Electronic – 11-16V DC voltage stabilization for 13.8V powered ham radio

Why couldn't I just use a regulator for this purpose?

Mainly, because every chip can't be right next to the regulator. The further your chip is from the regulator that's supplying it, the more resistance and inductance there is in the connection from the regulator to the Vcc pin (and from the ground pin on the way back).

If the current draw of your chip changes, this resistance and inductance will result in a change in the voltage at the Vcc pin.

I have no idea how to select the appropriate capacitance value.

There's two ways to look at this.

1. When your chip changes its current draw, that di/dt will create a voltage drop across the inductance back to the voltage source. You want a capacitor that can supply (or sink) the current delta until the current from the source can respond.

   Unfortunately choosing a capacitor this way requires knowing two things that you often don't know: What will be the di/dt generated by the chip (this one you might actually know in some cases), and what's the inductance of the connection to the source (this you could simulate with a good power integrity tool, but that's expensive).

2. You can design your bypass capacitors to provide a low-impedance connection to ground at all frequencies you're interested in.

   A low valued capacitor will have a high impedance at low frequencies because \$Z=\dfrac{1}{j\omega{}C}\$.

   A high-valued capacitor will require a larger package and have a high impedance at high frequencies because of its equivalent series inductance (ESL), for which \$Z=j\omega{}L\$.

   The solution is to put several values of capacitor in parallel, so that all frequencies are covered. A good capacitor vendor will provide ESL and ESR characteristics so that you can simulate your combination of capacitors and find a combination that works.

My research indicates that I need an electrolytic capacitor for this application

A common set-up is a 0.1 uF ceramic capacitor at the Vcc pin of each chip, and a few large-valued electrolytics spread around the board (not necessarily one per chip). Whether this is appropriate for your design isn't clear from what you've shared.

Generally the high values (in bigger packages and often electrolytics) don't need to be as close to the chip as the small-value (small package) capacitors, because they are useful at lower frequencies where inductance separating them from the load (chip) has less effect. Maybe one 10 uF capacitor can be shared between 4 or more loads. And a few 47 or 100 uF capacitors can be sprinkled around the board.

I would be very suspicious of the 4.7uF capacitor actual value under bias. Try measuring it with a bridge that allows bias to be applied, or cob something together with a large series capacitor and a large value resistor to apply bias voltage (and check the manufacturer's data, of course). It's not uncommon for very small ceramic caps to lose 40% of their nominal value or more under bias. If you're in the unstable or conditionally stable region of operation, the loading will have an effect.

Note Figure 13 from the datasheet:

As you can see, the minimum required ESR increases from close to zero at higher capacitances up to maybe 20m\$\Omega\$ at 2uF. You need to guarantee that the regulator sees a combination of capacitance and ESR inside the stable zone under all conditions (worst case is probably high or very low temperature and taking tolerance and aging into account). A quick test would be to slap a 50m\$\Omega\$ resistor in series with the capacitor.

Using a physically large and higher voltage rated part may help (perhaps an 0805 25V part). Since you're using a CM you may wish to supply this particular cap if it turns out to be the problem.

Edit: Since you've supplied the capacitor part number, I looked up the characteristics. The typical capacitance of this part is 1.6uF at 3.3V DC bias!

That's at 25°C- if you need to operate over a wide temperature range you can't even count on that. And on top of that you have tolerance.