Wideband differentially-fed patch antennas under dual high-order modes for stable high gain are proposed in this communication. The working principle is verified on a differentially-fed circular patch antenna operating in TM31 and TM12 modes at first. Two open slots are loaded to the patch’s edge to reconstruct the current distribution of TM31 mode, thus substantially increasing the broadside radiation. An additional slot is introduced at the patch center to perturb the TM12 mode and reshape its current to be more in-phase, by which sidelobe radiation is dramatically reduced. With use of loading of slots and shorting pins, the two modes are allocated in resonant frequencies to make up an enhanced bandwidth of 13.4% and produce high gain up to 13.7 dBi, with the beamwidth and gain level nearly unchanged in band. After that, the proposed method is further developed on a rectangular patch antenna, where three cascaded slots and four shorting pins are loaded to perturb TM21 and TM03 modes, and reshape their current distributions. In a similar way, the broadside radiation of TM21 mode is enhanced and the sidelobe of TM03 mode is suppressed. At last, the antenna obtains a bandwidth of 12.4% and stable realized gain as high as 14.0 dBi.

In this brief, a novel planar topology is presented for the design of reconfigurable-bandwidth dual-wideband bandpass filters with fixed operation frequency and controllable stopband. The proposed design is started from a three-mode passive filtering structure with five transmission zeros, whose second and third passband edges can be independently allocated. Then, two PIN diodes are used as the tuning elements. With the help of these PIN diodes, three bandwidth states can be achieved. In contrast to the previous works with only independently tunable single passband edges, the first and fourth passband edges of the proposed filter can be reconfigurable in same absolute ranges, while the rest two ones are unaltered. For validation, a reconfigurable prototype is designed and measured. The measured results agree well with the theoretical analysis, verifying a simple design approach of DWB BPFs with new reconfigurable-bandwidth property.

In this paper, a novel wideband slotline antenna with high gain characteristic is presented by using a multi-mode radiator under the circumstance of the optimized ground plane. The proposed antenna is analyzed from a traditional slot antenna with one full-wavelength radiation mode. Subsequently, two pairs of slot stubs are symmetrically loaded along the arms of the initial antenna near the nulls of the magnetic current of the full-wavelength radiation mode. By suitably choosing the lengths of the loaded stubs, extra two radiation modes can be introduced and merged with the full-wavelength one, resulting in a wide impedance bandwidth with three resonances. Finally, the size of the ground plane and locations of stubs are investigated to suppress the sidelobes and ensure high gain within the impedance bandwidth. For validation, a prototype antenna is fabricated and its electrical performances are measured. The experimental results show that the operating fractional bandwidth (FBW) of the proposed antenna can be effectively increased to 40.8% while keeping the inherent narrow slot structure. Besides, the measured average peak gain and its corresponding ripple within the impedance bandwidth are 6.2 dBi and 1.1 dB, respectively, and the radiation patterns are maintained constant. Compared with the reported works, the proposed design can allow a slotline antenna to achieve high gain and constant radiation patterns in a wide bandwidth simultaneously.

In this paper, a series of novel reconfigurable-bandwidth notched-wideband bandpass filters (NWB BPFs) with controllable notch bands are proposed. The proposed filters start from a passive filtering structure, which is formed by a terminated cross-shaped resonator (TCSR) with a pair of parallel-coupled lines and two open-ended stubs. Theoretical analysis finds that the filter bandwidth can be independently controlled by the TCSR, while the center frequencies and bandwidth of notch bands are mainly controlled by the rest parts. According to this, a BPF with controllable notch bands can be designed. To achieve the reconfigurable-bandwidth NWB BPFs with controllable notch band, whose bandwidth and center frequency can be maintained unchanged under different work states, two PIN diodes and a varactor are employed. By controlling the work states of PIN diodes, three bandwidth states can be achieved with fixed center frequency. By controlling the applied voltage on the varactor, other NWB BPF with independently tunable lower passband edge can be realized. For verification, three prototypes are designed and measured. The measured results agree well with the theoretical analysis and simulated ones, verifying a simple and effective design approach of reconfigurable-bandwidth NWB BPFs.

In this brief, a new and planar topology is presented for the synthesis design of Chebyshev wideband bandpass filters (WB BPFs) with independently reconfigurable lower passband edge. The proposed design is based on a new T-shaped resonator, whose topology and parameters can be directly derived from a 5th-order Chebyshev LC circuit. Then, a varactor is employed as the tuning element. By controlling the supplied voltage on the varactor, the lower passband edge of the proposed filter can be independently tunable in continue manners, while the upper one is maintained fixed. For verification, a reconfigurable prototype is designed and measured. As the measured and simulated results agree well with each other, a simple and high-efficiency design of reconfigurable-bandwidth WB BPFs is verified.

In this paper, a novel and planar topology, which can be used to design notched-/dual-wideband bandpass filters (NWB/DWB BPFs) with controllable isolation bandwidth, is presented for interference rejection. Here, the isolation band is referred to notch band for NWB BPFs, while stopband between two passbands for DWB BPFs. The proposed topology is started from a novel T-shaped resonator with two poles and three zeros. Then, a pair of parallel-coupled lines and two open-ended stubs is added. With the help of the added parts, the extra four poles are introduced, and another two zeros are suppressed or excited according to whether it is required to realize a notched- or dual-band response. Due to the existence of multiple transmission poles and zeros, the excellent filtering responses, i.e., high isolation level, sharp selectivity, and good passband flatness, can be achieved. Besides, it is found that the isolation bandwidth of BPFs based on the proposed topology can be continuously varied from a narrow notch band to a wide stopband while the outer two passband edges are maintained unchanged by using suitable para-meters. To validate this, two prototypes are designed and measured, including a six-mode NWB BPF with 3-dB passband fractional bandwidth (FBW) of 94.1% and 20-dB notch FBW of 2.39%, and a three-mode DWB BPF with 3-dB passband FBWs of 36.2% and 22.6% and 20-dB stopband FBW of 14.5%.