Low-loss SIW filter based on LTCC technology and switch filtering assembly

Abstract

The invention discloses a low-loss SIW filter based on an LTCC technology and a switch filtering assembly. By embedding the capacitive metal cover plate into the SIW to introduce additional capacitance and connecting the capacitive metal cover plate to the bottom wide wall through the metal vertical through hole and introducing additional grounding inductance into the waveguide, the size of the resonator is further reduced, and compared with a traditional resonator, the Q value is obviously improved. On the other hand, by introducing the cross coupling topology, a transmission zero point is formed at the upper end of the passband, and the stop-band suppression degree is effectively improved. In the working process, the conduction or cut-off state of the diode is controlled through externally applied direct current bias voltage, parasitic inductance 0.7 nH exists in the conduction state of the diode, the parasitic inductance 0.7 nH and a 3pF capacitor are connected in series at the 3.4 GHz position of the filter passband center to generate series resonance, then a quarter-wavelength line is inversely equivalent to an open circuit, signals of a branch circuit are cut off, and therefore the output of the filter is achieved. The switch has the advantages of being simple in structure and low in loss.

Description

A low-loss SIW filter and switching filter component based on LTCC technology Technical Field

[0001] This invention belongs to the field of wireless communication filter technology, specifically relating to a SIW filter with low insertion loss and miniaturization, and a single-pole double-throw (SPDT) switch assembly with high suppression and high isolation performance. Background Technology

[0002] In recent years, with the rapid development of wireless communication technology and the emergence of new-generation communication standards, wireless communication systems need to simultaneously support multiple frequency bands and multiple operating modes, significantly increasing the design complexity of the system. Microwave filters, as key passive components in radio frequency front-end systems, can effectively suppress interference signals without attenuating the desired signal, thereby improving the transmission distance, communication capacity, and reliability of wireless systems. Therefore, developing filters with low insertion loss, high suppression, miniaturization, and high integration has become a research hotspot in the current field of wireless communication.

[0003] Substrate integrated waveguide (SIW) filters have attracted widespread attention due to their advantages such as low loss, high quality factor (Q value), low cost, ease of fabrication, and easy integration with planar circuits. SIW is a waveguide structure that utilizes vertical metal vias to form equivalent metal walls, combining the high performance of waveguide structures with the compactness of planar circuits, making it ideal for high-performance, miniaturized filter designs. Meanwhile, low-temperature co-fired ceramic (LTCC) technology is widely used in microwave and millimeter-wave circuits. This technology offers advantages such as high dielectric constant, low loss, high conductivity, and excellent frequency characteristics, and can embed lumped components such as inductors and capacitors internally, providing a superior approach to the miniaturization and three-dimensional integration of RF circuits.

[0004] To meet the urgent needs of 5G and future wireless communication systems for low loss, miniaturization, and high integration, this invention proposes a low-loss substrate integrated waveguide (SIW) filter and filter switching circuit design based on LTCC technology. This scheme fully utilizes the advantages of the multi-layer stacked structure of LTCC to realize a low-loss SIW filter structure, and effectively solves the problem of high loss caused by directly loading the resonator with a diode in traditional switching circuits by controlling the energy transfer path through the on and off states of the diode. Summary of the Invention

[0005] This invention is based on the low-temperature co-fired ceramic (LTCC) process and provides a low-loss substrate integrated waveguide (SIW) filter and filter switching circuit design based on LTCC technology.

[0006] This invention is achieved through the following technical solution: a low-loss SIW filter based on LTCC technology, wherein the filter has a coplanar waveguide feeding structure, a fourth-order cross-coupled resonator of a capacitor-loaded SIW, and a PCB switching circuit structure.

[0007] Furthermore, the SIW structure is as follows: an additional capacitance is introduced by embedding a capacitive metal cover plate into the SIW, and it is connected to the bottom wide wall through a metal vertical through-hole.

