CN114597619B - Broadband isolator based on negative group delay network - Google Patents

Abstract

The present invention discloses a broadband isolator based on a negative group delay network, including a non-reciprocal phase shifter, a directional coupler, a negative group delay circuit structure and two transmission lines. The negative group delay circuit structure consists of six microstrip lines, two coupled lines and four resistors. When forward-conducting, the coupler only couples a small amount of energy to the upper loop, so the interaction between the incident wave and the active device can be ignored, and the isolator has low loss and high linearity. The present invention connects a negative group delay network in series in the path to offset the group delay of other circuits in the path, so that the total group delay of the loop is zero in a wider frequency band near the center frequency, so as to broaden the isolation bandwidth of the isolator.

Description

Broadband isolator based on negative group delay network

Technical Field

The invention belongs to the field of non-reciprocal devices and relates to a broadband isolator based on a negative group delay network, which can be applied to modern microwave and optical fields such as communications, radars and sensor networks.

Background technique

With the advent of the 5G communication era, the components of the communication system will further develop in the direction of miniaturization and low power consumption, so higher integration of devices is required. Therefore, people have become more and more interested in the research of non-magnetic non-reciprocal devices such as isolators and circulators. This type of non-reciprocal device plays a vital role in modern microwave and optical applications including communications, radar and sensor networks. They can double the network capacity of the physical layer, while providing many other advantages at the network layer including communications, radar and sensor networks. For example, these devices can protect active sources from damage by circuit reflected power and enable in-band full-duplex communication to work normally, while playing the role of decoupling and isolation.

The application of isolators solves a series of practical problems in radar systems, such as inter-stage isolation, impedance, and sharing, greatly improves the performance of radar systems, and is a key component in the system. Therefore, isolators are required to have the characteristics of low insertion loss, high isolation, wide operating frequency band, high power resistance, and good temperature characteristics.

There are usually many ways to realize non-reciprocal devices. Traditional isolators usually use ferrite materials with external magnetic field bias to realize their non-reciprocal transmission characteristics. However, since the preparation process of ferrite materials is difficult to be compatible with traditional integrated circuit processes, non-reciprocal devices usually appear in communication systems as discrete components, which to a certain extent limits the overall miniaturization of the system. Therefore, it is necessary to study the non-magnetized design of non-reciprocal devices. Compared with traditional ferrite isolators and circulators, active non-reciprocal devices have a more compact structure, smaller size, lower cost, and are more compatible with modern integrated circuit technology. However, active isolators implemented using transistors have problems such as small power carrying capacity and small dynamic range.

Reference 1 (Wang Y, Chen W, Chen X. Highly Linear and Magnetless Isolator Based on Weakly Coupled Nonreciprocal Metamaterials [J]. IEEE Transactions on Microwave Theory and Techniques, 2019, 67 (11): 4322-4331.) uses a non-reciprocal phase shifter loaded with a directional coupler to realize an active isolator. When forward-conducting, the coupler only couples a small amount of energy to the upper loop, so the interaction between the incident wave and the active device can be ignored, and the isolator exhibits high power capacity and high linearity. However, the isolator has an extremely narrow bandwidth, with a center frequency designed at 1.81 GHz. A single isolator has only one frequency point with an isolation of 10.3 dB. After three-stage cascading, the 20 dB bandwidth is still only 13 MHz, and the relative bandwidth is only 0.7%.

Summary of the invention

In order to solve the above technical defects in the prior art, the present invention proposes a broadband isolator based on a negative group delay network.

The technical solution for achieving the purpose of the present invention is: a broadband isolator based on a negative group delay network, comprising a non-reciprocal phase shifter, a transmission line 1, a coupled directional coupler, a transmission line 2 and a negative group delay circuit structure connected in series in sequence, wherein the isolation end of the coupled directional coupler is connected to the transmission line 1, and the coupling end is connected to the transmission line 2.

