Here's a Python implementation you can tailor to Excel (mostly just need r2, t2, x2, y2). Note the difference between square-rooting the radius (right) and not (left):

```
import matplotlib.pyplot as plt
from matplotlib.patches import Circle
import numpy as np
r1 = np.random.rand(1000)
t1 = np.random.rand(1000) * np.pi * 2.0
x1 = r1 * np.cos(t1)
y1 = r1 * np.sin(t1)
r2 = np.sqrt(np.random.rand(1000))
t2 = np.random.rand(1000) * np.pi * 2.0
x2 = r2 * np.cos(t2)
y2 = r2 * np.sin(t2)
plt.figure(figsize=(8, 4))
ax1 = plt.subplot(121)
circle = Circle((0, 0), 1, facecolor='none',
edgecolor=(0, 0, 0), linewidth=2, alpha=1)
ax1.add_patch(circle)
plt.plot(x1, y1, '.', color=(0, 0, 0), alpha=1)
ax2 = plt.subplot(122)
circle = Circle((0, 0), 1, facecolor='none',
edgecolor=(0, 0, 0), linewidth=2, alpha=1)
ax2.add_patch(circle)
plt.plot(x2, y2, '.', color=(0, 0, 0), alpha=1)
```