Abstract
In this paper, a tunable bandpass filter using coupled line with a wide tuning range is proposed. The proposed filter has a simple structure which is composed of a coupled-line section and two pairs of varactors. Meanwhile, simultaneously tuning on bandwidth and center frequency are introduced by varactors. The tunability is mainly realized by varactors connected to one end of the coupled line and varactors between ports and coupled line provide an impedance matching. A theoretical analysis is presented to illustrate the tunability by using even- and odd-mode theory. Additionally, the detailed effect of the two types of varactors is researched, respectively. To verify the concept, a prototype is designed, fabricated, and measured. The transmission zero exhibited in measurement is introduced by bias circuits. The measured results show that the tunable bandpass filter achieves a tunable center frequency of 0.494-1.257 GHz (87.15%) and a 3-dB bandwidth of 0.282-0.943 GHz (334%).
Highlights
Reconfigurable or high-performance microwave devices, such as power dividers [1]–[3], phase shifters [4]–[7], couplers [8]–[10], and filters [11]–[33], are extensively studied in past several years
The tunable bandpass filters (BPFs) with widespread applications can be classified as filters with tuning frequency with constant absolute bandwidth [15], [19], controllable operating bandwidth with fixed center frequency [29], and both bandwidth and frequency
EVEN- AND ODD-MODE ANALYSIS Fig. 1 shows the schematic diagram of the proposed tunable BPF, which consists of a section of coupled line loaded with two types of tunable capacitors
Summary
Reconfigurable or high-performance microwave devices, such as power dividers [1]–[3], phase shifters [4]–[7], couplers [8]–[10], and filters [11]–[33], are extensively studied in past several years. The proposed varactor loaded coupled-line structure is introduced between two quarter-wavelength coupled-line sections to implement the simultaneously phase and frequency tunable coupler. Enhancement in both bandwidth and phase tunable range has been come true. A tunable BPF using a coupled line with a wide tuning range is proposed and analyzed based on the work [34]. EVEN- AND ODD-MODE ANALYSIS Fig. 1 shows the schematic diagram of the proposed tunable BPF, which consists of a section of coupled line loaded with two types of tunable capacitors.
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