# A New Dual-Band High Power Ferrite Circulator

TL;DR: In this paper, the design, simulation and performance enhancement of a new structure for X-band high power, low loss, low bias, triangular ferrite waveguide circulator are presented.

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)

Jump to: [1. INTRODUCTION] – [2. THEORY OF THE DUAL BAND CIRCULATOR] – [2.1. Dual Band Circulator] – [2.2. Bandwidth] – [2.3. Reflection Loss] – [3. DESIGN AND SIMULATION RESULTS] and [4. SUMMARY AND CONCLUSION]

### 1. INTRODUCTION

- 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.

### 2.2. Bandwidth

- 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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Progress In Electromagnetics Research C, Vol. 10, 15–24, 2009

A NEW DUAL-BAND HIGH POWER FERRITE

CIRCULATOR

H. Razavip our, R. Saﬁan, G. Askari, F. Fesharaki

and H. Mirmohamad Sadeghi

Information and Communication Technology Institute

Isfahan University of Technology

Isfahan, Iran

Abstract—The design, simulation and performance enhancement of

a new structure for X-band high-power, low-loss, low-bias, triangular-

ferrite 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 10.4 GHz) with

only a magnetic bias of 10 Oe are obtained.

1. INTRODUCTION

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. Figures 1(a) and (b) show

the three dimensional view and the location of the ferrite in a two

dimensional view of E- and H-plane circulators. Each of them has

advantages which stems from the properties of the waveguide used as

the guiding structure or the location of the ferrite in the circulator

structure. In general, the power handeling of the E-plane circulator

is higher than the H-plane. This is due to the fact that the ferrite

is located at the point where the electric ﬁeld is minimum in the

waveguide. In addition, RF losses caused by the dielectric properties

of the ferrite will be smaller, thereby reducing the heating eﬀects.

Corresponding author: R. Saﬁan (rsaﬁan@cc.iut.ac.ir).

16 Razavipour et al.

H

dc

H

Z

X

Y

dc

(a) (b)

Figure 1. Geometries of E-plane and H-plane junctions of waveguide

circulators. Dotted line = Electric ﬁeld intensity.

Another problem that reduces the handling of high-power application

is that ferrite is a brittle material. Increasing the amplitude of one of

E or H ﬁelds to extremely high value in the ferrite region may tends to

ferrite crashing. An optimum way to keep it safe against any damage

is to place it in a dielectric substrate.

There have been several theoretical attempts to analyze and design

diﬀerent E-plane waveguide circulators [7, 9]. These analysis has led to

diﬀerent physical implementations of E-plane circulators [1–4]. But,

as far as we know there has not been any theocratical or experimental

attempts to design dual band circulator in the literature. In this paper,

a design procedure for high-power, dual-band or Left-Handed Right-

Handed (LH-RH) dual-band circulator is presented. The Ansoft HFSS

software is employed to optimize the response of circulator.The ﬁrst

part includes a brief theory of the dual band ferrite circulator and

diﬀerent techniques which can be used to increase the bandwidth and

decrease the insertion loss. The second part includes the design process

and optimization results.

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.

Progress In Electromagnetics Research C, Vol. 10, 2009 17

2.1. Dual Band Circulator

In general, circulators are three port networks. Hence, the associated

scattering parameters matrix is a 3 by 3 matrix. There are two possible

representation for a lossless circulator which is deﬁned as S

LH

and S

RH

with S parameter matrices,

S

LH

=

Ã

0 0 1

1 0 0

0 1 0

!

S

RH

=

Ã

0 1 0

0 0 1

1 0 0

!

In a “left handed circulator” (LHC) which is deﬁned by S

LH

the signal

circles counterclockwise and in the “right hand circulator” (RH) which

is deﬁned by S

RH

the signal circle in the clockwise direction. Any single

band circulator adopts one of these arrangements.

In a dual band circulator there are two possible demonstration.

A regular dual band circulator has right hand or left hand circulation

in two diﬀerent frequency bands. But, another possibility is a “LH-

RH dual band circulator” which has right hand circulation in one

frequency band and left hand circulation in an other one. Left hand-

right hand (LH-RH) circulators can be used as power combiner in

dual-band or multi-band transmitters [13] or in Radar applications.

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.

