(chapter 4 - design of the spdt with modified cea-leti desi_205)

8/2/2019 (Chapter 4 - Design of the SPDT With Modified CEA-LETI Desi_205)

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Design and Characterization of Reliable RF-MEMS

Routin circuits for s ace a lications

Chapter 4: Design of the SPDT

with modified CEA-LETI designs

CHAPTER 4: DESIGN OF THE SPDT WITH

MODIFIED CAPACITIVE CEA-LETI DESIGNS

4.1 DEFINITION OF THE TOPOLOGY OF THE DESIGN

From a theoretical point of view, the first step in the design of the SPDT is to choose the

topology that is going to be used. The possible configurations were presented in Chapter 1

and, between them; the one which will be used is the /4. In the analysis of the different

topologies for the specific application, the parameters that are taken into account are the fact

that the SPDT is for space applications and the limitations of the technology. Below, the

reasons of the chosen topology are shown.

The first configuration that is discarded is the one that combines resistive and capacitive

switches. The reason is that the available technology does not allow the fabrication of both

types of MEMS at the same time. Despite both types have the same actuation method, the

masks of the fabrication process does not coincide. However, it is possible that in future

implementations, this option should be studied.

Since the environment where the SPDT will be is the space, the structure should be as simple

as possible. For this reason the topology with filters is discarded. At the same time, if the filter

is eliminated, the probability of failure and the complexity of the design decrease.

Continuing with the concept of space application, the stress that the component will suffer is

very high. This appreciation makes that the design with the free flexible membrane not useful

because a little movement in the equipment will vary the behaviour. Moreover, the radiation

suffered by the satellite could also change the movement of the membrane.

In conclusion, since the structure should be as simple as possible, the most suitable is the /4

topology. From this point it can be discussed the suitability of using one or two switch

depending on the level of isolation and the input matching. In following points, this

discussion will be treated.


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4.1.1 TYPES OF JUNCTION AND AIRBRIDGES

The most suitable topology proposed in 4.1, requires two lines which will be joint by a

junction. This junction should be specifically designed so as to acquire the maximum input

matching and to minimize the insertion losses. With these conditions four types of junctions

are proposed: T-straight, Y-junction, U-wide and U-narrow. They are going to be discussed

below.

The first junction, T-straight is studied in [1] using different types

of airbridges. This type of junction separates the signal in two

parallel paths which form a 90 angle with the input signal as it

can be seen in Figure 4.1. The airbridges are disposed so as to

avoid the radiation of the cut ground planes and the propagation

of the undesired modes. Depending of the length of the out

lines, more airbridges can be added so as to make the line smaller.

The most relevant problem that the T-straight presents is the disposition of the three ports.

The ideal disposition should be that both input ports are in the same plane, so, others corners

should be added. This will affect to the behaviour introducing more undesired modes and

losses.

So as to avoid the three planes problem, the suitable junctions are Y and U. The first one will

have to straight lines and the second one curved lines. This difference implies that the length

of the line will vary. For the same reason of the one presented in the previous type, airbridges

are also necessary. In Figure 4.2 and schema of both configurations is shown.

Figure 4.1: Scheme of the T-straight

IN

OUT 1 OUT 2

IN

OUT 1 OUT 2

IN

OUT 1 OUT 2

Figure 4.2: Scheme of the U-junction (left) and Y-junction (right)


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Concerning on the used airbridges, the ones that will be used are the conventional design [1].

Despite not having substantial differences between different airbridges, CEA-LETI

recommends airbridges of 20um width because they have tested them with excellent results.

The width of the airbridge is set so as to avoid the actuation with the power that will pass

through the central conductor.

4.2 IMPLEMENTATION OF THE DESIGNS WITH ONE MEMS

With the different options presented in 4.1.1 five different designs are conceived using the

selected MEMS in Chapter 2. One is done with T-straight, one with Y-junction and three withU-junction. As it will be seen below, U-junction present better performances so more

importance will be given to this topology with the three designs. A value that will be common

in all the designs is the length of the /4 line and will be calculated with a central frequency of

13GHz and an r=11.9 as follows.

