Circulator - Knowledge (XXG)

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two ferrites can be thought of as one continuous ferrite with an embedded stripline center conductor. For practical manufacturing reasons, the center conductor is not generally embedded in ferrite, so two discrete ferrites are used. The static magnetic bias field is typically provided by permanent magnets that are located external to the circulator ground planes. Magnetic shielding incorporated into the circulator design prevents detuning or partial demagnetization of the circulator in the presence of external magnetic fields or ferrous materials, and protects nearby devices from the effects of the circulator's static magnetic field.

1481: 1950: 1033: 2077:. Negative differential resistance diodes can amplify signals, and often perform better at microwave frequencies than two-port devices. However, since the diode is a one-port (two terminal) device, a nonreciprocal component is needed to separate the outgoing amplified signal from the incoming input signal. By using a 3-port circulator with the signal input connected to one port, the biased diode connected to a second, and the output load connected to the third, the output and input can be uncoupled. 1459:. Wave cancellation occurs when waves propagate with and against the circulator's direction of circulation. An incident wave arriving at any port is split equally into two waves. They propagate in each direction around the circulator with different phase velocities. When they arrive at the output port they have different phase relationships and thus combine accordingly. This combination of waves propagating at different phase velocities is how junction circulators fundamentally operate. 1903: 1550: 1865:. Such a ferrite material requires a relatively small magnetic field and low energy level to flip its magnetic polarity. This is distinctly advantageous for a switching circulator, but the absence of permanent magnets would be a disadvantage of a non-switching junction circulator that must retain its magnetic bias despite exposures to the potentially demagnetizing effects of stray magnetic fields, nearby ferrous materials, and temperature variations. 2054: 1794: 1718: 1640: 38: 1467:

above the stripline circuit and one ferrite disk below the stripline circuit. Stripline circulators do not have to be constructed with disk- or triangle-shaped ferrites; the ferrites can have almost any shape that has three-way symmetry. This is also true of the resonator (the center junction portion of the center conductor)- it can be any shape that has three-way symmetry, although there are electrical considerations.

1569:. The resonator is often just one ferrite, but it is sometimes composed of two or more ferrites, which may be coupled to each other, in various geometrical configurations. The geometry of the resonator is influenced by electrical and thermal performance considerations. Waveguide junction circulators function in much the same way as stripline junction circulators, and their basic theory of operation is the same. 1840: 1895: 1786: 987: 1470:

The ferrites are magnetized through their thicknesses, i.e., the static magnetic bias field is perpendicular to the plane of the device and the direction of signal propagation is transverse to the direction of the static magnetic field. Both ferrites are in the same static ad RF magnetic fields. The

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offer one solution. One study employed a structure similar to a time-varying transmission line with the effective nonreciprocity triggered by a one-direction propagating carrier pump. This is like an AC-powered active circulator. The research claimed to be able to achieve positive gain and low noise

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transmission phase shift. That is, the forward phase shift is different from the phase shift in the reverse transmission direction. It is this difference in phase shifts that enables the non-reciprocal behavior of the circulator. A differential phase shifter consists of one or more ferrite slabs,

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Self-biased junction circulators are unique in that they do not utilize permanent magnets that are separate from the microwave ferrite. The elimination of external magnets significantly reduces the size and weight of the circulator compared to electrically-equivalent microstrip junction circulators

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junction circulator comprises two ferrite disks or triangles separated by a stripline center conductor and sandwiched between two parallel ground planes. A stripline circulator is essentially a stripline center conductor sandwich on ferrite, between ground planes. That is, there is one ferrite disk

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using transistors that are non-reciprocal in nature. In contrast to ferrite circulators which are passive devices, active circulators require power. Major issues associated with transistor-based active circulators are the power limitation and the signal-to-noise degradation, which are critical when

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E-field animation of microwave signal propagation through a high-power S-band differential phase shift circulator. In this animation, the signal propagating through the upper differential phase shifter is seen to have a higher velocity than the signal in the lower differential phase shifter. Just

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Depending on which circulator port an incident signal enters, phase shift relationships in the hybrid couplers and the differential phase shifts cause signals to combine at one other port and cancel at each of the remaining two ports. Differential phase shift circulators are often used as 3-port

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mismatches between it and the surface to which the circulator is mounted. A permanent magnet that is bonded to the circuit face of the ferrite substrate provides the static magnetic bias to the ferrite. Microstrip circulators function in the same way as stripline junction circulators, and their

