Wideband Filtering Response Research Articles

High‐selectivity wideband four‐way filtering power divider with input absorptive feature

AbstractIn the paper, a high‐selectivity wideband four‐way filtering power divider with input absorptive feature is presented. It consists of two parallel‐coupled lines (CLs), two three‐coupled lines (TCLs), two open‐ended stepped branches, one absorptive branch, and two isolation resistors. The wideband filtering response is achieved by cascading the TCLs and CLs. While high selectivity is obtained by loading the open‐ended stepped branch, where two extra transmission zeros are generated. In addition, wide absorptive bandwidth with good isolations between adjacent output ports are realized by combining the absorptive branch with the isolation resistors. Equations are derived by using the two‐parity mode analysis, and main parameters are investigated in detail. For validation, a prototype was designed and fabricated. Test results show that the 3‐dB FBW can reach 87% with a 10‐dB input absorptive FBW of 200%. Besides, for the output ports with 10‐dB return loss and 10‐dB isolation, the FBWs are 94% and 91.5%, respectively. It also features high frequency selectivity and low insertion loss.

A Simple Wide-Angular Scanning Phased Array With Wideband Filtering Response

This article presents a low-profile planar phased array with improved reflection (wideband filtering response) and radiation (wide-angular scan) performance. On one hand, the filtering response with harmonic suppression is integrated into the design of the single-layer array element without extra filtering resonators, such as external filters. As a result, the designed array possesses a reflection bandwidth of 4.6–5.3 GHz and two radiation nulls at either the upper or lower band edge of the reflection curve. On the other hand, inspired by the wide-beam radiation of a circular patch loaded with parasitic monopoles, the proposed array is able to realize its beam scanning coverage of −60°–+60° with low sidelobe levels (SLLs) in its E-plane. The reflection and radiation properties are validated by full-wave simulation and measurement of an eight-element array prototype. The filtering and low-SLL performance benefit for the array to avoid out-of-band interferences and in-band ones from other directions when it scans in a wide-angular area.

Performance enhancement of dielectric resonator antenna by using cross-resonator based filtering feed-network

A wideband filtering dielectric resonator antenna (DRA) is demonstrated in this paper. The filtering characteristics is obtained by integrating a triple pole cross-resonator filter in the feed line of the slot coupled rectangular DRA. The transmission poles of the resonator are adjusted in order to get the wideband filtering response. The proposed filtering DRA offers an impedance bandwidth of 15% from 3.06 GHz to 3.56 GHz. Electric field distribution of DRA within the passband confirmed that the rectangular DRA drives in TE111 mode which ensured the broadside radiation. A satisfactory stable gain pattern of 5.9 ± 0.3 dBi within the pass-band has been achieved. The gain response falls sharply with two radiation-nulls beyond the passband at 3.9 GHz and 4.4 GHz and that increases the selectivity of the antenna. In conclusion, proposed design offers a robust technique to convert a conventional slot coupled rectangular DRA into a wideband antenna along with frequency selective gain response. Proposed configuration manifests as an ideal contender for some specific uses in S-band such as Wi-Max, TD-LTE (Time-Division Long Term Evaluation) application as it avoids the interference adjacent bands.

A Simple, Compact Filtering Patch Antenna Based on Mode Analysis With Wide Out-of-Band Suppression

A simple, compact filtering patch antenna with wide out-of-band suppression is presented, where the filtering mechanism is first analyzed and implemented based on mode analysis of a conventional patch antenna. According to the mode analysis, undesired higher-order modes can be effectively suppressed by selecting a proper length ratio of two sides of the patch and the feeding position, thus realizing a wide upper stopband. To further enhance the filtering response, another two simple filtering structures loaded on the patch antenna are also proposed. First, a split-ring-shaped slot is etched on the patch to generate a radiation null at the lower-band edge for improving skirt selectivity. Second, a U-shaped strip is etched underneath the patch and connected with the feeding probe, which can introduce another null at the upper band edge. As a result, a high suppression level of 23 dB in lower and upper stopbands can be realized, respectively, for the proposed filtering antenna, while the upper stopband can extend up to $2.3 f_{0}(f_{0}$ is the center frequency of the antenna). Furthermore, wide passband response can also be achieved by the extra in-band resonances existing in the slot and the strip. A filtering antenna prototype is fabricated and measured for demonstration. Good agreements between the simulated and the measured results are observed, indicating a large impedance bandwidth of 22.6%, high antenna efficiency of 95.6%, and an average gain of about 7.4 dBi. Compared with the reported filtering antennas, the proposed filtering antenna can achieve better wideband filtering response but with a simpler configuration.

Wideband Filtering Phase Shifter Using Transversal Signal-Interference Techniques

A wideband filtering phase shifter is presented in this letter using transversal signal-interference techniques. The proposed structure creates two signal-propagation paths by introducing extra coupling between two short-ended stubs. Cascaded coupled-line sections and parallel short-ended stubs can generate a constant passband and multiple transmission zeros (TZs) in the stopband and meanwhile provide the arbitrary value of phase shift within the filtering band range. The positions of TZs and phase shift range can be easily controlled. Explicit relations between the objective filtering band and the related parameters are given, and cases with different in-band phase shift values are studied. To validate the design, a prototype is built, simulated, and tested using microstrip lines. The experimental results agree with the predicted ones, demonstrating that the device can realize any given in-band phase shift with a wideband filtering response.

