YIELD RATE IS THE INTEREST EARNED BY THE LENDER ON MONIES LOANED WHICH I9S EXPRESSED AS A PERCENTAGE OF THE TOTAL INVESTMENT. YIELD RATE IS DETERMINED BY THE AMOUNT RETURNED TO THE LENDER OF A A SECURITY.
whereas,
the coupon rate of a bond is the amount of interest paid annually, expressed as a percentage of the face value of the bond.

When a bond is issued, an interest is paid on that bond to the investors or the purchasers of the bond. This is called coupon.

Yield is coupon/par value of the bond.

Coupon tells you what the bond paid when it was issued, but the yield – or “yield to maturity” – tells you how much you will be paid in the future.
See how it works :
When a bond is first issued, it has a variety of specific features, such as the size of the issue, the maturity date, and the initial coupon. For example, in 2012 the Treasury may issue a 30-year bond due in 2042 with a “coupon” of 2%. This means that an investors who buys the bond and holds it until face value can expect to receive 2% a year for the life of the bond – or $20 for every $1000 invested.

Once the bond is issued, however, it trades in the open market – meaning that its price will fluctuate throughout each business day for the 30-year life of the bond. Now, fast-forward ten years down the road. In 2022, interest rates have gone up and new Treasury bonds are being issued with yields of 4%.

So, even in this situation, how does someone earn a 5% yield on a bond with a 2% coupon? Simple: in addition to paying out the $20 each year, the investor will also benefit from the move in the bond price from $500 back to its original $1000 at maturity. Add the annual payment with the $500 principal increase – spread out over 20 years – and the combined effect is a yield of 5%. This yield is known as the yield to maturity.

The coupon rate is the interest paid on the Bond issued, while debt yield can be looked at as the rate of return on your bond investment.