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The magnetization polarity of the ferrite, and hence the direction of circulation of a switching circulator, is controlled using a magnetizing coil that loops through the ferrite. The coil is connected to electronic driver circuitry that sends current pulses of the correct polarity through the

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This class of circulator offers a considerable size reduction compared with the junction circulators. On the other hand, lumped-element circulators generally have lower RF power handling capacity than equivalent junction devices and are more complex from a mechanical perspective. The discrete

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The ferrite resonator is magnetized through its height, i.e., the static magnetic bias field is perpendicular to the plane of the device and the direction of signal propagation is transverse to the direction of the static magnetic field. The static magnetic bias field is typically provided by

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junction circulator comprises a junction of three waveguides, the ferrite resonator, and impedance matching structures. Many of these circulators contain pedestals located in the central junction, on which the ferrite resonator is located. These pedestals effectively reduce the height of the

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Microwave circulators fall into two main classes: differential phase shift circulators and junction circulators, both of which are based on cancellation of waves propagating over two different paths in or near magnetized ferrite material. Waveguide circulators may be of either type, while more

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circulator based on N-path filter concepts. It offers the potential for full-duplex communication (transmitting and receiving at the same time with a single shared antenna over a single frequency). The device uses capacitors and a clock and is much smaller than conventional devices.

1881: 232:. The permeability is a function of the direction of microwave propagation relative to the direction of static magnetization of the ferrite material. Hence, microwave signals propagating in different directions in the ferrite experience different magnetic permeabilities. 104:, connects to the device. For a three-port circulator, a signal applied to port 1 only comes out of port 2; a signal applied to port 2 only comes out of port 3; a signal applied to port 3 only comes out of port 1. An ideal three-port circulator thus has the following 2009:, since a signal can travel in only one direction between the remaining ports. An isolator is used to shield equipment on its input side from the effects of conditions on its output side; for example, to prevent a microwave source being detuned by a mismatched load. 1814:

In a lumped-element circulator, conductors are wrapped around the ferrite, forming what is typically a woven mesh. The conductor strips are insulated from each other by thin dielectric layers. In some circulators, the mesh is in the form of traces on a

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or ribbon bonds. Another advantage of microstrip circulators is their smaller size and correspondingly lower mass than stripline circulators. Despite this advantage, microstrip circulators are often the largest components in microwave modules.

236: 1496: 1663:. The top right circulator port connects to receiver and signal processing circuitry, and the lower right circulator port connects to the transmitter power amplifier near the center of the module. In this instance, the circulator performs a 1914:

components. These circulators are 4-port devices having circulation in the sequence 1 - 2 - 3 - 4 - 1, with ports numbered as shown in the schematic. There are various feasible circulator architectures, the most common of which utilizes a

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The performance disadvantages of microstrip circulators are offset by their relative ease of integration with other planar circuitry. The electrical connections of these circulators to adjacent circuitry are typically made using

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Though ferrite circulators can provide good "forward" signal circulation while suppressing greatly the "reverse" circulation, their major shortcomings, especially at low frequencies, are the bulky sizes and the narrow bandwidths.

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for receiving path and broadband nonreciprocity. Another study used resonance with nonreciprocity triggered by angular-momentum biasing, which more closely mimics the way that signals passively circulate in a ferrite circulator.

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are usually of the junction type. Two or more junction circulators can be combined in a single component to give four or more ports. Typically permanent magnets produce a static magnetic bias in the microwave ferrite material.

456: 535: 1561:. In contrast with a stripline junction circulator, the ferrite itself is the resonator, rather than the metal central portion of a stripline center conductor. The ferrite resonator may have any shape that has three-fold 2974: 1687:. The ferrite substrate is sometimes bonded to a ferrous metal carrier, which serves to improve the efficiency of the magnetic circuit, increase the mechanical strength of the circulator, and protect the ferrite from 977:

that would propagate in the direction of the static magnetic bias field, which is through the thickness of the ferrite. The plus and minus subscripts of the propagation constants indicate opposite wave polarizations.

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usually positioned on the broad wall(s) of the waveguide. Permanent magnets located outside the waveguide provide static magnetic bias field to the ferrite(s). The ferrite-loaded waveguide is another example of a

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bands. In a junction circulator, the size of the ferrite(s) is proportional to signal wavelength, but in a lumped-element circulator, the ferrite can be smaller because there is no such wavelength proportionality.

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Each of the two counter-rotating modes has its own resonant frequency. The two resonant frequencies are known as the split frequencies. The circulator operating frequency is set between the two split frequencies.

