Substrate Integrated Waveguide based Hybrid Cavity Filter for ... - ITRA

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Athira Gopinath is with the Amrita Centre for Wireless Networks & ... Amrita School of Engineering, Amritapuri, Amrita Vishwa Vidyapeetham,. Amrita University ...
International Conference on Communication and Signal Processing, April 6-8, 2017, India

Substrate Integrated Waveguide based Hybrid Cavity Filter for Ku Band Applications Athira Gopinath and Rahul Lal P  Abstract—In this paper a hybrid cavity substrate integrated waveguide filter is proposed and demonstrated for Ku band application. Hybrid cavity which is the combination of both circular and rectangular cavity, showcases a better frequency selectivity and Quality Factor in comparison with other cavity based substrate integrated waveguide filters. Quality Factor requirements are met by the introduction of shorting posts at specified points inside the cavity. Filter operates at a frequency of 13GHz with an optimized Q factor of 377.096.The detailed analysis of the proposed structure is simulated and studied using the ANSYS HFSS software. Index Terms—Bandpass Filter, Hybrid Cavity, Substrate Integrated Waveguide (SIW), Q Factor.

I. INTRODUCTION

A

breakneck development of mobile and wireless communication system calls for more and more filters with high selectivity, small size and low profile. While working in a particular band filters can take into account the required frequencies to go across and reject the unwanted frequencies. High quality filter enhances the functioning of the whole communication system. Filters are necessary at the transmitter and receiver end of any communication system as the sending and receiving antenna can handle a broad bandwidth. In RF communication, filters with compact size and high performance have been widely implemented using micro strip lines [1], co-planar waveguides [2, 3] and metallic waveguides. Transmission lines like micro stripline and coplanar waveguides are easy to fabricate and being planar in nature it can be easily integrated with planar circuits implemented on PCB. But due to the low power handling capacity of such transmission lines, restrict them to handle lower frequencies. On the other hand metallic waveguides can handle high power and are used as filters [4], couplers [5], and power dividers [6] etc...Non-planar behavior of conventional waveguides makes it difficult to blend it with the planar counterparts.

Athira Gopinath is with the Amrita Centre for Wireless Networks & Applications (AmritaWNA), Amrita School of Engineering, Amritapuri, Amrita Vishwa Vidyapeetham, Amrita University, India. (email: [email protected]) Rahul Lal P, is with Department of Electronics and Communication, Amrita School of Engineering, Amritapuri, Amrita Vishwa Vidyapeetham, Amrita University, India.(email: [email protected])

To beat the constraints of transmission lines, a new promising platform called substrate integrated waveguide came into existence. SIW is an inherent dielectric filled waveguide, by densely arraying the metallic shorting posts which link up the upper and lower of ground plates. Substrate integrates waveguide has the chief qualities of both transmission lines and conventional waveguides. The planar nature of SIW helps ease them to merge with planar circuits and makes the system to be more compact. SIW can guide the signals ranging from sub-GHz to sub-THz frequencies based on the quality of the substrate used. Since SIW is able to carry more power, the losses are less compared to transmission lines [7]. Several SIW filters are implemented using different geometries with low Q factor [8]. The current paper deals with a substrate integrated waveguide based filter with hybrid cavity operating in Ku band are created. Hybrid cavity with metalized posts at designated locations within them enhances the Q factor of the filter. The design and simulation results are discussed in detail under the coming sections. Section II describes the filter design of SIW. Section III mentions about simulation and analysis of Hybrid Cavity filter. II. FILTER DESIGN A. SIW Filter Design The hybrid cavity filter is designed and simulated over a dielectric substrate RT/Duroid5880 with a dielectric constant H r =2.2, loss tangent, tan δ = 0.0009 and having a thickness of h=0. 254mm. The design equations are as follows:The resonant frequency of a rectangular waveguide is given as [9] 2

c § p3 · § q3 · ¸ ¨ ¸ ¨ 23 © x ¹ ¨© y ¸¹

fc

2

(1)

Where x’ and ‘y’ are the length and breadth of rectangular waveguide and ‘p’ and ‘q’ are the mode number of waveguide. For TE10 mode, equation (1) is reduced to

978-1-5090-3800-8/17/$31.00 ©2017 IEEE

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fc

c 2x

(2)

For a Dielectric Filled Waveguide, the length of the waveguide became

x

xd

(3)

Hr

0

Og

23 2

§ 23f c · § 3 · ¨ ¸ ¨ ¸ © c ¹ ©x¹

2

S Parameters(dB)

The conducted wavelength is presented by; (4)

2r d

5

-30

Insertion Loss Reflection Loss

-50

& p d 4r

10

(5)

xd 

2r

2

0.95 p

12

14

16

18

20

22

24

26

Frequency(Hz) Fig. 2. Variation of S parameters with respect to frequency

The spacing between metallic vias

as

-20

-40

The diameter (2r) and pitch (p) should satisfy the conditions

Og

-10

(6)

For the analysis, the designed value for diameter r =0.5mm and pitch p= 2mm and spacing between metallic visa is taken as a s =7.88mm.

B. Hybrid cavity with metallized post at center Inorder to obtain filter characteristics a metallized post is provided at the center of the hybrid cavity. The existence of metallized post at the center of the cavity tends to distribute the electromagnetic field around the metallized post .Geometry of the hybrid cavity with metallized post at the center is demonstrated in Fig.3.