[0008] Furthermore, the coupling of R1 and R2, R2 and R3, R3 and R4, R1 and R3, and R2 and R4 in the fourth-order SIW resonator is achieved through the induction window on the metal through-hole wall between the shared resonators; the second resonant unit R2 is located above the first resonant unit R1, and the third resonant unit R3 is located to the left of the second resonant unit R2, with the second resonant unit R2 and the third resonant unit R3 being symmetrical about the central axis plane; the fourth resonant unit R4 is located below the third resonant unit R3, and the fourth resonant unit R4 is symmetrical about the first resonant unit R1.

[0009] Furthermore, the cross-coupling of R1 and R3, and R2 and R4 introduces a transmission zero at low frequencies; a window is opened in the metal wall W1 between R1 and R4, and anti-polarity coupling is introduced through the metal lead S1.

[0010] Furthermore, the first resonant unit R1 includes a coplanar waveguide feed input port, a metal shielding wall W1, a capacitive metal cover plate C1, an inductive metal via L1, and a metal lead S1; the second resonant unit R2 includes a metal shielding wall W2, a capacitive metal cover plate C2, and an inductive metal via L2; the third resonant unit R3 includes a metal shielding wall W2, a capacitive metal cover plate C3, and an inductive metal via L3; and the fourth resonant unit R4 includes a coplanar waveguide feed output port, a metal shielding wall W1, a capacitive metal cover plate C4, an inductive metal via L4, and a metal lead S1.

[0011] A filter switching circuit includes a filter with the structure described above.

[0012] Furthermore, the filter switching circuit includes a T-junction and two quarter-wavelength stubs, and a switching diode and a bias voltage source are loaded on the single-pole double-throw switch bypass quarter-wavelength stub. The bias voltage source controls the conduction and cutoff states of the switching diode. A DC blocking capacitor is loaded on the stub. The bias voltage source includes an emission blocking resistor and an inductor. The LTCC filter is connected to the PCB test substrate through an internal metallized via. The input and output ports of the LTCC filter are both connected to the PCB test substrate through grounding vias.

[0013] Furthermore, all single-pole double-throw (SPDT) switch transmission lines are CPWG structures; wherein, the output terminal of the LTCC filter and the input port of the SPDT switch are soldered onto the PCB test substrate, the dielectric material of the PCB substrate is Rogers 4350, and the metal traces are copper.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1) Low loss: The substrate integrated waveguide filter used has the advantages of low loss and high Q value. In the 3.3-3.68GHz operating frequency band, the insertion loss of the output signal of the conducting branch is less than 1dB within the passband.

[0015] 2) Miniaturized Design: This invention utilizes low-temperature co-fired ceramic (LTCC) technology to implement the filter switch, fully leveraging the multi-layer interconnect structure of LTCC to achieve greater design freedom and effectively reduce circuit size. Compared to traditional SIW resonators, the capacitor-loaded SIW resonator used has a smaller size and higher compactness. The overall size of the filter circuit is 7.8mm × 8mm × 2.8mm. In the frequency range of 3.4-3.6GHz, the simulated loss is less than 0.9dB. By generating transmission zeros at 3.95GHz and 5.05GHz respectively, the selectivity and out-of-band rejection are enhanced, with near-end rejection greater than 40dB and far-end rejection greater than 60dB.

[0016] 2) High Isolation: This invention controls the conduction and cutoff states of the switching diode by applying an external DC bias voltage. When the diode is on, its equivalent inductance is negligible, and when connected in series with the capacitor, it forms a resonant short circuit at the center of the filter's passband, effectively isolating the signal in that branch. The open-circuit effect achieved by reversing the admittance polarity causes the signal to be transmitted through another branch. To further improve the isolation of the cutoff branch, this invention utilizes two resonators in the filter to collaboratively control the switching state, introducing two transmission zeros in the conducting branch, thereby significantly improving the isolation performance in the off state, achieving an isolation of over 30 dB within the passband.

