For a rectangular waveguide having width a and height b, the cutoff wavelength for TM11 mode is equal to

• A. <img src="/_files/images/electronics-and-communication-engineering/microwave-communication/12-88-1.png">
• B. <img src="/_files/images/electronics-and-communication-engineering/microwave-communication/12-88-2.png">
• C. <img src="/_files/images/electronics-and-communication-engineering/microwave-communication/12-88-3.png">
• D. <img src="/_files/images/electronics-and-communication-engineering/microwave-communication/12-88-4.png">