Communication Systems Microwave Theory and Techniques Paper 10 1442

Design and Implementation of Band Pass Filters in Waveguide using Simulation Tools

Sarun Choocadee and Somsak Akatimagool

Department of Teaching Training in Electrical Engineering, Faculty of Technical Education King Mongkut's University of Technology North Bangkok, Thailand

E-mail: sarun_kmitnb@hotmail.com.ssa@kmutnb.ac.th

Abstract - This paper presents a design and implementation of

rectangular waveguide filters by using the simulation tools. The

waveguide filters are designed by using numerical analysis

based on the Wave Iterative Method (WIM) called WFD

(Waveguide Filters Design). This simulation program can

analyze the electrical network of inductive filter. The sample

rectangular waveguide filters is designed on structure consisting

of three circuits as a simple band pass filter, filter with two

inductive irises and three inductive irises in cascade. We

determinate the operating frequency equal to 4.0-4.8 GHz

approximation. Then the inductive waveguide filters were

implemented by using an aluminum material. The analyzed

results of inductive iris by WFD agree well with results of CST

Microwave Studio®. Finally the measured results of sample

waveguide filters are consistent with the simulation tools.

Keyword: Inductive Iris, Waveguide Filters Design, Wave Iterative Method (WIM)

I. INTRODUCTION

Presently, the development of technologies for wireless communications, particularly for use in microwave frequency range is critical to develop the economy and the domestic industry significantly, and is part of the technology research and development continuously. Microwaves filter were found to be necessary because the communication system can be used to separate the signal that would want to use. [n several articles, researchers have studied the filters in waveguide and are most interesting the simulation programs [1-4].

The most popular waveguide filter is an iris filter [5-6]. The researchers rely on using 3D simulators such as CST Microwave Studio®, Advanced Design System (ADS) to design of an iris waveguide filter. The problems of design are often lack equipment and tools used to design and to build. Revolution in microwave engineering, numerical methods related to electromagnetic wave have been extracted such as FDTD (Finite Differential Time Domain) [1], Smoothed Piecewise Linear model (SPEL) [2] , TLM (Transmission Line Matrix) [3], Moment method [4]. Each method has the disadvantages and limitations of usage for research and education. Some analysis methods for waveguide circuit are available in [2] and [7]. The most inductive iris in waveguide has been designed through approximate modeling utilizing full wave Mode Matching Method (MMM) and Transmission Line Matrix (TLM) with high accuracy. Therefore, the development and optimization of methods are necessary and important for an efficient electromagnetic simulation tool of waveguide analysis.

The 8th Electrical Engineeringl Electronics, Computer, Telecommunications and Information Technology (ECTI) Association of Thailand - Conference 2011

This paper proposed a design and implementation of the simple inductive iris filters by using Wave Iterative Method

(WIM), the CST Microwave Studio® and network analyzer. The result can be development to microwave filter design for satellite communications and applications in the education and the telecommunications industry.

[I. NUMER[CAL ANAL YS[S

An analysis of the electromagnetic wave properties within waveguide consists of TE and TM field components. The most wave analysis will be calculated in spectral domain base on the series integration equation to present the electromagnetic field and to analyze the two ports network

parameters that the result of frequency response reflects the characteristic of various filter circuit. In this research, we will present the cooperation of waves between the spatial domain and frequency domain.

The calculating concept for the electromagnetic wave

propagation in waveguide is based on the Wave Iterative Method (W[M) [8]. The operating process, shown in Fig.l, will present the amplitude and direction of the incident, reflected, and transmitted wave which propagate in the waveguide iris. On the iris, the waves are calculated in the spatial domain (pixels) and the waves in the free space are calculated in the frequency domain (modes). The alternating between both domains, we use the Fast Fourier Transform (FFT) for reduction of computation time.

Reflected Coefficient Scattering Coeflicient Reflected Coefficient

, " Dominanc��ode (rEIO) AOI - -- ... i ............... ...

""" - - - AOl Dominance MO:tk: (TElO)

. ..------l ... ............ , ' ,

, ' ,

�----t.:_ERel1fc

.

ted Wave Bl� ---+ 82 Reflected wave:fj'

_-.

