GPS Antenna Design: Types and Working Principles

A GPS antenna is a specialized antenna designed to receive signals from Global Positioning System (GPS) satellites orbiting Earth. These antennas play a vital role in enabling GPS devices to determine their location, velocity, and time.

These antennas are capable of operating within the L-band frequency range used by GPS, which spans from 1.2276 GHz to 1.57542 GHz. They are specifically designed to work with the L1 band (1.57542 GHz), L2 band (1.2276 GHz), and multiple frequencies (L1 and L2). The radiation pattern of a GPS antenna is typically hemispherical to cover the sky evenly.

The following parameters are considered during GPS antenna design:

• Antenna type
• Operating frequency
• Size of antenna
• Impedance matching
• Feed mechanism
• Dielectric material

Let’s examine these parameters in more detail:

• Antenna type: GPS antennas can be designed in several configurations, including patch antennas, helical antennas, or ceramic chip antennas. Patch antennas are relatively simple to design.
• Frequency: The antenna should operate in the GPS L-band frequency range.
• Size: The size is determined by the wavelength of the GPS signal. It should be a fraction of a wavelength for optimal performance.
• Impedance: It should be matched to a 50 Ohm transmission line for maximum power transfer.
• Feed: This provides the signal to the antenna. It’s often a coaxial cable connected to the 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 the balanced antenna impedance to the unbalanced impedance of the transmission line.

How GPS Antennas Work

A GPS antenna receives signals from GPS satellites orbiting the Earth. These signals carry timing and location information. This information is then used by the GPS receiver to determine the antenna’s position on the Earth’s surface.

• The GPS receiver measures the time it takes for each satellite signal to travel from the satellite to the GPS receiver antenna. Since signals travel at the speed of light ($3 \times 10^8$ m/sec), the time delay can be converted into distance using the formula:

  $distance = speed \times time$

• To determine its position, a GPS receiver needs signals from at least three satellites. By knowing the distance from each satellite and the satellites’ precise locations, the receiver can perform trilateration. This involves finding the 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 GPS device moves, the receiver continuously tracks signals from multiple satellites to update its position in real-time. Furthermore, some receivers employ techniques such as differential GPS (DGPS) to enhance accuracy.

GPS Antenna Types

Here are some common types of GPS antennas designed for various applications and use cases:

• Patch antenna: These are widely used due to their compact size and ease of integration. They consist of a metal patch on one side and a ground plane on the other side. They offer high gain and a good radiation pattern.
• Helical antenna: These are used where circular polarization is needed. They consist of a wire wound in a helix pattern around a central support. They are used in applications requiring signal reception at low elevation angles.
• Ceramic GPS antenna: These are also known as ceramic chip antennas. They are constructed using ceramic materials that have favorable electromagnetic (EM) properties. They are usually made using surface mount technology so they can easily be integrated onto circuit boards. They are fabricated using multilayer ceramic technology, where conductive patterns are printed on ceramic layers and stacked to create the antenna structure. The ceramic material also provides mechanical robustness, electrical insulation, and thermal stability.
• Other types: Active antennas, dipole antennas, patched cavity antennas, choke ring antennas, quadrifilar helix antennas, microstrip antennas, and more.

Figure-1 depicts SGP series of GPS SMT patch antenna of ceramic type.

Here are the typical specifications of a 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

Here is a list of GPS antenna manufacturers of various types:

• Novatel Inc.
• Trimble Navigation Limited
• Garmin Ltd.
• Gilsson Technologies
• MEINBERG RADIO CLOCKS GmbH & Co. KG
• Linx Technologies, Merlin, US
• SAN JOSE TECHNOLOGY, INC.
• Lowrance
• Antcom Corporation

Conclusion

GPS antennas are essential components of GPS receiver systems. They play a critical role in capturing and processing the weak signals from GPS satellites. The design of a GPS antenna can significantly impact sensitivity and overall performance. Among the different GPS antenna types, ceramic patch antennas are commonly used in a 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.