A high power radio frequency filter

Abstract

The present invention proposes a high-power radio frequency filter, which includes an input port, a first series resonance unit, a second parallel resonance unit, a third series resonance unit, a fourth parallel resonance unit, a fifth series resonance unit, a sixth parallel resonance unit, a seventh series resonance unit, an eighth parallel resonance unit and an output port in sequence along the transmission direction of the radio frequency input signal. The present invention defines the insertion loss of the high-power bandpass filter, the suppression index at 4.5MHz and 27.095MHz outside the band, and the simulation and implementation method of the high-power filter, adopts an anti-high-power design, and the bandwidth is defined as including 11.05MHz to 16.05MHz. For 27.09MHz, the suppression is greater than 50dB, and for 6MHz, the suppression is greater than 40dB. The high-power bandpass filter of the present invention is specifically implemented by ADS modeling and simulation, and is completed by optimizing the values ​​of inductance and capacitance.

Description

Technical Field

[0001] The invention belongs to the field of electromechanics, and in particular relates to a high-power radio frequency filter. Background Art

[0002] The European Loop Line vehicles need to receive CDMA signals from trackside equipment, and at the same time, they need to ensure the normal operation of the transponder. A transponder is an electronic module that can transmit and reply information. In recent years, due to the rapid development of radio frequency technology, transponders have a new term and meaning, and are also called smart tags or labels. Smart tags are actually an innovation of radio frequency tags, consisting of adhesive labels and ultra-thin radio frequency tags. The activation signal of the transponder is 27.095MHz, and the output power of the transmitter board is 43dBm (20W). These signals are all transmitted in a coaxial cable, so a high-power radio frequency filter is needed at the radio frequency front end to filter out the 27.095MHz signal to ensure the normal reception of the 13.5MHz CDMA signal.

[0003] The invention defines the insertion loss of a high-power bandpass filter, the suppression indexes at out-of-band 4.5MHz and 27.095MHz, and the simulation and implementation methods of the high-power filter. Summary of the invention

[0004] In view of the above problems, the present invention proposes a high-power radio frequency filter, which includes an input port, a first series resonance unit, a second parallel resonance unit, a third series resonance unit, a fourth parallel resonance unit, a fifth series resonance unit, a sixth parallel resonance unit, a seventh series resonance unit, an eighth parallel resonance unit and an output port in sequence along the transmission direction of the radio frequency input signal;

[0005] The third series resonant unit is composed of three inductors and one capacitor connected in series.

[0006] Further, the first series resonant unit includes a first capacitor and a first inductor, one end of the first capacitor is connected in series with the first inductor, and the other end of the first capacitor is connected to the input port;

[0007] The second parallel resonant unit includes a second capacitor and a second inductor. One end of the second capacitor is connected to the first capacitor and the other end is grounded. Both ends of the second capacitor are connected in parallel with the second inductor.

[0008] Furthermore, the third series resonant unit includes a third inductor, a fourth inductor, a fifth inductor and a third capacitor, one end of the third inductor is connected to an end of the second capacitor away from the ground end, and the other end of the third inductor is connected in series with the fourth inductor, the fifth inductor and the third capacitor in sequence.

[0009] Further, the fourth parallel resonant unit includes a sixth inductor and a fourth capacitor, one end of the fourth capacitor is connected to an end of the third capacitor away from the second parallel resonant unit, and the other end is grounded, and both ends of the fourth capacitor are connected in parallel with the sixth inductor;

[0010] The fifth series resonant unit includes a seventh inductor and a fifth capacitor, one end of the seventh inductor is connected to an end of the fourth capacitor away from the ground end, and the other end of the seventh inductor is connected to the fifth capacitor.

[0011] Further, the sixth parallel resonant unit includes an eighth inductor and a sixth capacitor, one end of the eighth inductor is connected to the fifth capacitor, and the other end is grounded, and both ends of the eighth inductor are connected in parallel with the sixth capacitor.