4.2.1 T-STRAIGHT DESIGN

Using the T-straight junction and AMA design with the modifications proposed in Chapter 2,

the SPDT presented in Figure 4.3 is designed. The Coplanar Line used is 45/80/45 (G/W/G)

that results a characteristic impedance of 50Ohms. The used airbridges are 20um width as it

was recommended by the foundry.

Figure 4.3 Layout of the T-straight design

1.7 mm

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1

The length of the line (1.7mm) is bigger than the predicted in the theory due to the losses in

input matching of the junction. This length of the line can be reduced using airbridges so as to

change the velocity of propagation of the signal. Without airbridges, a maximum input

matching of 18dB is achieved at 13GHz and is under 15dB between 12GHz and 14GHz and,

losses are approximately 0.5dB in the same range. However, with three airbridges in each arm

separated 300um, the length of the line can be reduced till 1.6mm and the input matching and

losses have the same values than before (Figure 4.4).

As it was announced in 4.1.1, the T-straight topology needs

additional corners so as to have both output ports in the same

plane. The proposed design is shown in Figure 4.5 and it is

based on a 90 corner. This type of corners introduces

undesired modes and losses that are eliminated with the

airbridges.

The results of the simulations with the corners are showed in

Figure 4.6. In this case, a better input match is achieved arriving to 25dB at 13GHz and also

the losses decrease in the range of interest. However, the isolation between the input port and

the actuated one has similar values with the previous design.

11 .5 12.0 12.5 13.0 13.5 14.0 14 .511.0 15.0

-0.7

-0.6

-0.5

-0.4

-0.3

-0.8

-0.2

freq, GHz

d

B(S(1,2

))

m3m4

m3freq=dB(S(1,2))=-0.427

12.00GHz

m4freq=dB(S(1,2))=-0.357

14.00GHz

Figure 4.5: Layout of the T-straight design

with 90 corners.

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-18

-16

-14

-12

-20

-10

freq, GHz

dB

(S(1,1

)) m1m2

m1freq=dB(S(1,1))=-14.791

12.00GHzm2freq=dB(S(1,1))=-15.956

14.00GHz

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-20

-18

-16

-14

-22

-12

freq, GHz

dB(S(1,3

))

Figure 4.4 Results of the simulation of the design T-straight with airbridges. Port 2 contains

the non-actuated MEMS while port 3 contains the actuated one.

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4.2.2 Y-JUNCTION DESIGN

So as to avoid the possible perturbations of the 90 corners, the design with the Y-junction is

done. The idea is to have the /4 lines as straight as possible so as to improve the losses

caused by corners in previous designs. The used Coplanar Line is also 45/80/45 and the length

is 1.7mm for each arm. The MEMS used is the AMA design modified in Chapter 2 as it can

be seen in Figure 4.7.

In the junction and in corner areas, airbridges of 20um are also

inserted. Moreover, through the lines, other ones are added but

they improve neither the performances nor the length of the

line.

The results of the simulations are shown in Figure 4.8. They

demonstrate that the input matching is increased (till 28dB in

13GHz) while the losses are maintained to a maximum of

0.3dB in the interest band. The isolation is nearly constant in the entire band around 15dB.

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-1

-2

0

freq, GHz

dB

(S(1,3

))

m3m4

m3freq=dB(S(1,3))=-0.255

12.03GHzm4freq=dB(S(1,3))=-0.147

14.01GHz

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-24

-22

-20

-18

-16

-14

-12

-26

-10

freq, GHz

dB

(S(1,1

))

m7 m8

m7freq=dB(S(1,1))=-18.471

12.03GHzm8freq=dB(S(1,1))=-18.815

14.01GHz

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-20

-15

-25

-10

freq, GHz

dB(S(1,2

))

Figure 4.6: Results of the simulations of the T-straight with corners. Port 2 contains

the actuated MEMS while Port 3 contains the non actuated one

Figure 4.7: Layout of the Y-junction

design

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The worst problem that this design presents is that at 15GHz a little resonance appears due to

the sharp shape of the junction.

