KR20040006952A - Microstrip Ring with a Compact Tunable Microwave Bandgap Structure - Google Patents

Abstract

PURPOSE: A micro-strip ring having a small tunable microwave band gap structure is provided to shift a frequency of an attenuation pole to a low frequency band by adhering a capacitor on a structure of microwave band gap ring. CONSTITUTION: A micro-strip ring having a small tunable microwave band gap structure includes a feeding line, a circular ring, and a band gap. The small frequency change microwave band gap structure is formed on an upper surface of a substrate. A straight-line type feeding line is formed at both sides of the circular ring. The circular ring is formed between the straight-line type feeding lines. The circular ring has a predetermined radius. The band gap is formed by cutting an upper end of the circular ring. A cutoff band is formed around an attenuation pole.

Description

Microstrip Ring with a Compact Tunable Microwave Bandgap Structure

The present invention relates to a microstrip ring structure with a narrow gap, in particular the stop band is formed due to reflection of electromagnetic waves in the narrow gap in the ring and the stop band is formed by changing the reactance value attached between the gaps. The capacitors attached between the gaps shift the center frequency of the stopband to the lower frequency range, the inductor shifts the center frequency of the stopband to the high frequency region, and attach a varactor to the ring for use as a microwave switch. The present invention relates to a microstrip ring structure having a miniaturized frequency-variable microwave bandgap structure.

Photonic Bandgap (PBG) structure, which has been studied for the first time in the field of optics, can effectively control electromagnetic waves in a specific frequency range.

The PBG structure in the microwave region is also called a microwave bandgap (MBG) structure or an electromagnetic bandgap (EBG) structure and is generally implemented on a microstrip to improve antenna performance and amplifier power efficiency. It is used for various purposes such as high Q of resonator, suppression of harmonic components, and design of new duplexer.

As the applied microstrip circuit of the MBG structure, a method of drilling a dielectric substrate, a method of etching the ground plane in a periodic shape, a method of modifying the microstrip line itself, and the like are known. The application examples of the MBG structure studied as such a microwave circuit show the practicality well, but there is a difficulty in the practical application of the MBG structure in the microwave circuit which is inevitably miniaturized because the conventional MBG structure generally requires a very large area. This is because one period of the MBG structure is equal to one-half the length of the wavelength corresponding to the MBG center frequency, and at least five to six periods are required to prevent electromagnetic waves from passing through a specific frequency range.

Accordingly, in the present invention, one of the miniaturized structures is a frequency tunable that can adjust the region of the stop band by applying a microstrip ring structure having a narrow gap that does not require any periodicity. It is aimed at implementing the MBG structure.

In addition, it is another object to attach a chip capacitor between the gap of the frequency variable MBG to adjust the stopband characteristics.

In addition, it is another object to attach a varactor between the gap of the frequency variable MBG to be used as a microwave switch.

In order to achieve the above object, the present invention is a microstrip ring structure formed on the substrate, the feed line is formed in a straight line on both sides, and is formed in connection with the feed line of the both sides and the center radius Circular ring having a and formed by shorting the upper end of the ring Including a narrow bandgap of size; Center radius of circular ring And the size of the band gap According to the attenuation frequency (Where n is a positive odd number, c is the speed of light in a vacuum, Is an effective dielectric constant) and features a microstrip ring having a small frequency variable microwave bandgap structure in which a stopband is formed around its attenuation frequency.

1 shows a microstrip ring with a circular ring as one embodiment of a narrow gap microstrip ring structure according to the present invention.

Figure 2a shows the center radius of the ring of Figure 1 And the size of the gap Line width of the ring Graph showing return loss (S ₁₁ )

Figure 2b is the center radius of the ring of Figure 1 And the size of the gap Line width of the ring Graph showing the results of insertion loss (S ₂₁ ).

Figure 3a is the center radius of the ring of Figure 1 Line width When fixing the gap size Graph showing return loss (S ₁₁ )

Figure 3b is the central radius of the ring of Figure 1 Line width When fixing the gap size Graph showing the results of insertion loss (S ₂₁ ).

Figure 4 is a graph showing the measured resonant frequency of the microstrip ring resonator and MBG ring in accordance with the present invention.