Fundamental Mode (TEw ......... ,

i Fundamental �odc (lEw) ... J�pldent Wave AI -----JIo> � Al Incident Wave

I

r----------+�----------� Spectral Domain (Mode) Pixel Domain (pixel) Spectral Domain (Mode)

Fig.l. Wave Iterative Method in the waveguide process

In the Fig.l, the first step, the TE 10 field which is the dominant mode will propagate into the iris circuit, then the higher mode waves caused by the scatter on the conductor surface will incident and reflect within the waveguide. The infinite numbers of reflected and transmitted waves are produced at the iris circuit interface. Finally the calculation of waves will use the principle of mode matching at input and output port of waveguide.

Page 248

The initial value of dominant mode, TE is LO

A�o) = _ [2 sin( 7rX ) •

,Y �-;;J; a (I)

where a, b is the dimension of waveguide. The reflected

waves (Br'l!) in n iteration on the iris circuit are

E(n) = S A(n-l) :r,:t} J':,y :r,:t} , (2)

At the input port of waveguide, the incident waves (Ae,y) of higher order modes will feedback into the obstacle of

waveguide. The equation of incident waves (Am,n ) is

= r B(II) +A';1,M 'In, 'II 'rn,n 1,0 ' (3)

Therefore, the relation of incident waves at n iteration is,

(4)

When a and b are the dimensions of waveguide, n is the number of iteration, i is the number of waveguide port, r is the reflection coefficient at input/output port and S is the scattering parameter of iris circuit.

The scattering parameter ($);,y) of waves in the real

domain for two ports network follow as

8 [8 1 = "(",11) J,·Y (5)

when 811 = 822 is equal -I in the conductor area and 812 = 821 is equal 1 for the free space. The transform of waves form the real domain to spectrum domain, we use the Fast Fourier Transform (FFT)

The reflection coefficient (rm,n) of waves in spectrum

domain at input and output port of waveguide can be written by following equation.

r rn.n

T/c/ 1- Z Y /TM

T/c/ () = r /TM = rn,n m.n l+zyT%�r'

o Tn ..• n (6)

when Zo is the intrinsic impedance of dominant mode, and

111';;/1\1 is the TE/TM mode admittance in m,n order modes. 'In.n

III. SIMULATION RESULTS (WFD)

The simulation program is a numerical analysis by using wave iterative method. This simulation program, called WFD (Waveguide Filters Design), consists of main menu, parameter setup, design and display window, as shown in the Fig.2. The WFD is constructed by using GUI (Graphic User Interface) of MATLAB®. The user can setup the initial

The 8th Electrical Engineeringl Electronics, Computer, Telecommunications and Information Technology (ECTI) Association of Thailand - Conference 2011

Communication Systems Microwave Theory and Techniques

values that used for calculating of two ports network, calculate the properties of microwave filter and select the display windows of simulated results. The simulation program is possible to analysis and to design the waveguide

filter.

Waveguide filter Design

Fig.2. Waveguide Filter Design (WFD) Tool

In this paper, we present the inductive iris circuit in the rectangular waveguide by using the developed WFD simulation program. The WFD simulated result will be compared by CST Microwave Studio® and theoretical results.

The desired frequency response characteristic of the high pass filter (HPF) was considered. The dimensions of rectangular waveguide consist of the width (a) equal to 6.4 cm., height (b) equal to 3.2 cm. and the iris width equal to 3.2 cm., as shown in Fig.3. The cutoff frequency of the waveguide is at 2.34 GHz.

'""'

c::::! � � -g .... ·2 � � �

Fig.3. Inductive iris structure

0

·2

-4

·6

-8

-10 -511_WFD -12

•••••• 511_ CST -14 -521_WFD -16 --- 521_ CST -18

-20 2 3 4 5

Frequency (GHz)

FigA. Comparison of dB(SII), dB(S21) of high pass filter

between the WFD and CST tools at % = 0.5

6

Fig.4, presents the comparison of dB(S 11) and dB(S21) of inductive iris circuit between WFD tool and CST simulation, then the width of iris equal to 3.2 cm., we can obtain the -3 dB cutofffrequency at 3.43 GHz.