So as to treat the presented problem, the sharp shapes are

eliminated resulting in the design presented in Figure 4.9.

However, the results do not improve as expected so this design is

not considered anymore. The most important problem is that the

junction has been improved but more corners are added.

4.2.3 U-JUNCTION DESIGNS

From the design presented before in Figure 4.9, the question that comes immediately to the

mind is if it is possible to eliminate the corners while maintaining the same junction. The

answer is, logically, yes, and this solution is developed in this part. As it has seen that it could

be a good solution, three different designs are presented: Narrow-Tee, Wide-Tee and Non-

inductive MEMS with constant width of the lines. The two firsts are developed with the

1 1.5 12 .0 1 2.5 13 .0 13.5 1 4.0 1 4.511.0 15.0

-25

-20

-15

-10

-5

-30

0

freq, GHz

dB(S(1,1

))

m5m6

m5freq=dB(S(1,1))=-18.815

11.99GHzm6freq=dB(S(1,1))=-16.404

13.99GHz

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-8

-6

-4

-2

-10

0

freq, GHz

dB(S(1,3

))

m7 m8

m7freq=dB(S(1,3))=-0.262

11.99GHz

m8freq=dB(S(1,3))=-0.291

13.99GHz

11. 5 12 .0 12 .5 13.0 13. 5 14. 0 14. 511.0 15.0

-30

-20

-10

-40

0

freq, GHz

dB(S(1,2

))

Figure 4.8: Results of the simulation of the Y-junction design. Port 2 is the

one with the actuated MEMS and Port 3 is the non-actuated one

Figure 4.9: Layout of possible

improvements in Y-junction design


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MEMS used in the previous designs but the last one uses the MEMS presented in Chapter 2

as non-inductive.

The three designs are based in three different types of lines but all of them have a

characteristic impedance of 50Ohms. The dimensions of the lines are calculated building an

equivalent SPICE model that has been optimized with the tuning option of ADS so as to reach

the specifications defined at the beginning of Chapter 2. At the same time, the optimal number

of airbridges is added so as to reduce the size of the design as much as possible.

Narrow-Tee

This design is presented in Figure 4.10. A part of the

three airbridges inserted in the junction so as to avoid

the radiation of the line, two other ones are added in

each /4 line. The sizes of the lines are:

- Input line: 50/80/50 and L=607.35um

- Tee-junction: 26/40/26

- /4 line: 1.67mm

The size of the /4 line has not been reduced for a theoretical point of view. However, since

the junction used is straight, the line should be larger than 1.67mm so the airbridges

compensate the effect of the straight line.

The results for this design are presented in Figure 4.11. A maximum input matching of 33dB

is achieved in the central frequency while it is under 20dB in all the interest range. The

insertion losses are over 0.3dB in all the range and the isolation is between 15 and 20dB.

These results are mostly positives and accomplish the specification except for the isolation.

Figure 4.10: Layout of the Narrow-Tee design

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Wide-Tee

As it has been commented before, the fact that the junction

is narrow does not allow reducing the size of the design. For

this reason, the design presented in Figure 4.12 has been

thought with a wide Tee. The sizes of each part are:

- Input line: 45/80/45


- /4 line: 1.63mm

This design is smaller than the previous one due to the effect of the two airbridges added in

each /4 line. The obtained reduction is about 40um which is not a huge value but it makes

the design as compact as possible.

