High-isolation triplexer
By designing improved composite resonator and coplanar waveguide low-pass filter on the common port of the tri-computer, the problem of insufficient isolation of the existing tri-computer is solved, and the impedance matching and high isolation of the three channels are achieved, thereby reducing signal crosstalk and stray problems.
Patent Information
- Application Number
- CN202510366605.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-26
- Publication Date
- 2025-05-09
AI Technical Summary
The existing tri-computer does not require an additional matching structure to achieve good band interpolation and out-of-band filtering characteristics of the three channels in the common port. However, the isolation is insufficient, making it difficult to achieve channel isolation above 46dB.
A high isolation triple is designed, and the impedance matching and high isolation of the three channels at the common ports are achieved by loading the modified composite resonator at the end of the J converter and combining the coplanar waveguide low-pass filter composed of LC.
The better impedance matching of the three channels in the common ports is achieved, and the isolation between channels is improved, with an isolation of better than 46dB, greatly reducing the problem of signal crosstalk and clock spurious between radio frequency channels.
Smart Images
Figure CN119965506A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of communication technology, and in particular to a high-isolation triplexer. Background Art
[0002] Today's communication needs are developing in the direction of multi-band and multi-service. Many devices not only need to receive (transmit) multi-band RF signals, but also need to receive (transmit) high-quality clock signals. Therefore, the demand for RF front-end devices that are compatible with RF signal and clock signal transmission is gradually increasing.
[0003] In the prior art, a novel design method for high isolated microstripdiplexer without extra matching circuit was proposed in (A novel design method for high isolated microstripdiplexer without extra matching circuit, IEEE Access 2019. 7). This method successfully realized the design of a duplexer without an extra matching network by utilizing the impedance transformation characteristics between special resonators, providing a new idea for subsequent related designs.
[0004] (Novel diplexer and triplexer avoiding additional matching circuitoutside filters, IEEE Access 2020. 8) proposed a design method of loading multiple branches on the common port to design duplexers and triplexers. This design method requires a large circuit area to design the impedance matching network, which makes the overall circuit volume larger. In addition, since there is no transmission zero designed in each frequency band, the isolation within the working frequency band is poor.
[0005] In 2024, the applicant proposed an internally matched high-isolation duplexer - CN118920045A, which simultaneously achieved common port internal matching and high-isolation duplexer characteristics by loading parallel short-circuit and open-circuit branches at the end of the J transformer to form an open-circuit short-circuit resonator and coupling the J transformer with a half-wavelength uniform impedance resonator.
[0006] Some special English explanations that will be mentioned in this article: J converter: inverted converter; Frequency: frequency; |S 21 |: Transmission coefficient from port 1 to port 2; |S 11 |: reflection coefficient of port 1; |S 31 |: Transmission coefficient from port 1 to port 3; |S 41 |: Transmission coefficient from port 1 to port 4; |S 23 |: Isolation coefficient from port 2 to port 3; |S24 |: Isolation coefficient from port 2 to port 4; |S 34 |: Isolation coefficient from port 3 to port 4; S: source; LL1 (LL2, LL3): load; L: inductance; C: capacitance; Z: characteristic impedance; θ: electrical length. Summary of the invention
[0007] The purpose of the present invention is to propose a design method for a high-isolation triplexer based on a duplexer, so that the triplexer can simultaneously achieve good in-band insertion loss and out-of-band filtering characteristics of three channels without adding an additional matching structure at the common port, and finally achieve a channel isolation of at least better than 46dB; the triplexer has two bandpass channels (1.8GHz and 2.4GHz) and a low-pass channel (cut-off frequency is 100MHz), which can be well applied in systems with clock signal transmission. And because the three channels simultaneously achieve good impedance matching at the common port, the isolation between channels is better than 46dB, which greatly reduces the signal crosstalk and clock spurious problems between the RF paths.
