KR19990030747A - Micro Strip Bandpass Filters - Google Patents

Abstract

The disclosed band pass filter is used for band filtering a very high frequency signal of a specific band in various portable mobile communication fields, including portable telephone, GPS and PCS fields.

According to the present invention, the lower surface of the dielectric substrate is grounded, and the upper surface, which is electromagnetically open, is arranged with a plurality of micro strip resonators longitudinally short-circuited and a cross groove having a size and shape according to a band frequency in the micro strip resonator. It is easy to manufacture by providing a microstrip bandpass filter that band-filters the desired frequency by using the microstrip line, which is one of the planar transmission lines that are easily integrated with other passive microwave devices and active microwave devices. It is small and has a narrow bandpass characteristic of significantly less than 3%.

Description

Micro Strip Bandpass Filters

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to microstrip band pass filters used in various portable mobile communication fields, including portable telephones, global position systems (GPS) and personal communication systems (PCS).

The development of the information and communication field, which is essential in the highly information society, is spreading all over the world, and accordingly, research and development related to the information and communication field are actively progressing.

In particular, the mobile communication field in the information and communication is not only wide market, but also the research and development is rapidly progressing, and is actively participating in the mobile communication field in various countries around the world, the demand is expected to increase significantly.

Radio Frequency (RF) components that make up a system of mobile communication devices include power amplifiers, low noise amplifiers, voltage controlled oscillators, temperature compensation crystal oscillators, high frequency filters, and mixers.

Among these components, research and development of high frequency filter using dielectric resonator has been developed in the 1980s, and materials with excellent high dielectric constant and temperature characteristics have been applied to the field of mobile communication devices. Currently, Motorola Inc. in USA and Murata Inc. in Japan And Matsushida Corporation dominate most of the world market.

On the other hand, as miniaturization and light weight of mobile communication components continue, a ceramic dielectric having high dielectric constant and low loss is developed, and the volume and weight of the high frequency filter are continuously reduced due to the improvement of component manufacturing technology.

In fact, Murata, Japan, has been making miniaturized filters by developing resonators with materials with high dielectric constants and developing peripheral circuit designs.

In general, since the length of the high frequency dielectric resonator is inversely proportional to the square root of the dielectric constant, a material having a high dielectric constant should be used to downsize the filter.

At the same time, it is necessary to have a high Q value and a small temperature change of the resonance frequency in order to have excellent filter characteristics.

Microwave filters, on the other hand, are manufactured using micro strip lines, and are being developed into smaller, lighter, and less expensive devices, and demand thereof is increasing.

Microwave filters are two-port circuits used to control the frequency response of a microwave system by transmission in the passband frequency and attenuation in the cutoff band.

Typical microwave filters include low pass filters, high pass filters, band pass filters, and band stop filters, depending on the requirements of the system.

Applications of these microwave filters can also be found in microwave communication, radar, test systems or measurement systems.

Flat-panel transmission lines are the basic passive elements in the design of microwave circuits, and microstrip lines, one of the most important structures, can be easily connected and fabricated in active devices, so they are widely used in the design of microwave integrated circuits. .

The first flat transmission lines were developed by R.M.Barrett in the form of flat strip coaxial lines, similar to the strip lines used to produce power distribution circuits for antenna systems during World War II.

This is H. Howe. Reported by Jr, H. Wheeler built a flat transmission line in 1936 with two flat coplanar strips.

However, active development of flat transmission lines was not made until the 1950s.

An important theoretical study on the characteristics of the strip line was carried out by S. Chohb et al., Followed by couplers, hybrids, filters, antennas and other components of the strip line.

Microstrip lines were developed in 1952 at the International Telephone and Telegraph Corporation (ITT) Laboratory.

The first microstrip lines used very thick dielectric substrates and were not very practical.

In the 1960s, however, thinner substrates were used and are now widely used.

Ultra high frequency filter theory was started by Mason, Sykes, Darlington, Fano, Lawson and Richard before World War II.In late 1930, the image parameter method was developed and applied to the design of high frequency filter. Today, most filter designs are designed by the Insertion Loss Method, which is based on circuit synthesis.

Also in 1948, P. I. Richard established the concept important for the design of ultra-high frequency filters by integrating the distributed element filter theory with filters using distributed transmission lines.

