content_image/365929.jpg content_image/365930.jpg content_image/365931.jpg content_image/365932.jpg content_image/365933.jpg content_image/365934.jpg
and 

<img src='content_image/365929.jpg'>

<img src='content_image/365930.jpg'>

where λ refers to TE and TM waves. In addition it can be demonstrated [16] that we have 

<img src='content_image/365931.jpg'>

The coefficients a$_{λ}$ are determined by an integration with respect to the solid angle which includes the entire allowed domain Ω$_{0}$ 

<img src='content_image/365932.jpg'>

Hence, we can express the angular distribution of radiated power, defined as dP d Ω = c 8 $_{π}$r $^{2}$E × B ∗ , as follows: 

In addition we can write the total radiated power as: 

<img src='content_image/365933.jpg'>

<img src='content_image/365934.jpg'>

## IV. THE RADIATION PATTERN OF A COATED TAPERED FIBER TIP 

The tapered and metal-coated optical fiber tip used in NSOM[26–28] is characterized by a “funnel” geometry in which an aluminum layer (thickness of ∼ 100 nm) is evaporated onto a glass cone truncated at its apex by a small disk (diameter of 2 a ∼ 60 nm, see Fig. 2). 

The shape of the tip reveals a partially conical geometry. Therefore, the system is -to first approximation- equivalent to a conical antenna and it can be described by a quasi-multipole 

