Substrate integrated waveguide based 4 port directional coupler

Abstract

A coupler is a device that is used for the power combining or the power dividing purposes.

The applications of metamaterial based design in the devices has enabled the applications of

the microwave coupler to be used in larger scale of devices for various applications in the

microwave, optics and wireless sensors and receiver circuits. Their precise shape, geometry,

size, orientation and arrangement can affect waves of light (electromagnetic radiation) or

sound in an unconventional manner, creating material properties which are unachievable with

conventional materials. These metamaterials achieve desired effects by incorporating

structural elements of sub-wavelength sizes, i.e. features that are actually smaller than the

wavelength of the waves they affect.

The main purpose of this thesis is to design a 4 port Substrate Integrated Waveguide (SIW)

coupler that would be used to achieve size reduction with the use of CRLH achieving

compactness with SIW, since it is found that they are compact in nature when compared to

the microstrip or the rectangular waveguide.The microstrip devices are not found to be too

efficient for higher frequency applications which are caused due to the fact that the

wavelength at higher frequencies is small. These smaller wavelengths impose higher

tolerances to those devices also the manufacturing process is found to be difficult which gave

rise to the wide range of usage to the substrate integrated waveguide. Therefore these

substrate integrated waveguides were found to be a transition occurring between the

microstrip and the Dielectric Filled Waveguide (DFW) [21].

The complete coupler characteristics are studied and analysed using CST Microwave studio

suite. The S-parameter plot in dB obtained from the simulation of various designs are used

for the analysing the performance of the coupler. Then the performance of the coupler is

analysed after introducing the Composite Right/Left Hand (CRLH) metamaterials in the

coupler at various positions such as at its centre and in the ports.

It is found that the coupler with the CRLH at the centre (Design2) is found to provide better

results with the S 11 value to be -35Db, S21 to be -3dB, S31 to be -5dB, with the 41

h port

isolated.

Miniaturisation is one of the important objectives and is successfully accomplished.