Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 56

More common as a transmission line on an inner layer of a PC board, strip line consists of a thin strip or rectangle of metal sandwiched between two ground planes embedded in a uniform dielectric constant, as shown in Figure 1.30c. The impedance of these lines is much lower than the equivalent‐width microstrip line, but they have an advantage of being fully TEM in nature and so often the design of components such as coupled lines is easier as the even‐ and odd‐mode velocity factors are the same. An approximate formula for computing the value of a stripline impedance with a zero thickness strip is (Pozar 1990)

(1.88)

(1.89)

More complex formulas that include a broad range of applicability and include effects for finite strip thickness and asymmetric placement of the strip can be found in many references (IPC 2004; Cohn 1954).