TWI422151B - A quad-passband bandpass filter - Google Patents

Description

Quad band pass filter

The present invention relates to a filter, and more particularly to a four-band pass filter.

Multi-frequency multi-mode communication components mean that a single mobile phone must support GSM, Bluetooth, Worldwide Interoperability for Microwave Access (WiMAX), Ultra Wideband (UWB), Wireless LAN (wireless LAN) ), wireless local area network (WiFi), mobile satellite communication system (Mobile satellite communication system) and global positioning system (GPS) and other standards. Not only to accommodate a wider range of frequencies and more standards, but also to have multiple input multiple output (MIMO) antennas that support wideband applications. This integration means that the number of RF components and the number of antennas in each handset are increasing, resulting in problems in terms of size, power consumption and coexistence.

Therefore, one of the important components of the front-end system, the Planar bandpass filter also needs to include multi-frequency multi-mode and miniaturization. The size and frequency response of the filter can affect the volume and signal integrity of the system. In the front end of a multi-frequency radio transmitter and receiver RF circuit, the multi-frequency filter must become a critical component. In addition, if the operating bands of the above systems can be integrated into a filter component having a multi-band response, it is also A very popular research topic before.

In the case of a multi-frequency filter, in order to meet the requirements of the system specifications, it is necessary to appropriately select the structure of the resonator and its frequency characteristics. Among them, the filter with miniaturization characteristics has been one of the research focuses, that is, how to design the filter with the least resonator or structure. For example, resonators have been proposed in the form of U-shaped hairpin resonators, open-loop resonators and negative-wear linear resonators, and various types of resonators have been successfully designed to constitute filters. However, all of the above filters have the disadvantage of being oversized. Stepped Impedance Resonator (SIR) is one of the methods widely used to move mixed waves to achieve dual-frequency or multi-frequency response, and can be miniaturized by controlling the parameters of its resonators. Structure and control the frequency of its mixed waves. Although the design method of the planar filter is quite large. However, a multi-band filter constructed with a stepped impedance resonator is one of the best choices. When designing and manufacturing the control lines of these wireless communication products, the filter components used by various manufacturers are mostly single-frequency passband filters of co-fired ceramics, and the filters are generated for these wireless communication products. The quality factor has a good effect and is small enough. However, filters with more than three frequencies are quite difficult to design and expensive, and require additional installation procedures. Therefore, the installation of such a high-frequency filter will increase the manufacturing cost and procedure of the product, resulting in a burden on mass production.

In addition, multi-frequency filters have become the main development topics for today's R&D and industrial applications. The current research focuses on two directions, the first is the miniaturization of the design size, and the second is the passband selectivity on the frequency response. In the past literature, the common design method of the planar dual-frequency filter is to design the passbands separately, and then through the overlapping of the circuits, Become a dual-frequency filter. These multiplexer-like circuit methods require an additional impedance matching network and require a large area of construction.

In order to solve the above problems, in order to meet the characteristics of miniaturization and diversification of a single component, it is desirable to provide a four-band pass filter to overcome the disadvantages of the prior art.

SUMMARY OF THE INVENTION A primary object of the present invention is to provide a four-band pass filter having a resonator structure that produces multiple transmission paths that cause transmission zeros across the passband to increase the selectivity of the passband.

To achieve the above main object, the present invention provides a four-band pass filter comprising a substrate, a first magnetically coupled resonator group, a plurality of signal output ports and a second magnetically coupled resonator group. The substrate has a ground plane, and the first magnetically coupled resonator group and the second magnetically coupled resonator group are electrically connected to each other and disposed on the substrate. The first magnetically coupled resonator group, the signal output and the coupling structure of the second magnetically coupled resonator group can form three transmission paths, and a total of five transmission zero points are generated.

According to one feature of a four-band pass filter of the present invention, the first magnetically coupled resonator group further comprises two asymmetric stepped impedance resonators composed of a magnetic coupling structure. The asymmetric stepped impedance resonator has an impedance ratio of 0.45 and a length ratio of 0.2.

A feature of a four-band pass filter according to the present invention, wherein the second magnetically coupled resonator group further comprises two asymmetric steps consisting of a magnetic coupling structure Impedance resonator. The asymmetric stepped impedance resonator has an impedance ratio of 0.55 and a length ratio of 0.8.

