Compact T-shaped ring bandpass filter with source-load coupled structure for WPT

A T-shaped ring band pass filter using source-load coupled technique is proposed in this paper. T-shaped ring structure effectively utilizes the area and makes it easier to tune filter's center operating frequency, which is also helpful in expanding the bandwidth. Source-load coupled technique is used in the proposed design to increase the transmission zeros on the operating frequency in both sides so that the out-of-band rejection can be further improved. First, validation in simulation is carried out to prove the use of source-load coupling. Then a demonstrating filter has been designed, optimized, fabricated and measured. The filter has low insertion loss of 0.35dB, return loss of -18dB when operating in 2.47GHz, and measurement shows good agreement with simulation. Such filter can be in good use in microwave power transmission in microwave-RFID application.