[0008] In order to achieve the above purpose, the design idea of the present invention is to design a triplexer with good matching of three channels at the common port and high isolation characteristics between ports. The specific technical scheme adopted is: a high isolation triplexer, including a dielectric substrate, a microstrip circuit is provided on the upper surface of the dielectric substrate, the circuit includes an input feeder, an output feeder, a J converter, and an improved composite resonator loaded at the end of the J converter; one end of the J converter performs tap feeding on the parallel open-circuit branches (improved composite resonators); the improved composite resonators are coupled through gaps, the bottom surface of the dielectric is a metal ground and a fifth-order LC low-pass filter with a coplanar waveguide structure is provided.
[0009] Furthermore, a coupling topology diagram of a high-isolation triplexer is proposed to clarify the number and composition of the resonant modes in the three passbands and the coupling form between them.
[0010] Furthermore, by analyzing the transmission line model of the common port of the triplexer, the theoretical basis of the impedance matching of the three ports is introduced and the impedance matching conditions at the common port are derived.
[0011] Furthermore, by analyzing the transmission line model of the common port of the triplexer, a method for improving the isolation of the triplexer is proposed: generating a transmission zero point within the working frequency band to improve the isolation between channels. The improved composite resonator is used to reasonably design the transmission zero point and the resonant frequency point, combined with the impedance transformation function of the J transformer, to achieve self-matching of the two bandpass channels at the common port without the need for additional matching network design; since the operating frequency of the low-pass channel is ≤100MHz, it is a stop band at f1 and f2, so the channel naturally has an isolation effect on the other two bandpass channels. In addition, the first L of the low-pass filter designed by the present invention is directly connected across the common port, and the LC low-pass circuit is designed in the coplanar waveguide structure on the bottom surface, which further increases the isolation of the bandpass channel between the low-pass channel and the medium surface.
[0012] Furthermore, a fifth-order LC low-pass filter in the form of a coplanar waveguide is constructed on the bottom surface of the circuit. The filter has a cutoff frequency of 100MHz and a stop band with a suppression effect of more than 20dB in the range of 0.5 to 4.5GHz.
[0013] Furthermore, circuit electromagnetic simulation and actual circuit results revealed that the triplexer has good matching at the common port and good isolation between channels.
[0014] Furthermore, the overall volume of the circuit is (λ g is the guided wavelength corresponding to 1.8 GHz).
[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The triplexer designed in the present invention has a novel topological structure. By using an improved composite resonator loaded at the end of the J transformer, LC forming a coplanar waveguide low-pass filter, and reasonably designing the transmission zero point position, good matching of three frequency bands and high isolation between channels are achieved at the common port at the same time.
[0016] 2. In the present invention, the impedance characteristics of the common port are analyzed to derive the conditions for achieving three-channel matching.
[0017] 3. The present invention proposes a zero point position allocation scheme, and sets a transmission zero point in each of the two bandpass filter operating bands to improve the isolation between channels. The coplanar waveguide low-pass filter composed of LC has a small volume and wide stopband characteristics, and the isolation between two channels is greater than 46dB.
[0018] 4. In the present invention, each bandpass filter has a transmission zero at high and low frequencies, which improves the out-of-band suppression capability of the filter.
[0019] 5. In the present invention, each bandpass channel is composed of two resonance modes, i.e., two-order resonators. Each bandpass channel uses only two-order resonators to make the channel isolation greater than 52dB (S23), which is better than some circuits composed of three-order resonators (generally, the more orders, the higher the isolation). In addition, without increasing the number of circuit layers, a low-pass filter with a coplanar waveguide structure is designed under the circuit board to output the clock signal and the high-frequency signal together without interfering with each other (high isolation).
[0020] 6. The LC low-pass filter has the advantages of high adjustability and good low-frequency response, and is very suitable for use as a filter for low-frequency clock signals. In addition, it also has the advantages of reducing the frequency multiplication amplitude of the clock signal. The fifth-order LC low-pass filter in the form of a coplanar waveguide on the bottom surface of the medium of the present invention can effectively improve the isolation of the channel from other channels. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 It is a schematic diagram of the structure of a high isolation triplexer in an embodiment.
