1. Research background
Satellite navigation systems are widely used in consumer electronics products and provide navigation, positioning and tracking functions. Russia, the United States, Europe and China have installed the Global Navigation Satellite System (GLONAS), Global Positioning System (GPS), Galileo and Beidou. The antenna is one of the key components to ensure low delay and good reception to provide high-precision positioning and reliable communication.
Microstrip patch antennas have become a popular choice in modern electronic products due to their small size, low cost, easy manufacturing, and small physical size that can be integrated into a limited space. Microwave ceramic dielectrics have been widely used as substrates for vehicle satellite navigation antennas, but conventional ceramic sintering technology usually uses high temperatures above 1200°C to densify the ceramics, and cannot be co-fired with low melting point base metal electrodes (silver, copper, aluminum, etc.) . Therefore, low-temperature co-fired ceramics (LTCC, sintering temperature 700-1000°C) and ultra-low-temperature co-fired ceramics (ULTCC, sintering temperature 400-700°C) have developed rapidly.
However, certain highly integrated, directly compact systems require satellite navigation antennas that can be fabricated directly on polymer-based printed circuit boards (PCBs). Therefore, it is necessary to completely change the manufacturing process of microwave ceramics and radio frequency devices, which will have low loss (high quality factor, Q×f ≥ 3000 GHz) and temperature stability (low resonance frequency temperature coefficient, TCF = +/-3 ppm/°C) ) And low-to-medium dielectric constant (8 <εr <40) microwave ceramics are densified below 200°C and allow direct printing/pressing on the PCB, thereby reducing manufacturing costs and saving energy, and achieving full integration.
2. Research results
Dr. Dawei Wang (first and corresponding author) from the team of Professor Ian M. Reaney from the University of Sheffield, United Kingdom, with Dr. Shiyu Zhang from Loughborough University in the United Kingdom (co-author), Professor Di Zhou from Xi’an Jiaotong University, and Professor Kaixin Song from Hangzhou Dianzi University to address the above issues Using cold sintering technology, successfully prepared Bi2Mo2O9-K2MoO4 (BMO-KMO) composite microwave ceramics with a density greater than 95% at an ultra-low temperature of 150°C. Characterization methods such as XRD, Raman, BSE, and EDX proved that the two phases of BMO and KMO coexist without chemical reaction (Figure 1). BMO-10%KMO composite ceramics have near-zero temperature coefficient (TCF = -1 ppm/°C), medium dielectric constant (εr = 31) and high quality factor (Q×f = 3000 GHz) (Table 1). Furthermore, using cold sintering technology to integrate BMO-10%KMO composite ceramics directly with PCB design and manufacture a circularly polarized microstrip patch antenna that can be used for satellite navigation (Figure 2).
The working frequency range covers Beidou, GPS and Galileo navigation. Frequency (Figure 3), with 87%-88% high efficiency, good circular polarization (Table 2, circular polarization performance is particularly important for satellite navigation applications, because the relative directions of the transmitting and receiving antennas are not fixed, and circular polarization It can overcome the Faraday rotation effect brought by the ionosphere, thereby maximizing signal reception). For the first time, this work integrates cold-sintered ceramics with stable temperature directly on the PCB at low cost and low energy, which represents an important change in the manufacturing technology of radio frequency device substrates. This result was recently published in the Journal of the European Ceramic Society (Direct Integration of Cold Sintered, Temperature-Stable Bi2Mo2O9-K2MoO4 Ceramics on Printed Circuit Boards for Satellite Navigation Antennas, 40 (2020) 4029-4034).