Preferably, the non-reciprocal phase shifter comprises a transistor BJT, a radio frequency choke C ₁ , a radio frequency choke C ₂ , a radio frequency choke L ₁ , a radio frequency choke _VB , a radio frequency choke _Vce , a large resistor _R5 and four resistors _R1 , _R2 , _R3 and _R4 . One end of resistor _R1 is connected to one end of capacitor _C1 and one end of resistor _R2 , and the other end is grounded; the other end of resistor _R2 is connected to the input end; one end of resistor _R3 is connected to one end of capacitor _C2 and one end of _R4 , and the other end is grounded; the other end of resistor _R4 is connected to the output end; one end of resistor _R5 is connected to the base of transistor BJT and the other end of capacitor _C1 , and the other end is connected to a DC power supply _VB ; the other end of capacitor _C2 is connected to one end of inductor _L1 and the collector of transistor BJT; the other end of inductor _L1 is connected to a DC voltage _Vce ; the emitter collector of transistor BJT is grounded.

Preferably, the directional coupler is realized by a structure in which four sections of microstrip lines _TA1 , _TB1 , _TA2 , _TB2 are connected in sequence, wherein the impedances of the microstrip lines _TA1 and _TA2 are the same, and the impedances of the microstrip lines _TB1 and _TB2 are the same.

Preferably, the required coupling degree and isolation degree of the directional coupler are obtained by adjusting the characteristic impedance of the microstrip line.

Preferably, the negative group delay circuit structure includes six sections of microstrip lines _T1 , _T2 , _T3 , _T4 , _T5 , and _T6 , two sections of coupling lines _CL1 and _CL2 , and four series resistors _RA , _RB , _Ra , and _Rb . One end of the microstrip line _T1 is connected to one end of the microstrip line _T2 and one end of the resistor _Ra , and the other end is connected to one end of the microstrip line _T6 and an input end; the other end of the microstrip line is connected to one end of the microstrip line _T3 and one end of the resistor _Ra ; the other end of the microstrip line _T3 is connected to one end of the microstrip line _T4 and one end of the resistor R _B ; the other end of the microstrip line _T4 is connected to the microstrip line _T5 and one end of the resistor R _b ; the other end of the microstrip line _T5 is connected to the other end of the microstrip line _T6 and an output end; the other end of the resistor _Ra is connected to one end of the coupling line _CL1 , and the coupling line _CL1 is connected to the resistor R The port connected to resistor R _a is used as the input end, then the isolation end and the through end of the coupler are grounded, and the coupling end is open; the other end of resistor R _b is connected to one end of coupling line CL ₂ , and the port connected to coupling line CL ₂ and resistor R _b is selected as the input end, then the isolation end and the through end of the coupler are grounded, and the coupling end is open; the other end of resistor _RA is grounded; the other end of resistor _RB is grounded.

Preferably, the electrical lengths of the microstrip lines T ₁ , T ₂ , T ₄ , T ₅ , and T ₆ are equal, the electrical length of the microstrip line T ₃ is three times that of the microstrip lines T ₁ , T ₂ , T ₄ , T ₅ , and T ₆ , and the coupled lines CL ₁ and CL ₂ have different odd and even mode impedances but have the same electrical length as the microstrip lines T ₁ , T ₂ , T ₄ , T ₅ , and T ₆ .

Preferably, the two ends of the series route formed by the transmission line 1, the non-reciprocal phase shifter and the negative group delay circuit structure, and the transmission line 2, and the two ends of the series route formed by the directional coupler connected to the transmission line 1, the non-reciprocal phase shifter and the negative group delay circuit structure, and the transmission line 2 satisfy impedance matching.

Preferably, the phase sum of a transmission path formed by the transmission line 2, the negative group delay network, the non-reciprocal phase shifter, the transmission line 1 and the directional coupler is an integer multiple of 2π.

