Further,
......................(7.30)
From (7.29) and (7.30)
....................................(7.31)
Directivity 
= 1.5 which occurs at 
Further,
......................(7.30)
From (7.29) and (7.30)
....................................(7.31)
Directivity = 1.5 which occurs at
| Fundamentals of Antennas and Radiating systems |
|
....................................(7.29)