[0012] Furthermore, the seventh series resonant unit includes a ninth inductor and a seventh capacitor, one end of the ninth inductor is connected to an end of the eighth inductor away from the ground end, and the other end of the ninth inductor is connected to the seventh capacitor.

[0013] Further, the eighth parallel resonant unit includes a tenth inductor and an eighth capacitor, one end of the tenth inductor is connected to the seventh capacitor, and the other end is grounded, and both ends of the tenth inductor are connected in parallel with the eighth capacitor.

[0014] Furthermore, one end of the first inductor away from the first capacitor is connected to a radio frequency connector, the radio frequency connector has five pins, one of the pins is connected to the first inductor, and the other pins are grounded.

[0015] Furthermore, the filter is a bandpass filter, and the bandpass filter adopts an eighth-order LC filter circuit.

[0016] The invention defines the insertion loss of a high-power bandpass filter, the suppression index at 4.5MHz and 27.095MHz outside the band, and the simulation and implementation method of the high-power filter. The anti-high-power design is adopted, and the bandwidth is defined as including 11.05MHz to 16.05MHz. For 27.09MHz, the suppression is greater than 50dB, and for 6MHz, the suppression is greater than 40dB. The high-power bandpass filter of the invention is specifically implemented by ADS modeling and simulation, and is completed by optimizing the values ​​of inductance and capacitance.

[0017] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A schematic diagram of a high-power filter simulation model in an embodiment of the present invention is shown;

[0020] Figure 2 A schematic diagram of the simulation results of the insertion loss of a high-power filter in the embodiment of the present invention is shown;

[0021] Figure 3 A schematic diagram of the simulation result of the standing wave at the port of a high-power filter in an embodiment of the present invention is shown;

[0022] Figure 4 The schematic diagram shows the circuit design structure and connection relationship of the high-power filter in the embodiment of the present invention;

[0023] Figure 5 A schematic diagram of the insertion loss test results of a high-power filter in an embodiment of the present invention is shown;

[0024] Figure 6 A schematic diagram of the standing wave test results of a high-power filter port in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The signal from the antenna contains not only a 13.5MHz CDMA small signal, but also a 27.095MHz activation signal, which has a large amplitude and a power of 20W. If the 27.095MHz signal is not suppressed and directly passes through the LNA (low noise amplifier), the amplifier will not be able to withstand it and the device will be damaged. At the same time, it is also necessary to consider the suppression of the 4.5MHz signal from the transponder. The high-power bandpass filter is to achieve this purpose to ensure that the subsequent amplifier can effectively amplify the signal within the working band.

[0027] The present invention can effectively suppress the high-power activation signal 27.095MHz, ensuring that the 13.5MHz CDMA signal can be received normally. The present invention is a technical invention completed based on the standard of Subset-044. The present invention defines the insertion loss of the high-power bandpass filter, the suppression indicators at 4.5MHz and 27.095MHz outside the band, and the simulation and implementation method of the high-power filter. According to the understanding of SUBSET-044 (Issue 2.4.0), the bandwidth of the bandpass filter is 4.5MHz. Considering the subsequent despreading processing, a sideband of 0.5MHz is reserved, so it is defined as 13.5475MHz±2.5MHz, that is: 11.05MHz~16.05MHz.

[0028] LC filter is a passive filter. It is a filter circuit designed by combining inductance, capacitance and resistance. It can filter out one or more harmonics. The most common and easy-to-use LC filter structure is to connect the inductor and capacitor in series, which can form a low-impedance bypass for the main harmonics (3, 5, 7); single-tuned filter, double-tuned filter, and high-pass filter are all passive filters. Bandpass filter is a device that allows waves of a specific frequency band to pass while shielding other frequency bands. LC circuit generally refers to resonant circuit. For a passive one-port network containing capacitors, inductors and resistors, its port may be capacitive, inductive and resistive. When the voltage U and current I at the circuit port are in phase, the circuit is resistive. It is called resonance phenomenon, and such a circuit is called a resonant circuit.

