Issue link: https://resources.system-analysis.cadence.com/i/1339378
APPLICATION NOTE New Method for X-Band Bandpass Filter Design Figure 1: Layout of the BPF in AWR Microwave Office software. Microwave bandpass filters (BPFs) are the fundamental component used in many RF/microwave applications to eliminate interference from signals operating at nearby frequencies. This application note presents a straightforward and largely nonmathematical method for designing an edge-coupled, bandpass filter for X-band operations (8.4 - 9.3GHz) with a combi- nation of filter synthesis, closed-form edge-coupled transmission-line models, and EM analysis using the AWR Microwave Office circuit simulator within AWR Design Environment software. A miniature X-band, edge-coupled microstrip bandpass filter design example demonstrates this flow. The filter was imple- mented using edge-coupled microstrip lines on a Rogers RO4003 substrate material with Er = 3.66 and H = 8 mil. The temperature coefficient of dielectric constant was among the lowest of any circuit board material, and the dielectric constant was stable over a broad frequency range, specifically at X-band frequencies. The simulated results showed good filter response characteristics with the passband insertion loss approximately 5 dB and return loss greater than 12 dB over the pass bandwidth of 900MHz. Bandpass Filter Construction A BPF can be constructed from resonant structures, such as a waveguide cavity or open-circuit transmission lines (i.e., stubs). An impor tant parameter in filter design considerations is the fractional bandwidth, which is defined as the ratio of the passband bandwidth to the geometric center frequency. The inverse of this quantity is called the Q-factor. Simulation Model and Results Circuit Schematic Implementation Models can be created for many basic components (trans- mission lines, coupled lines, MCROSSX, MTEEX$, MSTEPX, and more). The electromagnetic (EM)-based X model elements and "$" based intelligent models were found to be more accurate compared to EM simulation. Simulation, tuning, and parameter sweeps were possible without compromising the accuracy using these circuit models. The schematic in Figure 1 was created by using the AWR Microwave Office elements library MACLIN asymmetric edge-coupled microstrip line model, which consists of the parameters W1, W2 (strip widths), S (gap between strips), and L (line length). 5 www.cadence.com/go/awr