Miniaturized Bandpass Filter with Controllable Transmission Zero using Low-Temperature Co-fired Ceramic (LTCC) Technology

The trend toward miniaturization of satellite payloads necessitates the development of increasingly smaller and more efficient receiver and transmitter systems. Consequently, the components that make up these receivers and transmitters must be compact and utilize multi-layer technology to create hybrid architectures. Microstrip-based high-rejection filters necessitate a significant amount of space, which hinders the implementation of radio frequency systems in package (SiPs). The objective of this study is to develop compact filters for satellite receivers. This research focuses on constructing a filter that has improved selectivity to reject unwanted image frequencies while keeping the filter order the same. A third-order grounded combline resonator loaded with a capacitor has been chosen as the fundamental configuration for the proposed bandpass filter design. The paper introduces a new method to improve the selectivity of the combline resonator bandpass filter by incorporating a transmission zero, which is achieved by introducing a U-shaped coupling structure between non-adjacent resonators in a separate layer. The position of the transmission zero can be accurately controlled by adjusting the length of the U-shaped coupling transmission line. An additional coupling pad has been inserted between the resonator and the U-shaped pattern on a separate layer to guarantee the coupling between the resonators and adjust the bandwidth. An innovative method was employed to build and simulate a filter for the Ku-band frequency range of 12.7 GHz to 13.0 GHz. The filter has a 1-dB absolute bandwidth of 310 MHz and achieves a rejection of 26 dB at 11.6 GHz, the image frequency for a standard payload receiver. The filter's dimensions are 6.5 mm × 2.58 mm × 0.89 mm, making it an essential component of the RF SiP.