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Because of their thin, planar shape, self-biased circulators can be conveniently integrated with other planar circuitry. Integration of self-biased circulators with semiconductor wafers has been demonstrated at

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Internal construction of two different lumped-element isolators. One type of isolator is a circulator having one port internally terminated. The termination in each of these isolators is a rectangular film

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airborne radar. The microstrip junction circulator is visible at the left end of the module. The left port of the circulator connects to the antenna port of the module and ultimately to an element of the

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E-field plot of the rotating standing wave pattern in the ferrite of a waveguide junction circulator. The direction of signal propagation is from bottom to upper right, and the upper left ferrite apex is

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Switching circulators are similar to other junction circulators, and their microwave theory of operation is the same, except that their direction of circulation can be electronically controlled.

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In 1964, Mohr presented and experimentally demonstrated a circulator based on transmission lines and switches. In April, 2016 a research team significantly extended this concept, presenting an

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In junction circulators and differential phase shift circulators, microwave signal propagation is usually orthogonal to the static magnetic bias field in the ferrite. This is the so-called

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in the resonator region to optimize electrical performance. The reduced-height waveguide sections leading from the resonator to the full-height waveguides serve as impedance transformers.

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coupled inductors. Impedance matching circuitry and broad-banding circuitry in lumped-element circulators are often constructed using discrete ceramic capacitors and air-core inductors.

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basic theory of operation is the same. In comparison with stripline circulators, electrical performance of microstrip circulators is somewhat reduced because of

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transmission line topology. A microstrip circulator consists primarily of a circuit pattern on a ferrite substrate. The circuit is typically formed using

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electromagnetic wave propagating in a magnetized ferrite cylinder. The static magnetic field is oriented parallel to the cylinder axis. This is known as

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Junction circulators use permanent magnets to provide the static magnetic bias for the ferrite(s). However, switching circulators typically rely on the

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circulators by connecting one circulator port to a reflectionless termination, or they can be used as isolators by terminating two circulator ports.

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properties of magnetized microwave ferrite material. Microwave electromagnetic waves propagating in magnetized ferrite interact with electron

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before the signals reach the quadrature hybrid on the right, the upper signal leads the lower signal by about 90°. Animation courtesy of

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or null at another port (port 3 if the microwave energy is coupled from port 1 to port 2 and not reflected back into port 2).

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Tanaka, S.; Shimomura, N.; Ohtake, K. (1965-03-01). "Active circulators - The realization of circulators using transistors".

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for a circulator (with each waveguide or transmission line port drawn as a single line, rather than as a pair of conductors)

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Geiler, Anton; Harris, Vince (September–October 2014). "Atom Magnetism: Ferrite Circulators - Past, Present, and Future".

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lumped-element inductors and capacitors can be less stable when exposed to vibration or mechanical shocks than the simple

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Differential phase shift circulators are mainly used in high power microwave applications. They are usually built from

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are integers. Solving the two preceding equations simultaneously, for proper circulation the necessary conditions are

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it is used as a duplexer for sustaining the strong transmit power and clean reception of the signal from the antenna.

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If losses are neglected for simplification, the counter-rotating modes must differ in phase by an integer multiple of

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Qin, Shihan; Xu, Qiang; Wang, Y.E. (2014-10-01). "Nonreciprocal Components With Distributedly Modulated Capacitors".

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A waveguide junction circulator contains a magnetized ferrite resonator, which is located at the junction of three

946: 2747:(2016-02-01). "Magnetless Microwave Circulators Based on Spatiotemporally Modulated Rings of Coupled Resonators". 3088: 1693: 360:{\displaystyle B={\begin{bmatrix}\mu &j\kappa &0\\-j\kappa &\mu &0\\0&0&1\end{bmatrix}}H} 2037:, without allowing signals to pass directly from transmitter to receiver. The alternative type of duplexer is a 543: 1697: 1578: 1048:, such as a disk, hexagon, or triangle. An RF/microwave signal entering a circulator port is connected via a 852:{\displaystyle \Gamma _{+}=j\omega {\sqrt {\mu _{0}\epsilon }}\,{\sqrt {\frac {\mu ^{2}-\kappa ^{2}}{\mu }}}} 631: 1165:

and similarly, for the remaining port (port 3 if signal propagation is from port 1 to port 2) to be nulled,

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of the ferrite. This permeability is mathematically described by a linear vector operator, also known as a

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magnetizing coil to magnetize the ferrite in the polarity to provide the desired direction of circulation.

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This article is about radio frequency (RF) or microwave frequency passive circulators. For other uses, see

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with metallized vias to make connections between layers. The conductive strips can be thought of as non-

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Palmer, William; Kirkwood, David; et al. (June 2016). "A Bright Future for Integrated Magnetics".

