Designing GPS (GNSS) Ceramic Antenna
Introduction:
The key parameter for a good GPS antenna should exhibit optimal polarization, gain, and return loss.
- Right-hand circular polarization (RHCP) is preferred as it aligns with GPS satellite signals, enhancing reception.
- Adequate gain, typically between 2 to 5 dBi, is crucial for improving signal strength and accuracy in positioning.
- Low return loss, ideally more significant than 10 dB, indicates effective impedance matching and minimal signal reflection, ensuring sound transmission and reception.
Together, these parameters are essential for GPS antennas' reliable and accurate performance.
Global Positioning System (GPS) technology is a crucial innovation for navigation and positioning, utilizing a network of satellites that transmit signals to receivers on Earth. GPS primarily operates on L1 (1575.42 MHz) and L2 (1227.60 MHz) frequencies, with the newer L5 band (1176.45 MHz) enhancing accuracy for safety-critical applications. The signals are modulated with information that allows receivers to calculate distances based on the time taken for the signals to reach them from multiple satellites—typically four or more—which enables triangulation of precise three-dimensional positions. The development of Global Navigation Satellite Systems (GNSS) has further evolved this technology, incorporating other constellations such as GLONASS, Galileo, and BeiDou, providing enhanced reliability and accuracy. Understanding these operating frequencies and their implications is vital for designing efficient GPS antennas, such as ceramic antennas, which are favored for their compact size, durability, and performance in various applications.
Principle of radiation:
The radiation principle of the GPS ceramic antenna is similar to any patch antenna [1]. The radiating length of the current plus the fringing field radiates at the half-wavelength of the operating frequency, as shown in the equation (3) bellow:
For compactness, the high dielectric (dk ~ 22) ceramic and large thickness are used to miniaturize and bandwidth. However, reducing the patch size led to a decrease in gain.
Antenna design and simulation
The design of the antenna is operating in the frequency range from 1.57 to 1.58GHz at the L1 band. As shown in the figure below, the antenna also integrated with IC at the bottom layer which further increate thickness. The antenna is feed with a prob feeding techniuque for impedance macthcing and circuir polarization.
The total size of the antenna is 10.27 x 10.27 mm2 with the return loss of S11<-10dB for the operating frequency. The radiation pattern in is shown to be hemispherical with a good performing gain and directivity.
