Design of GPS antenna

A GPS antenna is a specialized type of antenna designed to receive signals from GPS (Global Positioning System) satellites in orbit around the Earth. These antennas play important role to enable GPS devices in determining their location, velocity and time. These antennas are capable to work with L-band frequency range used by GPS i.e. 1.2276 GHz to 1.57542 GHz.

They are specifically designed to work with L1 band (1.57542 GHz), L2 band (1.2276 GHz) and multiple frequencies (L1 and L2). The radiation pattern of GPS antenna is usually hemispherical in order to cover sky evenly.

Following parameters are considered during GPS antenna design. It includes antenna type, operating frequency, size of antenna, impedance matching, feed mechanism, dielectric material etc.
• Antenna type : GPS antenna can be designed in one of the following configurations which include patch antenna, helical antenna or ceramic chip antenna. Patch antennas are simpler to design.
• Frequency : It should operate in GPS L band frequency range.
• Size : It is determined by wavelength of GPS signal. It should be fraction of a wavelength for optimal performance.
• Impedance : It should be matched to 50 Ohm transmission line for maximum power transfer.
• Feed : It provides signal to the antenna. It should be coaxial cable connected to feed point of the antenna.
• Dielectric material : GPS antennas are designed on PCB substrates or ceramic materials.
• Matching circuit (e.g. balun) : Required to convert balanced antenna impedance to unbalanced impedance of transmission line.

How GPS antenna works

• A GPS antenna works by receiving signals from GPS satellites orbiting around the Earth. These signals carry timing and location information. This is used by GPS receiver to determine the antenna's position on the Earth's surface.
• The GPS receiver measures time it takes for each satellite signal to travel from satellite to the GPS receiver antenna. Since signals travel at the speed of light (3x108 m/sec), time delay can be converted into distance.
• To determine its position, GPS receiver needs signals from at least three satellites. By knowing distance from each satellites and the satellites' precise location, the receiver can perform trilateration. It finds intersection point of spheres with radii equal to the calculated distances from each satellite. This intersection point represents the receiver's position.
• As the user or the GPS device moves, the receiver continuously tracks signals from multiple satellites to update its position in real-time. Moreover some receivers employ techniques such as differential GPS (DGPS) to enhance accuracy.

GPS Antenna Types

Following are the common types of GPS antennas designed for different applications and use cases.
• Patch antenna : It is widely used due to its compact size and ease of integration. It consists of metal patch on one side and ground plane on the other side. It offers high gain and good radiation pattern.
• Helical antenna : It is used where circular polarization is needed. It consists of wire wound helix pattern around central support. It is used in applications requiring signal reception at low elevation angles.
• Ceramic GPS antenna : It is also known as ceramic chip antenna. It is constructed using ceramic materials having favourable electromagnetic (EM) properties. It is usually made as per surface mount technology so that it can easily be integrated onto circuit boards. It is fabricated using multilayer ceramic technology, where conductive patterns are printed on ceramic layers and are stacked to create the antenna structure. The ceramic material also provides mechanical robustness, electrical insulation and thermal stability.
• Other types include active antenna, dipole antenna, patched cavity antenna, choke ring antenna, quadrifilar helix antenna, microstrip antenna and so on.

GPS Antenna Ceramic patch type

Figure-1 depicts SGP series of GPS SMT patch antenna of ceramic type. Following are the typical specifications of GPS antenna from Taoglas.

•  Receive frequency: (1575.42 MHz +/- 1.023 MHz)
•  Center frequency: 1575.42 +/- 3 MHz
•  Bandwidth: 8 MHz (min.)
•  VSWR: 1.5 MAX.
•  Gain at zenith: 2 dBic (typical)
•  Axial ratio: 3 dB max.
•  Polarization: RHCP

GPS Antenna Manufacturers

Following are list of GPS antenna manufacturers of various types.
• Novatel Inc.
• Trimble Navigation Limited
• Garmin Ltd.
• Gilsson Technologies
• Linx Technologies, Merlin, US
• Lowrance
• Antcom Corporation

Conclusion: GPS antennas are essential components of the GPS receiver system. They play critical role in capturing and processing the weak signals from GPS satellites. The design of GPS antenna can impact sensitivity and overall performance. Among the different GPS antenna types, ceramic patch antenna is commonly used in variety of GPS enabled devices including Smartphones and tablets, Wearable devices like smartwatches and fitness trackers, Automotive navigation systems, Asset tracking devices and IoT devices with GPS capabilities.

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