Most GPS receivers come with built in antennas. Two popular types of antennas used in GPS receivers are "patch" and "quadrifilar helix" or "quad helix" in short. External GPS antennas are normally used when stronger satellite signals are needed. Many models are mounted magnetically to the roof of a vehicle and those made for buildings are often mast-mounted.
Most models are available with a wide range of connectors for all the various GPS receiver antenna jacks. You will need external GPS antennas in vehicles where the GPS receiver cannot be placed near a window. They are also great for use when hiking under heavy tree cover or in canyons. In fact they would be needed for all places that do not offer a good view of the sky.
GPS antennas work well when you lose signals temporarily while in moving vehicles. They help you maintain the best possible accuracy by having a lock on the greatest number of satellites. There are many types of GPS antennas. You have the ‘active’ GPS antenna that includes Low Noise Amplifier (LNA). Active antennas run off of the GPS receiver's power, this puts extra drain on the receiver's batteries.
Passive antennas or substrates do not include an LNA and therefore do not require power. The reradiating GPS antenna system has two antennas. The receiving antenna placed outside the vehicle and the transmitting or "reradiating," antenna placed near GPS receivers. The two are connected by coaxial cables with the system powered by either 12 volt vehicle supply or AC adaptor.