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-30

-25

-20

-15

-35

-10

freq, GHz

dB(S(1,1

))

m9 m10m9freq=dB(S(1,1))=-19.422

12.00GHzm10freq=dB(S(1,1))=-19.741

14.01GHz

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-0.4

-0.3

-0.2

-0.5

-0.1

freq, GHz

dB(S(1,3

))

m5m6

m5freq=dB(S(1,3))=-0.183

14.50GHzm6freq=dB(S(1,3))=-0.214

12.00GHz

11.5 12.0 12.5 13 .0 1 3.5 1 4.0 14.511.0 15.0

-20

-18

-16

-14

-22

-12

freq, GHz

dB(S(2,3

))

m7

m8

m7freq=dB(S(2,3))=-15.484

12.00GHz

m8freq=dB(S(2,3))=-19.409

14.01GHz

Figure 4.11: Results of the simulation of the Narrow-Tee design. Port 3

contains the non-actuated MEMS while Port 2 contains the actuated one

Figure 4.12: Layout of the Wide-Tee design

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-25

-20

-15

-10

-5

-30

0

freq, GHz

dB(S(1,1

))

m9m10

m9freq=dB(S(1,1))=-17.036

11.99GHz m10freq=dB(S(1,1))=-19.946

13.99GHz

11.5 12 .0 12 .5 13 .0 13 .5 14 .0 14.511.0 15.0

-0.4

-0.3

-0.2

-0.1

-0.5

0.0

freq, GHz

dB(S(1,3

))

m5

m6m5freq=dB(S(1,3))=-0.277

11.99GHz

m6freq=dB(S(1,3))=-0.136

13.99GHz

2 3

1


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The results of the simulations in Figure 4.13 show good agreement with the specifications.

They are similar than the presented in the narrow case in terms of insertion losses and

isolation, but with lower input matching (27dB maximum in central frequency). Another time,

the value which should be improved is the isolation since is between 15 and 20dB.

Non-inductive MEMS with constant width

For the moment it is seen that the U-junction gives the better results in terms of input

matching and insertion losses. For this reason it is proposed to use, with this configuration,

one of the proposed designs in Chapter 2: the

non-inductive AMA.

Since in the proposed MEMS the width of the

central conductor is constant, it is proposed to

maintain this width in all the design. With

different simulations with SPICE models it is also

confirmed that this size is the optimal one and the

size of the three lines are fixed to 69/116/69 that means 50Ohms of characteristic impedance.

In Figure 4.13 the design of the SPDT with the non-inductive MEMS is presented.

The size of the /4 line is fixed to 2.26mm which is higher than the theoretical one. The

reason is that the non-inductive MEMS losses its input matching when the inductive part is

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-20

-15

-10

-5

-25

0

freq, GHz

dB(S(1,2

))

m3m4

m3freq=dB(S(1,2))=-14.257

11.99GHzm4freq=

dB(S(1,2))=-18.758

13.99GHz

Figure 4.12: Results of the simulation of the Wide-Tee design. Port 3 contains

the non-actuated MEMS while Port 2 contains the actuated one

Figure 4.13: Layout of the design with non-inductive MEMS

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eliminated. This effect should be compensated by length of the lines and also by the

airbridges which are inserted in pairs in each line.

The results of the simulation are shown on Figure 4.14. The input matching is 50dB at 13GHz

while it is under 20dB in the range of interest. Insertion losses are about 0.2dB approximately

in all the range so they are quit constant. However, like in all the cases presented before, the

isolation is the worst parameter, being 15dB as maximum value.

4.3 IMPLEMENTATION OF THE DESIGNS WITH TWO MEMS

A common characteristic that all the presented designs have is the poor values of isolation.

They are between 15dB and 20dB, which are not very bad but they are really far from the

objective. The proposed solution is to add another MEMS on each branch of the SPDT with

U-junction so as to isolate more heavily the input and actuated output port. This decision

should take into account two important consequences. The first one is that the probability of

failure increases when more MEMS are added and the second one is that the values of inputmatching could be affected negatively.

