COMPACT MICROSTRIP BAND-PASS FILTER FOR EM1 REDUCTION

HUSSEIN MOHAMED HAGIHASSAN

This thesis is submitted as partial

Fulfilment of the requirements for the award of the

Master Degree of Electrical Engineering

Faculty of Electrical and Electronic Engineering University Tun Hussein Onn Malaysia

JUNE 2014

ABSTRACT

A compact microstrip band-pass filter design using parallel coupled lines is

presented in this work. The parallel coupled resonator's dimensions are calculated

theoretically and the equivalent circuit is analyzed. The frequency response is then

approximated using CST software. The filter is integrated with Defected Ground

Structure (DGS) to alter current distribution over the ground plane and hence changing

the resonance properties of the filter's element.

The proposed structure offers a simple and compact design while exhibiting wide

stop-band characteristics in comparison with conventional coupled microstrip line filter

design. The fabrication and measurements of 2GHz prototype DGS integrated parallel-

coupled bandpass filter are presented.

The measured results agree well with the simulations and calculations data. The

introduction of DGS suppresses the second, third and fourth harmonic responses

enhancing the stop band criteria. In addition, the DGS causes resonance frequency shift

on some resonator elements, miniaturizing the length and make the overall size 20.8%

more compact compared to the conventional ones.

vii

ABSTRAK

Sebuah penapis laluan jalur yang kompak telah dihasilkan melalui projek ini.

Penapis tersebut adalah dari jenis jalur kembar selari yang mana dimensi fizikalnya

diperolehi menggunakan kaedah pengiraan sedia ada, manakala litar sepunya yang

terhasil dianalisis untuk mendapat gambaran tentang sambutan frekuensi serta digunakan

bagi membandingkan dengan data yang diperolehi melalui simulasi. Dalam projek ini

simulasi bagi membuat anggaran sambutan frekuensi telah dilakukan menggunakan

perisian CST. Penapis ini kemudiannya disepadukan dengan struktur dikenali sebagai

defected ground structure (DGS) dimana sebahagian dari lapisan rujukan (ground layer)

telah di gores dengan corak tertentu bagi mengubah corak aliran arus permukaan, dan

secara tidak langsung menukar sifat ayunan elemen pengayun penapis tersebut.

Penapis yang terhasil menawarkan rekabentuk yang kompak serta kaedah penghasilan

yang mudah, dan pada masa yang sama mempunyai ciri jalur henti yang lebih baik jika

dibandingkan dengan penapis biasa. Dalam projek ini prototaip penapis tersebut telah

dihasilkan dan sambutan frekuensinya telah diukur dan dianalisis.

Keputusan yang diperolehi menunjukkan satu dapatan pengukuran yang sangat

menghampiri data simulasi dan pengiraan telah diperolehi. Penambahan struktur DGS

pada penapis telah menyekat sambutan harmonik kedua, ketiga dan keempat, dan ini

telah menyumbang kepada pelebaran ciri jalur henti penapis tersebut. Tambahan lagi,

DGS tersebut juga telah menyebabkan frekuensi ayunan sebahagian dari elemen

pengayun teranjak, menjadikan panjang pengayun menjadi lebih pendek dan

menyebabkan saiz keseluruhan penapis mengecil sebanyak 20.8% berbanding dari yang

biasa.

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