CN113300070A - Broadband high-power directional coupler covering VLF-VHF frequency band and implementation method thereof - Google Patents
Broadband high-power directional coupler covering VLF-VHF frequency band and implementation method thereof Download PDFInfo
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- CN113300070A CN113300070A CN202110546899.7A CN202110546899A CN113300070A CN 113300070 A CN113300070 A CN 113300070A CN 202110546899 A CN202110546899 A CN 202110546899A CN 113300070 A CN113300070 A CN 113300070A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P5/00—Coupling devices of the waveguide type
- H01P5/12—Coupling devices having more than two ports
- H01P5/16—Conjugate devices, i.e. devices having at least one port decoupled from one other port
- H01P5/18—Conjugate devices, i.e. devices having at least one port decoupled from one other port consisting of two coupled guides, e.g. directional couplers
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Abstract
The invention discloses a broadband high-power directional coupler covering a VLF-VHF frequency band, which mainly solves the problems of increased loss and limited power capacity of the existing directional coupler during low-frequency covering. The directional coupler comprises a first coaxial transmission line with a ferrite core, two sampling comparison circuits which are connected to two ends of the first coaxial transmission line and have circuit structures which are symmetrical relative to the middle of the first coaxial transmission line, and a main power channel and a coupling power output channel which are connected with the sampling comparison circuits. Through the design, the invention adopts the mixed circuit consisting of the coaxial transmission line and the lumped parameter resistor capacitor, and utilizes the opposite characteristics of the current of the inner conductor and the outer conductor of the coaxial transmission line to carry out the topology design of the corresponding sampling comparison circuit, compensate and reduce the parasitic parameters of the resistor, so that the directional coupling circuit can be conveniently accessed into a radio frequency microwave communication and test system to play the roles of monitoring and protecting.
Description
Technical Field
The invention relates to a directional coupler, in particular to a broadband high-power directional coupler covering a VLF-VHF frequency band and an implementation method thereof.
Background
The broadband high-power directional coupler is an important component of radio frequency microwave communication, testing and other systems, is mainly used for measuring the forward power and the reverse power passing through the system, and is usually connected behind a high-power transmitter and in front of a radiation antenna and tested equipment. By reading the signals in the positive direction and the negative direction, the information such as the size of the actual transmission signal, the size of the reflected power, the system load condition, the impedance matching state of the transmitter and the antenna, the system electric connection condition and the like in the system can be obtained. The real-time monitoring and control and the safe operation of the system are important.
Directional couplers fall into two broad categories, lumped and distributed. A typical circuit is shown in figure 1.
The most important way to obtain broadband characteristics at present is to cascade the sections of quarter wavelength in multiple stages, and obtain the coupling coefficients of multiple stages and the corresponding characteristic impedance by using an odd-even mode analysis method during design. This approach is suitable in the rf-microwave range, because of its short physical length, e.g. 1GHz-2GHz, 2GHz-6GHz, quarter wave in the order of centimetres, and the limitation of this approach is that the volume becomes less realistic when the low end of the operating frequency falls below 100MHz, e.g. the quarter wave at 30MHz is 7.5 metres. Thus, two solutions have been proposed, one of which is to fold the circuit using a multilayer printed board; the other is to give up a quarter wavelength and adopt an eighth or shorter electrical length for comprehensive design, both of which have their limitations, such as increased loss, limited power capacity, increased thickness of the whole circuit, etc. of the folded circuit method, uneven coupling curve, poor coupling directivity, need of a large number of complex peripheral compensation circuits, repeated design iteration work, etc. By the two methods, the directional coupler working at 1MHz-100MHz and 30MHz-1GHz can be developed, and the passing power can reach 1 kW. However, both of these approaches are difficult to satisfy as the low end of the frequency continues to fall to kHz and the power continues to rise.