11. 5 12. 0 12. 5 13. 0 13. 5 14. 0 14. 511.0 15.0

-50

-40

-30

-20

-60

-10

freq, GHz

dB(S

(1,1

))

m7 m8

m7freq=dB(S(1,1))=-20.48

12.00GHz m8freq=dB(S(1,1))=-20.11

14.00GHz

11.5 12. 0 12.5 13.0 13.5 14.0 14.511.0 15.0

-0.8

-0.6

-0.4

-0.2

-1.0

0.0

freq, GHz

dB(S(1,3

))

m5m6

m5freq=

dB(S(1,3))=-0.175

11.97GHzm6freq=dB(S(1,3))=-0.251

14.00GHz

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-16

-14

-12

-10

-18

-8

freq, GHz

dB(S(1,2

))

m3

m4

m3freq=dB(S(1,2))=-16.029

12.00GHz

m4freq=dB(S(1,2))=-14.387

14.05GHz

Figure 4.14: Results of the simulation of the design with the non-inductive

MEMS. Port 3 contains the non-actuated MEMS while Port 2 contains the

actuated one


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For the first consequence, an intermediate solution can be proposed. It is based on add another

MEMS which will be never actuated, it works only as an airbridge. On the other hand, for the

input matching, the dimensions of the lines can be modified so as to reach the objective. In

this part, three new designs are presented so as to solve the problem of input matching and

isolation and it is discussed the suitability of actuate or not the second MEMS.

4.3.1 NARROW-TEE WITH TWO SWITCHES

From the Narrow-Tee design presented before, another MEMS is added in each branch

resulting in the design of the Figure 4.15. The dimensions of the lines are computed with

equivalent SPICE models so as to reach the objective input matching. However, these values

are quite far from the results of the simulation and should be

readjusted by heart with these values:



- /4 line: 72/118/72 L=1.97mm

- Line between MEMS: 115/50/115 L=227um

The results are presented in Figure 4.16. As it was expected,

the input matching becomes poorer but still under 15dB in the

interest range. However, the isolation is between 20 and 35dB

that means that it has been improved in 10dB when the two switches in the same branch are

actuated. Insertion losses keep similar values than with one switch (over 0.2dB in the entire

band).

1

Figure 4.15: Layout of the Narrow-Tee with

two switches design

11 .5 12 .0 1 2.5 1 3.0 13 .5 14 .0 1 4.511.0 15.0

-20

-15

-10

-5

-25

0

freq, GHz

dB(S(1,1

))

m9

m10

m9freq=dB(S(1,1))=-16.586

12.00GHzm10freq=dB(S(1,1))=-21.895

14.00GHz

11.5 12.0 12 .5 13 .0 13 .5 14.0 14 .511.0 15.0

-0.8

-0.6

-0.4

-0.2

-1.0

0.0

freq, GHz

dB(S(1,3

))

m1m2

m1freq=dB(S(1,3))=-0.219

12.00GHzm2freq=dB(S(1,3))=-0.147

14.00GHz

2 3

1

1


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4.3.2 WIDE-TEE WITH TWO SWITCHES

This design (Figure 4.17) is conceived as an extension of the Wide-Tee model presented

before. As it was done in 4.3.1, the initial dimensions of the lines are computed with the

SPICE model but, as before, they do not match very well with the EM simulation. The

dimensions of the lines so as to satisfy the specifications are:



- /4 line: 72/118/72 L=1.51mm

- Line between MEMS: 115/50/115 L=227um

This design is more compact than the one presented in

4.3.1 and, as it can be seen in Figure 4.18, the input

matching and the isolation are strongly better. However,

referring to the insertion losses, despite being constant

in the band of interest (over -0.5dB), an important drop

in this value is achieved near 15GHz. The implications of this could be that a small

fabrication error could make the design useless. The reason of this little resonance is that in

the phase of the S13 parameter at 15GHz, an electrical length of 180 is achieved. To solve

this inconvenience it has been tried to vary the length of the lines and it is seen that there is a

trade off between the position of this resonance and the input matching. When one gets better

the other become worse. For this reason, the design is finally set with the values presented at

the beginning.

