Microwave diplexer purely based on direct synchronous and asynchronous coupling

A diplexer realized purely based on direct coupling is presented. No cross-coupling is involved in the design process. The microwave diplexer is achieved by coupling a dual-band bandpass filter onto two individual channel filters. This design eliminates the need for employing external junctions in diplexer design, as opposed to the conventional design approach which requires separate junctions for energy distribution. A 10-pole (10th order) diplexer has been successfully designed, simulated, fabricated and measured. The diplexer is composed of 2 poles from the dual-band filter, 4 poles from the Tx bandpass filter, and the remaining 4 poles from the Rx bandpass filter. The design was implemented using synchronously and asynchronously tuned microstrip square open-loop resonators. The simulation and measurement results show that an isolation of 50 dB is achieved between the diplexer Tx and Rx bands. The minimum insertion loss is 2.88 dB for the transmit band, and 2.95 dB for the receive band

Symmetric 3dB filtering power divider with equal output power ratio for communication systems

This paper presents a two-way filtering power divider (FPD) with an equal output power ratio of 1:1. This implies that each of the FPD output port would receive 50% of the power at the input port. To achieve miniaturisation, a common square open-loop resonator is used to distribute energy between the two integrated Chebyshev bandpass filters. In addition to distributing energy, the common resonator also contributes one pole to each integrated bandpass filter (BPF), hence, reducing the number of individual resonating elements used in achieving the integrated FPD. To demonstrate the proposed design technique, a prototype FPD centred at 2.6 GHz with a 3 dB fractional bandwidth of 3% is designed, simulated and presented. The circuit model and microstrip layout results of the FPD show good agreement. The microstrip layout simulation responses show that a less than 1.1dB insertion loss and a greater than 16.5dB in-band return loss were achieved. The overall footprint of the integrated FPD is 37mm by 13mm (i.e. 0.32λg x 0.11λg, for λg = guided-wavelength of the 50Ω microstrip line at 2.6 GHz). The integrated FPD reported in this paper shows some promising merits when compared to similar devices recently reported in literature

Substrate integrated waveguide (SIW) bandpass filter with novel microstrip-CPW-SIW input coupling

A Substrate integrated waveguide bandpass filter is presented with a novel CPW-to-SIW transition at both the input and output ports which also served as the input and output couplings into the filter. The CPW-to-SIW transition structures presented here exploited the step impedance between the 50 ohms input/output feedline and the transition to control the input/output couplings of the filter. The SIW filter is also shown to have very minimum milling or etching requirement which reduces the fabrication error. The proposed SIW filter has been validated experimentally and results presented. The results show that a simulated return loss of 15 dB and an initial measured return loss of 16 dB were achieved. An improved measured return loss of 22 dB was later achieved after some tuining adjustments were performed on the filter input and output couplings. A minimum insertion loss of 1.3 dB was also achieved across the band