# Some Microwave Engineering Questions

1. Jun 29, 2015

### better361

Hey guys, I am currently self studying some microwave engineering through Pozar's textbook, and I have a couple of conceptual questions.
1.What is the point of defining a generalized reflection coefficient $$\tau(0) e^{-2j\beta l}$$ if real reflections happen at boundaries?
2. Is there an analog to shunt conductance in basic circuit theory?
3. What exactly does it mean that we have small conductor and dielectric losses?
4. Pozar says that because the generator and load are mismatched, reflections will occur at that boundary also. But later he says the voltage on the line is just: $$(V_o)^{+}(e^{j\beta l}+\tau_l e^{-j\beta l})$$, which seems to imply the voltage is only due to initial wave and one reflected wave, which is at the load.
5. How do I tell if a line is lossless or not, without being given transmission line parameters?(Here is an example from the book: A radio transmitter is connected to an antenna having an impedance 80+j 40 ohms with a 50 ohms coaxial cable....)

2. Jun 29, 2015

### EM_Guy

1. The reflection coefficient at the load is the ratio of the reflected voltage to incident voltage at the load. But there are times when for various reasons, we want to know what the ratio of the reflected voltage to incident voltage is at other places along the transmission line. So, we have a generalized reflection coefficient.
2. Shunt conductance is a shunt resistance. Well, if you have a shunt resistor, then you can express it in terms of its resistance or its conductance.
3. Conductor losses are $I^2 \times R$ losses. Dielectric losses refer to power losses in dielectrics due to the complex permittivity of the dielectric. The dielectric has a loss tangent.
4. If the generator and load are both mismatched, you will have reflections at both boundaries. This becomes a very complex problem. Often, the goal is to make sure that the generator is matched to the transmission line. Then you only have to concern yourself with the load and the transmission line.
5. If a transmission line is lossless, then its equivalent lumped circuit model would only include a series inductor (lossless) and a shunt capacitor (lossless). If a transmission line is lossy, then its equivalent lumped circuit model would include a series resistor and a series inductor and a shunt conductance and a shunt capacitor. The propagation constant of a lossy line is $\gamma = \alpha + j \beta$. For a lossless line, $\alpha = 0$.