[0029] The present invention refers to using a high-power radio frequency filter at the radio frequency front end to filter out 27.095MHz signals to ensure normal reception of 13.5MHz CDMA signals.

[0030] The main index definition of high-power bandpass filter is calculated based on the requirements of Subset-044 standard and the link of the on-board equipment of the actual antenna transponder transmission system. The minimum requirements are as follows:

[0031] In-band insertion loss:

[0032] In-band insertion loss refers to the signal attenuation within the operating frequency when the input broadband signal passes through a low-power bandpass filter. Within the signal passband (11.05MHz~16.05MHz), ≤4dB.

[0033] Out-of-band suppression:

[0034] Out-of-band suppression refers to the attenuation of the filter outside the defined passband frequency range, or the attenuation for a specific frequency band. Out-of-band suppression refers to the degree of suppression of signals outside the passband, and is the attenuation of the signal at a specified frequency point after passing through the bandpass filter. For 27.095MHz, the maximum possible suppression is required. According to the RF board link budget, it needs to be ≥50dB, and for 6MHz, it needs to be ≥40dB.

[0035] Port standing wave:

[0036] Port standing wave refers to the return loss within the working band of 11.05MHz to 16.05MHz (the return loss RL (Return Loss) refers to the ratio of the power reflected back from the RF input signal to the input signal power, the smaller the return loss, the better), ≤-10dB.

[0037] Insertion loss in the passband frequency range is defined as the ratio of the filter's input power to its output power. -3dB is often used as the definition standard, which is often referred to as the so-called "3dB bandwidth". In some test and measurement applications (such as spectrum measurement), the filter's passband insertion loss is not very important, because the insertion loss generated by the filter can be corrected in the final result as part of the system error. In high-power applications, the filter's loss is very important. Even if there is only 1dB of insertion loss, the power loss will reach about 20%.

[0038] Figure 1 FIG. 1 shows a schematic diagram of a high-power filter simulation model in an embodiment of the present invention. Figure 1 In the present invention, the ADS simulation design is used to simulate the bandpass filter. In order to ensure the flatness of the amplitude-frequency characteristic in the passband, the maximum flatness (Butterworth) structure is adopted. The bandpass filter design of the present invention has a center frequency of 13.55MHz, a 1dB bandwidth of 5MHz, an operating frequency band of 11.05MHz to 16.05MHz, and three design frequency suppression points, one is 27.095MHz, one is 6MHz, and the other is 4.5MHz. First, an ideal model is established, and a simulation is performed to check. After obtaining preliminary results, the selected inductors and capacitors are replaced with actual models for simulation optimization. The high-power bandpass filter of the present invention adopts an eighth-order LC circuit to achieve the required performance.

[0039] Figure 1In the figure, capacitor C1 and inductor L1 are connected in series to form a first-order filter circuit. The value of capacitor C1 is 470pF, and the value of inductor L1 is 500nH. Capacitor C2 and inductor L5 are connected in parallel to form a second-order filter circuit. One end of capacitor C2 is connected to capacitor C1, and the other end is grounded. Inductor L5 is connected in parallel to both ends of capacitor C2. The value of capacitor C2 is 390pF, and the value of inductor L5 is 390nH. Inductor L2, inductor L3, inductor L4 and capacitor C 3 are connected in series to form a third-order filter circuit, one end of the inductor L2 is connected to the capacitor C2, wherein the values ​​of the inductors L2, L3, and L4 are all 500nH, and the value of the capacitor C3 is 100pF; the capacitor C4 and the inductor L6 are connected in parallel to form a fourth-order filter circuit, wherein the capacitor C4 is connected to the capacitor C3, and the inductor L6 is connected in parallel to the capacitor C4, the value of the capacitor C4 is 680pF, and the value of the inductor L6 is 220nH; the capacitors C5, Inductor L7 is connected in series to form a fifth-order filter circuit, inductor L7 is connected to one end of capacitor C4 far from the ground, and the other end of inductor L7 is connected in series with capacitor C5, the component value of capacitor C5 is 91pF, and the component value of inductor L7 is 1.8μH; capacitor C6 and inductor L8 are connected in parallel to form a sixth-order filter circuit, wherein inductor L8 is connected to capacitor C5, capacitor C6 is connected in parallel to inductor L8, the component value of capacitor C6 is 560pF, and the component value of inductor L8 is 270nH; capacitor C7 and inductor L9 are connected in series to form a seventh-order filter circuit, inductor L9 is connected to inductor L8, inductor L9 is connected to capacitor C7, the component value of capacitor C7 is 160pF, and the component value of inductor L9 is 1.0μH; capacitor C8 and inductor L10 are connected in parallel to form an eighth-order filter circuit, wherein inductor L10 is connected to capacitor C7, capacitor C8 is connected in parallel to inductor L10, the component value of capacitor C8 is 130pF, and the component value of inductor L10 is 1.2μH.

