A microwave isolator

Abstract

A microwave isolator of the present invention can solve the technical problems of conventional ferrite microwave isolators, such as complex structure, large size, low reliability, narrow operating frequency range, and failure to meet the needs. It includes a front-stage attenuation network, a non-reciprocal semiconductor device, and a rear-stage attenuation network; the front-stage attenuation network is connected to the front-stage link as the input stage of the isolator; the rear-stage attenuation network is connected to the rear-stage link as the output stage of the isolator; the radio frequency link formed from the input stage to the output stage is a transmission channel; an electromagnetic shielding structure is set between the input / output ends of the non-reciprocal semiconductor device and on both sides of the radio frequency link formed from the input stage to the output stage of the isolator. The present invention adopts semiconductor devices, and the product has a wide operating frequency range, a wide relative bandwidth, and a wider range of application; the operating frequency range of the present invention is almost unlimited, and can cover DC-terahertz. As long as such semiconductor chips support a high operating frequency, it can be applicable to a high frequency range.

Description

Technical Field

[0001] The invention relates to the field of microwave circuit modules / components, and in particular to a microwave isolator. Background Art

[0002] In the field of microwave circuit modules / components, there is a non-reciprocal device or circuit with microwave unidirectional transmission characteristics (referred to as microwave isolator), whose basic characteristics are: Figure 1 As shown in (A), there is only a small loss when the microwave signal is transmitted in a specified direction, but there is a large loss (isolation) when it is transmitted in other directions.

[0003] Because of the unique characteristics of microwave isolators, they are widely used in various microwave circuit modules / components, subsystems, and complete machines to achieve functions such as inter-stage isolation, crosstalk prevention, impedance matching, decoupling, and duplex transmission, thereby protecting the system and effectively improving system stability and reliability. Common application scenarios are as follows:

[0004] 1) Inserting a microwave isolator between the front and rear stages in the RF link can improve the impedance matching of the front and rear stages, prevent the output power generated by the rear stage circuit from being reversely transmitted to the front stage and affecting the normal working state of the front stage, thereby protecting the front stage circuit;

[0005] 2) In microwave transceiver circuits, microwave isolators are used as duplexers (as shown below) Figure 1 (B) to send the transmitted signal directly to the antenna for transmission; at the same time, the received signal from the antenna will also directly enter the receiver. The signal is not allowed to reach the receiver directly from the transmitter, thereby protecting the receiver.

[0006] 3) In the power synthesis circuit (as follows Figure 1 (C) Microwave isolators are often used to improve the isolation of the synthesis system and prevent intermodulation caused by crosstalk between two amplifiers.

[0007] In the middle of the last century, a major breakthrough in microwave technology was the discovery of ferrite. Ferrite is a type of ceramic magnetic material composed of metal oxides. Since ferrite gyromagnetic material is an anisotropic magnetic material, its magnetic permeability changes with the external magnetic field; this material produces gyromagnetic properties (also known as tensor magnetic permeability properties) under the combined action of an external microwave field and a constant DC magnetic field. It is this gyromagnetic property that causes the polarization rotation of electromagnetic waves propagating in ferrites (Faraday effect) and strong absorption of electromagnetic wave energy (ferromagnetic resonance). Circulators and isolators are microwave one-way devices developed using the gyromagnetic properties of this material under the combined action of a DC magnetic field and a microwave field (as shown in Figure 2).

[0008] in Figure 2(A) is a circulator. Microwave signals can only be transmitted in one direction, that is, from 1 to 2, from 2 to 3 and from 3 to 1. Conversely, the signal from 2 to 1, from 3 to 2 and from 1 to 3 is isolated; when a 50 ohm load is connected to one port of the circulator, an isolator is formed, such as Figure 2 (B) shown.

[0009] The existing ferrite microwave isolators have the following shortcomings:

[0010] 1) The conventional operating frequency range is 100MHz to 40GHz. Theoretically, it can be achieved below 100MHz, but the difficulty lies in the requirement of low magnetic moment of ferrite, very low bias magnetic field requirement, and large size, which is not easy or even impossible to achieve. At the same time, the upper limit operating frequency can also reach 100GHz in theory, but due to the high operating frequency, the processing accuracy of the product is difficult to guarantee, production and debugging are difficult, and the product size is still large relative to other devices in the same system. Therefore, it is basically not adopted.