Compared with the prior art, the present invention has the following significant advantages:

1. The directional coupler in the present invention can ensure that the wave propagates almost along the transmission line from port 2 to port 1 without interacting with the field effect tube, etc., to obtain high linearity and low loss; when propagating from port 1 to port 2, the wave resonates in the upper loop microwave resonant cavity, the energy is effectively absorbed, and the isolator exhibits high isolation performance;

2. The present invention reduces the group delay of the total phase of the loop at the center frequency by loading a negative group delay network, so that the circuit meets the requirement of zero total phase in the widest possible frequency band, thereby widening the bandwidth of the isolator;

3. The present invention adopts a structure in which four sections of microstrip lines are connected to realize a coupler structure, thereby avoiding the situation in which the coupling line cannot be processed directly because the spacing between the two lines is too narrow, and has a lower processing accuracy requirement, while improving the structural stability.

Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

Figure 1 is a schematic diagram of the isolator.

Figure 2 shows the schematic diagram of the isolator.

FIG3 is a negative group delay circuit structure of the present invention.

FIG. 4 shows the circuit structure of the coupler used in the present invention.

FIG5 is a circuit structure of a phase shifter used in the present invention.

FIG. 6 is a schematic diagram showing the overall circuit structure of the isolator implemented in the example.

FIG. 7 shows the S parameters obtained by combining the circuit structure with the layout simulation of the present invention.

Detailed ways

It is easy to understand that according to the technical solution of the present invention, without changing the essential spirit of the present invention, a person skilled in the art can imagine various embodiments of the present invention. Therefore, the following specific embodiments and drawings are only exemplary descriptions of the technical solution of the present invention, and should not be regarded as the whole of the present invention or as a limitation or limitation of the technical solution of the present invention. On the contrary, the purpose of providing these embodiments is to enable those skilled in the art to understand the present invention more thoroughly. The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the innovative concept of the present invention.

The present invention is conceived as a broadband isolator based on a negative group delay network, comprising a non-reciprocal phase shifter (1), a transmission line 1 (4), a coupled directional coupler (2), a transmission line 2 (5) and a negative group delay circuit structure (3) connected in series in sequence, wherein the isolation end of the coupled directional coupler (2) is connected to the transmission line 1 (4), and the coupling end is connected to the transmission line 2 (5).

In a further embodiment, the non-reciprocal phase shifter (1) comprises a transistor BJT, a RF choke _C1 , a RF choke _C2 , a RF choke _L1 , a RF choke _VB , a RF choke _Vce , a large resistor _R5 and four resistors _R1 , _R2 , _R3 , _R4 . One end of resistor _R1 is connected to one end of capacitor _C1 and one end of resistor _R2 , and the other end is grounded; the other end of resistor _R2 is connected to the input end; one end of resistor _R3 is connected to one end of capacitor _C2 and one end of _R4 , and the other end is grounded; the other end of resistor _R4 is connected to the output end; one end of resistor _R5 is connected to the base of transistor BJT and the other end of capacitor _C1 , and the other end is connected to a DC power supply _VB ; the other end of capacitor _C2 is connected to one end of inductor _L1 and the collector of transistor BJT; the other end of inductor _L1 is connected to a DC voltage _Vce ; the emitter collector of transistor BJT is grounded.

In a further embodiment, the directional coupler (3) is realized by a structure in which four sections of microstrip lines _TA1 , _TB1 , _TA2 , and _TB2 are connected in sequence, wherein _TA1 and _TA2 have the same impedance, and _TB1 and _TB2 have the same impedance. Due to the symmetry of the circuit structure, if the intersection point where the microstrip lines _TB1 and _TB2 are connected is selected as the output end, the intersection point of the microstrip lines _TA2 and _TB2 is the through end of the coupler, the intersection point of the microstrip lines _TA1 and _TB2 is the coupling end of the coupler, and the intersection point of the microstrip lines _TA1 and _TB1 is the isolation section of the coupler. The coupling degree and isolation degree of the required directional coupler are obtained by adjusting the characteristic impedance of the microstrip line. Such a coupler has lower requirements on processing accuracy and higher stability.

