Analysis of Substrate Integrated Waveguides

By using a transverse resonance technique, the frequency characteristics of slotted substrate integrated waveguides (SSIWs), slotted half mode substrate integrated waveguides (slotted HMSIWs) and slotted parallel plate SIWs loaded with capacitances and inductances are analyzed theoretically and related to those of conventional waveguides. In practice, the slotted SIWs and HMSIWs are distributed structures, so that they are loaded with ladders of capacitances and inductances across their slots. The cut-off frequencies of the slotted SIWs and HMSIWs loaded with specific capacitances and inductances are then calculated from our analytic technique. These numerical predictions are both compared with and also in some cases used to clarify the corresponding values of cut-off frequencies estimated by HFSS and also by CST Microwave Studio by means of using S-parameters. Field plots for some of these practical examples are used to provided further insights regarding the design and operation of these structures. A tuneable resonator and tuneable single port narrow band antenna are designed. A rudimentary design of a bandpass filter (in the form of a SIW loaded with both inductances and capacitances in series across the slot) is also outlined.

Finally, a modal analysis technique for a general composite waveguide structure, essentially consisting of three sections of SIW, is developed from first principles. This method is used to establish matrices which are used to calculate the S-parameters of the full structure. Though the technique itself is not entirely original, its application is a novel one which can be applied to a whole range of hybrid waveguide structures. Some specific examples of the general case which have practical importance, namely rectangular SIW sections at either end of a slotted SIW region via means of a step with E-planes and H-planes respectively, are considered. The operational characteristics of these waveguide structures are analyzed by means of examining their S-parameters over a suitable range of frequencies. These predicitions are then compared with, and also in some cases, used to interpret the S-parameter estimates from HFSS. The calculated predictions from the modal analysis for these examples are useful for the determination of frequency characteristics of SSIWs, which are instrumental in the novel design of a plethora of microwave devices. In fact, the mode matching method is compared with CST Microwave Studio to estimate the cutoff frequency of a slot SIW antenna.