Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you expect companies with fat patent portfolios representing a lot of proprietary intellectual property to prosper over the long term, the Guggenheim Ocean Tomo Patent ETF (NYSE: OTP) could save you a lot of trouble. It focuses on the 300 companies with the most valuable patents relative to their book value.

Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The patent ETF's expense ratio -- its annual fee -- is 0.6%, which is a bit higher than many ETFs, but also considerably lower than most stock mutual funds.

This ETF has performed reasonably, but it's also very young, with just a few years on the books. It beat the S&P 500 in 2007, 2008, and 2009, but has lagged it over the past year and a half. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver. Note that, due in part to its youth, this ETF is rather tiny, with total assets of close to $10 million. If that's a deal-breaker for you, consider simply adding it to your watchlist.

With a low turnover rate of 14%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

What's in it?
Several of this ETF's components made strong contributions to its performance over the past year. Storage giant EMC (NYSE: EMC) gained 12%, breaking revenue and income records along the way. EMC also owns most of VMware (NYSE: VMW), which recently reported revenue up 32%. Qualcomm (Nasdaq: QCOM), up 20%, has a bright future, with its technology installed in many smartphones.

Other companies didn't add as much to the ETF's returns last year, but could have an effect in the years to come. General Electric (NYSE: GE) gained just 4%, but holds much potential from its many diverse operations and its expansion into developing fields such as solar energy and developing economies such as India and China.

Boeing (NYSE: BA) shed about 7%. It's good news that it has finally debuted its much-delayed 787 Dreamliner, but it looks like big money from the model is still many years away. 3M (NYSE: MMM) lost 9%, and some are worrying that it's doing more following than leading, despite its reputation as a legendary innovator.

The big picture
Demand for technology and innovation isn't going away anytime soon. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

Learn about the best dividend ETFs. And if you're looking for some great investments beyond ETFs, consider these 10 stocks for your retirement portfolio.