[0017] 3) High suppression: This invention introduces a cross-coupled topology into the circuit and combines it with the intrinsic characteristics of a capacitively loaded SIW resonator to form additional transmission zeros in the upper and lower sidebands of the passband. This structure is not only simple and easy to implement, but also significantly enhances the sideband roll-off characteristics and stopband suppression capability, enabling the out-of-band suppression of the upper stopband to exceed 55 dB. Attached Figure Description

[0018] Figure 1 is a structural diagram of a low-loss SIW filter based on LTCC technology provided in an embodiment of this application; Figure 2 is a schematic diagram of the coupling topology of a low-loss SIW filter based on LTCC technology provided in an embodiment of this application; Figure 3 is a simulation result diagram of a low-loss SIW filter based on LTCC technology provided in an embodiment of this application; Figure 4 is a structural diagram of a low-loss SIW filter switching circuit based on LTCC technology provided in an embodiment of this application; Figure 5 is a schematic diagram of a low-loss SIW filter switching circuit based on LTCC technology provided in an embodiment of this application; Figure 6 is a simulation result diagram of a low-loss SIW filter switching circuit based on LTCC technology provided in an embodiment of this application. Detailed Implementation

[0019] A low-loss SIW filter based on LTCC technology, the filter having a coplanar waveguide feeding structure, a fourth-order cross-coupled resonator of capacitor-loaded SIW, and a PCB switching circuit structure.

[0020] Furthermore, the SIW structure is as follows: an additional capacitance is introduced by embedding a capacitive metal cover plate into the SIW, and it is connected to the bottom wide wall through a metal vertical through-hole.

[0021] Furthermore, the coupling of R1 and R2, R2 and R3, R3 and R4, R1 and R3, and R2 and R4 in the fourth-order SIW resonator is achieved through the induction window on the metal through-hole wall between the shared resonators; the second resonant unit R2 is located above the first resonant unit R1, and the third resonant unit R3 is located to the left of the second resonant unit R2, with the second resonant unit R2 and the third resonant unit R3 being symmetrical about the central axis plane; the fourth resonant unit R4 is located below the third resonant unit R3, and the fourth resonant unit R4 is symmetrical about the first resonant unit R1.

[0022] Furthermore, the cross-coupling of R1 and R3, and R2 and R4 introduces a transmission zero at low frequencies; a window is opened in the metal wall W1 between R1 and R4, and anti-polarity coupling is introduced through the metal lead S1.

[0023] Furthermore, the first resonant unit R1 includes a coplanar waveguide feed input port, a metal shielding wall W1, a capacitive metal cover plate C1, an inductive metal via L1, and a metal lead S1; the second resonant unit R2 includes a metal shielding wall W2, a capacitive metal cover plate C2, and an inductive metal via L2; the third resonant unit R3 includes a metal shielding wall W2, a capacitive metal cover plate C3, and an inductive metal via L3; and the fourth resonant unit R4 includes a coplanar waveguide feed output port, a metal shielding wall W1, a capacitive metal cover plate C4, an inductive metal via L4, and a metal lead S1.

[0024] A filter switching circuit includes a filter with the structure described above.

[0025] Furthermore, the filter switching circuit includes a T-junction and two quarter-wavelength stubs, and a switching diode and a bias voltage source are loaded on the single-pole double-throw switch bypass quarter-wavelength stub. The bias voltage source controls the conduction and cutoff states of the switching diode. A DC blocking capacitor is loaded on the stub. The bias voltage source includes an emission blocking resistor and an inductor. The LTCC filter is connected to the PCB test substrate through an internal metallized via. The input and output ports of the LTCC filter are both connected to the PCB test substrate through grounding vias.

[0026] Furthermore, all single-pole double-throw (SPDT) switch transmission lines are CPWG structures; wherein, the output terminal of the LTCC filter and the input port of the SPDT switch are soldered onto the PCB test substrate, the dielectric material of the PCB substrate is Rogers 4350, and the metal traces are copper.

