[DESCRIPTION] [Invention Title]

TUNABLE DEVICE FOR MICROWAVE/MILLIMETER WAVE APPLICATION USING A TRANSMISSION LINE STRIP [Technical Field]

<i> The present invention relates to a tunable device for microwave/millimeter wave application using a transmission line strip; and, more particularly, to a tunable device for microwave/millimeter wave application using a transmission line strip, which is applied to a step- impedance, an open strib and an open resonator, which reduce a manufacturing cost and acquires good reliance due to not need a ground using the transmission line strib. [Background Art]

<2> As an income level is getting higher, a need for using one mobile communication device operated in a multi-band or a different communication system is getting increased. Thus, the need of tunable devices for implementing a radio frequency system operated in a multifunctional multi- band is increased. Since the tunable devices may be used in a multi-band, a size and a weight of products are reduced, and a high function of the products may be implemented.

<3> Semiconductor varactors and tunable MEMS (Micro Electromechanical Systems) capacitors using MEMS, which changes an electric capacitance, are used as tunable capacitors which are used to change a resonant frequency or a band-stop frequency consecutively.

<4> Moreover, tunable dielectric capacitors which change dielectric constant (or permeability) of a dielectric substance based on an intensity of an electric field (or magnetic field) are used. Here, tunable dielectric capacitors are called as dielectric varactors. The tunable dielectric capacitors are mainly used in filters, phase shifters, attenuators, limiters, oscillators, dividers, antennas, and impedance matching circuits for a microwave or a millimetric wave.

<5> An example of a tunable bandpass filter using a tunable capacitor is described in US patent Nos. 4,835,449, 6,717,491B2, and 5,888,942, Korean patent Nos. 10-0344785 and 10-0393804, and Korean patent publication No. 10- 2005-0110430. Moreover, an example of a tunable band-stop filter is described in US patent publication No. 2006/0152303A1, and US patent No. 5,448,210. And, an example of a tunable antenna is described in US patent No. 5,448,210. Further, an example of a tunable dielectric capacitor is described in US patent Nos. 6,531,936B2, 6,686,817B2 and 6,404,6141Bl.

<6> A conventional tunable resonator connects a tunable capacitor between a ground and an opened end part of the tunable resonator, and varies a resonant frequency by changing a dielectric constant or an electric capacitance of the tunable capacitor.

<7> However, in case that a conventional tunable resonator is manufactured on a flat type substrate having a ground and a transmission, which are located on a different plane from each other, such as microstrip or stripline structures, processes for puncturing the substrate, and connecting a tunable capacitor to a ground through a via-hole are further included in a manufacturing process of the conventional tunable resonator. These processes have demerits that a manufacturing cost is high and it is difficult to be implemented. Especially, these processes have demerits that a characteristic change depends on a position of the via-hole in a high frequency.

<8> A tunable resonator having a non-ground is suggested to improve these demerits. The tunable resonator is described in reference documents, V. Pleskachev and I. Vendik, "Figure of merit of tunable ferroelectric planar filter," Millimeter and Submillimetric waves (MSMW'04): Kharkov, Ukraine, June, pp. 21-26, 2004; I. Vendik, 0. Vendik, V. Pleskachev and M. Nikol'ski, 'Tunable microwave filters using ferroelectric materials," IEEE Transaction on Applied Superconductivity, vol. 13, no. 2, pp. 716-719, 2003; and V. Pleskachev and I. Vendik, "Figure of merit of tunable ferroelectric planar filters," Proc. 33 European Microwave conference, Munich, pp. 191-194, 2003. <9> Fig. 1 illustrates a tunable resonator using an open-circuited

resonator (or a tunable device using a transmission line strib applied to a conventional open-circuited resonator). Hereinafter, the tunable device using the open-circuited resonator is called as a tunable resonator for convenience.

<io> Fig. 2 illustrates a conventional tunable resonator which needs a ground. Fig. 3 illustrates a tunable bandpass filter using a tunable resonator. As shown in Fig. 1, a reference character i denotes a physical length between the resonator 11 and a transmission line strib 13, and subscripts 0 and 1 denote the resonator 11 and the transmission line strib 13.

<π> As shown in Fig. 1, the tunable resonator 10 includes a resonator 11, a transmission line strib 13 and a tunable capacitor 12. Thus, the tunable resonator 10 shown in Fig. 1, which is different from a conventional tunable resonator shown in Fig. 2, does not need a ground through the transmission line strib 13. However, the conventional tunable resonator 20 connects a tunable capacitor 12 connected to the resonator 11 to a ground 14 through a via-hole in case that the ground is located on a different plane. Feeding lines 101 and 102 for inputting/outputting a signal from a tunable bandpass filter 100 shown in Fig. 3 are connected to both sides of the tunable resonators in parallel.

<i2> However, referring to the tunable resonator 10 showed in Fig. 1, an electrical length of the transmission line strib 13 in configuration of the tunable resonator 10 is longer than a half wavelength (λ _g /2), where λ _g denotes a guided wavelength. That is, an electrical length (θo) of the resonator 11 shown in Fig. 1 is longer than an electrical length (^ ₁ ) of the transmission line strib 13, where θ denotes the electrical length. <i3> A figure of merit depending tunability acquired from an insertion loss and a resonant condition is defined in reference documents described above, and an electrical length of the transmission line strib 13 having an optimum figure of merit is acquired.