Disclosure of Invention
The invention aims to provide a broadband high-power directional coupler covering a VLF-VHF frequency band and an implementation method thereof, and mainly solves the problems that the loss is increased and the power capacity is limited when the existing directional coupler covers low frequency.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a broadband high-power directional coupler covering a VLF-VHF frequency band comprises a first coaxial transmission line with a ferrite core, two sampling comparison circuits, a main power channel and a coupling power output channel, wherein the two sampling comparison circuits are connected to two ends of the first coaxial transmission line, and the circuit structures of the two sampling comparison circuits are symmetrical relative to the middle of the first coaxial transmission line; the sampling comparison circuit comprises a second coaxial transmission line, a sampling resistor R3, a compensation capacitor C2, a resistor R2, a sampling resistor R1 and a resistor R4, wherein the inner conductor of the second coaxial transmission line is connected with the inner conductor of the first coaxial transmission line, the sampling resistor R3 is connected between the outer conductors of the first coaxial transmission line and the second coaxial transmission line, the compensation capacitor C2 is connected in parallel with two ends of a sampling resistor R3, the resistor R2 is connected with the common end of the outer conductor of the sampling resistor R3, the compensation capacitor C2 and the first coaxial transmission line, the sampling resistor R1 and the resistor R4 are connected with the other end of the resistor R2, and the compensation capacitor C1 is connected in parallel with two ends of the sampling resistor R1; the other free end of the sampling resistor R1 is connected with the other end of the inner conductor of the second coaxial transmission line, the other end of the outer conductor of the second coaxial transmission line is grounded, the main power channel is connected with the common end of the sampling resistor R1 and the inner conductor of the second coaxial transmission line, and the coupling power output channel is connected with the other free end of the resistor R4.
Furthermore, the main power channels in the two sampling comparison circuits are respectively a main power input channel and a main power output channel, and the corresponding coupled power output channels in the sampling comparison circuits are respectively a forward coupled power output channel and a reverse coupled power output channel.
Based on the directional coupler, the invention also provides a method for realizing the broadband high-power directional coupler covering the VLF-VHF frequency band, which comprises the following steps:
(S1) determining two of the sampling comparison circuits as a forward sampling comparison circuit and a reverse sampling comparison circuit according to a main power input channel selected by a main power input;
(S2) sampling voltages from the inner and outer conductors of the respective coaxial transmission lines by the sampling resistors in the forward sampling comparator circuit and the reverse sampling comparator circuit, respectively;
(S3) the signals of the addition and subtraction are obtained in the two coupled power output channels by using the inherent characteristic that the current directions of the inner and outer conductors of the coaxial transmission line are opposite, and the detected values of the forward coupled power and the reverse coupled power are obtained.
Further, the calculation formula of the voltage and the current on the coaxial transmission line with any length l is as follows:
wherein Z is0γ is the characteristic impedance of the coaxial line and the transmission characteristic of the coaxial transmission line.
Furthermore, the voltage obtained by monitoring the port of the forward coupling power output channel is in direct proportion to the sum of the voltages of the sampling resistors in the forward sampling comparison circuit; the voltage monitored by the port of the reverse coupling power output channel is in direct proportion to the voltage difference of the sampling resistor in the reverse sampling comparison circuit.
Compared with the prior art, the invention has the following beneficial effects:
the invention adopts a hybrid circuit consisting of a coaxial transmission line and a total parameter resistor capacitor, utilizes the current opposite characteristics of inner and outer conductors of the coaxial transmission line to carry out the topological design of a corresponding sampling comparison circuit, compensates and reduces the parasitic parameters of the resistor, so that the typical frequency of the coupler is 9 kHz-250 MHz, the passing power is more than 3kW, the loss is less than or equal to 0.2dB, the coupling flatness is +/-0.5 dB, and the directivity is more than or equal to 20 dB. The characteristic impedance in the whole frequency band is 50 omega, the existing radio frequency system can be conveniently accessed, and the transmission power exceeding 3kW can be monitored. And the directional coupler is composed of a coaxial transmission line and a forward and reverse sampling circuit. The forward and reverse sampling circuits are completely the same in structure, but the signal flow directions in the circuits are different, and coupled signals with different forward and reverse directions are output by utilizing the addition and subtraction of the signals. Vice versa, if the input and output signals are reversed, the opposite forward and reverse coupling type output can be obtained.