5A to 5C are photographs showing respective field distributions at 2.82 GHz, 5.6 GHz, and 8.46 GHz.

Fig. 6 shows an actual photograph of a microstrip MBG ring equipped with a chip capacitor.

7 is a graph illustrating transmission characteristics measured by connecting capacitors and inductors of various values on an MBG ring structure according to another embodiment of the present invention.

8 is various (Top) and Graph showing the change of attenuation pole frequency according to the value of (bottom part).

Figure 9 illustrates a microstrip ring with a rectangular ring as another embodiment of a circular microstrip ring structure with a narrow gap in accordance with the present invention.

<Description of the symbols for the main parts of the drawings>

: Radius of the ring : Feeder line width

: Size of band gap : Line width of the ring

L : length of square ring W : length of square ring

In general, the microstrip ring resonator has inductance except for the resistance component. And capacitance Can be modeled as a parallel connection. Therefore, the characteristics of return loss and insertion loss of a given microstrip MBG ring are inherent in the case of gaps in the ring. Wow It can be seen as a parallel LC equivalent circuit with slightly transformed values in. The characteristic impedance of the parallel LC circuit is the resonance frequency In this frequency range, the MBG ring strongly reflects the incoming microwaves from the input because it is very large in the vicinity. Attaching a capacitor or an inductor to the gap portion of the ring changes the overall L and C values of the microstrip MBG ring and can be used as a method of modifying the location of the stopband and the shape of the characteristic curve.

Adjusting the stopband in this manner is very useful for applying the microstrip MBG ring to miniaturized microwave switches and the like.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, Figure 1 shows a structure having a circular ring which is an embodiment of a microstrip ring with a narrow gap according to the present invention, Is the mean radius of the ring, Is the line width of the ring, Represents the size of the gap, and Represents the line width of the feeder.

In addition, Figure 9 shows a structure having a rectangular ring as another embodiment of a narrow gap microstrip ring according to the present invention, L is the horizontal length W is the vertical length, Is the line width of the ring, Represents the size of the gap, and Represents the line width of the feeder.

In general, the microstrip ring is excited from the feeder through a coupling gap between the feeder and the ring. In contrast, microstrip MBG rings have a fundamentally different structure from conventional microstrip rings in that there is no coupling gap between the feeder and the ring and there is a gap in the ring itself.

In addition, in the microstrip MBG ring structure, multiple reflection phenomenon with fixed phase correlation required for MBG formation is caused by the strong discontinuity of the impedance due to the gap in the microstrip ring. do.

If the input and output stages are located one quarter of the ring circumference about the gap, the stopband is the attenuation frequency. Formed around, Equation related to is shown in Equation 1 in the case of a circular ring, and Equation 2 in the case of a rectangular ring.

here Is a positive odd number, Is the speed of light in a vacuum, Is the effective dielectric constant, Is the size of the gap, Is the center radius of the ring, and L and W are the horizontal and vertical lengths of the rectangular ring, respectively. Gap size Is usually Or the attenuation pole is nearly equal to the resonant frequency of the odd mode in the ring resonator since it is much smaller than 2 ( L + W ).

In the microstrip MBG ring, a desired MBG center frequency and bandwidth can be implemented using simple design parameters. Obtaining the basic characteristics of MBG for the physical size of the microstrip MBG ring is very useful for implementing MBG structures in microwave circuits. In Equations 1 and 2, it can be seen that the center circumference of the microstrip MBG ring is the main factor for determining the MBG frequency. In addition, the characteristics of MBG are the line width of the microstrip MBG ring. Gap gap It is also affected by the results can be seen from the following examples.

As an example the permittivity for forming a microstrip MBG ring , thickness Use RT / Duroid substrate with the center radius of the ring , The size of the gap The width of the ring The value of was changed.

Figures 2a and 2b show the characteristics of the return loss (S ₁₁ ) and insertion loss (S ₂₁ ) of the microstrip MBG ring obtained under the above conditions, where the center frequency and the 3 dB cutoff frequency of the MBG are the line width of the ring. It can be seen that the decrease with increasing. This characteristic is due to the decrease in the center frequency of MBG because the capacitance and inductance values affected by the physical size of the ring increase as the ring width increases. In addition, as the line width of the ring increases, the insertion loss fluctuates in the frequency region other than MBG because the characteristic impedance difference between the microstrip ring and the feed line increases.