Four K.Kuroda formulas have been proposed, which are used to convert lumped elements into transmission line sections and are used by K. Kuroda to separate the elements of the filter using transmission line sections.

Types of microstrip filters include commensurer line filters, stepped impedance filters, coupling line filters, filters using coupled resonators, filters using capacitive coupled resonators, direct coupled waveguide cavity filters, hairpin filters, inter Digital filters and hybrid filters.

1 is a view showing an embodiment of a conventional microstrip band pass filter.

Here, reference numeral 1 denotes a dielectric substrate.

The lower surface of the dielectric substrate 1 is grounded and the upper surface is electromagnetically open.

On the upper surface of the dielectric substrate 1, a plurality of micro strip resonators 2 having an inductance component are arranged to be short-circuited in the longitudinal direction.

The plurality of micro strip resonators 2 are connected to the connecting portion 3 having a capacitance component, and the input terminal 4 and the output terminal 5 are connected to the left and right micro strip resonators 2.

In one embodiment of the conventional microstrip band pass filter configured as described above, an ultrahigh frequency signal having a predetermined frequency to be band filtered is input to the input terminal 4.

Then, the inductance component of the plurality of micro strip resonators 2 and the capacitance component of the connecting portion 3 are resonated to band pass filter the signal having a predetermined frequency.

That is, broadband band pass filtering is performed by the plurality of micro strip resonators 2 arranged in a short circuit with each other.

The band pass filtered signal by the plurality of micro strip resonators 2 is output through the output terminal 5.

At this time, signals having a frequency outside the pass band are reflected by the micro strip resonators 2 and are not output to the output terminal 5.

The conventional embodiment described above requires a plurality of microstrip resonators 2 having inductance components and a plurality of connections 3 having capacitance components in order to band-filter ultra-high frequency waves of a desired frequency. Is difficult, and this causes a problem in that the miniaturization of a product using the micro strip band pass filter is problematic.

2 is a view showing another embodiment of a conventional band pass filter.

Here, reference numeral 11 denotes a dielectric substrate.

An input micro strip resonator 12 and an output micro strip resonator 13 are provided on both sides of the dielectric substrate 11, and an intermediate micro strip resonator is disposed between the input micro strip resonator 12 and the output micro strip resonator 13. 14 is provided.

An input terminal 15 and an output terminal 16 are connected to the input micro strip resonator 12 and the output micro strip resonator 13, respectively.

In another embodiment of the conventional microstrip band pass filter configured as described above, an ultra-high frequency signal of a predetermined frequency to be band filtered to the input microstrip resonator 12 is input through the input terminal 15 as in the above-described embodiment.

The high frequency signal of the selected frequency among the inputted high frequency signals is sequentially transmitted from the input micro strip resonator 12 through the intermediate micro strip resonator 14 and the output micro strip resonator 13, and the signal of the predetermined frequency is band filtered. The filtered microwave signal is output to the output terminal 16.

The other conventional embodiment described above reduces the number of micro strip resonators and does not need to form a connection between the micro strip resonators.

However, in order to band-filter the desired ultrahigh frequency with high selectivity, the distance between the input microstrip resonator 12, the intermediate microstrip resonator 14 and the output microstrip resonator 13 should be farther away. There was.

It is therefore an object of the present invention to provide a microstrip bandpass filter using a microstrip line which is easy to manufacture and is one of the plate-shaped transmission lines that are easily integrated with other passive microwave devices and active microwave devices.

Another object of the present invention is to provide a microstrip band pass filter having a small size and a narrow band pass characteristic with a large efficiency of 3% or less.

1 is a plan view showing an embodiment of a conventional band pass filter,

Figure 2 is a plan view showing another embodiment of a conventional band pass filter.

3A and 3B are a perspective view and a plan view showing one embodiment of a band pass filter of the present invention;

4 is a plan view showing another embodiment of the cross groove in the band pass filter of the present invention,

5 is a plan view showing another embodiment of a cross groove in the band pass filter of the present invention,

6 is a view for explaining the operating characteristics of the band pass filter of the present invention,

7A and 7B are plan views showing another embodiment of the band pass filter of the present invention.