In a further embodiment, the negative group delay circuit structure (2) comprises six sections of microstrip lines _T1 , _T2 , _T3 , _T4 , _T5 , _T6 , two sections of coupled lines _CL1 , _CL2 , and four series resistors _RA , _RB , _Ra , _Rb . The electrical lengths of the microstrip lines _T1 , _T2 , _T4 , _T5 , _T6 are equal, the electrical length of the microstrip line _T4 is three times the electrical length of the first five sections of the microstrip lines, and the coupled lines _CL1 , _CL2 have different odd and even mode impedances but have the same electrical length as the first five sections of the microstrip lines. One end of the microstrip line _T1 is connected to one end of the microstrip line _T2 and one end of the resistor R _a , and the other end is connected to one end of the microstrip line _T6 and the input end; the other end of the microstrip line is connected to one end of the microstrip line _T3 and one end of the resistor R _A ; the other end of the microstrip line _T3 is connected to one end of the microstrip line _T4 and one end of the resistor R _B ; the other end of the microstrip line _T4 is connected to the microstrip line _T5 and one end of the resistor R _b ; the other end of the microstrip line _T5 is connected to the other end of the microstrip line _T6 and the output end; the other end of the resistor R _a is connected to one end of the coupling line CL ₁ , and the port connected to the coupling line CL ₁ and the resistor R _a is selected as the input end, then the isolation end and the through end of the coupler are grounded, and the coupling end is open; the other end of the resistor R _b is connected to one end of the coupling line CL ₂ , and the port connected to the coupling line CL ₂ and the resistor R _b is selected as the input end, then the isolation end and the through end of the coupler are grounded, and the coupling end is open; the other end of the resistor R _A is grounded; the resistor R The other end of _B is grounded.

The present invention adopts non-reciprocal phase shifter, directional coupler, negative group delay network circuit and two transmission lines in series to achieve. The negative group delay circuit offsets the group delay of other circuits in the path, so that the total group delay of the loop is zero in a wider frequency band near the center frequency, thereby expanding its bandwidth.

When the wave propagates from port 2 to port 1, the directional coupler only couples a small amount of signal to the upper loop containing the negative group delay network and the non-reciprocal phase shifter, thereby ensuring that the wave propagates almost along the transmission line without interacting with the field effect tube, etc., to obtain high linearity and low loss. When the wave propagates in the opposite direction, that is, from port 1 to port 2, the wave resonates in the upper loop, the energy is effectively absorbed, the negative group delay circuit and the group delay of other circuits in the path are offset, and the total group delay of the loop is zero in a wider frequency band near the center frequency. At this time, the circuit exhibits high isolation and wide isolation bandwidth.

In order to better explain the working principle of the isolator, the circuit is disassembled into two parts, as shown in Figure 2. The upper circuit contains transmission line 1, transmission line 2, non-reciprocal phase shifter and negative group delay circuit structure, which is a two-port network, and the two ports are port 5 and port 6; the lower circuit contains a directional coupler, which is a four-port network, and the four ports are port 1, port 2, port 3, and port 4. In order for the isolator to obtain a larger isolation, the loop needs to have a transmission zero point, and the transmission zero point requires that ports 5, port 6 and ports 3 and port 4 meet impedance matching, and the phase sum of the entire transmission path (from port 5 through transmission line 2, negative group delay network, non-reciprocal phase shifter, transmission line 1 to port 6, and then from port 4 to directional coupler to port 3) is an integer multiple of 2π.

The more frequency points near the center frequency at which the loop phase sum satisfies the phase sum being an integer multiple of 2π, that is, the smaller the absolute value of the slope near the zero point, the larger the isolation bandwidth of the resulting isolator.

Example 1

The present invention adopts PCB technology, as shown in FIG1, which is the schematic diagram structure of the present invention for realizing the isolator, wherein the negative group delay circuit structure is shown in FIG2, and the directional coupler circuit structure is shown in FIG3. FIG4 is the overall circuit structure of the isolator of the present invention. The present invention is designed using simulation software ADS, and the layout is drawn on the basis of considering electromagnetic interference, the pads required for the device and the actual layout, and electromagnetic simulation is performed on all microstrip lines in the present invention, and the Symbol is generated and then brought into the schematic diagram for joint simulation.

