Navman jupiter la000605d User Manual

LA000605D © 2007 Navman New Zealand. All rights reserved. Proprietary information and specifications subject to change without notice.

The features of each type of antenna are shown in Table 2-4, comparing an externally 

mounted active antenna with a passive patch antenna mounted on the same PCB as the 

module.

antenna requires close proximity to receiver

consumes power

can be mounted remote from receiver

gives good performance in poor signal situations

has built in additional filtering

low cost

requires a coaxial connector

2.4.2 Active antenna
An active antenna comprises a passive antenna with a built in LNA that requires a power 

supply. Active antennas are used when the antenna input is connected to the receiver 

through a coaxial cable (usually longer than 3 m) or any high loss transmission path. 

The GPS signals experience loss in the transmission path from the antenna. The loss is 

overcome by the antenna’s LNA, which amplifies the signal before it enters the transmission 

path. 
The amplification is also used to enhance the signal in areas of low signal. If the coaxial 

cable is shorter than 3 m it may experience too much gain at the receiver and degrade the 

performance. There are some variations as to how the antenna will receive its power, but it is 

usually supplied through the coaxial cable via the antenna input as shown in Figure 2-5.
Refer to Table 2-5 for the recommended active antenna characteristics.

2.4.3 Passive antenna
A passive antenna does not require any power because it has no amplifier. This is not the 

best choice if signal strength is a concern, however, it may be sufficient if the signal path is 

kept to a minimum (usually below 300 mm). An advantage to using a passive antenna is the 

ability to mount directly onto the application. For best performance, a passive patch antenna 

should have a metal ground plane (about 80 mm in diameter) placed directly under the 

antenna, and it is advisable to shield the module and application circuits from the antenna. 

For this reason the antenna and Jupiter 32 module should not be mounted on the same side 

of the PCB (see Figure 2-6). 
Any cover close to the antenna (called the superstrate) will cause the resonant frequency and 

efficiency of the antenna to drop. It is therefore recommended to keep any distance to the 

superstrate to a minimum of 3 mm from the top surface of the patch.
See Table 2-5 for recommended characteristics of both passive patch and active antennas 

for use with the Jupiter receiver.