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Design of C-Band Interdigital Filter and Compact C-Band Hairpin Bandpass Film Filter on Thin Film Substrate

Abstract:

With the development of modern electronic technology, microwave communication equipment tends to miniaturization, low cost, and high performance. While micro- wave integrated circuit modules become more and more abundant, the discrete circuit applications will be fewer and fewer. Now microwave integration technology has become mature, and microstrip and microstrip circuit are widely used in micro- wave integrated circuits due to small size, light weight, low cost, and so on.

This paper studies the C-band microstrip interdigital and hairpin filter, which is used in the transceiver channel. The C-band filter, which is soldered to the PCB board, could reduce the impact of spurious signals in the transceiver. The frequency source is an important part of the transceiver, which provides the local oscillator signal to the transceiver channels. The spurious signals of the transceiver system require less than 60 dBc. The experimental filter of this paper is fabricated on an Al2O3 ceramic substrate with a relative dielectric constant of 9.8, thickness of 0.381 mm and the PCB board is fabricated on a commercial substrate (Rogers R04350) with a relative dielectric constant of 3.66, and loss tangent of 0.004 more than Al2O3 ceramic. The first filter is designed in the PCB board with thickness of 0.381 mm.

The proposed filter of this paper has a better performance than the first filter. First, the precision of processing of the first filter designed in the PCB board is worse than Al2O3 ceramic substrate, and the loss tangent of Rogers R04350 is bigger than Al2O3 ceramic. Second, because the design of frequency source is complex and the PCB board is multilayer, the bottom of the original filter unpaved lot of ground and only around the filter is grounded, so the ground is not very good, and performance is less than the indicator of the design.

The size of proposed filters is relatively smaller than the first filter because of the dielectric constant, and consistency in the high and low temperature characteristics is also very good because of the advanced technology of the film. In order to realize miniaturization, film substrate is used to design the filter and simulation is conducted by means of the electromagnetic simulation software. At the end of the paper, the vector network analyzer is used to measure the filter, and the test results show that the performance of the filter reaches usage requirements.