Abstract
A microwave miniaturized bandpass filter using (Mg 0.95 Ca 0.05 )TiO 3 (abbreviated as 95MCT hereafter) ceramic substrate is investigated in the present paper. The paper studies the sintering and microwave dielectric properties of Al 2 O 3 , La 2 O 3 and SiO 2 co-doped 95MCT. The XRD pattern shows that a secondary phase MgTi 2 O 5 is easily segregated in 95MCT ceramic, however, through co-doping it can be effectively suppressed, and the microwave dielectric properties, especially, the Qf value can be significantly improved. Through optimizing the co-doping ratio of Al 2 O 3 , La 2 O 3 and SiO 2 , the sintering temperature of 95MCT ceramic can be lowered by 80°C, and the microwave dielectric properties can reach Qf=61856GHz and e r =19.84, which indicates the modified 95MCT ceramic have a great potential application in microwave communication devices. Based on this, we also designed a miniaturized microwave bandpass filter (BPF) on modified 95MCT substrate. Through a full wave electromagnetic structure simulation, the results show that the center frequency of the BPF is 2.45GHz and the relative bandwidth is 4.09% with the insertion loss of less than 0.2dB in the whole bandpass.
Highlights
With the rapid development of wireless communication, microwave filters have been continuously challenged with ever more stringent requirements
95MCT possesses the optimum microwave properties [7], since it is a solid solution between triangle structured MgTiO3 and orthorhombic structured CaTiO3, a minor deleterious MgTi2O5 phase is segregated in 95MCT ceramics
Since the sintering temperature of 95MCT ceramics is high of 1400°C to 1450°C, it is difficult for industry applications
Summary
With the rapid development of wireless communication, microwave filters have been continuously challenged with ever more stringent requirements. Three prerequisites have to be met, which includes near zero temperature coefficient of resonant frequency IJf, high permittivity İr as well as low dielectric loss, or high quality factor Q. MgTiO3 dielectric possesses an ilmenite structure with permittivity of 17 and IJf of -45 ppm/oC. CaTiO3 dielectric is a well-known incipient ferroelectric dielectric with significant characteristics of large IJf (+800ppm/oC) and large permittivity (170) [6]. Their combination is expected very suitable for producing ultrahigh Qf and compensated IJf value at microwave frequencies. Lowing the sintering temperature as well as maintaining the excellent dielectric properties is still a challenge for 95MCT. Through a full wave electromagnet structure simulation, it is proved that the BPF possesses both low insertion loss and compact size
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