Drawings
Fig. 1 is a schematic diagram of a typical circuit of a prior art directional coupler.
Fig. 2 is a schematic structural diagram of the present invention.
Fig. 3 is a schematic diagram of the voltage and current transmission structure of the coaxial transmission line of the present invention.
Fig. 4 is a diagram of forward power coupling for the P3 port in the directional coupler.
Fig. 5 is a reverse power coupling diagram of the P4 port in the directional coupler.
FIG. 6 is a diagram showing simulation results of the 9 kHz-250 MHz directional coupler.
Detailed Description
The present invention will be further described with reference to the following description and examples, which include but are not limited to the following examples.
Examples
As shown in FIG. 2, the broadband high-power directional coupler covering the VLF-VHF frequency band disclosed by the invention comprises a first coaxial transmission line b with a ferrite core C, and two sampling comparison circuits which are connected to two ends of the first coaxial transmission line and have symmetrical circuit structures relative to the middle part of the first coaxial transmission line, wherein the two sampling circuits have the same structure, only the signal flow directions in the circuits are different, and the signals are added and subtracted to obtain coupled signals with different forward and reverse directions for output. Vice versa, if the input and output signals are reversed, the opposite forward and reverse coupling type output can be obtained.
The sampling comparison circuit comprises a second coaxial transmission line, a sampling resistor R3, a compensation capacitor C2, a resistor R2, a sampling resistor R1, a resistor R4 and a compensation capacitor C1, wherein the inner conductor of the second coaxial transmission line is connected with the inner conductor of the first coaxial transmission line; the other free end of the sampling resistor R1 is connected with the other end of the inner conductor of the second coaxial transmission line, the other end of the outer conductor of the second coaxial transmission line is grounded, the main power channel is connected with the common end of the sampling resistor R1 and the inner conductor of the second coaxial transmission line, and the coupling power output channel is connected with the other free end of the resistor R4. In fig. 2, P1 and P2 are main power channels, and P3 and P4 are forward and reverse coupled power outputs. If P1 is the power input, then P2 is the power output at this time, P3 is the forward power coupling port, P4 is the reverse power coupling port; if P2 is the power input, then P1 is the power output, P4 is the forward power coupling port, and P3 is the reverse power coupling port.
The basic principle of the circuit utilizes the characteristic that the currents of the inner conductor and the outer conductor of the coaxial transmission line are equal in magnitude and opposite in direction, as shown in 0.
The voltage in the coaxial transmission line is for the voltage difference between two conductors, the current flows in the two conductors respectively, and the formula of the voltage and the current on the coaxial line with any length l is shown as follows.
Wherein Z0Is the characteristic impedance of the coaxial line and gamma is the transmission characteristic of the coaxial line. Therefore, when the size of the coaxial line is determined, the voltage and current of each point on the line can be calculated. If the voltage to ground at any point on the inner conductor is
The current is I (l), the voltage to ground on the outer conductor is
The current is-I (l).
The sampling resistors R1, R3, R5 and R7 respectively perform voltage sampling on the inner conductor and the outer conductor of the input end and the output end, and the added and subtracted signals are obtained at ports P3 and P4 by utilizing the inherent characteristics of the coaxial inner conductor and the coaxial outer conductor that the current directions are opposite, so that the detection values of the forward power and the reverse power are obtained.
Shown in fig. 4 as part a of the directional coupler. When signals are input from the P1 port, the power transmission direction on the coaxial wire core is rightward, the current directions on R1 and R2 can be obtained through circuit analysis, and the voltage obtained by monitoring the P3 port and U are shown in the figure at the momentR1+UR2In direct proportion, the higher the input power of the P1 port, the higher the detection voltage.