III. SIMULATION AND ANALYSIS A. Hybrid Cavity The geometry of hybrid cavity filter is as shown in Fig.1. As discussed earlier, since the spacing between the metallic vias is doubled inside the cavity, the field entering the cavity is entirely distributed throughout the volume. Fig. 3. Geometry of Hybrid cavity filter with metallized post at the center

The insertion and reflection loss are as demonstrated in Fig4. The high pass nature of the Hybrid Cavity is transformed into a band pass characteristics with a Q of 5.25 at 14.1313GHz. 0

Fig. 1. Geometry of Hybrid cavity SIW filter

Fig.2. indicates the insertion and reflection loss of Hybrid Cavity filter with no metallized post inside the cavity. Based on the result obtained the hybrid cavity filter still act as high pass filter like an ordinary SIW waveguide.

S Parameters(dB)

-2

-4

-6

-8

Insertion Loss Reflection Loss

-10

-12 12

13

14

15

16

17

18

Frequency(Hz)

Fig. 4. Variation of S parameters with respect to frequency

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19

C. Hybrid Cavity with 3 Metallized Post In order to maximize the Q factor and maintain symmetry, two more metallized post are provided beside to the shorting post at the center. This alters the volume inside the cavity and fields are forced to take alternate paths at the interface. The multiple recombination and splitting up of the fields within the cavity results in the enhancement of the Q factor of the filter. Geometry of hybrid cavity filter with three metallized posts is shown in Fig.5.

0

S Parameters(dB)

-10

-20

-30

-40

Insertion Loss Reflection Loss

-50

-60 12

14

16

18

20

22

24

26

Frequency(Hz)

Fig. 6. Variation of S parameter with respect to frequency

Fig. 5. Geometry of Hybrid cavity filter with three metallized posts.

With respect to the position of the metallized posts inside the cavity, Q factor of the filter is varied significantly. Table 1 shows the variation of filter characteristics with respect to the change in the offset length of metallic vias from the center metallic via. TABLE I VARIATION OF FILTER CHARACTERISTICS WITH RESPECT TO OFFSET LENGTH

Offset Length 2mm

Centre frequency 19.3535

Bandwidth

Q factor

8.404

Insertion loss -0.1354

4mm

20.667

9.5858

-0.1410

2.1560

6mm

16.0707

1.7071

-0.1854

9.4140

8mm

20.2727

3.9394

-0.1549

5.1461

10mm

19.4848

5.7778

-0.1671

3.3723

D. Hybrid Cavity with 7 metallized posts From Fig. 6. it is obvious that the Q factor of a hybrid cavity filter is not getting increased by changing the offset length alone. Furthermore for enhancement in Q factor, the area inside the cavity still needs to be reduced. For the sake of improving the Q factor of the hybrid Q filter, it is needed to incorporate more shorting posts at the optimized locations inside the hybrid cavity. Inorder to attain the above mentioned criteria 4 metallic vias are placed adjacent to the initial 3, there by utilizing the entire volume inside the cavity. As a result of this more fields get confined in the hybrid cavity, thereby enhancing the Q factor with a better a return loss. Geometry of hybrid cavity filter with a total of 7 metallized posts is shown in Fig.7.

2.302

From the analysis, for an offset length of 10mm a Q factor of 3.3723 is obtained at an operating frequency of 19.4848GHz. The Insertion and Reflection loss of hybrid cavity with three metallized posts with an offset length of 10mm are depicted in Fig. 6. For all the other cases the insertion loss is not beyond -10dB outside the pass band.

Fig. 7. Geometry of Hybrid cavity filter with seven metallized posts

The Insertion loss and Reflection loss of the same are depicted in Fig.8. Bandwidth is significantly reduced, thereby increasing the Q factor to a value 39 at an operating frequency of 14.2626GHz.

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IV. CONCLUSION Paper presents a novel type of SIW hybrid cavity filter operating in Ku band which finds application in satellite communication, Very Small Aperture Terminal, RADARS, etc.. Here, we efficiently exploit the geometry of the hybrid cavity and include metallic posts which further enhances the Q factor. The simulation results of Q factor after incorporating eleven metallic posts is 377.096 operating at 13.7236GHz .The proposed filter shows high selectivity and low profile with a low cost. Furthermore filter design can be modified to obtain better insertion loss.

0

S Parameter(dB)

-2 -4 -6 -8 -10 -12

Insertion Loss Reflection Loss

-14 -16 13.6

13.8

14.0

14.2

14.4

14.6

14.8

15.0

15.2

ACKNOWLEDGMENT

Frequency(Hz)

Fig. 8. Variation of S parameters with respect to frequency

E. Hybrid cavity with 11 metallized post According to the result addition of the metallic vias vertically shows a significant increase in the Q factor. In the preceding analysis an additional 4 shorting posts is added vertically so as to enhance Q. The geometry of the structure is as shown in Fig.9.

I am extending my heartfelt gratitude to our beloved Chancellor Sri Mata Amritanandamayi Devi for her great motivation, inspiration and genuine support throughout this research work. REFERENCES [1]

[2] [3]

[4]

[5]

[6]

Fig. 9. Geometry of Hybrid cavity filter with eleven metallized posts.

[7]

The Insertion loss and Reflection loss are as depicted in Fig. 10. The Q factor spiked to a value of 377 at the expense of an insertion loss of -2.8dB. [8] 0

[9]

S Parameter(dB)

-5

-10

-15

-20

Reflection Loss Insertion Loss

-25

-30 13.4

13.5

13.6

13.7

13.8

13.9

14.0

Frequency(Hz)

Fig. 10. Variation of S parameters with respect to frequency

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