<]4> In case of MSMW'4 of the reference documents, an electrical length of a resonator 11 having an optimum figure of merit acquired from the open- circuited resonator is about 80° A transmission line strib 13 having an electrical length of about 100° is described in the MSMW'4 That is, the electrical length (^ ₁ ) of the transmission line strib 13 in the reference documents is longer than a half wavelength as shown in Fig. 4 of the MSMW'4. However, the tunable resonator 10 having a condition described in the reference documents has a demerit such as a transmission zero.

<15> Firstly, a characteristic of the tunable resonator 10 described in reference documents will be described. Fig. 4 illustrates a tunable bandpass filter using a tunable resonator 203. Fig. 5 illustrates a bandpass filter using a resonator 203b in accordance with a prior art. Fig. 4 illustrates a case of having one of resonators shown in Fig.3.

<i6> Fig. 5 illustrates a bandpass filter using a resonator 203b in accordance with a conventional technique. The bandpass filter according to the conventional technique has components except a transmission line strib and a tunable capacitor shown in Fig. 4. Both ends of the resonator shown in Fig. 5 are opened. Fig. 6 shows a simulated graph of a resonant frequency of the tunable bandpass filter shown in Fig. 4. A physical length of the open- circuited resonator 203 and an electrical capacitance (CO of the tunable capacitor 204 are 13mm and 0.2pF respectively which are fixed, and a physical length ( 11) of the transmission line strib 205 is changed. λ _g /64, λ _g /32, λ g/8 and λ _g /4 shown in Fig. 6 are corresponding to 0.40625mm, 0.8125mm, 1.625mm, 3.25mm and 6.5mm. As shown in Fig. 6, if the physical length of the transmission line strib 205 is longer, a resonant frequency is lowered. Hereinafter, a width between a resonator and a transmission line strib is fixed with 0.6mm and a physical length ( £ o) of the resonator is fixed with 13mm in simulations. <17> Fig. 6 shows a simulated insertion loss change graph of the resonator

shown in Figs. 4 and 5. Fig. 7 shows an insertion loss graph in case that the physical length (^ ₁ ) of the transmission line strib 205 is the same with or less than the physical length ( £ ₀ ) of the resonator 203. A broken line and a dotted line shown in Fig. 7 are insertion loss graphs in case that the physical lengths of the transmission line strib 205 shown in Fig. 4 are 6.5mm( 4! i<# o) and 13 mm(-Ci=- ^β ₀ ) respectively.

<i8> A solid line shown in Fig. 7 shows an insertion loss graph of a bandpass filter acquired from Fig. 5. Here, a physical length ( 1 ₀ ) of the resonator 203 is fixed with 13mm. Notably, in case of the solid line and the broken line (-C ₁ ^ ₀ ), each of one pass-band and a resonant frequency is represented at, 4.26GHz and 3.99GHz. However, two pass-bands are represented at 3.75GHz and 4.33GHz on a dotted line in case that the transmission line strib 205 and the resonator 203 have the same physical length of 13mm {tr- l o ⁾ .

<i9> Fig. 8 shows a simulated insertion loss graph in case that a physical length (^ ₁ ) of the transmission line strib 205 is the same with or longer than a physical length ( i ₀ ) of the resonator 203. A solid line shown in Fig.

8 represents a case that the transmission line strib 205 and the resonator 203 have the same physical length of 13mm (£i=£ ₀ ).

<20> A broken line and a dotted line are corresponding to 15mm and 19mm in case that the physical length of the transmission line strib 205 is longer than the physical length of the resonator 203 ( -C i> -C ₀ ) • The broken line and the dotted line shown in Fig. 8 are corresponding to an optimum condition that the tunable resonator described in reference documents has an optimum figure of merit. <2i> However, two pass-bands are represented at & (solid line), but a pass-band of a low frequency is removed at 11> to (broken line, dotted line).

Notably, as shown in Fig. 8, in case of ii>lto, that is, resonant frequencies are 4.02GHz and 4.13GHz in case of H _x =15mm (broken line) and 1 ₀ =19mm

(dotted line). However, A resonant frequency is 3.99GHz and is lower than the transmission line strib having a longer physical length in case of the dotted line shown in Fig. 2d, that is, I i=6.5mm.

<22> In conclusion, if Figs 7 and 8 are compared, a lower frequency is acquired in case that the physical length (-Cpβ.δmm) of the transmission line strib is short than the case that the physical length of the transmission line strib is long 15mm or 19mm).

<23> Since the largest problem of conventional microwave devices is to have a large size, these characteristic of the tunable resonator described in the reference documents are demerits.

<24> In order to find a cause of the demerits of the tunable resonator described in the reference documents, an input impedance {Z _m ) of the tunable resonator shown in Fig. 1 is represented as expression 1 as below. <25> [Math Figure 1]

l-z ₀ tan(θ ₀ )*tan(θ ₁ )+ in

<26> A resonant condition of the tunable resonator described in the reference documents is represented as expression 2 as below. <27> [Math Figure 2]

<28> When the input impedance of the expression 1 is unlimited, a resonant condition of the tunable resonator shown in Fig. 1 is satisfied. In more

details, when a denominator term value of the expression 1 is "0" the tunable resonator resonates. That is, the resonant condition of the expression 1 is satisfied when the denominator term value becomes "0".

