Module 6 Distributed and lumped Elements University Past Paper PDF

1.​ What is Monolithic MICs and Discuss its construction.(4) Notes already uploaded 2.​ Explain the configuration of Planar capacitor film(5) 3.​ Discuss Microwave resonators with neat diagram(8) Two-dimensional (or planar) and three-dimensional resonators are used in MICs (filters, o...

1.​ What is Monolithic MICs and Discuss its construction.(4) Notes already uploaded 2.​ Explain the configuration of Planar capacitor film(5) 3.​ Discuss Microwave resonators with neat diagram(8) Two-dimensional (or planar) and three-dimensional resonators are used in MICs (filters, oscillators, amplifiers, and so forth). Open- and short-circuited distributed transmission lines are often used as resonators in the microwave range. It is difficult in practice to build a short-circuited resonator of exactly the desired length. It is also difficult to control the ground point of shorted resonators, but easy to control an open point. One  disadvantage of an opened resonator is radiation from the open end and, therefore, a low Q-factor. In practice the open-circuited resonators are preferred. To decrease radiation from the edges, hairpin configuration are used. As the spacing S is reduced, the canceling of the oppositely phased radiation fields in the open ends becomes more complete. Fringe effects are eliminated in ring- and square-shaped resonators. However, with certain dimensions, these resonators can radiate energy perpendicularly to the substrate surface. The wider the ring, the higher the possible mode of oscillations. When the width of the ring is greater than Λ0 /2, the high modes arise. In the limiting case, when 2 W/d ≥ 1, the ring resonator becomes a disk resonator. The bigger the radius of the disk, the higher the oscillation mode that arises. Patch resonators permit the increase the power-handling capability and decrease conductor losses as compared with narrow print line resonators. Three-dimension dielectric or ferrite resonators can be realized in various configurations. Resonators of cylindrical (or disk) shape are most frequently used in microwave circuits. In most applications, the ratio of height to diameter of a cylindrical resonator is chosen to be close to 0.4. The unloaded Q of a resonator depends on dielectric, conductive, and radiation losses. Dielectric resonators are evaluated by their dielectric constant ε, dielectric loss tangent, tanδ, and the temperature coefficient of the resonant frequency. Materials used for three-dimensional resonators are dielectrics or ferrites with high dielectric constants, typically around 40 to 70, so that most of the electromagnetic energy is concentrated within the dielectric resonator 4.​ Write a short note on inductors.(4) Lumped inductors in planar transmission lines can be realized using several different configurations. Typical inductance values for this simple type of inductor are 0.5 to 3.0 nH. In practice, a straight strip is used for the low inductance values between 1 and 3 nH. The meander line inductor [Figure (b)] is used to reduce the area occupied by the element. In the meander inductor, adjacent conductors have equal and opposite current flows, which reduce the total inductance. Mutual coupling effects are usually small if the spacing is greater than three strip widths. The strip width is much smaller than the substrate thickness. Spiral inductors can have a circular [Figure (d)], a rectangular [Figure (e)], or an octagonal [Figure (f)] configuration. The connection from the center of the spiral inductor to the outside can be made with a via and a trace on the opposite side of the substrate, an air bridge or a bond wire.The inductance value is The resistance of spiral inductors depends on frequency because of the skin effect. The Q of an inductor depends directly on the inductance. The two most important geometric parameters affecting Q are the conductor width-to-spacing ratio and the inductor outside diameter. The Q increases with an increase in the outside diameter. The Q-factor increases as the square root of the frequency due to the skin effect. Circular spiral inductors have higher Q than rectangular inductors; however, they also have lower inductance for an equivalent area. To realize high-quality inductors, thicker metal with higher conductivity (e.g., copper and gold) can be used to overcome the series resistive loss. Parasitic capacitances will cause a spiral inductor to have a self-resonance. The most basic parasitic capacitance is that which is created by the coupling between the turns of the inductor. When a ground plane is under the spiral inductor, we have additional parasitic capacitance between spiral and ground. The self-resonant frequency must be at least twice the maximum operating frequency for the inductance to have a constant value. The ideal case of the inductor is in free space with no ground plane. The presence of a ground plane affects the inductance value, which decreases as the ground plane is brought nearer. The spiral inductor should have the widest possible line, while keeping the overall diameter small. This implies that the separation between the turns should be as small as possible. However, in monolithic circuits processing limits require W > 5 µm and S > 5 µm, and in hybrid MICs W > 10 µm and S > 10 µm. The ratio of inner diameter to outer diameter equal to 0.5 optimizes the value Q, but not the maximum inductance value. 5.​ Explain attenuators with neat diagram.(10) Notes already uploaded 6.​ Write a short note on hybrid MIC(4) Notes uploaded 7.​ Explain the frequency characteristics of single layer square inductor.(7) Refer Qn 4 8.​ Explain in detail about thick film and thin film technology?