<Description of Symbols for Main Parts of Drawings>

100: dielectric substrate 110: input terminal

120: output terminal 130: micro strip resonator

140: crossing groove

According to the microstrip bandpass filter of the present invention for achieving this object, the lower surface of the dielectric substrate is grounded, the upper surface which is electromagnetically open is arranged with a plurality of microstrip resonators are longitudinally short-circuited Cross grooves are formed in the microstrip resonator.

The cross grooves are configured in various shapes, and provide a band pass filter for selecting a desired frequency by modifying the size and shape of the cross grooves.

Hereinafter, the microstrip band pass filter of the present invention will be described in detail with reference to the accompanying drawings of FIGS. 3 to 7.

3A and 3B are a perspective view and a plan view showing one embodiment of a band pass filter of the present invention.

Here, reference numeral 100 denotes a dielectric substrate having a bottom surface grounded and an top surface electromagnetically opened.

Reference numerals 110 and 120 denote input terminals and output terminals respectively formed on one side and the other side of the dielectric substrate 100.

Reference numerals 130 and 140 denote input microstrip resonators and output microstrip resonators which are short-circuited to the upper surface of the dielectric substrate 100 and arranged in a longitudinal direction.

The input micro strip resonator 130 and the output micro strip resonator 140 are respectively connected to the input terminal 110 and the output terminal 120, and the surfaces of the micro strip resonators 130 and 140 facing each other. In the middle portion of the transverse grooves 150, 160 are respectively formed.

The cross grooves 150 and 160 may be formed in various shapes.

For example, as shown in FIG. 3a, it may be formed in a quadrangular shape, as shown in FIG. 4, or may be formed in a semi-hole shape with a rounded inside, or as shown in FIG. Form.

In addition to the shape described above, the cross grooves 150 and 160 may be formed in various shapes.

6 is a plan view showing another embodiment of the microstrip band pass filter of the present invention.

According to another exemplary embodiment of the present invention, a plurality of intermediate micro strip resonators 170 are disposed between the input micro strip resonator 130 and the output micro strip resonator 140 connected to the input terminal 110 and the output terminal 120. Equipped.

Cross grooves 180 are formed on both left and right sides of the intermediate microstrip resonator 150.

When a microwave signal of a predetermined frequency is input to the micro strip band pass filter input terminal 110 of the present invention having the above configuration, the input microwave signal is band filtered through the micro strip resonators 130, 140, 170, It is output to the output terminal 120.

At this time, the signals having frequencies other than the bands set by the micro strip resonators 130, 140, 170 and the transverse grooves 150, 160, 180 are transferred to the micro strip resonators 130, 140, 170. Is reflected by the output terminal and is not output to the output terminal 120.

The size of the transverse grooves 150, 160, 180 may be adjusted between 0.05 and 0.25 mm to increase the frequency selectivity to about 3% or less.

And the size and shape of the micro strip resonators 130, 140 and 170, and the cross grooves 150, 160 and 180 formed in the micro strip resonators 130, 140 and 170, respectively. The size and shape of the microstrip bandpass filter changes.

In the present invention, the size and shape of the microstrip resonators 130, 140, 170 and the cross grooves 150, 160, 180 are changed to filter the microwave signal of a desired frequency.

In designing the microstrip bandpass filter of the present invention, the most important variables are the impedance and the effective dielectric constant of the microstrip resonators 130, 140, and 170.

The impedances and effective dielectric constants of the microstrip resonators 130, 140, and 170 are the dielectric constant of the dielectric substrate 100 to be used as in Equation 1 and Equation 2 below, and the microstrip of the microstrip band pass filter to be designed. It is determined by the width and thickness of the strip resonator (130, 140, 170).

[Equation 1]

[Equation 2]

Where Z is the impedance, ε _EFF is the effective dielectric constant, w is the width of the micro strip resonators 130, 140, 170, h is the thickness of the micro strip resonators 130, 140, 170, ε is the dielectric constant of the dielectric substrate 100, and η is 120 pi.

If the impedance (Z) and the effective dielectric constant (ε _EFF ) are calculated in Equations 1 and 2 and the resonance frequency to be filtered is known, the microstrip resonators 130 and 140 ( 170, the length L can be obtained.