<29> A resonant condition of the expression 2 described in reference documents is induced by simplifying the resonant condition of the expression 1. That is, the expression 2 is corresponding to a simplified expression of the expression 1 when the denominator term value of the expression 1 becomes "0", and the width of the transmission line strib 205 is the same with the width of the resonator 203.

<30> z, y and w of the expressions 1 and 2 denote an impedance, an admittance, and an angle frequency respectively. Here, an electrical length

( ) indicated in expressions is , wherein I , ε _r , f, c denote a physical length, an effective relative dielectric constant, a frequency and a speed of a light respectively. Hereinafter, for convenience, the denominator term and the numerator term of the expression 1 is called as a denominator term and a numerator term.

<3i> As mentioned above, the input impedance of the expression 1 includes more information for the tunable resonator shown in Fig. 1 than the resonant condition of the expression 2 described in the reference documents. That is, in case of the input impedance of the expression 1, since a zero point of the denominator term value is a resonant point, and the input impedance becomes "0", at a zero point of the numerator term value, it is important that a transmission zero which does not transmits a signal occurs. However, the transmission zero is not included in the resonant condition of the expression 2 described in the reference documents.

<32> Figs 9 to 13 show a resonant point and a transmission point of the tunable resonator which are calculated using the expression 1. In Figs 9 to 13, P ₁ , P2 and P ₆ points are resonant points where the denominator term value of the input impedance becomes zero, and P represents the transmission zero

where the numerator terra value of the input impedance becomes zero. Here, a physical length I ₀ of the tunable resonator 203 is fixed as 13mm. A resonance is generated at unlimited input impedance having the denominator term value of zero.

<33> Figs 9 to 13 show the resonant point and the transmission point which are calculated using the expression 1 when the physical length 1 ₁ of the transmission line strib is 6.5mm (λ _g /4), and an electric capacity 4 is

0.2pF. This is corresponding to a dotted line of Fig. 7 calculated by a simulation. Fig. 9 shows graphs of a denominator (dotted line) and a numerator (solid line). Fig. 10 shows an extended graph of the denominator (dotted line). As shown in Fig. 9, in case of 6.5mm (λ _g /4), the numerator (solid line) has always larger value than 0. As shown in Fig. 10, the denominator (dotted line) becomes 0 at P ₁ point of about 4GHz of P point, and the resonance occurs at the same frequency. This resonant frequency is matched with the resonant frequency of 3.99GHz of the dotted line shown in Fig. 7 as the simulated result in the same condition. And, as shown in Fig. 9, in case of I \ = 6.5mm (-C ₁ <£ ₀ ), since the numerator (solid line) of the input impedance is larger than 0, it is important that the transmission zero is not generated. <34> Hereinafter, in case that the physical length i \ of the transmission line strib 205 is 15mm and 19mm {lχ >£ ₀ ), reasons that two pass-bands are generated and passband having a lower frequency is removed will be described as below.

<35> Fig. 11 shows graphs of a denominator (solid line) and a numerator (dotted line), which are calculated using the expression 1 in case that the physical length of the transmission line strib line 205 is 15mm. Fig. 12 shows an extended numerator (solid line) and an extended denominator (dotted line). The numerator (solid line) shown in Fig. 11, which is different from the numerator (solid line) shown in Fig. 9, has a zero point at P point.

That is, the impedance value in the expression 1 becomes O at this point and a transmission zero, which does not transmit a signal, is generated. Moreover, in case that the physical length I ₁ of the transmission line strib is 6.5mm, the denominator (dotted line) becomes zero at P ₁ shown in Fig. 10. In case that the physical length of the transmission line strib is 15mm, the denominator becomes zero at P ₂ and P ₅ shown in Fig. 12.

<36> In other words, as shown in Fig. 12, two pass-bands are generated by the resonance generated at P ₂ and P ₅ . However, notably, as shown in Fig. 12, the resonance point P ₂ where the numerator (solid line) becomes zero is located near to the transmission zero P where the denominator (dotted line) becomes zero. In case that the physical length -C ₁ of the transmission line strib 255, which is shown in Fig. 8, calculated by the simulation is 15mm and 19mm (^i>^o), the resonance point P ₂ is located near to the transmission point Pi, and the pass-bands are removed by compensation between the resonance point and the transmission point. <37> Hereinafter, in case of the solid line { which is shown in

Fig. 8, calculated by the simulation, a generation cause of two pass-bands will be described as below. Fig. 13 shows a result calculated by the expression 1 in case that the physical lengths of the resonator 203 and the transmission line strib 255 are same with each other as 13mm ( I and an electric capacity Ci is 0.2pF. As shown in Fig. 13, the denominator of the input impedance becomes zero at two resonant points P ₂ and P ₅ , and a transmission zero P is located in the middle of two points P ₂ and P5.

<38> In case of a solid line shown in Fig. 8, which is acquired by a simulation at the same condition, a resonance occurs at two points P ₂

(3.75GHz) and P ₆ (4.33GHz) where a denominator becomes a zero. However, the transmission zero, which a transmission is not performed, is generated at a

middle point (4.11GHz) of two points P ₂ (3.75GHz) and P ₆ (4.33GHz).