The microstrip line in the present invention adopts 4003 process, wherein the dielectric constant ε _r =3.55, and the dielectric plate thickness H=0.508 mm. The transistor is selected as BFP840FESD transistor, and the device library provided by the official website is used for simulation.

The dimensions of the microstrip lines used at both ends are as follows: the width of the microstrip line _T7 is _W7 = 0.8 mm, and the length is _L7 = 1.6 mm; the width of the microstrip line _T8 is _W8 = 0.7 mm, and the length is _L8 = 0.2 mm.

The dimensions of the microstrip lines used in the negative group delay circuit structure are as follows: the width of microstrip line _T1 is _W1 =2.05mm, and the length is _L1 =46mm; the width of microstrip line _T2 is _W2 =2.05mm, and the length is _L2 =46mm; the width of microstrip line _T3 is _W3 =1mm, and the length is _L3 =139.6mm; the width of microstrip line _T4 is _W4 =2.12mm, and the length is _L4 =44.5mm; the width of microstrip line _T5 is _W5 =2.12mm, and the length is _L5 =44.5mm; the width of microstrip line _T6 is _W6 =1.07mm, and the length is _L6 =44.5mm; the CL of the coupled line used in the negative group delay circuit structure has a width of W=1mm, a length of L=46mm, and a spacing of S=0.2mm.

The dimensions of the microstrip line used in the directional coupler are as follows: the width of the microstrip line _Ta is _Wa = 2.3 mm, and the length is _La = 46.3 mm; the width of the microstrip line _Tb is _Wb = 0.45 mm, and the length is _Lb = 43.6 mm.

The selected resistor impedances are: R ₁ = 10Ω, R ₂ = 85Ω, R ₃ = 230Ω, R ₄ = 10Ω, R ₅ = 7500Ω, R ₆ = 265Ω, R ₇ = 278Ω, R ₈ = 65Ω, R ₉ = 50Ω.

The selected capacitance values are: C ₁ = 9pF, C ₂ = 0.8pF. The selected inductance value is: L ₁ = 22nH.

The voltages loaded on the transistor are: V _b = 1V, V _ce = 2V.

As shown in Figure 5, the S parameter simulation results of the isolator designed by the present invention show that the 20dB isolation bandwidth is 43MHz (941MHZ--984MHZ), and the relative isolation bandwidth is 4.47%. At the frequencies of 950MHZ and 976MHZ, there are two isolation peaks, which are 41.464dB and 51.237dB respectively.

In summary, the broadband isolator based on the negative group delay network of the present invention has a wide isolation bandwidth, a large power carrying capacity, a simple and easy-to-process structure, and is easy to realize circuit integration and system packaging.

The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

It should be understood that in order to simplify the present invention and help those skilled in the art understand the various aspects of the present invention, in the above description of the exemplary embodiments of the present invention, the various features of the present invention are sometimes described in a single embodiment or described with reference to a single figure. However, the present invention should not be interpreted as the features included in the exemplary embodiments are all necessary technical features of the patent claims.

It should be understood that the modules, units, components, etc. included in the device of an embodiment of the present invention can be adaptively changed to be arranged in a device different from the embodiment. The different modules, units, or components included in the device of the embodiment can be combined into one module, unit, or component, or they can be divided into multiple sub-modules, sub-units, or sub-components.

Claims (7)

