Wideband Filtering Power Divider With Unequal Power Division Ratio and All-Frequency Input Absorptive Feature

In this brief, a wideband filtering power divider (FPD) with unequal power division ratio and all-frequency absorptive feature is presented. It is consisted of two transmission lines (TLs), two coupled lines (CLs), two stepped open-circuited stubs, an isolation resistor, and two absorptive branches. By setting different parameters for the TLs, the CLs and the absorptive branches, unequal power distribution with good filtering responses and input absorptive feature is obtained. Besides, with the insertion of one isolation resistor, good impedance matching and isolation between output ports are realized. Theoretical analysis of the proposed FPD is derived and parametric studies are also given. For demonstration, a prototype with 1:3 power division ratio was designed and fabricated. Measurement results show that for 10-dB return loss, the fractional bandwidths (FBWs) of 200%, 80% and 98% can be achieved for the input and output ports, respectively. While the 3-dB passband FBWs are 82.5% and 99.5% for the two output ports, separately. Besides, the rectangular coefficients of the two outputs are 1.38 and 1.22, respectively, which indicate high frequency selectivity.

I. Introduction

Power dividers (PD) are essential components in communication systems, such as antenna feeding networks and power amplifiers. In the past decades, various developments have been reported on broadband [1], [2], reconfigurable [3], [4], multi-band [5], [6], and arbitrary power division ratio [7], [8], [9] PDs. Recently, with the improvement of modern technologies, the concept of multifunctional fusion is gradually attracting the attention of scholars. Thus, filtering power dividers (FPDs) [10], [11], [12], [13], which combines the functions of frequency selectivity and power division, are emerged. Except the filtering function, several reports also integrate the absorptive feature into the FPDs [14], [15], [16]. This is benefit for protecting the operations of preceding active stages, such as the mixers, multipliers and amplifiers, from deteriorated by the undesired RF-signal-power reflections generated in the out-of-band region [17]. In [14], a resistively terminated bandstop filter is connected to the input of the PD for achieving input-absorptive feature. However, it exhibits narrow absorptive bandwidth and poor frequency selectivity. In [15], the 10-dB absorptive bandwidth is widened to 286% by loading three resonated absorptive stubs. In [16], a compact wideband absorptive FPD with good isolation is proposed by using composite T-shape network. But the output ports are poorly matched. Besides, the reported absorptive FPDs all exhibit equal power distributions. As for wideband unequal power distribution, two PDs with 4:1 and 8:1 power division ratio are presented in [10] by using the three-mode resonator. However, the absorptive feature is not merged in the FPD. To the best of the authors’ knowledge, there is little papers devoted to the design of FPD with wideband, unequal power distribution, and absorption feature simultaneously.