Shown in fig. 5 as part B of the directional coupler. At the same time as that in FIG. 4, the power transmission direction on the coaxial cable core is rightward, and the current directions on R6 and R7 can be obtained through circuit analysis, and at this time, the voltage obtained by monitoring the P4 port and U are shown in the figureR7-UR6Proportional, and the greater the P1 port input power, the greater the detection voltage.
The voltage at the P3 port is much larger than that at the P4 port and is proportional to the input power at the P1 port by adjusting the resistance in the circuit, so that the P3 can indicate the forward coupling signal, whereas if the signal is input from the P2, which can be regarded as the reflected signal, the P4 port monitors the voltage and the UR7+UR6And proportional to the reflected signal. The difference between P3 and P4 indicates directionality.
In this embodiment, the resistance values of the sampling resistors R1 and R7 are higher according to the coupling ratio, and the requirements on power and voltage tolerance are also higher. The sampling resistors R3 and R5 have small resistance values, but pass large power and require small parasitic parameters.
The compensation capacitors C1, C2, C3 and C4 in the figure are for compensating parasitic inductance and parasitic capacitance of the resistor itself. Because the time constant difference of each RC circuit in the directional coupler is large, sampling signals cannot be aligned accurately in certain frequency bands, and the added and subtracted values have difference, so that the accuracy and the direction of the coupling value are affected. Because parasitic parameters of different resistors have larger difference and the same resistor can be distinguished due to discreteness, a capacitor is required to be added to make up and adjust the time constant of the forward and reverse sampling circuit, so that forward and reverse signals are superposed at correct time and are completely offset or strengthened, and higher directivity can be obtained. The forward and reverse signals are matched and accurately offset, and the coupling and directivity characteristics are improved. The time constant of the RC circuit is:
τ＝RC；
wherein, τ represents the time required for the voltage across the capacitor to rise to a maximum value of 0.63 times, and R and C are the resistance and the capacitance in the RC circuit, respectively.
For example, the sampling resistor R1 has a large resistance value, and a large parasitic capacitance is introduced; and the resistance of the sampling resistor R3 is smaller, and the parasitic capacitance is also smaller. Their time constant τ will be different by up to 105A rank. It is therefore necessary to adjust the time constants of the two circuits to reduce the difference.
Therefore, the capacitors C1, C2, C3 and C4 are added to adjust and compensate parasitic capacitances of R1, R3, R5 and R7, respectively, so that time constants of the RC circuits do not affect the coupling accuracy and the directivity.
As can be seen from the simulation results in FIG. 6, the loss of the directional coupler is less than or equal to 0.2dB, the coupling flatness is less than or equal to +/-0.5 dB, and the directivity is greater than or equal to 20 dB. The selected coaxial cable and the divider resistor meet the high-power working requirement of 3 kW. And when the power is required to be higher or the device works in a high-temperature environment, a radiator and a forced air cooling device can be additionally arranged in the device in practical use.
Through the design, the invention adopts the hybrid circuit consisting of the coaxial transmission line and the lumped parameter resistor capacitor, utilizes the current opposite characteristics of the inner conductor and the outer conductor of the coaxial transmission line to carry out the corresponding topological design of the sampling comparison circuit, compensates and reduces the parasitic parameters of the resistor, so that the directional coupling circuit can simultaneously work in a frequency band of 9 kHz-100 MHz, the passing power is more than 3kW, the loss is less than or equal to 0.2dB, the coupling flatness is +/-0.5 dB, and the directivity is more than or equal to 20 dB. Each port is matched with a 50 omega system, and can be conveniently accessed into a radio frequency microwave communication and test system to play a role in monitoring and protection. Therefore, the method has constant and high use value and popularization value.