3A and 3B show reflection loss (S ₁₁ ) and insertion loss (S ₂₁ ) of the MBG ring according to the change in the gap size of the ring, and the center radius of the ring under the same conditions as in FIGS. 2A and 2B. , Line width And the size of the gap was changed. As shown, unlike the effect of the center radius or line width of the MBG ring on the MBG characteristics, it can be seen that there is almost no change in the MBG cutoff frequency with respect to the gap change. This is because the cutoff frequency of the stopband is mainly determined by the inductance value of the structure. Therefore, the results of FIGS. 3A to 3B show that since the gap size is very small compared to the circumference of the ring, the change in the effective series inductance of the microstrip with the gap size is very small. It can be seen that such a change in the gap only slightly affects the center frequency of the MBG, that is, the frequency of the attenuation pole, because as the gap size increases, the total circumferential length of the ring decreases slightly. 3A and 3B, the MBG partial bandwidth at 20dB was about 86% in all cases, and the 3dB cutoff frequency was formed around 1.67GHz. However, when the gap size exceeds 2mm, MBG begins to disappear and a very complicated phenomenon occurs. As a result, it can be seen from the characteristic curves of FIGS. 2A to 3B that the cutoff frequency and the center frequency of the MBG are mainly determined by the radius of the ring with respect to the length of the circumference of the ring rather than the line width and the size of the gap of the microstrip ring.

Also, in a ring resonator, resonance occurs when standing waves form around the ring, which occurs when the value corresponding to an integer multiple of the in-tube wavelength is equal to the length of the circumference of the ring. The defects of the attenuation poles corresponding to the second harmonics in the microstrip MBG ring can be easily understood by considering the frequency corresponding to the harmonics of the ring resonator and the field distribution in the microstrip MBG ring. The reflection condition in the MBG ring gap occurs when the voltage or electric field intensity of the gap portion is maximum. Conversely, reflection conditions at the MBG ring input and output stages occur when the voltage is zero. It can be seen that the above two conditions cannot be satisfied simultaneously in the even mode (n = 2, 4, ...) of Equation 1. Therefore, the MBG ring has an attenuation pole near a frequency corresponding to the odd mode of the ring resonator.

The center radius of the microstrip MBG ring as an embodiment for examining the above phenomenon , Line width , The size of the gap In order to compare the resonant frequency of the ring resonator, a microstrip ring resonator of the same size as the MBG ring was fabricated. Permittivity RT / Duroid6010 was used.

Figure 4 shows the resonance frequency of the ring and the MBG frequency measured in the microstrip ring manufactured under the above conditions, the resonance frequency corresponding to the odd mode of the ring resonator and the center frequency of the MBG well match in the ring resonator It can be seen that there is no MBG at the frequency corresponding to the even mode. In addition, the radius of the ring in Equation 1 Effective dielectric constant By substituting the value of, the resonant frequencies in odd mode can be obtained with values of 3.82 GHz and 8.64 GHz, respectively. FIGS. 5A and 5C show field distributions at 2.82 GHz and 8.64 GHz corresponding to the respective resonant frequencies in odd mode. shows the maximum of the electric field distribution. 5b shows a maximum field distribution at 5.6 GHz, which is a value corresponding to an even mode frequency. As shown in the field distributions of Figs. 5A to 5C, in the case of the resonant frequency in the odd mode, the electric field strength is maximized at the boundary of the gap and is minimized at the contact between the ring and the feed line so that electromagnetic waves from the input terminal (left side of the ring) It will not pass through the output (right side of the ring). However, in the even-mode resonant frequency of 5.6 GHz, the electromagnetic waves from the input pass through the ring where there is no gap in the MBG ring, so that the electromagnetic waves from the input pass through the ring without the gap in the MBG ring. It can be seen that it is not formed.

In addition, the MBG structure capable of adjusting the MBG center frequency or the shape of the MBG of the microstrip ring according to the present invention is very useful in microwave devices such as microwave switches or stopband filters.

As mentioned above, the microstrip MBG ring can be represented by a parallel LC equivalent circuit, and the position of the MBG and the shape of the frequency characteristic curve can be adjusted by attaching a capacitor or an inductor between the gaps of the microstrip ring.

