Microstrip Dual-mode Bandpass Filter With Novel Rectangular-loop Perturbation

As the rapid progress and application of wireless communication techniques, the RF components have a development tendency of miniaturization, high performance, low cost and multi-layer integration. As an important component of communication system, the performance of filter will play a key role in communication system. Miniaturization, low insertion loss and high spurious responses suppression of filter have attracted much attention. Microstrip dual-mode bandpass filter not only has the advantage of miniaturization, high performance and low cost, but also is easy to integrate. Microstrip dual-mode bandpass filter with novel rectangular-loop has been studied in this dissertation to realize miniaturized broadband bandpass filter which is easy to adjust. The work involved in this thesis includes four main parts, as follows:Firstly, a novel double loop dual-mode bandpass filter is proposed which consists a full wavelength rectangular resonator and a rectangular-loop for the purpose of perturbation. The rectangular-loop has two tunable parameters which increase the degree of freedom of dual-mode and make the miniaturization easier. Tapped coupling can be used to change the transmission zeros so that the performance of filter is improved. A prototype filter is designed and fabricated with measured center frequency of 2.41GHz, fractional bandwidth of 17.77%, low passband insertion loss of 0.67dB, high passband return loss of 17dB and wide stop band with rejection better than 20dB.Secondly, a meandering dual-mode microstrip bandpass filter using rectangular-loop perturbation is proposed. The meandering structure has the advantage of small size and the gradually changed tapped input/output structure arranged at 180°geometrically along a straight line enhances the performance of the filter and the adjustability of transmission zeros. A prototype filter is designed and fabricated with center frequency of 2.45GHz. The measured fractional bandwidth is 10.98%, insertion loss is 0.8dB, and return loss is over 15dB.Thirdly, a dual-mode dual-band bandpass filter with rectangular-loop perturbation and stacked structure is presented. The dual-band filter consists of two dual-mode resonators with rectangular- loop perturbation on different layers, which need only single input and output. This structure has the advantage of tuning two passbands easily and independently, good performance,and tuning transmission zeros easily. The center frequencies of the proposed filter are 2.4GHz and 3.8GHz, and the minimum insertion loss of the two passbands is 3.37 dB and 1.85 dB, respectively.At last, a dual-band bandpass filter is realized by meandering dual-mode resonator with novel rectangular loop perturbation is presented. The dual-band filter consists of two dual-mode resonators which needs only single input and output. This structure has the advantage of tuning two passbands easily and independently and good performance. The center frequencies of the proposed filter are 2.38GHz and 3.56GHz, and the minimum insertion loss of the two passbands is 1.42 dB and 2.34 dB respectively.