11.5 12.0 12 .5 13.0 13.5 14 .0 14.511.0 15.0

-30

-20

-10

-40

0

freq, GHz

dB(S(1,2

))

m5

m6

m5freq=dB(S(1,2))=-20.039

12.00GHz

m6freq=dB(S(1,2))=-34.433

14.00GHz

Figure 4.16: Results of the simulation of the Narrow-Tee design with two MEMS.

Port 3 contains the non-actuated MEMS while Port 2 contains the actuated ones

3

1

Figure 4.17: Layout of the Wide-Tee with two

switches design

2


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4.3.3 TWO NON-INDUCTIVE SWITCHES WITH CONSTANT WIDTH

The third design is based on the design with non-inductive MEMS presented in 4.2.3. In this

case, as the option of the two actuated MEMS at the same time does not reach the

specifications, it is proposed to add another non-actuated MEMS. In Figure 4.19 the design is

showed.

The dimensions of all the lines are 69/116/69 so as

to have 50 Ohms of characteristic impedance.

However, the length varies depending on the line:

- Input line: L=607.35um

- From Tee-junction to first switch: L=367um

- Between switches: L=1.6mm

11.5 12 .0 12.5 13.0 13.5 14 .0 14 .511.0 15.0

-30

-20

-10

-40

0

freq, GHz

dB(S(1,1

))

m10m11

m10freq=dB(S(1,1))=-15.386

12.05GHz

m11freq=dB(S(1,1))=-17.861

14.01GHz

11.5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-6

-4

-2

-8

0

freq, GHz

dB(

S(1,3

))

m3 m4

m3freq=dB(S(1,3))=-0.403

11.70GHzm4freq=dB(S(1,3))=-0.551

14.51GHz

11.5 12.0 12.5 13.0 13 .5 14.0 14 .511.0 15.0

-40

-30

-20

-10

-50

0

freq, GHz

dB(S(1,2

))

m5

m6m5freq=dB(S(1,2))=-15.721

11.70GHz

m6freq=dB(S(1,2))=-31.437

14.51GHz

Figure 4.18: Results of the simulation of the Wide-Tee design with two MEMS. Port 3

contains the non-actuated MEMS while Port 2 contains the actuated ones

Figure 4.19: Layout of the design with two non-inductive

MEMS and only one actuated

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The results for this design are shown in Figure 4.20. Between 12 and 14GHz, an input

matching lower that 20dB is achieved (maximum of 32dB in 13GHz). However, the

computed insertion losses are higher than with one MEMS but also accomplish the

specifications. In terms of isolation, there has not been a notable improvement so it has no

sense to introduce an element that could damage the structure and is not improving the

characteristics.

11. 5 12.0 12.5 13.0 13.5 14.0 14.511.0 15.0

-0.8

-0.6

-0.4

-1.0

-0.2

freq, GHz

dB(S(1,3

))

m5 m6

m5freq=dB(S(1,3))=-0.438

11.96GHzm6freq=dB(S(1,3))=-0.411

14.00GHz

11.5 12.0 12 .5 13.0 13.5 14 .0 14.511.0 15.0

-30

-25

-20

-15

-35

-10

freq, GHz

dB(S(1,1

))

m1 m2

m1freq=dB(S(1,1))=-20.133

12.00GHz

m2freq=dB(S(1,1))=-20.102

14.00GHz

11.5 12.0 12.5 13.0 13 .5 14.0 14.511.0 15.0

-16.5

-15.0

-13.5

-12.0

-18.0

-10.5

freq, GHz

dB(S(1,2

))

m3

m4m3freq=dB(S(1,2))=-13.0

12.00GHz

m4freq=dB(S(1,2))=-14.7

14.00GHz

Figure 4.20: Results of the simulation of the design with two inductive MEMS.