Another application (Figure 2(b)) is implementing the power sections

of a dual-band radar by means of two simple dual-band circulators (or

two broadband circulators) and one LH-RH dual-band circulator.

f1

f2

f2 f1

f1

f2

Broad Band

Antenna

Narrow Band

Transmitter 1

LH-RH Dual-Band

Circulator

(a)

f1

f2

(b)

Broad Band

Antenna

LH-RH Dual-Band

Circulator

Transmitter 1

Receiver 2 Receiver 1

Transmitter 2

Narrow Band

Transmitter 2

Figure 2. Schematics of two applications for LH-RH dual-band E-

plane circulator.

18 Razavipour et al.

2.2. Bandwidth

One important property of a circulator is its bandwidth which is

diﬀerent for E- and H-plane structures. Although E-plane circulators

have the capability of high power handeling, generally their bandwidth

is narrower compared to the H-plane structures. Hence, in general

there is a tradeoﬀ between bandwidth and high-power handling

properties. The physical structure of the E- and H-plane waveguides

dictates this trade-oﬀ. In most of the applications the high power

capability is superior to the bandwidth, hence, most of the circulators

are E-plane. But, some speciﬁc alteration in the ferrite structure

may lead to increasing the bandwidth in the E-plane structure.

For example, increasing the height of the ferrite post increases the

bandwidth. But, as the result of increasing the length of the ferrite,

concentration of the peak of T E

10

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. A well known technique is placing a

stack of thin dielectric disks of diminishing dielectric constant on top

of each ferrite disk [14]. Adding a single dielectric would also increase

the bandwidth but it has a lower impact. Here, we have placed two

short lengths of the ferrite on both sides of the E-plane waveguide to

increase the high power capability of the circulator. Also, the space

between the two pieces of ferrite is ﬁlled with a dielectric to increase

the bandwidth (Figure 3).

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. The triangular intersection is used in several cases [8, 15]

to decrease the reﬂection loss. As illustrated in Figure 4, implementing

the triangular ferrite can be done in two diﬀerent geometries. Based on

the performed simulations structure (a) has a better insertion loss than

(b). This is due to the fact that the propagating wave in Figure 4(a)

hits the tapered side of the ferrite post while in Figure 4(b) it faces

with the ﬂat surface of ferrite post, so the reﬂection in Figure 4(b)

is considerably larger than the reﬂection of tapered ferrite in the

geometry of Figure 4(a).

Progress In Electromagnetics Research C, Vol. 10, 2009 19

r

h

d

Figure 3. Physical geom-

etry of the triangular fer-

rite posts and the dielec-

tric ﬁlling around them.

(a) (b)

Figure 4. Geometries of two kinds

of ferrite placement in the waveguide

junction.

2.4. Modal Description of the Ferrite in E-plane Circulator

To simplify the analysis of the structure we have assumed that the

ferrite post and the dielectric ﬁlling have similar dielectric constant.

Hence, we can assume that the combination of the ferrite and the

dielectric ﬁlling form a cylindrical dielectric resonator. The theory of

fundamental cylindrical dielectric resonator mode presented in [5, 6].

Based on this approximation the lowest order mode of the ferrite

resonator is the T M

111

mode which is the dominant cylindrical

dielectric resonator. In the E-plane circulator the half height ferrite is

placed on the side wall of a waveguide as shown in Figure 1. The normal

mode components, E

z

and H

y

of the T E

10

waveguide can couple to the

similar ﬁeld components of the ferrite resonator. The application of a

dc magnetic ﬁeld in the Z direction will reorient the standing wave of

the resonator. With a proper reorientation a three-port circulator will

be obtained. The reorientation of the standing wave is caused by the

splitting of the T M

111

mode into the T M

+

111

and T M

−

111

modes by the

tensor permeability of the ferrite resonator. These modes correspond

to right-handed and left-handed circular polarization respectively. By

controlling the degree of this split, it is p ossible to adjust the resonant

frequency of circulator for gaining a nonreciprocal response.

Assuming the dielectric resonator ﬁlls the full height of the

waveguide junction, the approximate center frequency of the split mode

in free space is [5, 10–12],

2πr

λ

0

r

²µ

eﬀ

−

λ

0

2L

= 1.84 (1)

where λ

0

is the free space wavelength, r is the radius of the cavity, ² is

the relative permittivity, µ

eﬀ

is the relative eﬀective permeability and

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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 [3]....

