This paper presents a simple reconfigurable bandpass filter switching from 2.4 to 5 GHz based on PIN diodes. The proposed filter is intended to add frequency-tunability to antenna systems used in cognitive radio applications. It consists of a bent connecting stub with two open-circuited quarter-wave stubs grounded via PIN diodes. By controlling the didoes states, the electrical length of the stubs can be switched from quarter-wave to half-wave and vice versa, so as to tune the filter center frequency. The proposed design approach consists of ensuring communication at 2.4 GHz while blocking the 5 GHz band in the ON state, whereas in the OFF state, the filter is intended to reject the 2.4 GHz band and passing the 5 GHz band. A prototype of the proposed filter is fabricated and measured to validate the proposed concept. Both simulated and measured results show a two-state filter with a wide tuning range from 2.4 to 5 GHz and a good stopband rejection level better than 40 dB. Moreover, a flat group delay of about 0.55–0.7 ns is achieved within the operating bandwidth in both states. The proposed filter is able to achieve simultaneous bandwidth and frequency control, showing an important tool to meet modern system requirements.
Fully-Integrated Tunable Q-Enhanced Linear Low Noise Amplifier for Wireless Receivers