[0022] Figure 2 It is a coupling topology diagram of a high isolation triplexer in an embodiment.
[0023] Figure 3 This is a common port impedance matching model of a high isolation triplexer in an embodiment.
[0024] Figure 4 This is a real shot of the top surface circuit of a high isolation triplexer in the embodiment.
[0025] Figure 5 This is a real shot of the bottom circuit of a high-isolation triplexer in the embodiment.
[0026] Figure 6 It is the S parameter simulation and test curve of the high isolation triplexer in the embodiment.
[0027] Figure 7 1 is a simulation and test curve of the isolation of each port of the high isolation triplexer in the embodiment. DETAILED DESCRIPTION
[0028] The present invention is explained in detail and completely below with reference to the accompanying drawings and specific embodiments.
[0029] The design idea of the triplexer of this embodiment is to realize two bandpass filters with good in-band filtering characteristics and a low-pass filter with wide stopband by using impedance matching at the common port. The specific implementation is as follows: Figure 1This is the high isolation triplexer structure proposed in this patent. The circuit is a two-layer structure, the upper layer is a microstrip line, and the lower layer is a coplanar waveguide circuit and a metal ground (the part in the dotted box). The upper layer circuit is a filtering structure of two bandpass filters, and the lower layer circuit is a low-pass filter structure. The upper layer is specifically composed of input and output feed lines, J converters, and improved composite resonators. The lower layer is specifically composed of coplanar waveguide transmission lines, inductors, and capacitors.
[0030] The improved composite resonator is a half-wavelength resonator loaded on a J converter and open at both ends. This patent achieves a similar step impedance effect and miniaturization of the circuit by constructing a triangular microstrip structure at both ends of the open branch. When the improved composite resonator resonates, a transmission pole (resonance mode) will be generated, and a transmission zero point will be generated at low frequency and high frequency. Specific circuit size parameters ( x, t represents the length of the microstrip line, w represents the width of the microstrip line, r Indicates the radius of the grounding hole) as follows, W 1= 0.4, W 2= 0.7, W 3= 1.85, W f = 1.9, x 1= 8.2, x 2 = 8.75, x 3= 4.1, x 4= 3.6, x 5= 7.85, x 6= 9.15, x 7= 5.85, t 1= 2, t 2= 3.9, t 3= 3.45, t 4= 3.05, t 5= 5.95, t 6=3.7, g 1= 0.4, g 2 = 0.95, g 3= 0.2, r = 0.3 (the units of the above parameters are all in mm), L 1= L 3 = 110nH, L 2=180nH, C 1= C 2 = 33pF.
[0031] Figure 2It is a coupled topology of a high-isolation triplexer, which can intuitively understand the resonant mode composition of each filter. S represents common port 1, LL1 and LL2 represent ports 2 and 3, and LL3 represents port 4. The center frequencies of the two bandpass filters are f 1 and f 2. Each of the two bandpass filters has two resonant modes. The parallel resonance of the open-ended branches forms a resonant mode. The dotted line between the resonant modes represents the gap coupling, and the solid line represents the J-converter coupling. A fifth-order LC low-pass filter is directly connected to the common port. The cutoff frequency of the low-pass filter is f c =100MHz, the low-pass filter f 1 and f 2 is the stop band. Many communication systems need to combine and output signals such as clocks through the RF port, so this low-pass filter can well feed the clock signal to the next level system through the RF port. Similarly, this design can also be used to separate the clock signal from the RF port.
[0032] The following is an analysis of the matching of the public port. Figure 3 An ideal transmission line equivalent model of the common port of a triplexer is shown. f 1. f 2 represents the center frequency of the two bandpass channels, and f 1< f 2. f c is the cut-off frequency of the low-pass filter. From the transmission line impedance equation, we can get: , Among them, Z o represents the characteristic impedance of the open end of the open branch 2, Z2 represents the characteristic impedance of the open branch 2, Z in3 represents the input impedance of the open branch 2, and θ2 represents the electrical length of the open branch 2. As can be seen from the figure: the open branch 2 f There is a transmission zero point at 2, and Z is known. o =∞, substituting into: , Combining the above two formulas, we can get: , Z in2 ∠ represents the input impedance of the improved composite resonator 1.