Design of High-Selectivity Asymmetric Three-Way Equal Wideband Filtering Power Divider

An asymmetric three-way equal wideband filtering power divider with high selectivity is presented in this paper. The proposed three-way filtering power divider is an asymmetric structure which is composed of two different $\lambda $ /4 transformers, a pair of short-ended parallel coupled lines, an open-ended parallel coupled line, and a three-line parallel coupled line. Based on 2:1 unequal Wilkinson power divider, an equal three-way power divider is obtained with energy subdivided by three-line parallel coupled line. Subsequently, a Wilkinson power divider with the wideband filtering response is realized by adding a pair of short-ended parallel coupled lines that can provide multiple transmission zeros and poles. Presented with an equivalent circuit, the design procedure for asymmetric three-way equal filtering power divider is developed. Moreover, the reasons for and associated measures of large magnitude imbalance are also analytically developed. The measured results show that the proposed filtering power divider has more than 57.3% 1-dB fractional bandwidth, less than 0.4 dB insertion losses, better than 19.5 dB return loss, and more than 14.9 dB isolation from direct current to 3.3 GHz.

Differential BPFs with Multiple Transmission Zeros Based on Terminated Coupled Lines

AbstractDifferential bandpass filters (BPFs) named Filter A and Filter B based on Terminated Coupled Lines (TCLs) are proposed in this letter. The TCLs contributes to not only three poles in differential-mode (DM) for wideband filtering response but also multiple zeros in both DM and common-mode (CM) offering wide DM out-of-band rejection and good CM suppression. Fabricated filters centred at 3.5 GHz with wide DM passband and wideband CM suppression have been designed and measured. The filters improved the noise suppression capability of the communication and radiometer systems. The simulated and measured results are in good agreement.

A Novel Wideband Filtering Power Divider With Embedding Three-Line Coupled Structures

This paper presents a novel wideband filtering power divider. Instead of the T-junction in the traditional power divider design, a three coupled-line structure is utilized to provide the equal power division to every outputs. Together with the quarter-wavelength coupled line in each way, a wideband filtering response can be obtained. In order to enhance the frequency selectivity, a pair of half-wavelength open stubs are loaded between the three-line coupled structure and parallel coupled lines to produce a pair of transmission zeros on both sides of the passband. To enhance the upper stopband rejection, two additional open stubs are installed at output ports. A new three-port equivalent network for the three-line coupled structure is proposed, and the circuit model for the filtering power divider can be developed for illustrating the working mechanism and the design process. Furthermore, the generalized Chebyshev function is applied to synthesize and analyze the whole structure systematically. For demonstration, a prototype of the wideband filtering power divider operating at 3 GHz is designed and fabricated. The measured results show a 16-dB bandwidth of 62%, an isolation better than 16.5 dB, and a 29-dB wide stopband from 4.39 to 7.73 GHz ( $1.1f_{0}$ ).

Compact wideband microstrip-to-microstrip vertical transition with extended upper stopband

In this article, a compact wideband microstrip-to-microstrip (MS-to-MS) vertical transition designed with a slotline stepped-impedance resonator (SIR) is first presented. Compared with the existing wideband transitions, this proposed transition centered at f0 can tremendously extend its upper stopband via two introduced transmission zeros around 3f0 and 5f0. With the designed equivalent circuit, the working principle is theoretically discussed. To realize the size compactness of this proposed wideband transition, the slotline SIR is replaced by two back-to-back connected slotline Y-junctions. Finally, a prototype wideband transition is simulated and fabricated. A wideband filtering response with its upper stopband up to 6.06 GHz under attenuation better than 15 dB is experimentally achieved as expected in the simulation.

Wideband balanced‐to‐unbalanced filtering unequal power divider with wide stopband and isolation

A novel wideband balanced-to-unbalanced filtering unequal power divider with wide stopband and isolation is proposed. The wideband filtering response with high frequency selectivity can be realised easily using the modified two-port coupled lines with short- and open-circuit stubs, thus generating two transmission zeros near the passband. The complete closed-form equations are presented. A fabricated prototype with 1 : 2 power dividing ratio is simulated and measured to validate the proposed design.

Wideband Microstrip-to-Microstrip Vertical Transition With High Filtering Selectivity Using Open-Circuited Slotline SIR

In this letter, a wideband microstrip-to-microstrip vertical transition using open-circuited slotline stepped-impedance resonator (SIR) is proposed. By controlling the impedance ratio of the slotline SIR, two transmission zeros (TZs) can be properly created and relocated to improve the passband selectivity. To determine the characteristic of this transition, its transmission-line circuit model is presented for analysis and design. Finally, a prototype transition is designed and fabricated for experimental verification. Not only high filtering selectivity via emergence of these TZs but also wideband filtering response with out-of-band suppression of about 22 dB in a frequency range up to $2.51f_{0}$ is experimentally achieved.