Page 249

$ ::::., �

"0 ::::l .... ·2 OJ) � �

-5

-10

-Sll_WFD

-15 ••••• S11 CST

-S21_WFD

-20 ___ 521_CST

-25

-30 .j-_ ................ �.....,..._ ........ _..,....._.,......... ........ _ ......... _ ........ _"'T

4

Frequency ( GHz)

FigS Comparison of dB(Sll), dB(S2l) of high pass filter

between the WFO and CST tools at % = 0.375

6

Fig.5, presents the comparison of dB(Sll) and dB(S2l) of inductive iris between WFD tool and CST simulation, of the inductive iris circuit width equal to 4.0 cm. We can obtain the -3 dB cutoff frequency at 4.S2 GHz. This comparison revealed good agreement.

IV. DESIGN OF A SAMPLE INDUCTIVE IRIS WAVEGUIDE FILTER

The sample implementation of inductive IfIS filters in rectangular waveguide is design by using CST Microwave Studio® at the center frequency about 4.5 GHz. The building

parts will use an aluminum as a material. An example of a simple band pass filter has been fabricated according to the configuration parameters of an inductive iris in the Fig.6. This iris was placed within the rectangular waveguide that consists of the width (a) equal to 6.4 cm., height (b) equal to 3.2 cm. and the length of waveguide equal to 9.6 cm. The port 1 and 2 are connected by the short vertical monopole that is excited by wave of the fundamental mode, as depicted in Fig.6. Fig.7 shows the experiment set of the band pass waveguide filter measured on N5230C network analyzer of

Agilent Technologies.

Fig.6. Photo of the simple waveguide filter

The 8th Electrical Engineeringl Electronics, Computer, Telecommunications and Information Technology (ECTI) Association of Thailand - Conference 2011

Communication Systems Microwave Theory and Techniques

Fig. 7. The experimental set of waveguide iris filter

0 ,.... ___ --------__

-5 S' -10

:::.. � -15 -= .3 ·2 -20 Ql) '"

� -25

-30

-- S11_CSTSim

--- S11 _Mea.sured

-- S21_CSTSim

-35 .j----. ........ �_ ........ _..,.....---. ................. _....,....� __ ................

2.0 2.6 3.2 3.8

Frequency (GHz) 4.4

Fig.8. Comparison of dB(Sll), dB(S2l) of band pass filter between the CST simulation and experiment

5.0

Fig.S, presents the frequency response of scattering parameters of dB(Sll) and dB(S2l), at iris width equal to 4.0 cm. The pass band frequency is 4.3 - 4.7 GHz, bandwidth 630 MHz, The resonant frequency and the band pass can be controlled by variation of iris width. We can see that the measured results agree well with the CST simulated results.

Fig.9. Configuration of two inductive irises

Fig.9, shows the configuration of the iris waveguide filter under design, the width of the waveguide (a) equal to 6.4 cm. and height (b) equal to 3.2 cm, the inductive iris circuit (d I) width equal to 2.4 cm. and the inductive iris circuit (d2) width equal to 2.4 cm. with the distance between the circuit I to circuit 2 equal to 3.2 cm. We use the above configuration data as the initial values and optimize the waveguide dimension using CST simulation tool.

Page 250

-5

-10

6' :::... -15

.. � -20

� -25

::E -30

-35

--S11_CSTSim

- -- SI1_Measured

--S21_CSTSim

....... S21_Measured

4

Frequency (GHz)

Fig. 10. Simulated and measured results oUilter using two inductive irises

6

Fig.IO, presents the frequencies response of scattering parameters of dB(S 11) and dB(S21) to cover the frequency range from 2 GHz to 6 GHz, using 2 inductive irises which the width (dl) and (d2) is equal to 2.4 cm., placed in the waveguide with the length of 12.8 cm. The pass band frequency is 4.12 - 4.75 GHz, and 630 MHz of bandwidth.

Fig.ll. Configuration of three inductive irises

Fig.1 I, shows the configuration of the iris waveguide filter under design, the width of the waveguide (a) equal to 6.4 cm. and height (b) equal to 3.2 cm. We use three inductive irises which the width (d 1) and (d3) is equal to 2.8 cm. and the width (d2) is equal to 4.2 cm. The distance of each iris is equal to 3.2 cm. We use the above configuration data as the initial values and optimize the waveguide dimension using CST simulation tool.