[0033] Continue by j1 (J is the electrical length of the converter 1) f 2 frequency is set to a quarter wavelength, and the left part is working at f 1 bandpass filter channel, we can get: , Z in1 represents the input impedance of bandpass channel 1.
[0034] Similarly, analyzing the impedance condition on the right side, we can obtain the input impedance of bandpass channel 2: , Translating the above two sets of impedance conditions, we can say that: when the operating frequency is f Channel 1 only allows signals at its frequency to pass through, and greatly hinders signals of other frequencies, such as f 2 and low frequency f c . Similarly, the operating frequency is f Channel 2 is only allowed in f 2 frequency signals pass through, which greatly hinders signals of other frequencies, such as f 1 and low frequency f c .
[0035] Combined with the impedance condition of the low-pass filter: , In summary, the triplexer designed in this patent has three frequency bands that can achieve good impedance matching at the common port at the same time, and the isolation between the frequency bands is good.
[0036] Figure 4 , Figure 5 This is a real shot of the processing circuit. The dielectric constant of the medium used is 4.4 and the thickness is 1mm. ,λ g is the waveguide wavelength corresponding to 1.8 GHz. Figure 4 It can be seen that the upper surface of the circuit is composed of a microstrip circuit. Figure 5 It can be seen that the bottom surface of the circuit is composed of a coplanar waveguide circuit and LC.
[0037] Figure 6 This is a comparison chart of the simulation and test results of the triplexer. The dotted line represents the measured curve, and the solid line represents the simulation curve. Figure 6 The figure above is the response diagram of two bandpass filters (S parameter curves of port 2 and port 3 and port 1). It can be clearly seen from the figure that there is at least one transmission zero on both sides of each passband, achieving good out-of-band suppression effect, and good in-band return loss, reducing energy reflection. The measured curve is consistent with the simulation curve, which proves the correctness of the design idea and circuit model. The working frequency bands of the two bandpass filters of the measured triplexer ( f 1 and f2) 1.8GHz and 2.4GHz, with relative bandwidths of 5.6% and 4.05% respectively. The insertion losses of the two passband channels of the triplexer were measured to be 2.6B and 3.2dB respectively.
[0038] Figure 6 The figure below is the channel response of the low-pass filter (S parameter curves of port 4 and port 1). From the figure, we can see that the low-pass filter channel has a good stopband suppression effect. f 1 and f The suppression near the 2nd frequency is greater than 50dB. The actual measurement shows that the suppression capability is greater than 20dB at 0.5 ~ 4.5GHz. The measured in-band differential loss of the low-pass filter channel of the triplexer is 1.1dB@<100MHz, and the in-band return loss is greater than 15dB.
[0039] Figure 7 This is a comparison chart of the simulation and test results of the isolation of the triplexer. Due to the good harmonic suppression effect of the transmission zero point meter and the low-pass filter designed in the band, the isolation of the 24-port, 34-port and 23-port of the triplexer is measured to be 46dB, 52dB, and 52dB, respectively. The present invention successfully achieves the impedance matching of the three channels at the common port and the high isolation of each channel.
[0040] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the examples. Those skilled in the art can also make various equivalent changes or substitutions without violating the spirit of the present invention, and these equivalent changes or substitutions are all included in the scope defined by the claims of this application.