A feature of a four-band pass filter according to the present invention, wherein the first magnetically coupled resonator set produces a resonant mode of 2.4/5.2 GHz.

A feature of a four-band pass filter according to the present invention, wherein the second magnetically coupled resonator group produces a resonant mode of 3.5/6.8 GHz.

A feature of a four-band pass filter according to the present invention, wherein the locations of the transmission zeros are 2 GHz, 3 GHz, 5 GHz, 5.8 GHz, and 7.7 GHz, respectively.

The above and other objects, features, and advantages of the present invention will become more apparent and understood.

While the invention may be embodied in various forms, the embodiments illustrated in the drawings It is not intended to limit the invention to the particular embodiments illustrated and/or described.

In electronic circuits, the effects of filters include: (1) noise filtering, (2) harmonic interference suppression, (3) surge absorption, (4) power supply purification, (5) EMI protection, and (6) signals. Separation and so on. The design of the filter is composed of a resonator structure, so a high efficiency filter The formation of the device requires a resonator structure with high quality factors and a good matching circuit.

Referring to Figure 1a, there is shown a block diagram of a four-band pass filter 100 of the present invention. The four-band pass filter 100 includes a substrate 120, a first magnetically coupled resonator group 130, at least two signal input and output ports 150, 160 and a second magnetically coupled resonator group 140. The substrate 120 has a ground plane 110 and is selected from a commercial substrate 120 having a dielectric constant of 2.2, a substrate 120 height of 0.787 mm, and a loss tangent of 0.0009. The first magnetically coupled resonator group 130, the coupling structure of the signal input and output ports 150, 160 and the second magnetically coupled resonator group 140 can form three transmission paths, and a total of five transmission zero points 170 are generated. Figure 1b is shown in conjunction with Figure 4. The transmission zeros 170 are located at 2 GHz, 3 GHz, 5 GHz, 5.8 GHz, and 7.7 GHz, respectively. The generation of the transmission zero 170 can increase the selectivity of the pass band and reduce the occurrence of the signal error rate.

In the first magnetically coupled resonator group 130, the structure further includes a first asymmetric stepped impedance resonator 131 and a second asymmetric stepped impedance resonator 132, and generates a magnetic coupling effect. The impedance ratio of the first asymmetric stepped impedance resonator 131 to the second asymmetric stepped impedance resonator 132 is 0.45 and the length ratio is 0.2; and a resonant mode of 2.4/5.2 GHz is generated. In the second magnetically coupled resonator group 140, it further includes a third asymmetric stepped impedance resonator 141 and a fourth asymmetric stepped impedance resonator 142, and generates a magnetic coupling effect. The impedance ratio of the third asymmetric stepped impedance resonator 141 to the fourth asymmetric stepped impedance resonator 142 is 0.55 and the length ratio is 0.8; and a total of 3.5/6.8 GHz is generated. Mode of vibration.

A conventional stepped impedance resonator (SIR) was proposed by M. Makimoto and S. Yamashita in 1980 and applied to filters. By changing the stepped impedance resonator structure to control the insertion loss and the odd-even modal response, the length of the resonant cavity can be shortened more effectively. A typical microstrip line resonator consists of a single half-wavelength microstrip line, while a stepped impedance resonator consists of two characteristic impedance transmission lines. The resonator is bilaterally symmetric and consists of two different microstrip transmission lines of impedances Z ₁ and Z ₂ (impedance ratio K = Z ₂ / Z ₁ ). If K<1, low impedance - high impedance - low impedance; if K > 1, high impedance - low impedance - high impedance. It should be noted that if K<1, there is only low impedance-high impedance or high impedance-low impedance, which is a typical asymmetric stepped impedance resonator (ASIR) 180. The typical asymmetric stepped impedance resonator 180 has the advantages of small size and high degree of design freedom, and is quite suitable for designing a miniaturized multi-band filter. When the conventional stepped impedance resonator is K<1 or K>1, the input impedance is derived in the same way. The conventional stepped impedance resonator is composed of two different impedances Z ₁ , Z ₂ and their input admittances Y _in1 and Y _in2 , respectively, and the electron lengths are θ ₁ , θ ₂ and total length θ _T = _{2, respectively.} ( θ ₁ + θ ₂ ). Y _in is