(10) Passive circuits of Hybrid Microwave Integrated Circuits use distributed elements, lumped elements, or a combination of both. The distributed microwave passive circuits are fabricated by using two main technological processes: thin film and thick film. Also, there are several different techniques used to fabricate planar circuits, which include PCB, LTCC, DBC, and others. Thick-film technology is useful in low-cost manufacture and has been developed for HMICs operating at frequencies up to about 20 GHz. The thick-film technology includes printing, baking, and trimming processes. Special pastes are placed on a screen with areas opened for circuit pattern. Some of the paste is squeezed through these open areas and paste is transferred onto the substrate. Conductive paste (silver, gold, palladium-gold, and so forth) is used for conductors, resistive paste is used for resistors, and dielectric paste is used for capacitors and coupled lines. Cleaning and drying take place after printing. Then a baking process returns the material to the solid state. After baking, laser trimming is used to adjust resistors. To complete the circuits, other passive and active components are typically attached by soldering. The most commonly used dielectric materials are Al2O3 (96%), AlN, and BeO (see Appendix A). Thick-film technology allows a combination of RF and digital functions on a common alumina substrate. Thin-film technology involves sputtering a metal (chromium, nickel, and so forth) that has good adhesive performance with substrate to form a thin (approximately 100°–200°A) adhesive layer. The next step is sputtering a layer of Au having a similar thickness. After this step is the optical printing. The circuit pattern is formed by using photolithographic techniques. A photoresist for optical printing is exposed to collimated ultraviolet light. After etching, the photoresist is removed. Then, a high-conductivity metal is electroplated on to provide the necessary thickness of the metal film of three to five skin depths. The skin depths vary for different metals and depend on the microwave frequency. Finally, gold electroplating provides an environmental protective layer. A gold-plated surface can weaken a solder joint because of migration of the gold into the solder connection during solder reflow. Pretinning the solderable gold surface prior to assembly can help reduce the gold migration. The key adhesion factor (metal to dielectric substrate) is surface roughness. The surface should be polished to roughly an order of magnitude better than the resistive film thickness. Typical substrate materials are Al2O3 (99.6%), AlN, BeO, and quartz.Thin-film technology provides excellent characteristics: minimum lines and space width (~0.0005 in.) and resistor tolerances (~0.1%). In comparison with thick-film technology, the thin-film process can achieve a higher accuracy of print circuit and about 20% less loss. However, the thin-film process is very expensive, and the dielectric surface must be extremely smooth for good adhesion. 9.​ Discuss different configurations of capacitors in MICs(10) Refer Qn 2 10.​Compare short circuit and open circuit resonator.(5) Two-dimensional (or planar) and three-dimensional resonators are used in MICs (filters, oscillators, amplifiers, and so forth). Open- and short-circuited distributed transmission lines are often used as resonators in the microwave range. It is difficult in practice to build a short-circuited resonator of exactly the desired length. It is also difficult to control the ground point of shorted resonators, but easy to control an open point. One disadvantage of an opened resonator is radiation from the open end and, therefore, a low Q-factor. In practice the open-circuited resonators are preferred. 11.​Discuss discontinuities in MICs.(5) Discontinuities in microwave circuits include open and short ends, air bridges, gaps, steps in width, bends (or corners), and T- and Y-junctions. The influence of discontinuities on parameters of MIC grows with an increase in operation frequency, because physical dimensions of discontinuities become commensurable with wavelength in transmission line. Gap in the strip conductor is used to build up a coupling element in filters and dc blocks. However, it can have parasitic properties as a part of a print circuit where surface-mount components require a definite space between strip conductors. There are electrical fields between each strip conductor end and the ground plane, as well as between the two conductor ends. A gap in stripline or microstrip line can be equivalently represented as a π-capacitor circuit. Open-circuit ends of planar transmission lines are part of open matching stubs, open-circuit resonators used in filters and other devices. The open end of a strip conductor emits some radiation and fringing field that can be seen as either adding to capacitance between the open end and ground or increasing the effective line length. Short circuits) are used in filters, matching stub lines, and resonators to obtain grounded points on the upper surface of substrate. A real short circuit causes field and current distortions in the strip conductor. Air bridges are common in spiral inductors and coplanar waveguides. The air bridge technique is used in order to reduce parasitic capacitances due to the high-permittivity substrate. The parasitic capacitance in this structure depends on the air gap between the two metal lines in the area of crossover. Bends or corners are used for changing the direction of a strip conductor, as well as in rectangular resonators, coupled line directional couplers, filters, and so forth. Steps are changes in width of a strip conductor or, in other words, junction of two cascaded planar transmission lines with different characteristic impedances. These discontinuities occur in transformers, filters, directional couplers, dividers/combiners, and matching networks. T junctions are used in dividers/combiners, directional couplers, bias networks, and PIN-diode switches, and so forth. Discontinuities should be compensated for to improve matching of input/output ports.