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A stripline junction circulator contains a resonator, which is located at the central junction of the

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E-field scatter plot of an electromagnetic wave propagating through a waveguide junction circulator.

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for signal propagation from port 1 to port 2 (or from port 2 to port 3, or from port 3 to port 1):

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which can cause them to combine constructively or destructively at a given port. This produces an

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Lumped-element circulators are small-size devices that are typically used at frequencies in the

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Carchon, G.; Nanwelaers, B. (2000-02-01). "Power and noise limitations of active circulators".

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When one port of a three-port circulator is terminated in a matched load, it can be used as an

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The microstrip junction circulator is another widely-used form of circulator that utilizes the

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of the ferrite material. In a circulator, these propagation constants describe waves having

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Zeina, N.; How, H.; et al. (September 1992). "Self-Biasing Circulators Operating at K

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junction circulator having triangular ferrites and an irregular triangle-shaped resonator.

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Fay, C.E.; Comstock, R.L. (1965-01-01). "Operation of the Ferrite Junction Circulator".

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of the ferrite itself. The ferrites that are used in switching circulators have square

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E-Field Plots Showing Electromagnetic Wave Propagation in Waveguide Junction Circulators

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on port 3. The label on the permanent magnet indicates the direction of circulation.

451:{\displaystyle \mu =1+{\frac {\omega _{0}\omega _{m}}{\omega _{0}^{2}-\omega ^{2}}}} 2070: 1705: 1660: 530:{\displaystyle \kappa ={\frac {\omega \omega _{m}}{{\omega _{0}}^{2}-\omega ^{2}}}} 2502:

Monolithically Integrated Self-Biased Circulator for mmWave T/R MMIC Applications

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High-Power Liquid-Cooled Differential Phase Shift Circulator. Image courtesy of

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case. The microwave propagation constants for this case, neglecting losses are

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The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science

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Internal construction of a WR-90 (WG 16; R 100) waveguide switching circulator.

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Woven mesh conductor wrapped around the ferrite of a lumped-element circulator.

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Internal construction of a WR-112 (WG 15; R 84) waveguide junction circulator.

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that have been optimized to have low microwave losses. In contrast with the

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to the resonator, where energy is coupled into two counter-rotating circular

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is the frequency of the RF/microwave signal propagating through the ferrite,

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Electronic circuit in which a signal entering any port exits at the next port

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High-Power Liquid-Cooled Waveguide Junction Circulator. Image courtesy of

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Monolithic ferrites that are used for self-biased circulators are M-type

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junction circulator having disk ferrites and a triangle-shaped resonator.

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fields, enabling circulator operation up to high microwave frequencies.

84:(RF) signal to exit through the port directly after the one it entered. 1859: 1766: 2962: 2790:

Mohr, Richard (1964). "A New Nonreciprocal Transmission Line Device".

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junction circulator having disk ferrites and a disk-shaped resonator.

1012: 228:. In the case of magnetized ferrite, the permeability tensor is the 225: 2523:

Konishi, Yoshihiro (November 1965). "Lumped Element Y Circulator".

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Modern Ferrites, Volume 2: Emerging Technologies and Applications

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at one port (port 2 if the signal is incident upon port 1) and a

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in the ferrite and are consequently influenced by the microwave

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permanent magnets that are external to the waveguide junction.

908:{\displaystyle \Gamma _{-}=j\omega {\sqrt {\mu _{0}\epsilon }}} 2844:"Magnetic-free non-reciprocity based on staggered commutation" 2570:. International Microwave Symposium Digest. pp. 147–151. 2118:

Polder, D (1949). "On the Theory of Ferromagnetic Resonance".

1807: 3032:"Low Frequency Circulator/Isolator Uses No Ferrite or Magnet" 2175:

Bosma, H. (1964-01-01). "On Stripline Y-Circulation at UHF".

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Schematic diagram of a differential phase shift circulator.

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impedance transformers in a stripline junction circulator.

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Cui, Yongjie; Chen, Hung-Yu; et al. (December 2021).

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Ohm, E. A. (1956), "A Broad-Band Microwave Circulator",

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Reiskarimian, Negar; Krishnaswamy, Harish (2016-04-15).

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IEEE Spectrum: Technology, Engineering, and Science News

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Microwave diode reflection amplifier using a circulator

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Internal Construction of Stripline Junction Circulators

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Internal construction of a differential phase shifter.

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junction circulator used as an isolator by placing a

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