The main purpose of a ground plane is to:

What is wrong with this double-sided layout (green is the 0V rail on the blue side, red is the other side, all the other tracks not shown)?

A PCB of dimensions x cm is made from FR4 fibreglass with an ε_r of . Power and ground planes on adjacent internal layers cover the whole board. It's a 4-layer board with equidistant layer spacing and a total thickness of mm. What is the capacitance between the power and ground planes?

The same PCB (10 x 16 cm, FR4 fibreglass with an ε_r of 4.2) is mounted in a plastic case connected to a 1.3m long 12V DC power supply cable, which supplies a DC-DC point-of-load converter for the power plane. It shows a problem with radiated RF susceptibility at between 430 and 470MHz. What would be one of your first suspects?

At roughly what frequency does the impedance of an infinite copper ground plane (i.e., one without edges) produced in a 35μm thickness start to rise above its DC value?

Split ground planes are hazardous because:

Close spacing of V+ and 0V vias to the power and 0V planes is helpful at high frequencies because:

You are designing a board whose only digital component is a single-chip microcontroller running at 20MHz with just one 3V3 VCC pin. It's a four-layer board, other components are analogue inputs, a switchmode power converter and some power control. What should be your preferred supply rail layout for the micro?