Those who have registered with AdSense already aware about the maximum number of AdSense units possible within a single page is three. If you want more than three, you can add three link units. Any added units than the limit of three, will not appeared and the space you have used to add this fourth ad will appear in your blog as a blank space.
I agree, there is no solution to display more than 3 similar ads within a single page. But you can configure multiple ads appear with multiple pages. I have used a solution to add another three advertisements in my blog to appear on any page than my main page considering below scenario.
Scenario: I want to have 3 ads need to be appeared in both sidebars of my blog homepage. Any of the pages in my blog, other than homepage, should have another 3 ad units to be appeared in different place from the first. If it is not a homepage, the first three ads should not be appeared and the space for the same should not be left blank to avoid any weary look.
To achieve this gaol, I have done the setting as below:
I have added three 300×250 ads in the right sidebar to be appeared with my homepage and disappear immediately if it is not the homepage without leaving any space in the sidebar. I have used this article for this configuration.
I have added another three ads to appear with any other individual pages than my homepage. As per this configuration, a 468×60 ad will appear just above the post title and a 300×250 ad is below the post title. Another 300×250 ad will appear at the end of each post.
You can have a look of this configuration in this blog. If you go to my homepage, you can see a 120×600 ad unit at the top of left sidebar and two 300×250 ads in the right sidebar. When you click any post title to read, the above said 3 ads will be disappeared and later said 3 ads will be appeared, where 2 will be at the top of the post and another will be at the end of the article. If you go back to the homepage, again the previous three ads will be appeared.
With this configuration, I have eliminated the possibility of appearing any blank space anywhere in this blog and configured the ads to appear as I want it.Welcome if you have any queries.