[0011] 2) The relative working bandwidth of the product is narrow: usually ≤50%, not suitable for broadband applications;

[0012] 3) It is large in size and cannot be used in many systems or devices with smaller spaces. The lower the working frequency band, the larger the volume. For example, the volume of a company's 12-55MHz ferrite isolator is 80×80×28.

[0013] 4) The structure is complex and the reliability is relatively low.

[0014] With the development of electronic equipment technology, the demand for various types of microwave isolators is increasing. At the same time, the requirements for the performance of isolators are getting higher and higher, and the size requirements are getting smaller and smaller. The use of traditional oxygen technology systems to realize isolators can no longer meet the requirements of many modern systems. The above problems need to be solved urgently. Summary of the invention

[0015] The microwave isolator proposed in the present invention can solve some problems existing in conventional ferrite microwave isolators, such as complex structure, large size, relatively low reliability, narrow frequency range, and technical problems that cannot meet the needs of many occasions.

[0016] To achieve the above object, the present invention adopts the following technical solutions:

[0017] A microwave isolator, comprising a non-reciprocal semiconductor device and a front-end and rear-end attenuation network;

[0018] The front-stage attenuation network is connected to the front-stage link as the input stage of the isolator;

[0019] The post-stage attenuation network is connected to the post-stage link as the output stage of the isolator;

[0020] The radio frequency link formed from the input stage to the output stage is the signal transmission channel;

[0021] Electromagnetic shielding structures are arranged on both sides of the radio frequency link formed from the input stage to the output stage.

[0022] Furthermore, an electromagnetic shielding structure is also provided between the input / output terminals of the non-reciprocal semiconductor device.

[0023] Furthermore, the non-reciprocal semiconductor device may be any device having non-reciprocal signal transmission characteristics suitable for its application, such as a microwave amplifier, a mixer, an operational amplifier, etc.

[0024] Furthermore, the number of transmission channels is n, where n is a natural number greater than or equal to 1;

[0025] Each transmission channel is connected to the preceding link by a unidirectional device input attenuation network, and the output end of the non-reciprocal semiconductor device is connected to the subsequent circuit via an output attenuation network;

[0026] The n transmission channels share a front-end link as an input terminal, and are then respectively connected to corresponding back-end links through a power divider.

[0027] Furthermore, the number of transmission channels n=2.

[0028] Furthermore, the attenuation network may be any attenuation circuit having a signal attenuation function suitable for its application, such as a π-type or T-type attenuation network composed of a discrete resistor network, a fixed attenuator chip, and the like.

[0029] Furthermore, multiple stages of microwave isolators can be directly cascaded and applied to improve the unidirectional transmission characteristics of the system.

[0030] Furthermore, the front-stage link and the rear-stage link may be any microwave signal circuits suitable for their application occasions, such as an amplification link, a mixing link or a filter, etc.

[0031] It can be seen from the above technical solution that the microwave isolator of the present invention utilizes microwave semiconductor devices with non-reciprocal characteristics of microwave transmission to design the microwave isolator.

[0032] When the frequency band is high (e.g. ≥100MHz), the required microwave unidirectional transmission characteristics can be achieved by using semiconductor devices such as microwave amplifiers and mixers that have non-reciprocal microwave transmission characteristics, combined with simple and appropriate peripheral circuits;

[0033] When the frequency band is low (such as <100MHz), operational amplifiers and their peripheral circuits can be used to achieve non-reciprocity of signal transmission.

[0034] When the unidirectional index of a unidirectional circuit is very high, the following methods can be used:

[0035] 1) Multiple levels of microwave semiconductor devices with non-reciprocal microwave transmission characteristics are used in cascade;

[0036] 2) Connect appropriate attenuation networks in series before and after microwave semiconductor devices with non-reciprocal microwave transmission characteristics;

[0037] 3) Other electromagnetic shielding structures can also be used to assist in preventing the microwave unidirectional transmission characteristics from being deteriorated due to factors such as spatial coupling.

