A Closer Look
Figure 5 provides a schematic view of the DGS lowpass filter, which is comprised of two quasi-Yagi slots in the PCB’s metallic ground plane and two compensated microstrip capacitors,which are placed on the top layer and connected together by means of a 50-Ω feed line on the top circuit layer. To perform a computer-aided-engineering (CAE) software simulation, a four-pole LPF was simulated on RO4003 PCB material from Rogers Corp. with relative dielectric constant, εr, of 3.38 at 10 GHz in the material’s z-axis; a material thickness of 0.813 mm was used in the simulation. Figure 6 shows simulation results with Microwave Office. The dimensions for the compensation capacitors were calculated as m = 8 mm, n = 5 mm, and k = 4 mm.
The optimized quasi-DGS-unit was used to design a LPF, fabricated on substrate measuring 30 x 20 mm2 with εr = 3.38 and thickness (h) of 0.813 mm. Figure 7 shows a photograph of the fabricated structure. Measurements were carried out on a model HP8719D RF/microwave vector network analyzer (VNA) from Hewlett-Packard/Agilent Technologies and are shown in Fig. 8. The fabricated LPF has a 3-dB cutoff frequency at 2 GHz and out-of-band rejection of 20 dB from 3 to 11 GHz; insertion loss in the passband is only about 0.65 dB. Figure 8 shows good agreement between the measured and simulated results.
| Download this article in .PDF format |
This file type includes high resolution graphics and schematics when applicable.