User's Manual

Table Of Contents

Section 2 Microwave Path Engineering Basics TRACER 6000 Series Integrated System Manual

Figure 1 illustrates a wireless link configuration containing all the parameters necessary for the power

budget analysis.

Figure 1. Example Microwave Path with Parameters

The following sections further discuss the power budget analysis and its components.

Antenna Gain

Actual transmit and receive antenna gain values depend strictly upon the physical characteristics of the

antennas installed for each link. In other words, the size of the dish determines the antenna gain. Using a

parabolic dish antenna results in the best performance. Antenna gains are specified in terms of decibels of

gain referenced to an isotropic source (dBi). An isotropic source is a hypothetical antenna having equal

radiation in all directions. The equation for calculating gain over isotropic radiation is

where

k dish efficiency factor (usually 0.55)

λ carrier wavelength (c / f)

D dish diameter

The dish efficiency factor (k) is used to estimate how efficiently the dish reflector passes energy to the

feedhorn. The “standard” factor is 0.55 (measured performance of prime-focus dishes with a pyrimidal

waveguide feedhorn with no aperture blockage). Other dishes and feedhorn designs may have better or

worse efficiency. Table 1 on page 19 (standard) and Table 2 on page 19 (metric) provide gains using a 0.55

dish efficiency factor. Table 3 on page 19 (standard) and Table 4 on page 19 (metric) provide gains using a

0.40 dish efficiency factor. Dish manufacturers can provide gains for specific types of antennas.

The carrier wavelength (λ) and dish diameter (D) can be metric or standard units of

measure. Use the same unit of measure for both variables. For example, a carrier

wavelength of 0.124 meters requires a dish diameter in meters as well.

d, L

G 10 log k

π D⋅

------------

⎝⎠

⎛⎞

⋅

⎝⎠

⎜⎟

⎛⎞

⋅=

(dBi)