<39> When a physical length of a transmission line strib 205 is larger than 13mm (#i>#o)» a location of the transmission zero P is far away a high resonant frequency P ₆ and gets near a low pass-band P ₂ . <40> Thus, a resonance does not occur at a resonant point P ₂ in an optimum performance condition of a tunable resonator. That is, since a physical length of a transmission line strib of conventional tunable resonators is longer than a half wavelength, a transmission zero occurs. Although the conventional tunable resonators have a larger size, the conventional tunable resonators have a higher resonant frequency than in case that a physical length of a transmission line strib is smaller than a half wavelength.

<4i> An impedance matching circuit is added between a load and a feed line which provides a signal, and transfers a maximum power to the load at a specific frequency band. That is, if an impedance of the feed line is not matched with an impedance of the load, a reflective wave is generated by the load and a power loss is generated. An impedance matching circuit is mainly used in an antenna, a power amplifier, a low noise amplifier, a voltage controlled oscillator. A strib is mainly used for an impedance matching at a high frequency more than 1 GHz.

<42> Figs. 14 and 15 illustrate conventional methods which vary impedance using an open strib. As shown in Fig. 14, An open-strib 303 is connected to input/output transmission lines 301 and 302. A tunable capacitor 304 is connected between an end of the open-strib and a ground. An impedance is consecutively varied by changing an electric capacitance of the tunable capacitor 304. However, this device has a demerit that the tunable capacitor 304 is coupled to a ground. Although one open-strib is used in Fig. 14, a plurality of stribs are used so that an impedance is matched at a wide frequency band.

<43> Moreover, Fig. 15 shows a tunable device using a method for varying an impedance by changing a physical shape of the open-strib 305. The impedance

is adjusted by cutting a specific section of the open-strib 305 or an end of the open-strib 305. [Disclosure] [Technical Problem]

<44> It is, therefore, an object of the present invention to provide a tunable device for a microwave/mi llimetric wave using a transmission line strib applied to an open-circuited resonator which varies a resonant frequency to minimize a size of the tunable device and improve a tunability characteristic.

<45> It is another object of the present invention to provide a tunable device for a microwave/mi llimetric wave using a transmission line strib applied to a stepped impedance or an open-strib which does not need a ground.

<46> It is another object of the present invention to provide a tunable device for a microwave/mi llimetric wave using a transmission line strib for reducing a manufacturing cost and improving reliability and a manufacturing process by applying the tunable device to a multi-layer substrate or an LTCC(LoW Temperature Co-fired Ceramic) without perforating a puncture on a substrate and grounding. [Technical Solution]

<47> In accordance with an embodiment of the present invention, there is provided a tunable device for microwave/millimeter wave application using a transmission line strip, including: at least one open-circuited resonator coupled to each other and formed on a substrate; at least one transmission line strib installed on the open-circuited resonator and being opened; and at least one tunable capacitor connected between an open-end section of the open-circuited resonator and an open-end section of the transmission line strib, wherein an electrical length of the transmission line strib is smaller than or the same with a half wavelength of a guided wavelength.

<48> Both ends of the open-circuited resonator are opposite to both ends of the transmission line strib, and the tunable capacitor is connected between the open-end section of the open-circuited resonator and the open-end section

of the transmission line strib.

<49> In accordance with another embodiment of the present invention, there is provided a tunable device for microwave/millimeter wave application using a transmission line strip, including: at least one open strib formed on a substrate and connected to a transmission line strib directly; the transmission line strib installed on the open strib and being opened; and a tunable capacitor connected between an open-end section of the open strib and an open-end section of the transmission line strib.

<50> In accordance with another embodiment of the present invention, there is provided a tunable device for microwave/millimeter wave application using a transmission line strip, including: at least one stepped impedance formed on a substrate and included in a part of a transmission line strib; at least one transmission line strib installed on a low impedance section of the stepped impedance and being opened; and a tunable capacitor connected between the low impedance section of the stepped impedance and an open-end section of the transmission line strib.

<5i> In accordance with another embodiment of the present invention, there is provided a tunable device for microwave/millimeter wave application using a transmission line strip, including: a transmission line formed on a substrate for transmitting a signal; at least one transmission line strib installed on the transmission line and being opened; and a tunable capacitor connected between the transmission line and an open-end section of the transmission line strib.

<52> An electrical length of the transmission line strib is smaller than or the same with a half wavelength of a guided wavelength.

<53> The tunable capacitor is one of a semiconductor varactor, a tunable dielectric capacitorCor dielectric varactor), a tunable magnetic substance capacitor and a tunable MEMSCMicro Electromechanical System) capacitor.

<54> The substrate is a multi-layer substrate or a high temperature superconductor substrate.

<55> The tunable capacitor is a tunable dielectric capacitor.

<56> The open-circuited resonator, the transmission line strib or the open strib includes a stepped impedance having a high impedance section and a low impedance section.

<57> The tunable device is embedded in one of an MMICCMonolithic Microwave Integrated Circuit), an MIC(Microwave Integrated Circuit), an LTCC(LoW Temperature Cofired Ceramic) and a laminated printed circuit board for miniaturizing.

<58> The tunable device is included in a wireless communication module, and the substrate has a planar shape.

<59>

[Advantageous Effects]

<60> As described above, a tunable device for microwave/millimeter wave application using a transmission line strip applied to an open-circuited resonator in accordance with an embodiment of the present invention acquires a better tunable characteristic than the tunable device in reference documents described above.

