A new microwave dielectric composite ceramic (1-x) wt%LiMg0.9Zn0.06Ni0.04PO4-x wt%TiO2 (0 <= x <= 18 wt%) was synthesized in the low sintering temperature range of 850 degrees C -975 degrees C by the solid-state reaction method. The XRD diffractogram confirmed the coexistence of LiMg0.9Zn0.06Ni0.04PO4 and TiO2, and no second phase was detected. Due to their opposite tau f values, the tau f values of LiMg0.9Zn0.06Ni0.04PO4 solid solution ceramics were adjusted by adding different volume fractions of TiO2. The composite ceramic with x = 15 wt% sintered at 975 degrees C shows desirable microwave dielectric properties of epsilon r-10.30, Qxf -58,400 GHz (tan delta = 2.093 x10-4), and tau f -+ 4.04 ppm/ degrees C (at-12 GHz). Based on the 85 wt% LiMg0.9Zn0.06Ni0.04PO4-15 wt% TiO2 ceramics, a fourth order dielectric waveguide filter filled with composite ceramics is designed and packaged for the RF front-end of the China Mobile 5 G base station. The test results show that the center frequency of the filter is 4.65 GHz, the working bandwidth is 300 MHz, the filter has a good out of band rejection capability, and the insertion loss in band is 0.18 dB. Combined with the filter test data and material performance, the designed dielectric waveguide filter meets the communication requirements of the base station, and the higher Qxf microwave dielectric ceramic material can achieve low insertion loss and excellent frequency selection performance of the filter.

This letter presents a half-mode substrate integrated cavity bandpass filter with both continuous center frequency and 3 dB bandwidth tuning capabilities. The filter adopts a superposed two layers PCB with lumped varactors loading the central resonator to tune the center frequency. The first-invented semicircular metal sheet on the center rod not only reduces the filter size given a certain resonant frequency significantly by increasing the capacitance between the semicircular metal and the upper ground metal but also facilitates fine frequency tuning by using appropriate varactor Ctune. Surface mount varactors between two resonators change the inter-resonator coupling to adjust the 3 dB BW. Another varactor on the feed line can be used to adjust the external coupling. This filter demonstrates a BW range of 75-130 MHz around 1.5 GHz, a 3 dB BW range of 46-130 MHz around 1.3 GHz and a 3 dB BW range of 55-90 MHz around 1.11 GHz with 10 dB minimum return loss. Insertion loss ranging from 2.262 dB to 7 dB have been obtained.

A novel varactor tunable dual-band bandpass filter (BPF) using stub-loaded stepped-impedance resonators is proposed in this letter. Compared with the traditional tunable filters, the source-load coupling and T-shape stub-loaded lines are employed in this design. The proposed BPF architecture has the advantages of high selectivity and less control voltages. In the overall tuning range, the proposed filter is designed with 5-6 transmission zeros and more than 30 dB rejection between the two passbands. Meanwhile, only one control voltage is needed for each passband. A prototype of this filter is fabricated and measured. The measurement results show great agreement with simulated results, which show that the first passband can be tuned in a frequency range from 0.8 to 1.02 GHz, and the second passband varies from 2.02 to 2.48 GHz.