Referring to Figure 2, a typical asymmetric stepped impedance resonator 180 is shown. Unlike a conventional stepped impedance resonator, a typical asymmetric stepped impedance resonator 180 consists of only a low impedance and a high impedance transmission line. Its input admittance Y _in is When the resonance is in progress, the input admittance Y _in =0. After derivation from the above formula, K = tan θ ₁ tan θ ₂ ( odd mode) (3a)

K =-cot θ ₁ tan θ ₂ (even mode) (3b) The relationship between θ ₁ , θ ₂ and θ _T is formulated in more detail here: Then rewrite (4),

Referring to FIG. 3, a resonant mode diagram of a typical asymmetric stepped impedance resonator 180 is shown. By controlling the ratio of K and α in (5a) and (5b), different modal responses can be designed (f ₀ : the center frequency of the first resonance point, f _s1 : the center frequency of the second resonance point and f _s2 : the center frequency of the third resonance point) to conform to the specifications of the multi-band filter. For example, a dual-band filter is designed with a wireless local area network (WLAN) specification, with the first passband at 2.4 GHz and the second passband at 5.2 GHz. Therefore, 5.2/2.4=2.17, if K=0.5 is selected, the length parameter α of the resonator can be found to be 0.27 or 0.88. If considering the circuit size, α = 0.27 is a more suitable size parameter. Therefore, the passband position of a WLAN 2.4/5.2 GHz dual-band filter can be determined.

Taking the quad-frequency filter 100 of the preferred embodiment of the present invention as an example, a typical asymmetric stepped impedance resonator 180 of two different structural parameters (K and α ) can be arranged in an interleaved manner, the first magnetic coupling. The passband frequency positions of the first and second asymmetric stepped impedance resonators 131, 132 (K = 0.45; α = 0.2) of the resonator group 130 are designed at 2.4/5.2 GHz; the second magnetically coupled resonator group 140 The passband frequency positions of the third and fourth asymmetric stepped impedance resonators 141, 142 (K = 0.55; α = 0.8) are designed at 3.5/6.8 GHz to determine the passband position of the quadruple filter 100. (As shown in Figure 3, point A and point B, point C is the resonant mode of the uniform impedance resonator). However, the typical asymmetric stepped impedance resonator 180 can only determine the frequency position of each passband. As for the bandwidth, the passband attenuation speed, the implant loss and the passband rejection, the overall structure of the filter needs to be considered. Coupling coefficient between resonators, resonator order or frequency response type.

In the design flow, when the specifications of a given filter, such as the center frequency, bandwidth, chopping value, the component value of the resonator, and the value of the admittance converter value, can be found by looking up the table. After all component values are obtained, the theoretical coupling coefficients K _{i , i +1 of} the interleaved coupled filter and the external quality factors Q _{ei ,} Q _{e 0} can be obtained from the following equation

Where i=1 to i=m-1, FBW is a 3-dB bandwidth ratio. The coupling coefficient of the second path is expressed as:

After the theoretical coupling coefficient is calculated, the frequency characteristics of the coupled resonator can be obtained by simulation based on the coupling structure between the resonators (electrical coupling, magnetic coupling and hybrid coupling) and the coupling gap. Comparing the theoretical coupling coefficient with the structural coupling coefficient of the electromagnetic simulation, the coupling gap between each resonator can be determined. After fine tuning, the multi-band frequency response can be well obtained. Please refer to FIG. 4, which shows the frequency response diagram of the four-band pass filter 100. The center frequency of the passband is at 2.4/3.5/5.2/6.8 GHz, the implant loss (Insert loss, |S21|) is 1±0.05 dB, and the 3-dB bandwidth ratio is 5%-10%. The blocking degree is about 30 dB, the quality factor is about 40, the passband attenuation speed is 40 dB/GHz, the circuit area is 3×3 cm ² , and the transmission zero point 170 is 2 GHz, 3 GHz, 5 GHz, 5.8 GHz. With 7.7 GHz.