<6t> Moreover, a tunable device using a transmission line strib applied to an open-strib or a stepped impedance in accordance with an embodiment of the present invention has a merit of a non-ground.

<62> Lastly, a tunable device for a microwave/mi llimetric wave using a transmission line strib reduces a manufacturing cost and improves reliability and a manufacturing process by applying the tunable device to a multi-layer substrate or an LTCC(LoW Temperature Co-fired Ceramic) without perforating a puncture on a substrate and grounding. [Description of Drawings]

<63> Fig. 1 illustrates a tunable resonator having a conventional open- circuited resonator.

<64> Fig.2 illustrates a conventional tunable resonator which is grounded.

<65> Fig. 3 illustrates a tunable bandpass filter using a plurality of tunable resonators.

<66> Fig. 4 illustrates a tunable bandpass filter using one tunable

resonator. <67> Fig. 5 illustrates a bandpass filter using a conventional tunable resonator. <68> Fig. 6 shows a simulated change graph of a resonant frequency of the tunable bandpass filter shown in Fig. 4. <69> Fig. 7 shows a simulated change graph of an insertion loss of the bandpass filter shown in Fig.5. <70> Fig. 8 shows a simulated change graph of an insertion loss in case that a physical length of a transmission line strib is larger than or the same with a physical length of a resonator. <7i> Figs. 9 to 13 illustrate a resonant point and a transmission zero of a tunable resonator calculated by an expression 1. <72> Figs. 14 and 15 illustrate conventional methods which vary impedance using an open strib. <73> Figs. 16 and 17 illustrate a tunable bandpass filter using a tunable resonator in accordance with a first preferred embodiment of the present invention. <74> Fig. 18 shows a simulated insertion loss graph of the tunable bandpass filter shown in Figs 16 and 17.

<75> Fig. 19 shows a simulated resonant frequency change graph. <76> Fig. 20 illustrates a resonator and input/output feeding lines in accordance with an embodiment of the present invention. <77> Fig. 21 illustrates a conventional bandpass filter having three resonators which are connected to one another. <78> Fig.22 illustrates a tunable bandpass filter using a tunable resonator in accordance with a second embodiment of the present invention. <79> Fig. 23 shows an insertion loss of the band pass filters having five resonators shown in Figs 21 and 22. <80> Fig.24 illustrates a tunable bandpass filter using a tunable resonator in accordance with a third embodiment of the present invention. <8i> Figs. 25 and 26 illustrate a tunable bandpass filter using a tunable

resonator in accordance with a third embodiment of the present invention. <82> Fig. 27 illustrates a tunable hairpin device having four tunable resonators which are connected to one another. <83> Fig. 28 shows an insertion loss graph of the tunable hairpin shown in

Fig.27. <84> Fig. 29 illustrates a resonator and a transmission line strib of a tunable resonator having a stepped impedance shape. <85> Fig. 30 illustrates a tunable bandpass filter using a tunable resonator in accordance with an embodiment of the present invention. <86> Fig. 31 illustrates a bandstop filter using a tunable resonator in accordance with a fourth embodiment of the present invention. <87> Fig. 32 shows a simulated insertion loss graph of the bandstop filter shown in Fig.31. <88> Fig. 33 illustrates a conventional open-strib used in an impedance matching circuit. <89> Fig. 34 illustrates a tunable device using a transmission line strib applied to an open-strib in accordance with an embodiment of the present invention. <90> Fig. 35 shows a simulated insertion loss graph of the open-strib and the tunable device shown in Figs 33 and 34. <9i> Fig. 36 illustrates a tunable device using a transmission line strib applied to a plurality of open-stribs in accordance with an embodiment of the present invention. <92> Fig. 37 shows a simulated insertion loss graph of the tunable device shown in Fig.36. <93> Fig. 38 illustrates a tunable device using a transmission line strib applied to a stepped impedance in accordance with an embodiment of the present invention. <94> Fig. 39 shows a simulated insertion loss graph of the tunable device shown in Fig.38. <95> Fig.40 illustrates a conventional tunable device.

<96> Fig. 41 illustrates a tunable device in accordance with an embodiment of the present invention.

[Best Mode] <97> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Detailed description regarding a published function or configuration related to the present invention is omitted to evade ambiguousness.

<98>

<99> (First embodiment) <ioo> Figs. 16 and 17 illustrate a tunable bandpass filter using a tunable resonator in accordance with a first preferred embodiment of the present invention. <ioi> In configuration of a tunable resonator in accordance with a first embodiment of the present invention, an electrical length(Oi) is smaller than or the same with a half wavelength(λ _g /2) of a guided wavelength which is different from a conventional tunable resonator. As shown in Figs. 16 and 17, the tunable resonator in accordance with the present invention has tunable capacitors 405 and 407 which are connected between an end or both ends of the resonator 403 and transmission line stribs 406 and 408.

<1O2> As shown in Figs 16 and 17, input/output feeding lines 401 and 402 are electrically coupled to the tunable resonator. As described in the expression 1, if a width of the transmission line strib and the resonator is changed, the electrical length is changed and a resonant frequency of the tunable resonator is changed.

