How do I improve the radio reception of my car stereo?

Do I install an aftermarket antenna?

Are there aftermarket thingy I have to buy and attach to my stereo?

Nangyayari kasi kapag nag scan ako ng radio stations, marami sya ini-skip na station. Like for example kung minsan ma-detect nya 92.3 FM minsan hindi. Kung minsan naman okay lahat. Tsaka yung AM stations, kaunti lang nakukuha ko. Dito yan ah sa Metro Manila hmm....

Saan kaya problema nito?