环形器是一个多端口器件，其中电磁波的传输只能沿单方向环行，例如在下图中，信号只能沿①→②→③→①方向传输，反方向是隔离的，以此类推，故称为环形器。在近代雷达和微波多路通信系统中都要用单方向环行特性的器件。例如，在收发设备共用一副天线的雷达系统中常用环形器作双工器。在微波多路通信系统中，用环形器可以把不同频率的信号分隔开。隔离器用于屏蔽其输入侧的设备免受其输出侧的条件的影响；例如，以防止微波源由失配的负载失谐。
A ringer is a multi port device in which electromagnetic waves can only be transmitted in a single direction. For example, in the following diagram, signals can only be transmitted in the ① → ② → ③ → ① direction, and the opposite direction is isolated. Therefore, it is called a ringer. In modern radar and microwave multi-channel communication systems, devices with unidirectional circular characteristics are used. For example, in radar systems where the transmitting and receiving equipment share a pair of antennas, a ring-shaped device is commonly used as a duplexer. In microwave multi-channel communication systems, a ringer can be used to separate signals of different frequencies. Isolators are used to shield devices on their input side from the conditions on their output side; For example, to prevent the microwave source from being out of sync with mismatched loads.
No1
环形器的基本原理：
环形器是一种利用微波铁氧体材料做成的特殊器件，可以做成同轴结构，也可以做成波导结构。其中以微带三端环形器用的最多，用铁氧体材料作介质，上置导带结构，加恒定磁场，就具有环行特性。如果改变偏置磁场的方向，环行方向就会改变。
No1
The basic principle of a ring-shaped device:
A ring-shaped device is a special device made of microwave ferrite material, which can be made into a coaxial structure or a waveguide structure. Among them, the microstrip three end ring-shaped device is the most commonly used, using ferrite material as the medium, with an upper conduction band structure and a constant magnetic field, which has circular characteristics. If the direction of the bias magnetic field is changed, the circular direction will change.
No2
环形器的特点：
环形器的突出特点是单向传输高频信号能量，它控制电磁波沿某一方向环行传输，多用于高频功率放大器的输出端与负载之间，起到各自独立，互相“隔离”的作用。负载阻抗在变化甚至开路或短路的情况下都不影响功放的工作状态，从而保护了功率放大器。环形器具有体积小、频带宽、插损小等特点。
No2
The characteristics of a ring-shaped device:
The prominent feature of a ring-shaped device is the unidirectional transmission of high-frequency signal energy, which controls the electromagnetic wave to propagate in a certain direction in a circular manner. It is often used between the output end of a high-frequency power amplifier and the load, playing an independent and isolated role. The load impedance does not affect the working state of the power amplifier even in the event of changes or open circuits or short circuits, thus protecting the power amplifier. The ring-shaped device has the characteristics of small volume, wide frequency band, and low insertion loss.
No3
环形器的功能：
环形器的功能是保证微波功率的单向循环传输，而反向则是隔离的，将其等效为一个三口网络，它应是一个非互易网络。
No3
The function of the ring-shaped device:
The function of a ringer is to ensure unidirectional cyclic transmission of microwave power, while the reverse direction is isolated, equivalent to a three port network, which should be a non reciprocal network.
No4
环形器的性能问题：
对于相对频宽小于15％的低场环形器和隔离器，一般都不会出现峰值（即高次模）。对于大于25％宽频时，有人认为铁氧体结环形器，相当于开路谐振器。在这个谐振器中有混合谐振模、即高次模，这个高次模在中心导体和接地面间的纵向不均匀，磁场磁化不均匀，它扰乱了铁氧体环形器的场分布，同时，还有大量辐射能量，还由于高次模的产生使输入、输出电路中的阻抗元件直接耦合，还能形成附谐振电路。在这个谐振频率使损耗加大，使输出的相位发生旋转，破坏环行器的特性。
No4
Performance issues with the circulator:
For low field circulators and isolators with a relative bandwidth less than 15%, there is generally no peak (i.e. high-order mode). For frequencies greater than 25% broadband, some people believe that ferrite junction ring-shaped resonators are equivalent to open circuit resonators. In this resonator, there are mixed resonant modes, also known as higher-order modes. The longitudinal non-uniformity of this higher-order mode between the central conductor and the ground plane, as well as the uneven magnetization of the magnetic field, disrupts the field distribution of the ferrite ring-shaped device. At the same time, there is a large amount of radiated energy. The generation of higher-order modes also directly couples the impedance components in the input and output circuits, forming an attached resonant circuit. At this resonant frequency, the loss increases, causing the output phase to rotate and disrupting the characteristics of the circulator.
