MeMiTec/8GHz end-coupled, half-wavelength microstrip filter

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An end-coupled, half-wavelength resonator microstrip filter centered on 8.8GHz was designed on a very low cost FR-4 substrate. The design was first carried out using Momentum (Figure 1) and then implemented on the substrate using a Rapid PCB Prototyping system (Figure 2). In the Figure it is also possible to observe the box, where the filter was enclosed, in order to reduce irradiation, that would degrade its frequency response.

A good agreement was obtained by setting the electrical permittivity of the substrate to a value of 4.25 instead of 4.7, as claimed by the substrate constructor. This result stems out from the fact that the FR-4 is usually employed for applications at frequencies lower than 9GHz. As in the case of the microstrip patch antenna, the good agreement between the Momentum simulations and the experimental data demonstrate that X-band passive structures can be fabricated using very low cost substrate as the FR-4 even if the right value of the electrical permittivity should be determined.