In summary, the present invention discloses a four-band pass filter 100 including a substrate 120, a first magnetically coupled resonator group 130, a plurality of signal input and output ports 150, 160 and a second magnetically coupled resonator group. 140. The first magnetically coupled resonator group 130, the coupling structure of the signal input and output ports 150, 160 and the second magnetically coupled resonator group 140 can form three transmission paths, and a total of five transmission zero points 170 are generated. The center frequency of the four-band pass filter 100 is located at 2.4/3.5/5.2/6.8 GHz, which is quite suitable for use in a multi-band wireless communication system.

Although the present invention has been disclosed in the foregoing preferred embodiments, it is not In order to limit the invention, various modifications and changes can be made without departing from the spirit and scope of the invention. As explained above, various modifications and variations can be made without departing from the spirit of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

100‧‧‧ four-band pass filter

110‧‧‧ ground plane

120‧‧‧Substrate

130‧‧‧First Magnetically Coupled Resonator Group

131‧‧‧First asymmetric stepped impedance resonator

132‧‧‧Second asymmetric stepped impedance resonator

140‧‧‧Second magnetically coupled resonator group

141‧‧‧ Third asymmetric stepped impedance resonator

142‧‧‧fourth asymmetric stepped impedance resonator

150, 160‧‧‧Signal input and output

170‧‧‧Transmission zero

180‧‧‧Typical asymmetric stepped impedance resonator

Figure 1a is a block diagram of a four-band pass filter.

Figure 1b is a schematic diagram of the transmission path of the four-band pass filter.

Figure 2 is a block diagram of a typical asymmetric stepped impedance resonator.

Figure 3 is a resonant mode diagram of a typical asymmetric stepped impedance resonator.

Figure 4 is a frequency response diagram of a four-band pass filter.

100‧‧‧ four-band pass filter

110‧‧‧ ground plane

120‧‧‧Substrate

130‧‧‧First Magnetically Coupled Resonator Group

131‧‧‧First asymmetric stepped impedance resonator

132‧‧‧Second asymmetric stepped impedance resonator

140‧‧‧Second magnetically coupled resonator group

141‧‧‧ Third asymmetric stepped impedance resonator

142‧‧‧fourth asymmetric stepped impedance resonator

150, 160‧‧‧Signal input and output

Claims (5)

A four-band pass filter comprising: a substrate having a ground plane; a first magnetically coupled resonator group disposed on the substrate, the first magnetically coupled resonator group further comprising: a first non- a symmetric stepped impedance resonator; a second asymmetric stepped impedance resonator generating a magnetic coupling effect with the first asymmetric stepped impedance resonator; and wherein the first asymmetric stepped impedance The impedance ratio of the resonator to the second asymmetric stepped impedance resonator is 0.45 and the length ratio is 0.2; at least two signal input and output ports are disposed on the substrate and coupled to the first magnetically coupled resonator group The second magnetically coupled resonator group is disposed on the substrate and is electrically connected to the signal input and output ports. The second magnetically coupled resonator group further includes: a third asymmetric stepped impedance resonator; a fourth asymmetric stepped impedance resonator generating a magnetic coupling effect with the third asymmetric stepped impedance resonator; and wherein the third asymmetric step Stepped impedance resonator The impedance ratio of the fourth asymmetric stepped impedance resonator is 0.55 and the length ratio is 0.8; and wherein the first magnetically coupled resonator group, the signal input and output 埠 and the second magnetically coupled resonator group The coupling structure can form 3 transmission paths and generate 5 transmissions in total. Zero point. A four-band pass filter as described in claim 1, wherein the first magnetically coupled resonator group produces a resonant mode of 2.4/5.2 GHz. A four-band pass filter as described in claim 1, wherein the second magnetically coupled resonator group produces a resonant mode of 3.5/6.8 GHz. A four-band pass filter according to claim 1, wherein the substrate is a commercial substrate having a dielectric constant of 2.2, a substrate height of 0.787 mm, and a loss tangent of 0.0009. A four-band pass filter according to claim 1, wherein the transmission zeros are located at 2 GHz, 3 GHz, 5 GHz, 5.8 GHz, and 7.7 GHz, respectively.