[0027] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0028] As shown in Figure 1, to address the problems existing in the prior art, this invention provides a 5G high-selectivity LTCC bandpass filter based on substrate integrated waveguide. The invention will be described in detail below with reference to the accompanying drawings. The 5G high-selectivity LTCC bandpass filter based on substrate integrated waveguide provided in this embodiment mainly consists of a coplanar waveguide feeding structure and a cross-coupled fourth-order capacitor-loaded SIW resonator. A novel LTCC-based three-dimensional SIW structure is adopted, introducing additional capacitance by embedding a capacitive metal cover plate into the SIW and connecting it to the bottom wide wall through a metal vertical through-hole. This technology introduces additional ground inductance in the waveguide. Due to the introduction of the load capacitance, the electric field is mainly distributed above the embedded metal cover plate. Compared with traditional LTCC microstrip or stripline resonators, the Q value is significantly improved. The overall circuit size is 7.8mm × 8mm × 2.8mm, which helps to achieve miniaturized applications.

[0029] The first resonator includes a coplanar waveguide feed input port, a metal shielding wall W1, a capacitive metal cover plate C1, an inductive metal via L1, and a metal lead S1; the second resonator includes a metal shielding wall W2, a capacitive metal cover plate C2, and an inductive metal via L2; the third resonator includes a metal shielding wall W2, a capacitive metal cover plate C3, and an inductive metal via L3; the fourth resonator includes a coplanar waveguide feed output port, a metal shielding wall W1, a capacitive metal cover plate C4, an inductive metal via L4, and a metal lead S1. The second resonant unit R2 is located above the first resonant unit, and the third resonant unit R3 is located to the left of the second resonant unit R2. The second resonant unit R2 and the third resonant unit R3 are symmetrical about the central plane. Below the third resonant unit R3 is the fourth resonant unit R4, which is symmetrical to the first resonant unit R1.

[0030] As shown in Figure 2, the coupling of R1 and R2, R2 and R3, R3 and R4, R1 and R3, and R2 and R4 in the fourth-order SIW resonator is achieved through the induction window on the metal via wall between the resonators. The cross-coupling of R1 and R3, and R2 and R4 can introduce transmission zeros at low frequencies, improving out-of-band rejection characteristics.

[0031] As shown in Figure 3, the designed filter has a simulated loss of less than 0.9dB in the frequency range of 3.4-3.6GHz. By generating transmission zeros at 3.95GHz and 5.05GHz respectively, the selectivity and out-of-band suppression are enhanced, with near-end suppression greater than 40dB and far-end suppression greater than 60dB.

[0032] As shown in Figure 4, the switching circuit layer is located in the first layer of the circuit and includes switching diodes D1 and D2, bias capacitors C1 and C2, inductors L0, L1, and L2, and DC voltages VDD1 and VDD2. DC power supply VDD1 is connected to one end of inductor L1, and DC power supply VDD2 is connected to one end of inductor L2. The other end of inductor L1 is connected to one end of bias capacitor C1 and the positive terminal of switching diode D1. The other end of inductor L2 is connected to one end of bias capacitor C2 and the positive terminal of switching diode D2. The other end of bias capacitor C1 is connected to the ground metal layer through a common via, and the other end of bias capacitor C2 is connected to the ground metal layer through a via.

[0033] As shown in Figure 5, the single-pole double-throw switch mainly consists of a T-junction and two quarter-wavelength stubs. A switching diode and a bias voltage source are loaded on the bypass quarter-wavelength stub of the single-pole double-throw switch. The bias voltage source controls the conduction and cutoff states of the switching diode. A DC blocking capacitor is loaded on the stub. The bias voltage source includes an emission blocking resistor and an inductor. The LTCC filter is connected to the PCB test substrate through an internal metallized via. Both the input and output ports of the LTCC filter are connected to the PCB test substrate through grounding vias. The conduction or cutoff state of the diode is controlled by an externally applied DC bias voltage. When the diode is in the conduction state, there is a parasitic inductance of 0.7nH, which, in series with a 3pF capacitor, generates a series resonance at the center of the filter passband at 3.4GHz. A quarter-wavelength line is then inverted to act as an open circuit, isolating the signal in this branch and allowing the signal to pass through the other branch. This switch features a simple structure and low loss.

