Using target='_blank' sometimes opens in a new tab, and it usually does for Firefox and Chrome. Your best best is to use Frédéric's code:

<a href="javascript:window.open('some.html', 'yourWindowName', 'width=200,height=150');">Test</a>

<a href="http://google.com" onclick="window.open(this.href, 'windowName', 'width=1000, height=700, left=24, top=24, scrollbars, resizable'); return false;">Link</a>

You can make use of a hashchange-event!
Make a check-hash function and call it initially, so that loading the URL with the hash has the same behavior as changing the hash when already on-page.

You could create an array holding the IDs of the elements that should "listen" for such a hashchange, and give them a specific class (e.g. .hash-selected) when their ID equals the hash.

const hashes = ["#popup"]; // List of IDs that are "listening"
let lastHash = "";
function checkHash() {
  if (hashes.includes(lastHash)) // Remove class from last selected element
    document.querySelector(lastHash).classList.remove("hash-selected");
  if (hashes.includes(location.hash)) // Add class to current selected element
    document.querySelector(location.hash).classList.add("hash-selected");
  
  // Save current hash as 'lastHash' for first if-statement when calling 'checkHash()' again
  lastHash = location.hash;
}

checkHash(); // Initial function-call for same behavior on "page-open"
window.addEventListener("hashchange", () => checkHash());

body {margin: 0}
#popup {
  position: absolute;
  border-bottom: 1px solid black;
  width: 100%;
  transform: translateY(-100%);
  background: lightgreen;
}
#popup.hash-selected {transform: translateY(0)}

<div id="popup">
  <p>Some sample text</p>
  <a href="#">Close</a>
</div>
<a href="#popup">Open popup</a>

We could even easily fill the hashes-array with IDs of elements that have a specific class, like .hash-listen:

const hashes = [];
for (let el of document.querySelectorAll(".hash-listen"))
  hashes.push("#" + el.id);

// ...

Sidenote
To remove hashchanges from the browser-history, you should take a look at this answer that demonstrates the history.replaceState()-function.

Single line works just fine:

<a href="http://example.com/"
 onclick="return confirm('Please click on OK to continue.');">click me</a>

Adding another line with a different link on the same page works fine too:

<a href="http://stackoverflow.com/"
 onclick="return confirm('Click on another OK to continue.');">another link</a>

HTML alone does not support this. You need to use some JS.

And also consider nowadays people use popup blocker in browsers.

<a href="javascript:window.open('document.aspx','mypopuptitle','width=600,height=400')">open popup</a>