Port 3 contains the non-actuated MEMS while Port 2 contains the actuated ones


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4.4 CONCLUSIONS

In this chapter different designs have been presented with different topologies. Regarding at

the results of the simulations, resumed in Table 4.1 and Table 4.2, the most suitable topology

is the U-junction since it achieves better performances in terms of input matching and

insertion losses. Moreover, all the range of the frequencies is equally treated.

Discarding the other types of topology, it has been seen that the design with narrow tee

present better performances than the width tee in all the aspects. So, the two designs which

have similar performances are the narrow tee and the non-inductive MEMS design. In terms

of input matching the second one achieves near 50dB in the central frequency while the first

one arrives only till 32dB. However, both of them achieve values of input matching under

20dB in the range of interest and similar results in insertion losses (around 0.2dB maximum)

and isolation (between 15 and 18dB in both cases). In the case of one switch, the design with

better performances is the one which uses non-inductive MEMS.

Trying to improve the isolation, it has been seen that a second MEMS can be a possibility that

can be considered. In the design with non-inductive MEMS, the solution was not valid

because there was no design that, actuating both switches, reaches the desired specifications.

Moreover, if the MEMS was inserted but was not actuated, there were no improvements in the

isolation. However, in the case of the design with the wide tee and two switches, the

improvement in isolation was 10dB better than with one switch. In the case of two switches,

the design with better performances is the wide tee one.

The final decision of the suitable design should take into account the trade off between the

probability of failure and the isolation parameter. Since the application of this design is the

space communications, the probability of failure take relevance in front of the specifications.

Space equipment is very expensive so it is better to be sure that it is going to work than

predict greater performances. In conclusion, the best design for the space application is the

one with one non-inductive switch and constant width of the line.


16/16

45





Ku-Band (11-15 GHz)

S11 S31 S21 S23

T-Straight -13dB to -17dB -0.48dB -12dB to -25dB -12dB to -20dB

T-Corners -15dB to -25dB -0.32dB -15dB to -22dB -14.4dB to -20dB

Y-Junction -10.9 to -25dB -1.06dB -13dB to -16.8dB -14dB to -17.5dB

U-wide -14.2dB to -22dB -0.32dB -15dB to -20dB -14dB to -19dBU-wide-air -15dB to -26dB -0.35dB -13.6dB to -19.6dB -14dB to -20dB

U-narrow-air -18.7dB to -38dB -0.25dB -14dB to -20dB -15dB to -20dB

U-wide-air-

2switch

-12dB to -38dB -0.5dB -16dB to -45dB -16dB to -52dB

U-narrow-air-

2switch


Table 4.1: Values of S-Parameters for the exposed designs for the entire Ku-Band

Central Ku (12-14 GHz)

S11 S31 S21 S23T-Straight -15dB to -17dB -0.42dB -12.5dB to -25dB -12dB to -20dB

T-Corners -18dB to -25dB -0.25dB -14dB to -18.8dB -15dB to -19.2dB

Y-Junction -16.4dB to -26dB -0.29dB -14dB to -17.3dB -14.7dB to -17.5dB

U-wide -17dB to -22dB -0.26dB -15dB to -19dB -15.7dB to -19dB

U-wide-air -17dB to -22dB -0.3dB -14.3dB to -18.7dB -15dB to -19dB

U-narrow-air -18dB to -38dB -0.2dB -15dB to -19dB -15dB to -19dB

U-wide-air-

2switch


U-narrow-air-

2switch


Table 4.2: Values of S-Parameters for the exposed designs for the central Ku-Band

REFERENCES

[1] K. Beilenhoff, W. Heinrich, H.L. Hartnagel, Analysis for T-junctions for coplanar

MMICS IEEE MTT-S Digest 1994

(chapter 4 - design of the spdt with modified cea-leti desi_205)

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