# A Review on SIW and Its Applications to Microwave Components
## 6 Performance Attributes of the SIW  
The substrate-integrated waveguide transmission line technology has been recently gaining huge global acceptance in microwave engineering due to its notable performance attributes. Some of these performance characteristics of the SIW, according to [PERSON] and [PERSON] [13] include compact size, low radiation loss, ease of integration, elevated unloaded Q-factor, elevated power handling capability, thermal stability, etc. Some of these performance attributes are discussed in this section. The physical features of microwave and millimetre-wave devices would always respond to variations in the temperature of their operating environments. This is because the materials used in the implementation and fabrication of such devices/components are naturally temperature-dependent. SIW devices have good thermal stability when compared to similar devices implemented/fabricated with other commercially available transmission lines (that is, planar transmission lines and waveguides). To achieve this thermal stability in SIW components, attention must be paid in choosing the design substrate as explained in [33]. The paper highlighted the following vital three steps for a successful thermal stability analysis in SIW component design:  
* A stress assessment should be performed to obtain the physical change in dimensions in connection with environment temperature as the input;
* A full-wave field assessment should be conducted to verify the frequency shift versus the changes in the physical dimension and selected substrate permittivity;
* A redesign of the given device/component by compensating for the adjustments in the electrical parameters. According to [34; 35; 36], assigning opposite signs to the thermal expansion coefficient of permittivity and the physical dimensional thermal expansion coefficient can lower the temperature coefficient of a given device resonant frequency provided they can both combine effectively. For any given SIW component with substrate permittivity (i.e., dielectric constant), \(\varepsilon_{r}\), the thermal expansion coefficient in the width, \(\alpha\), and temperature, \(T\), the temperature coefficients, \(\tau_{f}\), of the TE\({}_{101}\) mode resonant frequency,\(f_{101}\), can be determined by means of Equation (8), provided the thermal expansion coefficient in the width is equivalent to that of the length [33]. \[\tau_{f}(TE_{101})=\frac{1}{f}\frac{\delta f}{\delta T}=-\left(\frac{1}{2} \frac{1}{\varepsilon_{r}}\frac{\delta\varepsilon_{r}}{\delta T}+\frac{1}{ \alpha}\frac{\delta\alpha}{\delta T}\right) \tag{8}\]  
The power handling performance of SIW devices/components makes the technology a preferred choice in the modelling, execution, and fabrication of microwave and millimetre-wave components operating in environments with high humidity [36]. According to [37; 38], microwave and millimetre-wave devices/components may dispel a considerable quantity of power, resulting to a general rise in temperature and local hot spots. This issue is a major contributing factor in the aging of a device structure in relation to the substrate material. For SIW filtering components including filters, multiplexers (e.g., diplexer/triplexers), filtering power dividers/combiners, filtering antennas, etc., the mean power handling capability is dependent on the filtering order, geometry, topology, bandwidth, and resonator unloaded quality factor.