Transmission lines
Wavelength of EM waves in a vacuum
$$\lambda=\frac{c}{f}$$
where $c$ is the speed of EM waves and $f$ is the frequency.
Wavelength of EM waves in a medium
The speed of EM waves depends on the substrate material because it takes time for the charges in the substrate to align to the waves.
$$D_k=\epsilon_r$$
$$\lambda=\frac{c}{f\sqrt{\epsilon_{eff}}}$$
If the length of an interconnect is greater than $\frac{1}{20}$ of the wavelength, RF behaviors must be considered.
Striplines and microstrips
Striplines are sandwiched between two copper reference planes.
Microstrips are placed above a copper reference plane and a dielectric.
Embedded microstrips are microstrips covered by a solder mask.
In a stripline, the fields exist between the stripline and the reference planes over and under the stripline. Therefore, the EM waves that travel along a stripline are TEM waves.
In a microstrip, the fields mostly exist between the strip and the reference plane below, but some of the fields fringe out into the air. Therefore, the waves are quasi-TEM waves.
Transmission lines
Transmission lines are designed to carry as much of the input power as possible to the load.
Characteristic impedance
$$Z_0=\sqrt{\frac{R+j\omega L}{G+j\omega C}} \approx \sqrt{\frac{L}{C}}$$
where R is the resistance in series with the inductance L, and G is the conductance in series with the capacitance C.
Loss
$$\alpha_t=\alpha_c+\alpha_d+\alpha_r$$
where $\alpha_t$ is total loss, $\alpha_c$ is the conductor loss (due to resistance R), $\alpha_d$ is the dielectric loss (due to conductance G), and $\alpha_r$ is the radiation loss due to radiation propagating into space (in microstrips).
Loss parameters in stripline
$$\alpha_d = 27.3 \sqrt{\epsilon_r} \frac{tan\delta} {\lambda}$$ $$\delta = D_f$$