[0040] Figure 2 FIG. 1 is a schematic diagram showing the simulation results of the insertion loss of the high-power filter in the embodiment of the present invention. Figure 3 The schematic diagram of the simulation result of the high-power filter port standing wave in the embodiment of the present invention is shown. From the simulation results, it can be seen that within the working band, the insertion loss at 11.05MHz to 16.05MHz is the largest: -3.715dB, outside the working band, the suppression at 27.09MHz is -62.012dB, the suppression at 6MHz is -52.547dB, and the suppression at 4.5MHz is -74.908dB. The worst point of the port standing wave within the working band is -11.598dB. Therefore, the simulation data can meet the design definition requirements.

[0041] Specifically, point m1 indicates suppression of -3.715dB at 11.05MHz, point m2 indicates suppression of -3.481dB at 16.05MHz, point m3 indicates suppression of -62.012dB at 27.09MHz, point m4 indicates suppression of -52.547dB at 6MHz, point m6 indicates suppression of -74.908dB at 4.5MHz, and point m5 indicates port standing wave suppression of -11.598dB at 13.23MHz.

[0042] Figure 4 The figure shows the circuit design structure and connection relationship diagram of the high-power filter in the embodiment of the present invention. Figure 4 In the embodiment, the filter is a bandpass filter, which adopts an eighth-order LC filter circuit. The filter includes an input port, a first series resonance unit, a second parallel resonance unit, a third series resonance unit, a fourth parallel resonance unit, a fifth series resonance unit, a sixth parallel resonance unit, a seventh series resonance unit, an eighth parallel resonance unit and an output port in sequence along the transmission direction of the RF input signal. The third series resonance unit is three inductors and one capacitor in series.