Claims
1. A high isolation triplexer, characterized in that: It comprises a dielectric substrate, a microstrip circuit is arranged on the surface of the dielectric substrate, and the microstrip circuit comprises an input feed line, an output feed line, a J converter and an improved composite resonator loaded at both ends of the J converter; One end of the J converter is connected to the input feeder, and the other end feeds the improved composite resonator; The improved composite resonators are coupled through gaps; a metal ground and a low-pass filter are provided on the bottom surface of the dielectric substrate, the low-pass filter includes an inductor, a capacitor and a coplanar waveguide circuit, and the coplanar waveguide circuit is connected to a common port on the surface of the dielectric substrate through a metal via.
2. The high isolation triplexer according to claim 1, characterized in that: The improved composite resonator is a half-wavelength resonator loaded on a J converter and open at both ends, and is composed of two open branches connected in parallel; the shape of the end of the open branch is a triangle.
3. The high isolation triplexer according to claim 2, characterized in that: When two open-circuit branches in the improved composite resonator resonate in parallel, a resonance mode is generated; at the same time, when the two open-circuit branches resonate separately, a transmission zero point is generated at the high and low frequencies of the resonance mode.
4. A high isolation triplexer according to any one of claims 1 to 3, characterized in that: The low-pass filter is a fifth-order LC low-pass filter, the inductor and capacitor components are both packaged in 0402 form, and the coplanar waveguide circuit type is a groundless coplanar waveguide circuit.
5. A high isolation triplexer according to any one of claim 3, characterized in that: The surface of the dielectric substrate is two bandpass channels, and the center frequencies are respectively f 1 = 1.8 GHz and f 2 = 2.4 GHz, each bandpass channel consists of two resonant modes; the bottom surface of the dielectric substrate is a low-pass channel with a cutoff frequency f c The frequency band is 100MHz, and the low-pass channel is composed of a fifth-order LC low-pass circuit and a coplanar waveguide line.
6. The high isolation triplexer according to claim 5, characterized in that: According to the resonant mode and transmission zero point of the improved composite resonator, combined with the transmission line equation theory, the conditions for the three channels to achieve simultaneous matching at the common port are: According to the transmission line impedance equation: ， Among them, Z o represents the characteristic impedance of the open end of open branch 2, and Z o =∞; Z2 represents the characteristic impedance of open-circuit branch 2, Z in3 represents the input impedance of the open branch 2, θ2 represents the electrical length of the open branch 2; f 1. f 2 represents the center frequency of the two bandpass channels, and f 1 < f 2; f c is the cut-off frequency of the low-pass filter; open branch 2 at f Design a transmission zero point at 2, and substitute: ， Combining the above two formulas, we can get: ， Z in2 To improve the input impedance of the composite resonator 1; the impedance transformation is continued through the J transformer 1; the electrical length θ of the J transformer 1 is set j1 satisfy: ， The improved composite resonator 1 is a device that works in f 1 bandpass filter channel, we can get: ， Z in1 is the input impedance of bandpass channel 1 at the common port; Similarly, by analyzing the impedance transformation of the improved composite resonator 2 and the J transformer 2, we can obtain: ， Z in4 is the input impedance of bandpass channel 2 at the common port; Translating the above two sets of impedance conditions, we can say that: when the operating frequency is f Channel 1 only allows signals at its frequency to pass through, and greatly hinders signals of other frequencies, such as f 2 and low frequency f c ; Similarly, the operating frequency is f Channel 2 is only allowed in f 2 frequency signals pass through, which greatly hinders signals of other frequencies, such as f 1 and low frequency f c ; Since the low-pass filter has a frequency f 1 and f 2 is the stop band, combined with the impedance condition of the low-pass filter, we get: ， Z in7 is the input impedance of the low-pass channel at the common port; From the above three sets of formulas, we can conclude that the triplexer designed in this patent has three frequency bands that can simultaneously achieve good impedance matching at the common port, and the isolation between the frequency bands is guaranteed.
7. A high isolation triplexer according to any one of claims 1 to 3, characterized in that: The dielectric substrate is a plate with a relative dielectric constant of 4.4 and a thickness of 1 mm; the overall volume of the circuit is ,λ g is the waveguide wavelength corresponding to 1.8 GHz.