Module 2 : Transmission Lines
Lecture 16 : Impedance Matching using Transmission Line continues
  Triple-Stub Matching

Inorder to overcome the drawback of double-stub mathching technique one can use three stubs seperated by distance, instead of the two stubs (see Figure). One still uses only two adjacent stubs (B, C or C, D) at a time for matching purpose. For those loads which have outside the forbidden region we use stub B and C as used earlier and stub D is disconnected. The disconnection is not physical and is achieved by simply adjusting the length of the stub to . The -stub appears open at the junction point D.

If the admittance at B happens to lie in the forbidden region, disconnect stub B by adjusting its length to , and use stubs C and D for double-stub matching. Disconnection of stub B effectively increases by and the admittance now corresponds to location C. So if the admittance at B is in the forbidden region, the admittance at C would definitely be out of it.
A three-stub matching technique therefore is the final destination in the impedance matching, as it can match all impedance/admittance without changing the stub locations.