[0043] The first series resonant unit includes a first capacitor C101 and a first inductor L101, one end of the first capacitor C101 is connected in series with the first inductor L101, the other end of the first capacitor C101 is connected to the input port, the first capacitor C101 component value is 470pF, and the first inductor L101 component value is 500nH; the second parallel resonant unit includes a second capacitor C102 and a second inductor L102, one end of the second capacitor C102 is connected to the first capacitor C101, and the other end is grounded, the second inductor L102 is connected in parallel at both ends of the second capacitor C102, the second capacitor C102 component value is 390pF, and the second inductor L102 component value is 390nH; the third series resonant unit includes a third inductor L103, a fourth inductor L104, and a fifth inductor L105. 04, a fifth inductor L105 and a third capacitor C103, one end of the third inductor L103 is connected to an end of the second capacitor C102 away from the ground end, and the other end of the third inductor L103 is connected in series with the fourth inductor L104, the fifth inductor L105 and the third capacitor C103 in sequence, the third inductor L103, the fourth inductor L104, and the fifth inductor L105 are all 500nH, and the third capacitor C103 is 100pF; the fourth parallel resonant unit includes a sixth inductor L106 and a fourth capacitor C104, one end of the fourth capacitor C104 is connected to an end of the third capacitor C103 away from the second filtering unit, and the other end is grounded, the sixth inductor L106 is connected in parallel at both ends of the fourth capacitor C104, and the fourth capacitor C10 4 component value is 680pF, and the component value of the sixth inductor L106 is 220nH; the fifth series resonant unit includes the seventh inductor L107 and the fifth capacitor C105, one end of the seventh inductor L107 is connected to the end of the fourth capacitor C104 far away from the ground end, and the other end of the seventh inductor L107 is connected to the fifth capacitor C105, the component value of the fifth capacitor C105 is 91pF, and the component value of the seventh inductor L107 is 1.8μH; the sixth parallel resonant unit includes the eighth inductor L108 and the sixth capacitor C106, one end of the eighth inductor L108 is connected to the fifth capacitor C105, and the other end is grounded, the sixth capacitor C106 is connected in parallel at both ends of the eighth inductor L108, the component value of the sixth capacitor C106 is 560pF, and the eighth inductor The component value of L108 is 270nH; the seventh series resonant unit includes a ninth inductor L109 and a seventh capacitor C107, one end of the ninth inductor L109 is connected to an end of the eighth inductor L108 far from the ground end, and the other end of the ninth inductor L109 is connected to the seventh capacitor C107, the component value of the seventh capacitor C107 is 160pF, and the component value of the ninth inductor L109 is 1.0μH; the eighth parallel resonant unit includes a tenth inductor L110 and an eighth capacitor C108, one end of the tenth inductor L110 is connected to the seventh capacitor C107, and the other end is grounded, the eighth capacitor C108 is connected in parallel at both ends of the tenth inductor L110, the component value of the eighth capacitor C108 is 130pF, and the component value of the tenth inductor L110 is 1.2μH.

[0044] Specifically, the high-power design: the circuit contains a signal with a frequency of 27.095MHz and a power of 20W (+43dBm), so the filter and the front end of the circuit need to be able to withstand a 20W signal. The circuit is designed according to a 50-ohm matching, the voltage on the capacitor is at least 36V, and the current through the inductor is at least 0.71A. Considering the reliability of the capacitor and inductor, sufficient derating design is required. The withstand voltage of the first three capacitors of the circuit, 390pF, 470pF and 100pF, is 600V, 600V and 500V, and the current of the first three inductors, 500nH, 390nH and 500nH, is: 4.3A, 4.4A and 4.3A.

[0045] Specifically, one end of the first inductor L101 away from the first capacitor C101 is connected to a radio frequency connector J1, and the radio frequency connector J1 has five pins, one of which is connected to the first inductor L101, and the other pins are grounded. The connector J1 is used for testing, and the four pins are grounded to reflect the signal index of the test circuit, which is convenient for testing signals.

[0046] The differences between the high-power bandpass filter and the existing filter are: 1) the LC structure is different, the number and value of inductors and capacitors are different, 2) the definition of the passband (working frequency band) is different, and 3) the definition of the suppression frequency and the suppression amount are different.

[0047] Specifically, in actual circuit design, the eighth filter unit is connected to the signal output terminal with a test point connector J2, which has five pins, one of which is connected to the tenth inductor L110, and the remaining pins are grounded. J101 is the signal input connector, which uses MCX, and J102 is the test point connector. The signal is input from J101 and tested from J102, which are connected to port 1 and port 2 of the network analyzer respectively. If a high-power signal test is connected, it is necessary to add at least 30dB attenuator at J102 to test whether there is a high-power signal leakage, and then test after confirming that there is no leakage to prevent damage to the instrument.