[...]

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##### References

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01 Oct 1962TL;DR: In this paper, a frequency equation of first and second-order approximations was derived in terms of the dimensions and the anisotropic dielectric constant,??, for rectangular parallelepiped resonators.

Abstract: Pieces of single crystals of rutile show high Q resonances in the microwave range. A piece about (1/7?)3 has a Q as high as that of a metal-walled cavity at room temperature. Lowering the temperature increases both the Q and the resonant wavelength. Q's of 105 were seen at 4°K. A frequency equation of first- and second-order approximations was derived in terms of the dimensions and the anisotropic dielectric constant, ??, for rectangular parallelepiped resonators. Accurate values of anisotropic ?? were obtained. In the anisotropic medium there are two types of resonant modes, one of which has an outside E field similar to an electric multipole, and the other an outside magnetic field similar to a magnetic multipole. These two types of modes degenerate into one type if the dielectric is isotropic. Resonators were also made of ceramic rutile and strontium titanate, both of which had Q values of thousands. An extremely high unloaded Q, of the order of a million, was seen at 1.4°K on a KRS-5 (ThBr-Thl) single crystal at X band.

200 citations

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Cairo University

^{1}TL;DR: In this article, an exact field theory treatment for the waveguide junction circulators is presented, being dependent on neither the geometrical symmetry of the junction nor the number of ports.

Abstract: In this paper an exact field theory treatment for the waveguide junction circulators is presented. The treatment is general, being dependent on neither the geometrical symmetry of the junction nor the number of ports. The electromagnetic fields in the joining waveguides are written in the form of infinite summation of waveguide modes. The solutions of the wave equations in the ferrite rod and in the surrounding air are obtained in the form of infinite summation of cylindrical modes. The fields at the ferrite air interface and at an imaginary boundary chosen arbitrarily between the air region and the waveguides are then matched. This process leads to an infinite system of nonhomogeneous equations in the field amplitudes. Three types of waveguide junction circulators using this technique are analyzed: the simple ferrite-rod Y junction, the simple ferrite-rod T junction, and the latching Y junction. Point-matching techniques are used to get numerical results for the field distributions and the circulator characteristics. Excellent agreement has been found between the published experimental measurements and the numerical results obtained by this technique.

34 citations

### "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 [13] or in Radar applications....

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Abstract: A useful quantity in the description of junction circulators is the difference between the split frequencies of the magnetized ferrite resonator. A knowledge of this quantity allows the loaded Q-factor of a junction using a weakly magnetized resonator to be determined. This paper derives an exact description of the former quantity in the case of the open quarter-wave long (partial-height) disk resonator used in the construction of commercial turnstile waveguide circulators. This is done by employing duality between a ferrite-filled circular waveguide having ideal electric wall boundary conditions and one having ideal magnetic wall boundaries. The effect of an image wall on the open flat face of the open resonator is considered separately. The paper includes some remarks about the susceptance slope parameters of disk and triangular open resonators.

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### "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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Abstract: When a circulator is used with a parametric amplifier or maser, the noise contribution of the circulator may be reduced by cooling it in liquid nitrogen or liquid helium. Compact devices are required to put in the dewar and, depending on the microwave frequency, a compromise may be necessary in choosing between a compact stripline circulator and a comparatively bulky H-plane waveguide circulator, because waveguide feeds will have lower loss than coaxial line. This problem may be eased by using a very compact E-plane waveguide circulator, as shown in Fig. 1(a).

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Abstract: This report describes the design and performance of an improved E-plane waveguide circulator. Although the E-plane circulator has the advantages of higher power operation and more compactness, it has received much less attention than its H-plane counterpart. This has probably been due to the difficulty of achieving broadband performance and the lack of adequate design information. It is proposed in this report that best performance occurs when the dimensions of the ferrite cylinder are adequate to support the fundamental cylindrical dielectric resonator mode. The junction dimensions are reduced to enhance the coupling of the incident energy to this dielectric resonator. At the junction, a novel approach is employed to convert the absorption type cavity to a transmission type. Reduced height transformers match the junction to the standard waveguide ports.

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