<io3> Fig. 18 shows a simulated insertion loss graph of the tunable bandpass filter shown in Figs 16 and 17. A physical length of the resonator 403 and the transmission line stribs 406 and 408 are fixed with 13mm and 2mm, respectively, and electric capacitances of the tunable capacitors 405 and 407 are changed.

:io4> A solid line, which is shown in Fig. 18, shows an insertion loss when

an electric capacitance of the tunable capacitor 405 shown in Fig. 16 is 0.2pF. A dotted line shows an insertion loss when electric capacitances of two tunable capacitors 405 and 407 shown in Fig. 17 are 0.2pF. A broken line shows an insertion loss when one of the electric capacitances of two tunable capacitors 405 and 407 is O.lpF and the other one is 0.2pF.

<1O5> As shown in Fig. 18, resonant frequencies of the solid line, the broken line and the dotted line are 4.08GHz, 4.01GHz and 3.93GHz, respectively. As shown in Fig. 18, the resonant frequency of the broken line is located on a nearly center of the solid line and the dotted line. In Fig. 16, a conventional bandpass filter that the tunable capacitor 405 and the transmission line strib are removed has a resonant frequency of 4.25GHz.

<iO6> Fig. 19 shows a simulated resonant frequency change graph. Fig. 19 shows a result graph when electrical capacitances of tunable capacitors 405 and 407 are changed and the other conditions are fixed. A rectangle and a circle shown in Fig. 19 are results simulated from Fig. 16 and 17 when electrical capacitances of two capacitors 405 and 407 are same with each other.

<iO7> As shown in Fig. 19, a frequency change of a resonant frequency in Fig. 16 is smaller than a frequency change of a resonant frequency in Fig. 17 by two times. If the tunable bandpass filter shown in Fig. 17 is used, a resonant frequency is variable largely.

<i08> Fig. 20 illustrates a resonator and input/output feeding lines in accordance with an embodiment of the present invention.

=i09> Input/output feeding lines 401 and 402 may be electrically coupled to a resonator 403 as shown in Fig. 16. Moreover, input/output feeding lines 411 and 412 may be directly coupled to resonators 415-417 of both sides as shown in Fig.20.

=iio> The tunable bandpass filter shown in Figs 16 and 17 has one tunable resonator. However, a plurality of tunable resonators may be coupled to each other.

:iπ> Moreover, resonators or transmission line stribs may be a stepped

impedance shape. <ii2> Further, as shown in Figs. 16 and 17, open-ends 401a and 402a of the feeding line may be connected to a ground. <U3> The tunable capacitor of the present invention may be a semiconductor varactor, a tunable dielectric capacitor, a tunable magnetic substance capacitor and a tunable MEMS capacitor. <114> The semiconductor varactor includes a semiconductor diode and a semiconductor MOS(Metal-Oxide Semiconductor) varactor. The tunable MEMS capacitor and the tunable dielectric(magnetic substance) capacitor is called as MEMS varactor and the dielectric(magnetic substance) varactor, respectively. <ii5> The tunable dielectric capacitor and a thin film for the same is introduced in Korean Patent number 10-0659974 and M. Lancaster, J. Powell and

A. Porch, "thin-film ferroelectric microwave devices," Supercond, Sci,

Technol, no. 11, pp. 1323. <ii6> The tunable resonator is applied to a hairpin, hairpin-comb, combline, a duplexer or diplexer.

<117>

<ii8> (Second embodiment)

<ii9> Fig. 21 illustrates a conventional bandpass filter having three resonators 502-504 which are connected to one another. Fig. 22 illustrates a tunable bandpass filter using a tunable resonator in accordance with a second embodiment of the present invention. Fig. 23 shows an insertion loss of the band pass filters having five resonators shown in Figs 21 and 22.

<12O> A rectangle shown in Fig. 23 shows an insertion loss of the resonators shown in Fig. 21, and a circle shows an insertion loss when an electric capacitance of the tunable capacitors 505-507 are 0.5pF. A physical width and length of the resonators 502-504 and the transmission line stribs 508-510 are 0.4xl0mm and 1x1 mm, respectively. A gap between the resonators is lmm. Moreover, the tunable resonator applied to the tunable bandpass filter may has the same structure.

<121>

<122> (Third embodiment)

<123> The tunable resonator in accordance with an embodiment of the present invention may be applied to a conventional hairpin or hairpin-comb

<i24> Fig. 24 illustrates a tunable bandpass filter using a tunable resonator in accordance with a third embodiment of the present invention. As shown in Fig. 24, a unable resonator includes a tunable capacitor 606 connected between an open-end section of a conventional resonator 603 and an open-end section of a transmission line strib 605. Input/output feeding lines 601 and 602 are electrically coupled to the resonator 603 as shown in Fig. 24.

<125> Figs. 25 and 26 illustrate a tunable bandpass filter using a tunable resonator in accordance with a third embodiment of the present invention.

<i26> As shown in Fig. 25, in a tunable resonator of the present invention, both open-ends of a resonator 603 and both open-ends of a transmission line strib 605 may be connected to each other by two tunable capacitors 606 and 606a.

<127> Moreover, a tunable resonator shown in Fig. 26 has the same structure with the tunable resonator shown in Fig. 17.

<128> Fig. 27 illustrates a tunable hairpin device having four tunable resonators which are connected to one another. Fig. 28 shows an insertion loss graph of the tunable hairpin shown in Fig. 27.