6 is a photograph of a chip capacitor attached between the gaps of the actually produced microstrip MBG ring. In this embodiment, the center radius of the microstrip ring is 6.25 mm, the line width of the ring is 0.5 mm, and the gap size is 0.2 mm so that the center frequency of the MBG is about 2.7 GHz. In addition, the MBG center frequency is the inductive component between the gaps as shown in the photo of FIG. Or capacitance component The value of was adjusted by changing.

FIG. 7 illustrates a result of measuring a transmission characteristic S ₂₁ for a change in capacitance component and inductance component values attached to FIG. 6, and a transmission characteristic curve in the center shows that there is no capacitor or inductor between gaps. Is located at 2.71 GHz. As shown in Figure 7, the basic microstrip MBG ring structure Wow When the device having the value of is connected, it can be seen that the position and bandwidth of the center frequency of the attenuation pole change. For example, in FIG. Is 0.2pF, the frequency of the attenuation pole is lowered from 2.71GHz to 1.93GHz, and the 20dB bandwidth decreases from 630MHz to 370MHz.

8 is Wow The attenuation pole changes with respect to the value of, and it can be seen that the frequency of the attenuation pole decreases when the capacitor is attached, and the frequency of the attenuation pole increases when the inductor is attached. Also Is very large When is decreased, the admittance value of the added component becomes very large, so that the MBG disappears. The dotted lines of the upper and lower portions of the upper and lower portions of the center line of FIG. 8 are obtained from a least square fit of data values, and the frequencies of the attenuation poles thus calculated are calculated by Equations 3 and 4, respectively. .

The very good agreement between the data points and the least-squares calculations obtained from them shows that the added capacitance or inductance component is the original value of the ring. And capacitance Shows that they are connected in parallel. Obtained from the data values Wow Values are 0.21 pF and 16.5 nH, respectively. After implementing the microstrip ring as a lumped constant element in Figure 8 To simulate the result of parallel connection The actual match between the two measurements is very good. Wow This means that the value of is almost correct. However, in the case of the inductor, the measured attenuation pole frequency is much smaller than the calculated value because of the parasitic inductance that occurs frequently in high frequency circuits.

The gain of the microwave amplifier can be increased by using an MBG structure that suppresses the generation of harmonics in the amplifier's external circuit. However, the use of the microwave MBG structure in the low frequency region requires a relatively large area.

As described above, the microstrip MBG ring according to the present invention can be implemented in a much smaller area than the general MBG structure having periodicity, and by attaching a capacitor on the MBG ring structure, the frequency of the attenuation pole can be moved to a very low place. .

Also, if you put a varactor on the microstrip MBG ring, The maximum gain can be obtained by electrically changing the value of and the frequency of the attenuation pole can be adjusted appropriately.

In addition, since the MBG ring does not require periodicity, it occupies a very small space on the microwave circuit compared to the conventional MBG structure requiring periodicity.

Therefore, the frequency variable MBG ring according to the present invention is very useful in comparison with the general MBG structure in terms of miniaturization and gain improvement of the microwave amplifier.

Claims (4)

In the microstrip ring structure formed on the substrate, Feed lines formed in a straight line on both sides, It is formed by connecting between the feed line of both sides and the center radius A circular ring having: Formed by shorting the top of the ring Including a narrow bandgap of size; Center radius of circular ring And the size of the band gap According to the attenuation frequency (here, Is a positive odd number, Is the speed of light in a vacuum, Is an effective dielectric constant), and a stop band is formed around the attenuation frequency of the microstrip ring having a small frequency variable microwave bandgap structure. The method of claim 1, The ring is formed as a rectangular ring having a horizontal length L and a vertical length W of a straight line, the attenuation frequency according to the horizontal length and vertical length of the ring Is changed, and a stopband is formed around the attenuation frequency, wherein the microstrip ring has a small frequency-variable microwave bandgap structure. The method of claim 1, The microstrip ring having a small frequency variable microwave bandgap structure, characterized in that the stop band characteristics can be adjusted by further attaching a chip capacitor between the gaps. The method of claim 1, The microstrip ring having a small frequency variable microwave bandgap structure, characterized in that it is further attached to the microstrip ring and used as an electrically controllable microwave switch.