Transactions on Antennas and Propagation
Download 1 Mb. View original pdf
|
| M is almost the same as V which is large, whereas when is small (close to 0°), M is almost the same as H which is small. Therefore, M has a similar distribution as (2) V < H . In this way, V is close to the minimum value of the total interval and H is close to the maximum value. Thus, when is large (close to 90°), M is almost the same as V and is small, whereas when is small (close to 0°), M is almost the same as H and is large. Thus, M has a distribution inverse with Therefore, when is close to -1, 3 l M is mainly determined by the distribution of polarization angle and is almost irrelevant to the distribution of H and V . Virtually, from our trials (partly shown in Section III, it is found that even a 3 l close to 0 (irrespective of positive or negative) can also yield a good similarity between M and , if H and V have similar interval length. To study the effect of interval length, anew concept, interval range ratio, is defined as 1 2 12 l 1 2 , ) , ) l l l l min( max( (6) which has the value between 0 and 1, and a larger value means that the two intervals have more similar interval length. It should be pointed out that when overlap ratio is close to 0 irrespective of positive or negative, and H and V have small range ratio, the distribution of M will be unpredictable and can be dissimilar with H or V or It would be interesting to find away to judge the distribution of M from the interval overlap ratio and range ratio. A formula is defined as follows to help make the decision 3 3 12 jg l l l (7) The principle of (7) is that for positive , jg increases with and l 12 , while for negative , jg decreases with the magnitude of and l 12 . Thus, jg is large when is positive and and l 12 are large, while jg is small when is negative and and l 12 are large. With the increase of jg from the minimum to maximum, the distribution of 3 l l 3 l 3 l 3 | l 3 l 3 l | 3 l 3 M varies gradually from being similar with to being similar with H and V In fact, both and l 12 demonstrate the difference of the two additive intervals, and jg, as a combination of these two factors, is an overall measure of the interval difference in relative dimension. IPD difference between parallel and perpendicular polarization transmission coefficients, i.e., the difference between 3 l H and V , is known as an important factor in leading to BSE, and this point is considered in studying radome BSE characteristics with the help of jg. C. Permittivity profile with the 1/r 2 law representation The permittivity decreases symmetrically according to an inverse-square profile from a given maximum value at the plane of symmetry and tends towards unity at the two radome surfaces bounded by air. The relative permittivity across the radome wall is assumed as [20] 2 2 ( ) [ | | 1] r b r a d r (8) where r is the relative permittivity, r is the distance from one radome surface (cf. Fig. 4), d is half of the radome thickness, is curvature coefficient within the range of [0,1), and the coefficients a and b are given as 1 ( ) /(1 ) Download 1 Mb. Share with your friends:
|