<129> A rectangle shown in Fig. 28 shows an insertion loss measured in a bandpass filter using a conventional resonator that transmission line stribs and tunable capacitors are removed. A triangle shows an insertion loss measured in a tunable bandpass filter using tunable resonators shown in Fig. 25 at the same condition with a condition of Fig.27.

<i30> In the triangle and the rectangle, a width and a length of resonators 611-614 and transmission line stribs are 0.6xl3mm and 0.5x0.7mm, respectively, and an electric capacitance(^L) of tunable capacitors are 0.5pF. ci3i> As shown in Fig. 28, a resonant frequency of the tunable bandpass filter using the tunable resonator shown in Fig. 25 is varied larger than a

resonant frequency of the bandpass filter using the tunable resonator shown in Fig.24.

<132> A tunable resonator shown in Fig. 29 is an example of a configuration having a resonator 631 and a transmission line strib 632 of a stepped impedance shape. If a width of the transmission line strib is narrow, the tunable resonator has a high impedance, but if a width of the transmission line strib is wide, the tunable resonator has a low impedance.

<i33> Fig.30 illustrates a tunable bandpass filter using a tunable resonator in accordance with an embodiment of the present invention.

<134> As shown in Fig. 30, a tunable resonator of the present invention has four open-ends. As described above, the tunable resonator of the present invention may have at least two open-ends.

<135>

<136> (Fourth embodiment)

<i37> Fig. 31 illustrates a bandstop filter using a tunable resonator in accordance with a fourth embodiment of the present invention. Fig. 32 shows a simulated insertion loss graph of the bandstop filter shown in Fig.31.

<138> In a tunable bandstop filter shown in Fig. 31, a part of two resonators 702 and 703 is electrically coupled to a transmission line strib 701. Open- transmission line stribs 706 and 707 and tunable capacitors 704 and 705 are coupled to an open-end of resonators 702 and 703. A width and a length of resonators 702 and 703 and transmission line stribs 706 and 707 are 0.6xl2mm and 0.6x4, respectively, and a gap between resonators 702 and 703 is 10mm.

<i39> A solid line shown in Fig. 32 shows an insertion loss of a bandstop filter using a resonator having a transmission line strib 701 and resonators 702 and 703. A broken line and a dotted line show simulated insertion loss graphs when electric capacitances(Q) of tunable capacitors 704 and 705 in a tunable bandstop filter shown in Fig.31 are 0.2pF and 0.4pF, respectively. :i40> The tunable resonator shown in Figs.25 or 26 may be applied instead of the tunable resonator of the tunable bandstop filter shown in Fig.31.

:141>

<142> (Fifth embodiment)

<143> An impedance matching circuit is a method for transmitting a maximum power in a specific frequency band using a resonance. In case of a load including an antenna, a low noise amplifier, a voltage controlled oscillator, and a power amplifier, maximum power is transmitted by adding an impedance matching circuit between the load and a feeding line. An impedance matching circuit is basically a resonant circuit and has a characteristic of a low bandpass filter. A tunable device of the present invention used in an impedance matching circuit and a filter is described below.

<i44> Fig. 33 illustrates a conventional open-strib used in an impedance matching circuit. Fig. 34 illustrates a tunable device using a transmission line strib applied to an open-strib in accordance with an embodiment of the present invention.

<i45> As shown in Fig. 34, i _N denotes a physical length of an open-strib, and s denotes the open-strib. A tunable device of the present invention does not need to be connected to a ground and is different from a short-circuited resonator having a short-end.

<i46> A conventional open-strib shown in Fig. 33 has an open-strib 803 which is connected to transmission lines 801 and 802 for transmitting a signal. The tunable device of the present invention shown in Fig. 34 has a tunable capacitor 804 which is coupled between an open transmission line strib 805 and an end of an open-strib 803. The tunable device of the present invention varies an impedance or a cutoff frequency by varying the tunable capacitor 804.

<i47> Fig. 35 shows a simulated insertion loss graph of the open-strib and the tunable device shown in Figs 33 and 34.

<148> A solid line shown in Fig.35 shows an insertion loss calculated in the open-strib shown in Fig. 33. A broken line and a dotted line show an insertion loss when an electrostatic capacitance of the tunable capacitance 804 shown in Fig. 34 is 0.2pF and 0.4pF, respectively. A physical length of the open-strib 803 and the transmission line strib 805 is 6mm and 4mm,

respectively.

<149> One open-strib 803 is shown in Figs 33 and 34, but a plurality of open- stribs having a gap of a predetermined distance may be used for acquiring a wider and sharper cutoff frequency characteristic of a low bandpass filter or matching an impedance at a wider frequency band.

<15O> An electrical length of a transmission line strib 805 may be smaller than or the same with a half wavelength of a guided wavelength.

<i5i> Fig. 36 illustrates a tunable device using a transmission line strib applied to a plurality of open-stribs in accordance with an embodiment of the present invention.

<i52> Three open-stribs are shown in Fig. 36. Fig. 37 shows a simulated insertion loss graph of the tunable device shown in Fig. 36. A solid line shown in Fig. 37 shows a simulated result calculated in a conventional open- strib without transmission line stribs 819-821 and tunable capacitors 816- 818. A broken line and a dotted line shown in Fig.37 show an insertion loss when an electric capacitance of the tunable capacitors 816-818 shown in Fig. 36 is 0.2pF and 0.4pF, respectively. A width and a length of the transmission line stribs 819-821 are fixed with Ix2mm. As shown in Fig. 37, a cutoff frequency of a low bandpass filter of the present invention moves to a low frequency according to the increase of the electric capacitance.

