Yes, you need to have a Google AdSense account to participate in Google Affiliate Network, The reason is Google Affiliate Network use to distributes payments via Google AdSense.
You can earn Money from affiliate program compare than Google adsense. Increase Your website traffic & Select Good Affiliate network.
There are many other affiliate networks than google,but google is more reliableIn some cases google banned you adsense account even if you are not voilating there rules.Any how google is best as affiliate network