CN106960995A - It is a kind of that there is wide upper stopband and the double mode LTCC bandpass filters of nonopiate feedback - Google Patents

Abstract

The invention discloses a dual-mode LTCC bandpass filter with a wide upper stop band and non-orthogonal feedback. The metal distributed on the top LTCC substrate and the bottom LTCC substrate in contact with the air is a microstrip line, and the two-layer substrate passes through the metal The striplines are connected, and the microstrip line is in a stepped shape next to the two I/O ports to form a broadside parallel coupled line that realizes a wide upper stop band, and the double-layer broadside parallel coupled line constitutes a square ring resonator. The aforementioned dual-mode bandpass filter with wide upper stopband and non-orthogonal feedback is characterized in that the microstrip line in the vertical direction and the stripline in the horizontal direction have the same length L. The present invention uses broadside parallel coupled lines with ladder impedance to realize a wide upper stop band, realizes 40dB suppression of the second harmonic (2f _o ) and 20dB suppression of the frequency 2.4f _o .

Description

A Dual-Mode LTCC Bandpass Filter with Wide Upper Stopband and Non-Orthogonal Feedback

technical field

The invention belongs to the technical field of basic electrical components, and relates to a dual-mode LTCC band-pass filter with a wide upper stop band and non-orthogonal feedback.

Background technique

Band-pass filters (BPF, Band-Pass Filter) with compact size, efficient out-of-band spurious suppression and good pass-band performance are widely required in modern communication systems (such as radar, satellite and mobile applications). Since the number of resonators of the filter is reduced by half, a dual-mode band-pass filter proposed in recent years has attracted much attention, and the dual-mode band-pass filter is further reduced in size compared with the single-mode filter.

However, a dual-mode bandpass filter using a resonator with one wavelength or a half wavelength has spurious passbands at frequencies 2f _o , 3f _o , 4f _o , where f _o is the center frequency of the dual-mode bandpass filter and Modern sensitive receivers require wider stopbands to suppress out-of-band interference. Therefore, there is a need for a dual-mode bandpass filter with a wide upper stopband. Additionally, most dual-mode filters use quadrature-feedback input/output (I/O) ports to excite two degenerate modes, which can make layout difficult when interfacing with other components.

Recently, low temperature co-fired ceramic (LTCC, Low Temperature Co-fired Ceramic) is considered as a multilayer packaging technology capable of reducing circuit size and improving performance. LTCC has advantages that planar circuits do not have in terms of circuit size, function, performance, and cost. It also helps microwave designers solve a series of problems such as multi-functional monolithic integration, mixed-signal monolithic integration, and circuit miniaturization. At the same time, the weight and volume are reduced by an order of magnitude compared with the traditional planar hybrid integrated circuit, which greatly improves the vertical integration level of the circuit in the Z direction. One of the most effective ways for high security and high performance.

Contents of the invention

The technical problem to be solved by the present invention is to propose a dual-mode LTCC band-pass filter structure with a wide upper stop band and non-orthogonal feedback for the defects of the background technology. The invention realizes a dual-mode band-pass filter with wide upper stop band and non-orthogonal I/O feedback in a 2-layer LTCC substrate. A wide upper stopband is achieved by using broadside parallel coupled lines with stepped impedance. The resonance characteristics are analyzed by the odd-even mode equivalent circuit method. A suppression of 40dB for frequency 2f _o and 20dB for frequency 2.4f _o is achieved. Non-orthogonal feedback and dual mode allow for easier layout of the filter while reducing its size and interfacing with other components.

The technical solution adopted by the present invention for solving the above-mentioned technical problems is a dual-mode LTCC bandpass filter with a wide upper stop band and non-orthogonal feedback. Stripline, the 2-layer substrate is connected by a metal stripline, and the microstrip line is in a stepped shape next to the two I/O ports, forming a wide-side parallel coupling line that realizes a wide upper stop band, and a double-layer wide-side parallel coupling line form a square ring resonator.

Further, the above-mentioned dual-mode LTCC bandpass filter with wide upper stopband and non-orthogonal feedback is characterized in that the microstrip line in the vertical direction and the stripline in the horizontal direction have the same length L.

Preferably, the characteristic impedance of the microstrip line at the port part is 50Ω.

Compared with the prior art, the present invention adopts the above technical scheme and has the following technical effects:

1. The present invention uses a wide-side parallel coupled line with stepped impedance to realize a wide upper stopband, and achieves 40dB suppression of the second harmonic (2f _o ) and 20dB suppression of the frequency 2.4f _o .

2. In order to strengthen the capacitive coupling to achieve a relative bandwidth of 11%, the square ring resonator is composed of two layers of broadside parallel coupled lines. The double-layer structure not only enables high coupling capacitance, but also reduces size by using vertical broadside coupled lines instead of planar edge coupled lines. The wide upper stopband is achieved by stepped impedance microstrip lines next to the I/O ports.

