You can make gates out of fences or iron bars. To create a gate you need: fences or iron bars, redstone and some blocks.
1) Make the framing for the gate. Try to make the empty space above the portcullis one block less high than the portcullis itself
2) Place the fences or iron bars.
3) Connect the redstone. Redstone should power the gate from the side like shown on the picture.
Magenta block indicates the powered block.
4) You're done! You can now build around the gate and make it look nicer!