The above-mentioned embodiment is only one of the preferred embodiments of the present invention, and should not be used to limit the protection scope of the present invention, but all the insubstantial changes or modifications made within the spirit and scope of the main design of the present invention, which still solve the technical problems consistent with the present invention, should be included in the protection scope of the present invention.
Claims (5)
1. A broadband high-power directional coupler covering a VLF-VHF frequency band is characterized by comprising a first coaxial transmission line with a ferrite core, two sampling comparison circuits, a main power channel and a coupling power output channel, wherein the two sampling comparison circuits are connected to two ends of the first coaxial transmission line, and the circuit structures of the two sampling comparison circuits are symmetrical relative to the middle of the first coaxial transmission line; the sampling comparison circuit comprises a second coaxial transmission line, a sampling resistor R3, a compensation capacitor C2, a resistor R2, a sampling resistor R3, a compensation capacitor C2, a resistor R1 and a resistor R4, wherein the inner conductor of the second coaxial transmission line is connected with the inner conductor of the first coaxial transmission line, the sampling resistor R3 is connected between the outer conductors of the first coaxial transmission line and the second coaxial transmission line, the compensation capacitor C2 is connected in parallel with two ends of the sampling resistor R3, the resistor R2 is connected with the common end of the outer conductor of the first coaxial transmission line, the sampling resistor R1 and the resistor R4 are connected with the other end of the resistor R2, and the compensation capacitor C1 is connected in parallel with two ends of the sampling resistor R1; the other free end of the sampling resistor R1 is connected with the other end of the inner conductor of the second coaxial transmission line, the other end of the outer conductor of the second coaxial transmission line is grounded, the main power channel is connected with the common end of the sampling resistor R1 and the inner conductor of the second coaxial transmission line, and the coupling power output channel is connected with the other free end of the resistor R4.
2. The wideband high-power directional coupler covering the VLF-VHF band as claimed in claim 1, wherein the main power channels of the two sampling and comparing circuits are the main power input channel and the main power output channel, respectively, and the corresponding coupled power output channels of the sampling and comparing circuits are the forward coupled power output channel and the reverse coupled power output channel, respectively.
3. The method for implementing a wideband high-power directional coupler covering the VLF-VHF band as claimed in claim 1 or 2, comprising the steps of:
(S1) determining two of the sampling comparison circuits as a forward sampling comparison circuit and a reverse sampling comparison circuit according to a main power input channel selected by a main power input;
(S2) sampling voltages from the inner and outer conductors of the respective coaxial transmission lines by the sampling resistors in the forward sampling comparator circuit and the reverse sampling comparator circuit, respectively;
(S3) the signals obtained by adding and subtracting are output in the two coupled power output channels by using the inherent characteristic that the current directions of the inner and outer conductors of the coaxial transmission line are opposite, and the detected values of the forward coupled power and the reverse coupled power are obtained.
4. The method as claimed in claim 3, wherein the calculation formula of the voltage and current on the coaxial transmission line with any length l is:
wherein Z is0γ is the characteristic impedance of the coaxial line and the transmission characteristic of the coaxial transmission line.
5. The method as claimed in claim 3, wherein the voltage monitored at the port of the forward coupling power output channel is proportional to the sum of the voltages of the sampling resistors in the forward sampling comparator circuit; the voltage obtained by monitoring the port of the reverse coupling power output channel is in direct proportion to the voltage difference of the sampling resistor in the reverse sampling comparison circuit.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115458895A (en) * | 2022-10-20 | 2022-12-09 | 成都华络通信科技有限公司 | High-power high-directivity bi-directional coupler |
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2021
- 2021-05-19 CN CN202110546899.7A patent/CN113300070A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115458895A (en) * | 2022-10-20 | 2022-12-09 | 成都华络通信科技有限公司 | High-power high-directivity bi-directional coupler |
| CN115458895B (en) * | 2022-10-20 | 2024-01-30 | 成都华络通信科技有限公司 | High-power high-directionality double directional coupler |
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