A new exchange-traded fund (ETF) is set to launch, offering investors a unique proposition of “100% downside protection” to the stock market, but with a few conditions. What Happened: The Calamos S&P 500 Structured Alt Protection ETF – May will be introduced on Wednesday under the ticker symbol “CPSM,” according to the press release. The ETF is designed to provide investors who purchase it on its first day of issuance with 100% protection to the S&P 500 over a one-year period. However, this protection comes with a trade-off. The ETF will also cap investors’ upside gains to the S&P 500 at a ran…