3. Since most dual-mode filters use the input/output (I/O) ports of quadrature feedback to excite two degenerate modes, which leads to layout difficulties when connecting with other components, the present invention uses non-orthogonal feedback This problem is solved while dual-mode bandpass filters are smaller in size compared to single-mode filters.

Description of drawings

Fig. 1 is a three-dimensional structural diagram and a planar structural diagram of the present invention.

Fig. 2 is an equivalent circuit diagram of odd and even modes of the present invention.

Fig. 3 is a yield analysis diagram of the present invention.

Fig. 4 is a diagram of simulation results and measurement results of the present invention.

detailed description

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings.

The present invention proposes a dual-mode bandpass filter with wide upper stopband and non-orthogonal feedback, which is implemented in a 2-layer low-temperature co-fired ceramic (LTCC) substrate and uses a broadside with stepped impedance Couple the lines in parallel to achieve a wide upper stopband. The 40dB suppression of the second harmonic (2f _o ) and 20dB suppression of the frequency 2.4f _o are achieved. In order to enhance the capacitive coupling to achieve a relative bandwidth of 11%, the square ring resonator is composed of two layers of wideside parallel coupled lines. The double-layer structure not only enables high coupling capacitance, but also reduces size by using vertical broadside coupled lines instead of planar edge coupled lines. The wide upper stopband is achieved by stepped impedance microstrip lines next to the I/O ports. Most dual-mode filters use the input/output (I/O) ports of quadrature feedback to excite two degenerate modes, which leads to layout difficulties when connecting to other components. Non-quadrature feedback solves this problem, while Dual-mode bandpass filters are smaller in size compared to single-mode filters.

In order to enhance the capacitive coupling to achieve a relative bandwidth of 11%, the square ring resonator is composed of two layers of wideside parallel coupled lines. The double-layer structure not only enables high coupling capacitance, but also reduces size by using vertical broadside coupled lines instead of planar edge coupled lines. The wide upper stopband is achieved by stepped impedance microstrip lines next to the I/O ports. _The vertical and horizontal sideband lines are designed to the width _of W1 and W2. The vertical and horizontal sideband lines have the same length L. The characteristic impedance of the microstrip line at the port part is 50Ω, and the width is W ₀ . L ₁ and W ₃ are the length and width, respectively, of the low-impedance line connected to the I/O feeder. Figure 1(a) shows the structure of the proposed bandpass filter.

Since the structure of the resonator with vertical broadside coupled lines is symmetrical, its characteristics were analyzed using the odd-even mode equivalent circuit method. Build the electric wall along the plane of symmetry and split the structure in half. Figure 2(a) and (b) show the equivalent odd-mode and even-mode circuits, respectively. The characteristic impedance of the I/O feeder line is Z ₀ , and the odd-mode and even-mode characteristic impedances of the vertical broadside coupling line are Z ₁₀ and Z _1e , respectively. _The electrical length of each side of a square ring resonator is θ, and its horizontal side lines have a characteristic impedance of Z2. By calculating the input impedance Z _odd and Z _even of the one-port transmission line circuit shown in Figure 2(a) and (b), the transmission and reflection coefficients of the two-port ring resonator can be derived by the following equations:

When the numerator of equation (2) is zero, when there is no transmission, the following equation with electrical length _θt can be obtained, and the impedances Z ₁₀ , Z _1e and Z ₂ can be derived from the following equations:

(α+1)cos ⁴ θ _t -2αcos ² θ _t +α-1＝0 (3)

The electrical length _θt in equation (3) is determined by the impedance ratio α defined in equation (4). The response of the resonator can be predicted by the impedance ratio α.

As shown in Fig. 1(a), in order to enhance the capacitive coupling to achieve a relative bandwidth of 11%, the square ring resonator consists of two layers of wideside parallel coupled lines. The double-layer structure not only enables high coupling capacitance, but also reduces size by using vertical broadside coupled lines instead of planar edge coupled lines. The wide upper stopband is achieved by stepped impedance microstrip lines next to the I/O ports. _The vertical and horizontal sideband lines are designed to the width _of W1 and W2. The vertical and horizontal sideband lines have the same length L. The characteristic impedance of the microstrip line at the port part is 50Ω, and the width is W ₀ . L ₁ and W ₃ are the length and width, respectively, of the low-impedance line connected to the I/O feeder.

The complete bandpass filter is assembled in a 2-layer LTCC substrate. Each layer of LTCC substrate has a thickness of 0.1 mm after being fired with Ferro-A6 material, a dielectric constant of 5.9, and a loss tangent of 0.002. AXIEM is a full-wave 3D electromagnetic simulation software based on spectral domain analysis, which is used to optimize the parameters of bandpass filters. The final optimal parameters are: W ₁ =0.32mm, W ₂ =0.3mm, W ₃ =1mm, L ₁ =3mm and L ₂ =1.5mm, where the parameters are defined in Figure 1(b).

The filter is implemented in a 2-layer low temperature co-fired ceramic (LTCC) substrate and uses broadside parallel coupled lines with stepped impedance to achieve a wide upper stopband. The 40dB suppression of the second harmonic (2f _o ) and 20dB suppression of the frequency 2.4f _o are achieved.

