A New Dual-Band High Power Ferrite Circulator
Abstract: The design, simulation and performance enhancement of a new structure for X-band high-power, low-loss, low-bias, triangularferrite waveguide circulator are presented. Dual circulation property is obtained by triangular shape of ferrite post. The effects of circulator’s structure parameters, such as ferrite parameters and magnetic DC bias, on isolation, insertion loss and return loss of circulator are discussed. The HFSS software is used for simulating the circulators. Final dual band designs with 20 dB return loss, 20 dB isolation and 0.1 dB insertion loss in dual frequency in X-band (8.2 GHz and 10.4GHz) with only a magnetic bias of 10Oe are obtained.
Summary (2 min read)
- Circulator is a versatile microwave device which plays an important role in satellite communications and radar applications.
- There are two different kinds of circulators, E-plane and H-plane, which are based on the two main categories of waveguides.
- In addition, RF losses caused by the dielectric properties of the ferrite will be smaller, thereby reducing the heating effects.
- A design procedure for high-power, dual-band or Left-Handed RightHanded (LH-RH) dual-band circulator is presented.
2. THEORY OF THE DUAL BAND CIRCULATOR
- In the first Section 2.1 general description of a dual band circulator in terms of its ideal scattering parameters is presented.
- A practical example which shows the application of the dual band circulator in a transmitter system is also included in this section.
- In the next two sections different techniques which can be used to achieve wider bandwidth and lower reflection loss are discussed.
- The last Section 2.4 talks about the modal distribution of the ferrite inside the circulator.
2.1. Dual Band Circulator
- In general, circulators are three port networks.
- Any single band circulator adopts one of these arrangements.
- A regular dual band circulator has right hand or left hand circulation in two different frequency bands.
- As illustrated in Figure 2(a), a LH-RH dual-band circulator can be used to mix two high power transmitters and send the signals with one broadband antenna.
- At the same time, the system provides proper isolation between two transmitters for multiplexing different channels.
- One important property of a circulator is its bandwidth which is different for E- and H-plane structures.
- Hence, in general there is a tradeoff between bandwidth and high-power handling properties.
- In most of the applications the high power capability is superior to the bandwidth, hence, most of the circulators are E-plane.
- But, as the result of increasing the length of the ferrite, concentration of the peak of TE10 mode in the ferrite region increases which decreases the high-power capability of the circulator.
- Another way to to broaden the bandwidth is done by improving the impedance match of the ferrite junction.
2.3. Reflection Loss
- The shape of the ferrite post plays an important role in matching of the junction to the waveguide structure.
- In general tapering the cross section of the ferrite in the direction of the incident wave decreases the reflection loss.
- Based on the performed simulations structure (a) has a better insertion loss than (b).
- Based on this approximation the lowest order mode of the ferrite resonator is the TM111 mode which is the dominant cylindrical dielectric resonator.
- These modes correspond to right-handed and left-handed circular polarization respectively.
3. DESIGN AND SIMULATION RESULTS
- The design process of the dual band circulator includes two parts.
- Applying a DC internal magnetic field to ferrite, the TM111 mode splits and the resonant frequency of the structure may change from the one obtained from Figure 5.
- In the first set the authors have studied the effect of the ferrite material parameters on the circulator characteristics.
- Among these parameters, M0 has the most effect on the circulator characteristics and the double band property is achieved by just tuning its value.
- The S-parameters of the simple dual- band E-plane circulator are shown in Figure 8.
4. SUMMARY AND CONCLUSION
- A new structure for high power E-plane X-band circulator is presented.
- Simulations demonstrate that this structure can have two types of dual-band response, simple dual-band and LH-RH dual-band.
- Design procedure for both dual-band structures is presented.
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Cites background from "A New Dual-Band High Power Ferrite ..."
...In the quest for a solution to this biasing issue, plaguing all magnet-based microwave ferrite devices [2,11], hexaferrites have been investigated in the past as self-biased magnetic materials and recently applied to nonreciprocal devices ....
"A New Dual-Band High Power Ferrite ..." refers background in this paper
...Left handright hand (LH-RH) circulators can be used as power combiner in dual-band or multi-band transmitters  or in Radar applications....
"A New Dual-Band High Power Ferrite ..." refers methods in this paper
...The triangular intersection is used in several cases [8, 15] to decrease the reflection loss....
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The effects of circulator ’ s structure parameters, such as ferrite parameters and magnetic DC bias, on isolation, insertion loss and return loss of circulator are discussed.