Integrated X-band miniaturized stack bandpass filtenna with metamaterial superstrate

Miniaturization and reliability of the communication front end remains as research interests in most high frequency system. One of the most assuring devices in order to achieve miniturization is Substrate Integrated Waveguide (SIW) technology. The first part of this thesis is focusing on the design and characterisation of a three-pole Chebyshev bandpass filter as a reference filter. The filter consist of three layers with 1.575 mm thick of RT/Duroid 5880 substrates. The concept of substrate integrated waveguide is used where the sidewalls of the resonators are formed by rows of copper vias. The diameter and the separation of the vias are 0.635 mm and 0.2 respectively. Compared to the wavelength at X-band, this separation is so small that the energy leakage through the sidewalls is negligible. The compact design of SIW bandpass filter able to produce the three pole bandpass filter responses. To realize compact and efficient communication front end, radiating element is another most important devices that need to be considered. In the second parts of the thesis, a single bowtie antenna is firstly designed using Rogers Duroid 5880 with the thickness and copper thickness of 0.787 mm and 0.035 mm respectively. It is designed to have a center frequency of 10 GHz. It consist of two side identical patches and a strip. One end of the strip is connected to the SMA connector. Conventionally, filters and antennas are integrated into a system by using standard 50Ω ports between them such as coxial connectors or transmission lines. However, bulkiness and difficulties in fabrication and incorporation with other electronic circuits are its major drawbacks. By integrating the filter and antenna into un-separated unit, the 50 Ω transition between both structures are ii removed which contributes to a more compact and efficient system. In the third parts of the thesis, the integration of the filter and antenna producing a filtenna is realized which consist of two resonators and the antenna that also acts as a resonator. The filtenna is able to produce comparable filtering performance with currently reported filter. In the fourth parts of this thesis, a novel negative index superstrate using Double H-shape Ring (DHSR) unit cell is designed for gain enhancement of filtenna. The pre-designed DHSR unit cell structure is used to develop a periodic structure with lateral dimension equal to the lateral dimension of the filtenna with 16 mm x 20 mm, for the miniaturization purposes. An array of 11 x 9 unit cells is constructed in a single layer of metamaterial (MTM) superstrate. A layer by layer NIM superstrate were incorporated with the designed filtenna to enhance the antenna gain of the broadside without effecting the filtering response. The distance between the filtenna and the first superstrate layer and between the superstrates have been optimized to obtain the optimum filtenna response. The distance from the filtenna to the bottom copper of the first layer superstrate is g1= 15 mm at λo/2, where the λo is the free space wavelength at the resonance frequency of the filtenna. Different superstrate layers are saparated with air gaps of g2= 3 mm. In addition, the effect of the MTM superstrate layers on the filtenna parameters have been studied. The results show more significant anticipated improvement in gain compared to the filtenna without superstrate. In this thesis, the approach is to design a miniaturize communication front end that utilize metamaterial structures loaded filtenna for X-band application. The miniaturization is achieved by using smaller overall lateral dimension of superstrate structures, SIW bandpass filter, patch antenna and unseparated filter/antenna. The proposed superstrates and the filtenna have an overall dimension of 0.67λo x 0.54λo x 1.19λo at 10.16 GHz with 10.6 dB total broadside gain in simulation and 9.8 dB in measurement. This miniaturize communication front end which consist of filter, antenna and gain enhancer affords smaller size with the overall volume of 0.43λo3 in the context of using metamaterial superstrate for gain enhancement reported in the earlier literatures.

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