<153> In the tunable device using a transmission line strib applied to an open-strib shown in Fig. 36, open transmission stribs 819-821 and tunable capacitors 816-818 are coupled to an end of three open-stribs. However, a transmission line strib may be connected to an end of three open-stribs 813- 815.

<i54> Fig. 38 illustrates a tunable device using a transmission line strib applied to a stepped impedance in accordance with an embodiment of the present invention. As shown in Fig. 38, tunable capacitors are coupled between open transmission line stribs and an end of low impedance sections 833-835 of stepped impedances 833-837 to vary a conventional stepped impedance having low impedance sections 833-835 and high impedance sections

836 and 837.

<155> The conventional stepped impedance device shown in Fig. 38 is corresponding to an electromagnetic crystal or a PBG (Photonic Band Gap).

<156> Fig. 39 shows a simulated insertion loss graph of the tunable device shown in Fig. 38. A solid line shown in Fig. 39 shows an insertion loss of a conventional stepped impedance device that tunable capacitors and transmission line stribs are removed. A broken line which is shown in Fig. 38 shows an insertion loss when an electric capacitance is 0.4pF. As shown in Fig. 39, a cutoff frequency or an impedance may be varied by varying an electric capacitance of the tunable capacitors.

<157>

<i58> (Sixth embodiment)

<159> Fig. 40 illustrates a conventional tunable device having a tunable capacitor which is coupled between a ground and a transmission line for transmitting a signal. Fig. 41 illustrates a tunable device in accordance with an embodiment of the present invention.

<i60> The conventional tunable device shown in Fig. 40 needs a ground, but the tunable device using a transmission line strib shown of the present invention in Fig. 41 does not need perforating a puncture on a substrate and grounding. That is, tunable device of the present invention does not need grounding since tunable capacitors 903 and 904 are coupled between transmission line stribs 905 and 906 and transmission line 901 to vary a frequency. Moreover, the tunable device may be used as an impedance matching circuit by further including stribs, inductors or capacitors shown in Fig. 41.

<i6i> Accordingly, a tunable device for microwave/mi llimetric wave using a transmission line strib in accordance with an embodiment of the present invention remove difficulty for perforating a puncture on a substrate and being connected with a ground through a via-hole. If tunable devices are applied to a multi-layer substrate, a manufacturing cost is reduced and a manufacturing process is improved.

<162> A tunable device for microwave/millimetric wave using a transmission line strib in accordance with an embodiment of the present invention may be manufactured on a substrate of a flat shape including a microstrip, a stripline or a coplanar waveguide.

<163> Moreover, a tunable device for microwave/millimetric wave using a transmission line strib in accordance with an embodiment of the present invention may be manufactured on a high temperature superconductor substrate.

<164> A resonator, an open-strib, or a transmission line strib in accordance with an embodiment of the present invention may have a stepped impedance shape having a low impedance section and a high impedance section.

<i65> Further, a tunable resonator of the present invention may be used in a bandpass filter or a bandstop filter having a hairpin shape, a hairpin-comb shape or a combline shape.

<166> Moreover, a tunable device for microwave/millimetric wave using a transmission line strib in accordance with an embodiment of the present invention may be used in a duplexer or a diplexer.

<167> A tunable device for microwave/millimetric wave using a transmission line strib in accordance with an embodiment of the present invention may be embedded in an LTCC(LoW Temperature Co-fired Ceramic) of a laminated type for miniaturizing. The LTCC may be a module for a transceiver having a bandpass filter, a balun amplifier and an amplifier.

<i68> In addition, a tunable device for microwave/millimetric wave using a transmission line strib in accordance with an embodiment of the present invention may be included in an MMIC(Microwave Monolithic Integrated Circuit) or an MIC(Microwave Integrated Circuit) which is manufactured on a semiconductor substrate.

<i69> Moreover, a tunable device for microwave/millimetric wave using a transmission line strib in accordance with an embodiment of the present invention may be manufactured on a printed circuit board having a plurality of laminated layers. Active devices may be further included on the PCB.

<i70> Further, a tunable device for microwave/millimetric wave using a

transmission line strib in accordance with an embodiment of the present invention may be manufactured on a silicon substrate by an RF CMOS process. In this case, an oxide may be used as an insulator, and a multi-layer circuit may be configured on the substrate.

<i7i> Moreover, in case of a plurality of tunable devices for microwave/mi llimetric wave using a transmission line strib in accordance with an embodiment of the present invention, an electrical length of transmission line stribs or an electric capacitance of tunable capacitors may be different from each other.

<i72> A feed line for supplying a signal is parallel coupled with resonators or is directly coupled with resonators.

<173> In all simulations and manufacturing of the present invention, a thickness of a substrate h is 0.635mm, and a microstrip structure having a relative dielectric constant ( ε _r ) of 10.2 is used. A simulation is performed in Ensemble 5.1 program and a measurement is performed in HP8510C network analyzer.

<i74> While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirits and scope of the invention as defined in the following claims.