1. A broadband isolator based on a negative group delay network, characterized in that it comprises a non-reciprocal phase shifter (1), a transmission line 1 (4), a directional coupler (3), a transmission line 2 (5) and a negative group delay circuit structure (2) which are connected in series in sequence, wherein the isolation end of the directional coupler (3) is connected to the transmission line 1 (4), and the coupling end is connected to the transmission line 2 (5); the negative group delay circuit structure (2) comprises six sections of microstrip lines _T1 , _T2 , _T3 , _T4 , _T5 , _T6 , two sections of coupling lines _CL1 , _CL2 , and four series resistors _RA , _RB , _Ra , _Rb , one end of the microstrip line _T1 is connected to one end of the microstrip line _T2 and one end of the resistor _Ra , and the other end is connected to one end of the microstrip line _T6 and the input end; the other end of the microstrip line is connected to one end of the microstrip line _T3 and one end of the resistor _Ra ; the other end of the microstrip line _T3 is connected to the microstrip line T6 and the input end. The other end of the microstrip line _T4 is connected to the microstrip line _T5 and one _end of the resistor R _b ; the other end of the microstrip line _T5 is connected to the other end of the microstrip line _T6 and the output end; the other end of the resistor R _a is connected _to one end of the coupling line CL ₁ , and the port connected to the coupling line CL ₁ and the resistor R _a is selected as the input end, then the isolation end and the through end of the coupler are grounded, and the coupling end is open; the other end of the resistor R _b is connected to one end of the coupling line CL ₂ , and the port connected to the coupling line CL ₂ and the resistor R _b is selected as the input end, then the isolation end and the through end of the coupler are grounded, and the coupling end is open; the other end of the resistor _RA is grounded; the other end of the resistor _RB is grounded. 2. The broadband isolator based on negative group delay network according to claim 1 is characterized in that the non-reciprocal phase shifter (1) comprises a transistor BJT, a radio frequency choke _C1 , a radio frequency choke _C2 , a radio frequency choke _L1 , a radio frequency choke _VB , a radio frequency choke _Vce , a large resistor _R5 and four resistors _R1 , _R2 , _R3 , and _R4 ; one end of the resistor _R1 is connected to one end of the capacitor _C1 and one end of the resistor _R2 , and the other end is grounded; the other end of the resistor R2 is connected to the input end; one end of _the resistor _R3 is connected to one end of the capacitor _C2 and one end of _R4 , and the other end is grounded; the other end of the resistor _R4 is connected to the output end; one end of the resistor _R5 is connected to the base of the transistor BJT and the other end of the capacitor _C1 , and the other end is connected to the DC power supply _VB ; the other end of the capacitor _C2 is connected to one end of the inductor _L1 and the collector of the transistor BJT; the inductor L ₁ The other end is connected to the DC voltage V _ce ; the emitter of the transistor BJT is grounded. 3. The broadband isolator based on a negative group delay network according to claim 1, characterized in that the directional coupler (3) is realized by a structure in which four sections of microstrip lines _TA1 , _TB1 , _TA2 , and _TB2 are connected in sequence, wherein the impedances of the microstrip lines _TA1 and _TA2 are the same, and the impedances of the microstrip lines _TB1 and _TB2 are the same. 4. The broadband isolator based on negative group delay network according to claim 3 is characterized in that the coupling degree and isolation degree of the required directional coupler are obtained by adjusting the characteristic impedance of the microstrip line. 5. The broadband isolator based on a negative group delay network according to claim 1, characterized in that the electrical lengths of the microstrip lines T ₁ , T ₂ , T ₄ , T ₅ , and T ₆ are equal, the electrical length of the microstrip line T ₃ is three times the electrical lengths of the microstrip lines T ₁ , T ₂ , T ₄ , T ₅ , and T ₆ , and the coupled lines CL ₁ and CL ₂ have different odd and even mode impedances but have the same electrical lengths as the microstrip lines T ₁ , T ₂ , T ₄ , T ₅ , and T ₆ . 6. According to claim 1, the broadband isolator based on the negative group delay network is characterized in that the two ends of the series route composed of the transmission line 1, the non-reciprocal phase shifter and the negative group delay circuit structure, and the transmission line 2, and the two ends of the series route composed of the directional coupler and the transmission line 1, the non-reciprocal phase shifter and the negative group delay circuit structure, and the transmission line 2 meet impedance matching. 7. The broadband isolator based on a negative group delay network according to claim 1 is characterized in that the sum of the phases of the transmission path formed by the transmission line 2, the negative group delay network, the non-reciprocal phase shifter, the transmission line 1 and the directional coupler is an integer multiple of 2π.