Surface acoustic wave (SAW) technology is an emerging field of science and technology that was developed in the late 1960s. It is an interdisciplinary subject combining acoustics and electronics. The development of surface acoustic wave technology is quite rapid. Its application field has evolved from the initial military radar to the entire radio communication, especially the rapid development of mobile communication technology, which further promotes the development of surface acoustic wave technology. Surface acoustic wave filter (SAWF) is a translating passive band made by utilizing the piezoelectric effect of piezoelectric quartz crystal oscillator material such as piezoelectric ceramic, lithium niobate or quartz, and the physical properties of surface acoustic wave propagation. The pass filter is a filter-dedicated device which is made of a piezoelectric material such as a quartz crystal or a piezoelectric ceramic, and utilizes its piezoelectric effect and physical properties of surface acoustic wave propagation. SAW filters are widely used in color televisions, mobile phones, GPS positioning, satellite communications and cable television. Package: LCCC (lead-free ceramic chip carrier) surface mount form (the smallest product is only 2.5*2mm, weighs about 22mg.) Center Frequency: The arithmetic mean of two cutoff frequency values ​​for a given relative insertion loss (eg, –3 dB) level. Passband Width (Bandwidth): The frequency spacing between two cutoff frequencies for a given relative insertion loss level. Passband ripple: refers to the difference between the maximum loss in the specified frequency domain within the passband. For the surface acoustic wave filter, the concept of a passband ripple is also given, defined as the difference in loss between the two largest peaks and valleys in the flat top passband. Stopband rejection: The maximum sidelobe level of the device in a given frequency band. Rectangular coefficient: refers to the ratio of the bandwidth of the two specified loss values. If not specified, it can be measured by the ratio of 40dB bandwidth to 3dB bandwidth. Group delay fluctuation : The maximum difference in group delay within the specified passband range. Insertion loss: Under a given termination load, the signal source is directly passed to the decibel before it is inserted into the filter. Typically, the insertion loss of a filter is measured by the insertion loss value of the maximum output level frequency point in the passband. Early SAW filters have large insertion loss, typically above 15 dB, which is unacceptable for communication devices that require low power consumption, especially the receive front end. In order to meet the requirements of modern communication systems and other applications, the development of high-performance piezoelectric materials and improved IDT design, the device insertion loss is reduced to 3 ~ 4dB, as low as 1dB. When the piezoelectric substrate is selected, the operating frequency of the SAW filter is determined by the width of the IDT electrode strip, and the narrower the IDT electrode strip, the higher the frequency. A 2~3GHz SAW filter can be fabricated using a semiconductor processing process of 0.35~0.42μm. Suppress interference signals and filter The SAW filter plays a good role in suppressing high-order harmonics, image information, emission and leakage signals, and various parasitic clutter disturbances of electronic information equipment, and can realize amplitude-frequency characteristics and phase-frequency characteristics of arbitrary precision required. Filtering, which is difficult to achieve with other filters. In recent years, SAW filters have been sliced ​​abroad and weigh about 0.2g. In addition, due to the use of new crystal materials and the latest fine processing technology, the upper limit frequency of SAW devices is increased to 2.5-3GHz, which further promotes SAW. Filters are widely used in the field of anti-EMI. The SAW filter enables the adjacent-frequency transmission of CATV with a very steep transition band, which doubles the spectrum utilization compared to the frequency-separated transmission. If the TV receiver does not use a SAW filter, it is impossible to work so stable and reliable. In fact, the main application areas of early SAW filters were both audio-visual home appliances represented by TV sets. After the 1980s, due to the rapid development of electronic information, especially the communication industry, SAW filters provided a broad market space. As a result, its production and demand have shown a rising trend. At present, the annual output of SAW filters in the world is more than 600 million, of which 430 million small RF (Radio Frequency Frequency, Radio Frequency) SAW filters for mobile communication. The transmitting and receiving ends of the mobile communication system must be filtered by the filter to function. Since the operating frequency band is generally 800 MHz.2 GHz and the bandwidth is 17.30 MHz, the filter is required to have low insertion loss, high stop band rejection and high mirroring. Attenuation, high power consumption, low cost, and miniaturization. Due to its advantages in operating frequency band, volume and cost performance, SAW filters are the leader in mobile communication systems, which are beyond the reach of piezoceramic filters and monolithic crystal filters. In the wireless paging system, the RF signal received by the BP machine needs to be filtered and then amplified, and the electrical characteristics of the filter directly affect the sensitivity and accuracy of the received signal. The BP machines produced in the early days generally use LC filters. Due to the complicated debugging of the LC filters, the selectivity and stability are poor, so they have been gradually replaced by SAW filters. With the rapid development of the Internet, there are more and more users accessing the Internet worldwide. However, the biggest disadvantage of using the Internet through the Internet is that the bandwidth is too narrow (tens of kilohertz), the download speed is extremely slow, and the network frequency resources of CATV are abundant. Therefore, the merchants are developing a broadband multimedia data broadcasting system based on CATV network, and the information transmission speed can be increased by several dozen times by CATV access. In these systems, a high-performance SAW filter is used to solve the adjacent frequency suppression problem. It can be seen that the market prospect of SAW filters is very impressive.
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SAW filter parameter table of a Japanese 920MHz band 
SAW filter applied to communication equipment