The aim of the course is to introduce the techniques suitable for the design of microwave circuits and components, starting the basic knowledge on ideal lines and electromagnetics. These techniques are required by the distributed nature of the circuits, usually of phisycal dimensions much larger than the operational wavelength. Modern planar structures will be considered in particular, focusing on the practical design of passive circuits (matching networks, couplers and dividers, filters, etc.) but including the basics of solid-state amplifiers.
Theoretical and practical lessons
Introduction. Circuit components from the electromagnetic point of view, distributed- vs lumped-parameter circuits.
Guiding structures. V/I waves in transmission lines. E/H waves in uniform structures with ideal conductors: TEM, TE/TM and hybrid modes; fundamental and higher order modes. Transmission lines of planar type: stripline, microstrip, slotline, coplanar waveguide, etc.; quasi-TEM approximation, effective dielectric constant, frequency dependence of line parameters (dispersion), losses.
Microwave junctions. Definition of junction and port: equivalent voltages and currents, normalized waves, reference planes. Matrix description of linear n-port junctions: S matrix, general properties, properties for reciprocal and lossless junctions, change of reference planes, relation to Z/Y matrices. ABCD matrix for cascaded 2-ports. Derivation of the equivalent circuit for n-port junctions and discontinuities by lumped elements and ideal lines.
Microwave circuits. The interconnection of lengths of guiding structures by junctions: modeling of discontinuities, higher-order mode interaction, introduction to CAD software.
Matching netwoks. Narrow and broad band matching: single and double stub, single and multiple quarter-wavelength transformers, frequency response, design examples.
Couplers and dividers. Wilkinson coupler. Directional couplers and hybrids: directivity and isolation, even and odd modes in coupled lines, design examples.
Resonators. Free and forced oscillations, external and inter-resonator couplings, the equivalent circuit of loaded resonators, impedance/admittance inverters.
Filters. The design technique by insertion-loss method: lowpass prototype filter; scaling and frequency mapping for lowpass, bandpass and stopband filters. Design examples (lowpass filters, coupled-lines bandpass filters, etc.)
Amplifiers. Power gain, stability circles, design for either maximum gain or minimum noise. Design examples of single-stage solid-state amplifiers.