Deriving microstrip stub equations
Stolen from: https://www.edn.com/design/test-and-measurement/4424529/So-you-think-you-understand-transmission-lines-

But anyways, that's the impedance of some transmission line that's open on the other end. You can see it decreases in impedance initially, which is the hallmark of a capacitor. Then it sharply decreases and starts going back up, which is a resonance and can be modeled by a inductor in series with the capacitor. 

If you look at the impedance of a transmission line:

$$
Z_{in}(l) = Z_0 \frac {Z_L + jZ_0 \tan(\beta l)} {Z_0 + jZ_L \tan(\beta l)}
$$

where \$ \beta = \frac {2 \pi} {\lambda}\$.

Try simplifying and graphing that equation when \$Z_L = 0\$ (shorted stub) and \$Z_L = \infty\$ (open stub).

You'll see the kind of behavior I described--increasing or decreasing impedance wrt frequency, and a resonance at \$l = \frac  \lambda 4\$.