[Equation 3]

Where C is 3 × 10 ¹¹ mm / sec and F ₀ is the resonant frequency.

The present invention determines the specification of the micro strip resonator (130, 140, 170) in the above Equation 3, and the cross grooves (150, 160, 180) to the determined micro strip resonator (130, 150) To form.

By forming the cross grooves 150, 160, 180 in the micro strip resonators 130, 140, 170, the size of the micro strip band pass filter may be significantly reduced.

The principle of moving signals from the micro strip resonators 130, 140, 170 to the neighboring micro strip resonators 130, 140, 170 is as follows.

First, as shown in FIGS. 7A and 7B, the impedance Z ₁ and the transverse grooves 150, 160, 180 on the microstrip resonators 130, 140, 170 are formed. Find the impedance (Z ₂ ).

Next, the length L ₁ of the micro strip resonators 130, 140, 170 and the length L ₂ of the section in which the cross grooves 150, 160, 180 are formed are obtained by the following Equation 4 And the ratio (m) of the impedance (m) and the ratio of the length (q) as shown in equation (5).

[Equation 4]

[Equation 5]

The resonance frequency?

[Equation 6]

Since the change of the resonant frequency in each of the microstrip resonators 130, 140 and 170 can be known using Equation 6, a microstrip bandpass filter capable of bandpass filtering the required high frequency signal may be designed. Can be.

The resonant frequencies of the micro strip resonators 130, 140 and 170 are affected by the resonant frequencies of the micro strip resonators 130, 140 and 170 of the previous stage.

The ratio R between these resonant frequencies is typically two.

That is, the frequency of the micro strip resonators 130, 140 and 170 positioned at a specific position uses twice the frequency of the micro strip resonators 130, 140 and 170 immediately preceding.

When the resonance frequency F ₀ of the microstrip resonator 130 of the first stage is obtained from a given value, Equation 7 is obtained.

[Equation 7]

The resonance frequency F ₂ of the microstrip resonator 140 or the microstrip resonator 170 of the second stage is obtained from Equation 7 below.

[Equation 8]

F ₂ = R × F ₀

In the above-described method, the width, length, thickness, and the like of each of the micro strip resonators 130, 140, and 170 may be determined, and the desired band pass filter may be manufactured by substituting the impedance and the effective dielectric constant.

As described above, the present invention forms a microstrip bandpass filter by forming a cross groove in the microstrip resonator, which can reduce the size of the microstrip bandpass filter, thereby miniaturizing and lightening the mobile communication device.

Claims (8)

A dielectric substrate having a bottom surface grounded and electromagnetically open; An input terminal and an output terminal formed on one side and the other side of the dielectric substrate, respectively; An input microstrip resonator and an output microstrip resonator, each of which is short-circuited to an upper surface of the dielectric substrate and is arranged in a longitudinal direction and is connected to the input terminal and the output terminal, respectively; And And the input microstrip resonator and the output microstrip resonator are each formed of transverse grooves formed in intermediate portions of the surfaces facing each other. The method of claim 1, And a plurality of intermediate microstrip resonators provided between the input microstrip resonator and the output microstrip resonator. The apparatus of claim 2, wherein the intermediate micro strip resonator comprises: an intermediate micro strip resonator; Microstrip bandpass filter, characterized in that the transverse groove is provided on the left and right sides. The method of claim 1 or 3, wherein the cross groove is; Microstrip bandpass filter, characterized in that formed in a square. The method of claim 1 or 3, wherein the cross groove is; A microstrip band pass filter, characterized in that it has a semi-hole shape with a rounded inside. The method of claim 1 or 3, wherein the cross groove is; Microstrip bandpass filter, characterized in that the outer side is wide, the inner side is formed in a narrow ladder. The apparatus of claim 1 or 2, wherein the micro strip resonator; A microstrip bandpass filter, characterized in that the resonance frequency is increased by two times. The apparatus of claim 1 or 2, wherein the micro strip resonator; Microstrip bandpass filter, characterized in that the resonance frequency is set as shown in equation (6). [Equation 6] Where q is the ratio of the sections in which the odd and transverse grooves of the microstrip resonator are formed, ω is the resonant frequency, m is the ratio of the impedance on the microstrip resonator and the impedance in the section where the cross groove is formed.