In order to enhance the capacitive coupling to achieve a relative bandwidth of 11%, the square ring resonator is composed of two layers of wideside parallel coupled lines. The double-layer structure not only enables high coupling capacitance, but also reduces size by using vertical broadside coupled lines instead of planar edge coupled lines. The wide upper stopband is achieved by stepped impedance microstrip lines next to the I/O ports.

Most dual-mode filters use the input/output (I/O) ports of quadrature feedback to excite two degenerate modes, which leads to layout difficulties when connecting to other components. Non-quadrature feedback solves this problem, while Dual-mode bandpass filters are smaller in size compared to single-mode filters.

In order to facilitate those skilled in the art to further understand and implement the present invention, the simulation and measurement examples of the present invention are now provided.

Since the manufacturing tolerance and material shrinkage are the main factors affecting the performance of the LTCC bandpass filter, the parameter W with ₁₀ % variation is chosen for the yield analysis. After analyzing 100 results, the yield is 85.85%, as shown in Figure 3. The results allow fabrication by LTCC.

Measurements were performed by an Agilent N5230C vector network analyzer and a CascadeMicrotech Summit 9000 Series probe test bench with 400 μm-GSG probes. The measured center frequency is 9GHz and the relative bandwidth is 11%. The measured S ₂₁ and S ₁₁ are better than -1.8dB and -12dB respectively in the passband. The expected target of 40dB rejection at 2f _o (18GHz) and 20dB rejection at 2.4f _o (23GHz) is achieved. Simulation and measurement results are shown in Figure 4.

The size of the proposed bandpass filter is only 7×4×0.23mm (not including the microstrip line area reserved for GSG probe testing), which is equivalent to 0.54×0.27×0.0015λ _g , where λ _g is the thickness of The waveguide wavelength for 0.2mm Ferro A6 substrate at 9.1GHz frequency, the performance comparison is summarized in Table 1 below. It can be seen that the proposed bandpass filter has the lowest passband insertion loss and the most effective second harmonic suppression.

Table 1

The above-mentioned prior art documents are respectively:

[1] Huang, X.D., and C.H.Cheng, A novel microstrip dual mode bandpass filter with harmonic suppression, IEEE Microwave Wireless compon Lett 16(2006), pp.404-406.

[2]H.W.Deng,Y.J.Zhao,W.Chen,B.Liu and Y.Y.Liu,Wide upper-stopbandmicrostripbandpass filter with dualmodeopen loop stepped-impedance resonatorand source-load coupling structure,Microwave Opt Tech Lett 54(2012),pp.1618 -1621.

[3] Jeon, B.K., Nam, H., Yoon, K.C., Jeon, B.W., Kim, Y.W., and Lee, J.C., Design of a patch dual-mode bandpass filter with second harmonic suppression using open stubs, IEEE Microwave Conference Proceedings (2010APMC ), pp.1106-1109.

In summary, the present invention discloses a dual-mode bandpass filter with a wide upper stopband and non-orthogonal feedback. The filter is implemented in a 2-layer low temperature co-fired ceramic (LTCC) substrate and uses broadside parallel coupled lines with stepped impedance to achieve a wide upper stopband. The 40dB suppression of the second harmonic (2f _o ) and 20dB suppression of the frequency 2.4f _o are achieved. In order to enhance the capacitive coupling to achieve a relative bandwidth of 11%, the square ring resonator is composed of two layers of wideside parallel coupled lines. The double-layer structure not only enables high coupling capacitance, but also reduces size by using vertical broadside coupled lines instead of planar edge coupled lines. The wide upper stopband is achieved by stepped impedance microstrip lines next to the I/O ports. Most dual-mode filters use the input/output (I/O) ports of quadrature feedback to excite two degenerate modes, which leads to layout difficulties when connecting to other components. Non-quadrature feedback solves this problem, while Dual-mode bandpass filters are smaller in size compared to single-mode filters.

The above descriptions are only preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments, but all equivalent modifications or changes made by those of ordinary skill in the art according to the disclosure of the present invention should be included within the scope of protection described in the claims.

Claims (3)

1. a kind of have wide upper stopband and the double mode LTCC bandpass filters of nonopiate feedback, it is characterised in that is distributed in top layer The metal of ltcc substrate and bottom ltcc substrate and air contact portion is microstrip line, and 2 laminar substrates are connected by metal band-shaped line, Microstrip line is in stepped shape by two I/O ports, forms the broadside parallel coupled line for realizing wide upper stopband, double-deck broadside Parallel coupled line constitutes square ring resonator.

2. according to claim 1 have wide upper stopband and the double mode LTCC bandpass filters of nonopiate feedback, it is special Levy is that the microstrip line of vertical direction and the strip line of horizontal direction have identical length L.

3. according to claim 1 have wide upper stopband and the double mode LTCC bandpass filters of nonopiate feedback, it is special Levy is that the characteristic impedance of port section microstrip line is 50 Ω.