[0038] Since the microwave unidirectional circuit design involved in the present invention does not involve ferrite materials, it does not have the inherent defects of the ferrite isolator introduced in the background technology.

[0039] The advantages of this method are:

[0040] 1) Using semiconductor devices instead of ferrite technology is beneficial to improving system integration and product reliability;

[0041] 2) The use of semiconductor devices has a wide operating frequency range, a wide relative bandwidth, and a wider range of applications. To some extent, the operating frequency range of the microwave unidirectional circuit involved in the present invention is almost unlimited, and can cover DC-terahertz. As long as the semiconductor chip supports a high operating frequency, it can be applied to a high frequency range.

[0042] 3) The use of semiconductor devices gives the design scheme greater freedom and makes it easier to implement;

[0043] Therefore, the microwave unidirectional circuit involved in the present invention has the advantages of wide operating frequency range, wide relative operating bandwidth, small size, simple structure, convenient application, etc. It can well meet the development needs of miniaturized electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the characteristics of existing microwave isolators;

[0045] Figure 2 It is a schematic diagram of the structure of the existing circulator and isolator;

[0046] Figure 3 It is a schematic diagram of the structure of the present invention;

[0047] Figure 4 is a schematic structural diagram of Embodiment 1 of the present invention;

[0048] Figure 5 is a structural diagram of Embodiment 2 of the present invention;

[0049] Figure 6 It is a schematic diagram of the structure of a π-type or T-type resistor network according to an embodiment of the present invention;

[0050] Figure 7 4 is a curve diagram of amplifier signal transmission characteristics according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions 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 only part of the embodiments of the present invention, not all of the embodiments.

[0052] like Figure 1 As shown, the microwave isolator described in this embodiment includes a non-reciprocal semiconductor device and attenuation networks of the previous and next stages;

[0053] The front-stage attenuation network is connected to the front-stage link as the input stage of the isolator;

[0054] The post-stage attenuation network is connected to the post-stage link as the output stage of the isolator;

[0055] The radio frequency link formed from the input stage to the output stage is the signal transmission channel;

[0056] Electromagnetic shielding structures are arranged on both sides of the radio frequency link formed from the input stage to the output stage of the isolator;

[0057] An electromagnetic shielding structure is also provided between the input / output terminals of the non-reciprocal semiconductor device.

[0058] The non-reciprocal semiconductor device may be a microwave amplifier, a mixer, an operational amplifier or other semiconductor devices having non-reciprocal transmission characteristics.

[0059] The attenuation network may be a π-type or T-type attenuation network composed of a discrete resistor network, or may be a fixed attenuator chip, or other forms of circuits or networks with attenuation effects.

[0060] The following is an explanation based on specific applications:

[0061] Embodiment 1:

[0062] The structural design diagram of Example 1 is shown in Figure 1 This embodiment is used to improve the reverse isolation from output to input in a radio frequency link without changing other link characteristic indicators.

[0063] In the figure, ① is the front-stage circuit in the RF link; ②④ are optional attenuation networks; ③ microwave amplifier circuit or operational amplifier circuit (including peripheral circuits); ⑤ is the back-stage circuit in the RF link; ⑥ the electromagnetic shielding structure on both sides of the RF link; ⑦ the electromagnetic shielding structure spanning the microwave isolator.

[0064] The optional attenuation network shown in ②④ and the microwave amplifier circuit or operational amplifier circuit (including peripheral circuits) shown in ③ constitute the microwave isolator in the structure.

[0065] According to the operating frequency of the microwave isolator, a microwave amplifier or an operational amplifier can be selected. Usually, when the operating frequency is ≥100MHz, a microwave amplifier is selected; when the operating frequency is <100MHz, an operational amplifier is selected.

[0066] The optional attenuation network shown in ②④ has three functions: 1) impedance matching of the front and rear stages; 2) adjusting the power level or dynamic characteristics of the RF link to prevent the circuit in the RF link from operating in a nonlinear state; 3) although the attenuation network does not have a unidirectional transmission characteristic, it does provide additional reverse isolation for the inverter.

[0067] The attenuation of the attenuation network shown in ②④ and the microwave amplifier circuit shown in ③ are designed based on the required electrical performance index requirements and taking into account the unidirectional transmission characteristics of the entire link, the dynamic range of the front and rear active devices, and the reverse transmission characteristics of the amplifier itself.