解决方法有
01 中心导体不能偏离对称面。保证中心导体的中心与样品圆心同心合一
02 铁氧体无气孔。铁氧体样品面的平整、光滑、无缺
03 铁氧体和接地之间有良好的接触
04 外加偏压磁场要均匀
05 装焊清洁无异物
06 样品接地面加软锡箔。焊点要平整、光滑、无虚焊现象
The solutions include
01 cannot deviate from the plane of symmetry. Ensure that the center of the central conductor is concentric with the center of the sample circle
02 Ferrite has no pores. The surface of the ferrite sample is flat, smooth, and flawless
03 There is good contact between ferrite and grounding
04 The applied bias magnetic field should be uniform
05 Welding is clean and free of foreign objects
06 Add soft tin foil to the grounding surface of sample The solder joints should be flat, smooth, and free from any virtual welding phenomenon
No5
环形器的应用：
01 隔离器
当三端口环形器的一个端口在匹配的负载端接时，它可以用作隔离器，因为信号可以在其余端口之间仅在一个方向上行进。隔离器用于屏蔽其输入侧的设备免受其输出侧的条件的影响;例如，以防止微波源由失配的负载失谐。
02 双工器
在雷达中，循环器被用作一种类型的双工器，以将信号从发射机路由到天线以及从天线到接收机，而不允许信号直接从发射机到达接收机。双工器的替代类型是在将天线连接到发射器和接收器之间交替的发射-接收开关（TR开关）。
在下一代蜂窝通信中，人们倾向于全双工无线电，因为它可以以相同的频率同时发送和接收信号。考虑到当前有限的、拥挤的频谱资源，全双工可以直接地有益于无线通信两倍的数据输入输出速度。仍然使用“半双工”执行无线通信，在不同的时间帧发送或接收信号，如果在相同的频率（通常在雷达中），以不同的频率同时发送和接收信号（由称为双工器的一组滤波器实现）。
03 反射放大器
反射放大器是一种利用诸如隧道二极管和耿氏二极管的负微分电阻二极管的微波放大器电路。负差分电阻二极管可以放大信号，并且通常在微波频率下比两端口器件表现更好。然而，由于二极管是单端口（两端）器件，需要非互易分量来将输出放大信号与输入-输入信号分离。通过使用具有连接到一个端口的信号输入的3端口环行器，连接到第二个的偏置二极管，连接到第三个的输出负载，输出和输入可以被断开。
No5
Application of ring-shaped device:
01 Isolator
When one port of a three port ringer is connected to a matching load terminal, it can be used as an isolator because the signal can travel in only one direction between the other ports. Isolators are used to shield devices on their input side from the conditions on their output side; For example, to prevent the microwave source from being out of sync with mismatched loads.
02 Duplex
In radar, a circulator is used as a type of duplexer to route signals from the transmitter to the antenna and from the antenna to the receiver, without allowing signals to directly reach the receiver from the transmitter. The alternative type of duplexer is the transmit receive switch (TR switch) that alternates between connecting the antenna to the transmitter and receiver.
In the next generation of cellular communication, people tend to prefer full duplex radio because it can simultaneously send and receive signals at the same frequency. Considering the current limited and congested spectrum resources, full duplex can directly benefit wireless communication with twice the data input and output speed. Still using “half duplex” to perform wireless communication, sending or receiving signals at different time frames, if simultaneously sending and receiving signals at different frequencies at the same frequency (usually in radar) (implemented by a set of filters called duplexers).
03 Reflection amplifier
A reflection amplifier is a microwave amplifier circuit that utilizes negative differential resistance diodes such as tunnel diodes and Gunn diodes. Negative differential resistance diodes can amplify signals and typically perform better than two-port devices at microwave frequencies. However, due to the fact that diodes are single port (two end) devices, non reciprocal components are required to separate the output amplification signal from the input-input signal. By using a 3-port circulator with a signal input connected to one port, connecting to the bias diode of the second, and connecting to the output load of the third, the output and input can be disconnected.