[0034] As shown in Figure 6, the aforementioned low-loss LTCC filter is cascaded with a switch, and designed using a hybrid electromagnetics and circuit simulation method. The total circuit area is 32 × 35 mm. 2 The center frequency is 3.5GHz, the absolute bandwidth is 200MHz, and the switching diodes used are all Skyworks SMP1345-079, with a forward voltage of 0.9V and a reverse cutoff voltage of -5V. Joint simulations were performed using the 3D electromagnetic simulation software HFSS and the electronic design automation software ADS, where S(2,1) represents the signal transmission characteristic curve of the on-channel and S(3,1) represents the signal transmission characteristic curve of the off-channel. Within the 3.3-3.68GHz operating frequency band, the in-band insertion loss of the on-channel output signal is less than 1dB, the return loss is greater than 25dB, the out-of-band near-end rejection is greater than 40dB, and the far-end rejection is greater than 70dB, meeting the requirements of 5G applications.

Claims

1. A low-loss SIW filter based on LTCC technology, characterized in that, The filter has a coplanar waveguide-fed structure, a fourth-order cross-coupled resonator of a capacitor-loaded SIW, and a PCB switching circuit structure.

2. A low-loss SIW filter based on LTCC technology according to claim 1, characterized in that, The SIW structure is as follows: an additional capacitance is introduced by embedding a capacitive metal cover plate into the SIW, and it is connected to the bottom wide wall through a metal vertical through-hole.

3. A low-loss SIW filter based on LTCC technology according to claim 1, characterized in that, The coupling of R1 and R2, R2 and R3, R3 and R4, R1 and R3, and R2 and R4 in the fourth-order SIW resonator is achieved through the induction window on the metal through-hole wall between the resonators; the second resonant unit R2 is located above the first resonant unit R1, and the third resonant unit R3 is located to the left of the second resonant unit R2. The second resonant unit R2 and the third resonant unit R3 are symmetrical about the central axis plane; the fourth resonant unit R4 is located below the third resonant unit R3. The fourth resonant unit R4 is symmetrical to the first resonant unit R1.

4. A low-loss SIW filter based on LTCC technology according to claim 3, characterized in that, The cross-coupling of R1 and R3, and R2 and R4 introduces a transmission zero at low frequencies; a window is opened in the metal wall W1 between R1 and R4, and anti-polarity coupling is introduced through the metal lead S1.

5. A low-loss SIW filter based on LTCC technology according to claim 3, characterized in that, The first resonant unit R1 includes a coplanar waveguide feed input port, a metal shielding wall W1, a capacitive metal cover plate C1, an inductive metal via L1, and a metal lead S1; the second resonant unit R2 includes a metal shielding wall W2, a capacitive metal cover plate C2, and an inductive metal via L2; the third resonant unit R3 includes a metal shielding wall W2, a capacitive metal cover plate C3, and an inductive metal via L3; the fourth resonant unit R4 includes a coplanar waveguide feed output port, a metal shielding wall W1, a capacitive metal cover plate C4, an inductive metal via L4, and a metal lead S1.

6. A switching filter component, characterized in that, Includes the filters described in claims 1-5.

7. A switching filter component according to claim 6, characterized in that, The filter switching circuit includes a T-junction and two quarter-wavelength stubs. A switching diode and a bias voltage source are loaded on the single-pole double-throw switch bypass quarter-wavelength stub. The bias voltage source controls the conduction and cutoff states of the switching diode. A DC blocking capacitor is loaded on the stub. The bias voltage source includes an emission blocking resistor and an inductor. The LTCC filter is connected to the PCB test substrate through an internal metallized via. The input and output ports of the LTCC filter are both connected to the PCB test substrate through grounding vias.

8. A switching filter component according to claim 7, characterized in that, All single-pole double-throw (SPD) switch transmission lines are CPWG structures; the LTCC filter output terminal and the SPD switch input port are soldered onto a PCB test substrate, the PCB substrate dielectric material is Rogers 4350, and the metal traces are copper.

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