Suppose a signal source with an output impedance Zg of 50 pu

Suppose a signal source with an output impedance Zg of 50 (purely real) is able to supply 2 mW of power to a load under matched conditions (i.e., when a 50- load is connected to the source). An amplifier with an input impedance of 42 – j32 is connected to the signal source through a 50- microstrip transmission line. The line has an effective relative permittivity of 4.2, and the operating frequency is 5.65 GHz.

a. How much power is actually delivered to the mismatched load?

b. What are the time-average incident and reflected power that flow along the
microstrip line?

Solution

Microstrip line is used to carry Electro-Magnetic Waves (EM waves) or microwave frequency signals. It consists of 3 layers, conducting strip, dielectric and Ground plane. It is used to design and fabricate RF and microwave components such as directional coupler, power divider/combiner, filter, antenna, MMIC etc.

   
    Microstrip line will have low to high radiation, will support 20 to 120 ohm impedance,supports Q factor of about 250. Difficult to mount chip in shunt mode but easy in series mode.
    The RF/microwave product made using microstrip line is less expensive and lighter in weight compare to its waveguide counterpart. Usually FR-4 dielectric substrate is used as PCB for microstrip based etching due to its low cost.

    Different types of discontinuities exist in RF/microwave layout design. These include bends, T-junction, cross-junction, step in width, coupling and open ends. Parasitic effect introduced by these discontinuities will be reduced by use of constant impedance tapers for example; curved bends are used in place of sharp bends. Sharp edges are changed to curved edges in RF layout. In certain cases radial stubs of different types (series and shunt) are employed.

    Microstrip based layout design is carried out by various RF & Microwave simulation software\'s from various companies such as Agilent, Eagleware, Microwave office, applied computational sciences, CST, Ampsa Multimatch etc.