[0068] The electromagnetic shielding structure on both sides of the RF link shown in ⑥ and the electromagnetic shielding structure across the microwave isolator shown in ⑦ are both intended to prevent the unidirectional transmission characteristics of the link from being deteriorated due to spatial coupling.

[0069] Embodiment 2:

[0070] The structural design diagram of Example 2 is shown in Figure 2 This embodiment is used to improve the isolation between any output and input, and between two output ports (output I and output II) without changing other link characteristic indicators.

[0071] Compared with Embodiment 1, Embodiment 1 can only improve the unidirectional isolation from output to input; while Embodiment 2 can improve the unidirectional isolation from output to input and simultaneously improve the bidirectional isolation between two output ports.

[0072] Among them, ① shows the front-stage link of the RF link; ② shows the power divider; ③ shows the front-stage attenuation network of the two microwave isolators; ④ shows the non-reciprocal semiconductor devices of the two microwave isolators; ⑤ shows the rear-stage attenuation network of the two microwave isolators; ⑥ shows the rear-stage link of the RF link; ⑦ shows the electromagnetic shielding structure on both sides of the RF link; ⑧ shows the electromagnetic shielding structure spanning the two microwave isolators.

[0073] Among them, the design principle of each microwave isolator circuit is the same as that in Example 1.

[0074] Assume that the attenuation of attenuation network ③⑤ is 10dB, and the reverse isolation of non-reciprocal semiconductor device ④ of each microwave one-way circuit is 20dB.

[0075] The attenuation network can be realized by using a T-type or T-type resistor network when the operating frequency is not too high. Figure 6 The type or T-type resistor network shown is used to realize an attenuation network with an attenuation of 10dB.

[0076] Among them, the non-reciprocal semiconductor device needs to select a suitable device according to the specific application occasion. In Example 1, an amplifier is used. In a certain product, SBB-5089 of Qorvo of the United States is selected. Its signal transmission characteristics are as follows: Figure 7 As shown in the figure on the left, S21 represents the forward transmission gain; S12 represents the reverse isolation. Therefore, the reverse isolation that can be achieved by using this type of device in the DC-4GHz range is ≥22.5dB.

[0077] In some cases, it is necessary to use other devices with non-reciprocal transmission characteristics such as mixers.

[0078] The front stage circuit in the embodiment may be an amplification link or a mixing link, and the rear stage circuit may be an amplification link, or a filter, etc. The circuit form needs to be finally determined according to the actual application requirements.

[0079] The reverse isolation from each output to the input of this example is increased by 40 dB compared with the original link without the microwave isolator. The mutual isolation between the two outputs is also increased by 40 dB.

[0080] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A microwave isolator, characterized in that: Including non-reciprocal semiconductor devices, a front-stage attenuation network and a rear-stage attenuation network; The front-stage attenuation network is connected to the front-stage link as the input stage of the isolator; The post-stage attenuation network is connected to the post-stage link as the output stage of the isolator; The radio frequency link formed from the input stage to the output stage is the signal transmission channel; Electromagnetic shielding structures are arranged on both sides of the radio frequency link formed from the input stage to the output stage; The number of transmission channels is n, where n is a natural number greater than or equal to 1; Each transmission channel is connected to the preceding link by a unidirectional device input attenuation network, and the output end of the non-reciprocal semiconductor device is connected to the subsequent circuit via an output attenuation network; The n transmission channels share a front-end link as an input end, and then are respectively connected to the corresponding back-end through a power divider; An electromagnetic shielding structure is also provided between the input end and the output end of the non-reciprocal semiconductor device; The non-reciprocal semiconductor device is one of a microwave amplifier, a mixer, and an operational amplifier.

2. The microwave isolator according to claim 1, characterized in that: The number of transmission channels n=2.

3. The microwave isolator according to claim 1 or 2, characterized in that: The attenuation network is a π-type or T-type attenuation network composed of a discrete resistor network or one of fixed attenuator chips.

4. The microwave isolator according to claim 1, characterized in that: The front-stage link and the rear-stage link are one of an amplification link, a mixing link or a filter.

Images