- Sll_CSTSim -5 --- Sll_Measured

-S21_CSTSim 5' -10 �HU. S21_Measured

� � -1 5

'0 .3 oS -20 bJ) '"

::2: -25

-30

-35 -I--_---+--_--'-� _

__

_ -................. ___.L __ -

�_

�

2.5 3.5 4.5

Frequency (GHz)

Fig.12. Simulated and measured results of filter using three inductive irises

5.5

The 8th Electrical Engineeringl Electronics, Computer, Telecommunications and Information Technology (ECTI) Association of Thailand - Conference 2011

Communication Systems Microwave Theory and Techniques

Fig.12, presents the frequency response of scattering parameters of dB(S 11) and dB(S21) to cover the frequency range from 2 GHz to 6 GHz, using three inductive irises. The pass band frequency is 4.24 - 4.88 GHz, and 640 MHz of bandwidth. We can see that the measured results agree well with the CST simulated results.

V. CONCLUSIONS

This paper has been presented the design and implementation of the simple inductive iris filters by using Wave Iterative Method (WIM), The WFD simulation based on iterative method and wave propagation is properly conceived for apply to the inductive iris in the rectangular waveguide. The capability of WFD simulation has been presented, it appears as an efficient alternative to the theory and CST simulation. Form our experiment, a waveguide band pass filters are implemented, the performance confirms the suitability of the developed WFD and CST simulation.

The interesting aspect of WFD simulation concerns its application to the analysis and design of different microwave circuits. In addition, this simulation has proven to be a useful tool for microwave circuit design as an education aid.

ACKNOWLEDGEMENT

The authors would like to thank the Faculty of Technical Education, Rajamangala University of Technology Thanyaburi for providing the network analyzer N5230C model of Agilent Technologies and CST Microwave Studio®

for measurement and data analysis.

REFERENCES

[1] T. Hiraoka, C. P. Chen, T. Anada, 1. P. Hsu, Z. W. Ma, and C. C. Christopoulos, "Electric field distributions in microwave planar circuits by small coaxial probe and comparison with FDTD method," in Microwave Conference, 2005 European, 2005, pp. 269-272.

[2] A. Mediavilla, A. Tazon, J. A. Pereda, M. Lazaro, I. Santamaria, and C. Pantaleon, "Neuronal architecture for waveguide inductive iris bandpass filter optimization," in Neural Networks, 2000. IJCNN 2000, Proceedings of the IEEE-INNS-ENNS International Joint Conference on, 2000, pp. 395-399 vol.4.

[3] 1. W. Bandler, A. S. Mohamed, and M. H. Bakr, "TLM-based modeling and design exploiting space mapping," Microwave Theory and Techniques, IEEE Transactions on, vol. 53, pp. 2801-2811, 2005.

[4] S. Seunghyun, K. Hyeong-Seok, 1. Hyun-Kyo, 1. Braunstein, and M. Un-Chul, "Frequency domain analysis of microstrip filters and antennae using an adaptive frequency sampling moment method," Magnetics,

IEEE Transactions on, vol. 42, pp. 607-610,2006. [5] V. K. Chaudhary, P. Verma, and U. Balaji, "Field theory based CAD of

inductive iris waveguide filter," in Microwave Conference, 2001. APMC

2001.2001 Asia-Pacific, 2001, pp. 318-321 voU. [6] Z. Yanfen, W. Qingyuan, W. Zheyu, and G. Xiu Xiao, "The Design of

an Iris Waveguide Filter at 35.75 GHz," in Millimeter Waves, 2008. GSMM 2008. Global Symposium on, 2008, pp. 348-350.

[7] A. Saltier, J. Bornemann, and W. J. R. Hoefer, "Field-Based Waveguide Filter Synthesis in the Time Domain," AEU - International Journal of Electronics and Communications, vol. 57, pp. 119-127,2003.

[8] S. Choocadee and S. Akatimagool, "Development of efficiency em simulation tool for capacitive and inductive obstacle analysis," in Electrical Engineering/Electronics Computer Telecommunications and Information Technology (ECTI-CON), 2010 International Conference on, pp. 1154-1158.

Page 251