[0048] Figure 5 The figure shows the results of the insertion loss test of the high-power filter in the embodiment of the present invention. Figure 6A schematic diagram of the standing wave test results of the high-power filter port in an embodiment of the present invention is shown. The test results show that: within the passband, the insertion loss at 11.05MHz to 16.05MHz is the largest: -2.7724dB, which is better than the simulation result of -3.715dB. The suppression at 27.09MHz is -65.13dB, which is better than the simulation result of -62.012dB. The suppression at 4.5MHz is: -89.14dB, which is better than the simulation result of -74.908dB. The port echo between 11.05MHz and 16.05MHz is better than -10dB, reaching the simulation result. All the above test indicators are better than the defined requirements. This design has met and can be applied in actual engineering.

[0049] The invention defines the insertion loss of a high-power bandpass filter, the suppression index at 4.5MHz and 27.095MHz outside the band, and the simulation and implementation method of the high-power filter. The anti-high-power design is adopted, and the bandwidth is defined as including 11.05MHz to 16.05MHz. For 27.09MHz, the suppression is greater than 50dB, and for 6MHz, the suppression is greater than 40dB. The high-power bandpass filter of the invention is specifically implemented by ADS modeling and simulation, and is completed by optimizing the values ​​of inductance and capacitance.

[0050] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-power radio frequency filter, characterized in that: The filter includes an input port, a first series resonance unit, a second parallel resonance unit, a third series resonance unit, a fourth parallel resonance unit, a fifth series resonance unit, a sixth parallel resonance unit, a seventh series resonance unit, an eighth parallel resonance unit and an output port in sequence along the transmission direction of the RF input signal; Wherein, the third series resonant unit is three inductors and one capacitor connected in series; The third series resonant unit includes a third inductor, a fourth inductor, a fifth inductor and a third capacitor, one end of the third inductor is connected to an end of the second capacitor away from the ground end, the other end of the third inductor is sequentially connected in series with the fourth inductor, the fifth inductor and the third capacitor, and the component values ​​of the third inductor, the fourth inductor and the fifth inductor are all 500nH; The eighth parallel resonant unit comprises a tenth inductor and an eighth capacitor, one end of the tenth inductor is connected to the seventh capacitor, the other end is grounded, and both ends of the tenth inductor are connected in parallel with the eighth capacitor; The first series resonant unit includes a first capacitor and a first inductor, one end of the first capacitor is connected in series with the first inductor, and the other end of the first capacitor is connected to the second parallel resonant unit; One end of the first inductor away from the first capacitor is connected to a radio frequency connector, the radio frequency connector has five pins, one of the pins is connected to the first inductor, and the other pins are grounded; The filter is a bandpass filter, and the bandpass filter adopts an eighth-order LC filter circuit; The filter is provided with three frequency suppression points.

2. The high-power radio frequency filter according to claim 1, characterized in that: The second parallel resonant unit includes a second capacitor and a second inductor. One end of the second capacitor is connected to the first capacitor and the other end is grounded. Both ends of the second capacitor are connected in parallel with the second inductor.

3. The high-power radio frequency filter according to claim 2, characterized in that: The fourth parallel resonant unit comprises a sixth inductor and a fourth capacitor, one end of the fourth capacitor is connected to an end of the third capacitor away from the second parallel resonant unit, and the other end is grounded, and both ends of the fourth capacitor are connected in parallel with the sixth inductor; The fifth series resonant unit includes a seventh inductor and a fifth capacitor, one end of the seventh inductor is connected to an end of the fourth capacitor away from the ground end, and the other end of the seventh inductor is connected to the fifth capacitor.

4. The high-power radio frequency filter according to claim 3, characterized in that: The sixth parallel resonant unit includes an eighth inductor and a sixth capacitor. One end of the eighth inductor is connected to the fifth capacitor, and the other end is grounded. Both ends of the eighth inductor are connected in parallel with the sixth capacitor.

5. The high-power radio frequency filter according to claim 4, characterized in that: The seventh series resonant unit includes a ninth inductor and a seventh capacitor, one end of the ninth inductor is connected to an end of the eighth inductor away from the ground end, and the other end of the ninth inductor is connected to the seventh capacitor.

Images