Microwave Engineering: Microwave Networks What are Microwaves? S-parameters Power Dividers Couplers Filters Amplifiers Microwave Engineering PowerPoint Presentation: Microwave engineering : Engineering and design of communication/navigation systems in the microwave frequency range. Microwave Engineering Applications : Microwave oven, Radar, Satellite communi-cation, direct broadcast satellite (DBS) television, personal communication systems (PCSs) etc. PowerPoint Presentation: What are Microwaves? (Pozar Sec. 1.1) = 30 cm: f = 3 x 10 8 / 30 x 10 -2 = 1 GHz = 1 cm: f = 3 x 10 8 / 1x 10 -2 = 30 GHz Microwaves: 30 cm – 1 cm (centimeter waves) Note: 1 Giga = 10 9 PowerPoint Presentation: Scattering Parameters (S-Parameters) Consider a circuit or device inserted into a T-Line as shown in the Figure. We can refer to this circuit or device as a two-port network. The behavior of the network can be completely characterized by its scattering parameters (S-parameters), or its scattering matrix, [S]. Scattering matrices are frequently used to characterize multiport networks, especially at high frequencies. They are used to represent microwave devices, such as amplifiers and circulators, and are easily related to concepts of gain, loss and reflection. Scattering matrix The scattering parameters represent ratios of voltage waves entering and leaving the ports (If the same characteristic impedance, Zo, at all ports in the network are the same). PowerPoint Presentation: Scattering Parameters (S-Parameters) Properties: The two-port network is reciprocal if the transmission characteristics are the same in both directions It is a property of passive circuits (circuits with no active devices or ferrites) that they form reciprocal networks. 1) Reciprocity 2) Lossless Networks A lossless network does not contain any resistive elements and there is no attenuation of the signal. No real power is delivered to the network. Consequently, for any passive lossless network, what goes in must come out PowerPoint Presentation: Microwave Integrated Circuits Microwave Integrated Circuits (MIC): Traces: transmission lines, Passive components: resistors, capacitors, and inductors Active devices: diodes and transistors. Substrate Teflon fiber, alumina, quartz etc. Metal Copper, Gold etc. Process Conventional printed circuit (Photolithography and etching) Components Soldering and wire bonding PowerPoint Presentation: Power Divider A T-junction power divider consists of one input port and two output ports. PowerPoint Presentation: Filters Filters are two-port networks used to attenuate undesirable frequencies. Microwave filters are commonly used in transceiver circuits. The four basic filter types are low-pass, high-pass, bandpass and bandstop. Low-pass High-pass Bandstop Bandpass PowerPoint Presentation: Low-pass Filters High-pass Filters Band-pass Filters Lumped Element Filters Some simple lumped element filter circuits are shown below. PowerPoint Presentation: Amplifier Design Microwave amplifiers are a common and crucial component of wireless transceivers. They are constructed around a microwave transistor from the field effect transistor (FET) or bipolar junction transistor (BJT) families. A general microwave amplifier can be represented by the 2-port S-matrix network between a pair of impedance-matching networks as shown in the Figure below. The matching networks are necessary to minimize reflections seen by the source and to maximize power to the output.