove being different from the shape of the receiver microstrip resonator.

18. The filter of claim 11, wherein said input/ output terminal is connected with a predetermined point of an upper portion of the microstrip resonator, and in a connection point of the input/ output terminal, the distance from the connection point to the center line of the microstrip resonator is longer than the distance from the connection point to an end portion of the traversing groove of the microstrip resonator, and in a response curve of the filter, the operational loss of the filter at the center frequency (Fo) of the filter is larger than or equal to the operational loss of the filter at the boundary (Fo ┬▒ ╬ö F) of the pass band of the filter.

19. A method for fabricating a microstrip band pass filter, comprising the steps of: mixing BaTi₄Og with Cr₂O3 or AI2O3 and preparing a dielectric substrate; rinsing the dielectric substrate based on a chemical process; depositing a conductive metallic layer on the dielectric substrate; defining a microstrip region using a photomask and etching the conductive metallic layer; and cutting the dielectric substrate to the size of a device and forming a predetermined shape of the same.

20. The method of claim 19, wherein said dielectric substrate has a dielectric rate of 35-92 ( ╬╡ _r = 35-92).

⁵ 21. The method of claim 19, wherein said conductive metallic layer is formed of a Cr layer having a thickness of 500-2000 A and a Cu layer having a thickness of 8-1 O m.

22. The method of claim 19, wherein said dielectric substrate is fabricated by the steps of: 1┬░ mixing BaTi₄O₉ with ZnO or Cr₂O3 or AI2O3 and drying a mixture at a temperature of 100-110 tj ; adding a distilled water to the mixture and milling a resultant mixture for 3-10 hours; filtering a dielectric powder having a size of 15~20 m after the milling I⁵ step using a sieve; drying the dielectric powder at a temperature of 100-110 TJ ; sintering the dielectric powder at 1150TJ under normal pressure; mixing the sintered structure with a distiUed water and milling the resultant mixture; 20 filtering the dielectric powder having a size of 15~20 n╬╣ after the milling sep using a sieve; drying the dielectric powder at a temperature of 100-110 TJ ; mixing the dielectric powder after the dry step with a paraffin and drying a resultant structure; 2 forming the dielectric powder after the dry step to shape of the substrate under a pressure of 50~60MPa; sintering the dielectric after the processing step in a furnace at a temperature of 1320- 1350 ┬░C ; and fmishing a fabrication of a dielectric substrate based on a mechanical process such as a pohshing with respect to the dielectric substrate after the sintering step.