Coplanar Band Pass Filter
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Coplanar Lumped Element Band Pass Filter

The example documented here is a second order lumped element bandpass filter for the center frequency of 22 GHz. Figure 9-6 shows the schematic of the filter containing coplanar interdigital capacitors, coplanar cross junctions, coplanar shorted ends, coplanar rectangular spiral inductors and coplanar lines. In this circuit the spiral inductors represents the parallel resonance circuits, where the parasitics of these inductors act as capacitances of resonance circuit. The layout of the circuit is shown in Figure 9-7. As it can be seen in these figures, two metal layers are used. The interdigital capacitors are designed in the metal layer 1 because of the low losses of such capacitors. The filter was designed and realized on GaAs. Figure 9-8 shows a photo of the realized filter. The simulated and measured scattering parameters of the filter are plotted in Figure 9-9 showing very good agreement between the measurement and simulation.

Photo of the Coplanar Lumped Element Bandpass Filter
Figure 9-6. Schematic of the Lumped Element Bandpass Filter Figure 9-7. Layout of the Lumped Element Bandpass Filter
Figure 9-8. Photo of the realized Lumped Element Bandpass Filter on GaAs. Figure 9-9. Measured and Simulated S-Parameters of the Lumped Element Bandpass Filter