Hao-Tao Hu

High-Selectivity Low-Pass Filters With Ultrawide Stopband Based on Defected Ground Structures

Compact microstrip low-pass filters (LPFs) with ultrawide stopband based on a defected ground structure (DGS) and their design procedures are presented in this paper. A key merit of the filter configuration is that the selectivity of the LPFs can be conveniently controlled, whereas the bandwidth is fixed. The LPFs are realized using open-circuited uniform impedance stubs and stepped-impedance stubs (SISs). The position of the transmission zeros can be freely controlled by tuning the impedance ratio of the SISs. To expand the stopband, the dumbbell DGS is used to suppress the spurious passbands of the LPFs. Two demonstration filters with a cutoff frequency at 1 GHz have been designed, fabricated, and measured. The measured results indicate good performance: broad stopband (>15 fc or 20 fc) low passband insertion loss (<;0.3 dB), compact size, and sharp skirt characteristic.

Design of filtering microstrip antenna array with reduced sidelobe level

For the requirements of efficient integration and simple fabrication, a new codesign approach for a microstrip filter with an antenna array with reduced sidelobe level is introduced in this communication. The microstrip patch antennas and the stub-loaded resonators are used to illustrate the synthesis of a bandpass filtering antenna array. By controlling the coupling strength between the resonators, a uniform or nonuniform power divider network can be obtained. A nonuniform power division is used to reduce the sidelobe level. The equivalent lumped circuit model is developed and analyzed in detail. Two types of eight-element filtering antenna array with uniform and tapered power-distribution among the elements have been designed. Simulated and measured results provide a good verification for the theoretical concepts.

Design of Microstrip Lowpass-Bandpass Triplexer With High Isolation

This letter proposes a lowpass-bandpass triplexer consisting of one lowpass channel and two bandpass channels. Stepped-impedance stubs are used in the lowpass filter (LPF) design, which bring a sharp selectivity. Defected ground structures are utilized to increase the impedance of one transmission line in the lowpass section, giving improved performance. High Isolation is achieved by careful consideration of the input signal splitting structure. To illustrate the concepts, a lowpass-bandpass triplexer is designed, fabricated and measured. The cut-off frequency of the LPF is chosen to be 1 GHz. The central passband frequencies are selected to be 2.4 and 5.8 GHz. Simulated and measured results are found to be in good agreement with each other. Isolations among the three bands are better than 40 dB.

A Compact Directional Slot Antenna and Its Application in MIMO Array

In this communication, a new design for the microstrip-fed slot antenna with a directive radiation pattern for WLAN/WiMAX application is presented. By utilizing a two-element array topology, a unidirectional radiation pattern is obtained. Without any directors and reflectors, the proposed slot antenna shows advantages in terms of compact size and high front-to-back gain ratio in the azimuthal plane. Four directional slot antennas are then placed in a square loop array to obtain nearly orthogonal patterns. Thus, a compact multiple input multiple output array with high isolation among those four elements is achieved. Simulated and measured results are presented to validate the practicality of the proposed antenna structures.

A Wideband U-Shaped Slot Antenna and Its Application in MIMO Terminals

A wideband microstrip multiple-input-multiple-output (MIMO) antenna with U-shaped slot is presented in this letter. To widen the impedance bandwidth, uniform and stepped U-shaped slot antennas are sequentially investigated. Two types of resonant modes are excited, including slot mode and monopole mode. Then, additional multiple slots embedded inside the U-shaped slot are employed to further widen the bandwidth. The proposed slot antenna features wide bandwidth (109%) and compact slot size ( 0.16λg ×0.27λg, where λg is the guided wavelength at the lowest operating frequency) simultaneously. The proposed slot antenna element is then applied in the MIMO antenna system. Both the two antennas are suitable for handheld devices, covering GPS/GSM1800/LTE/UMTS/WLAN/WiMAX/UWB (lower) band.

Design of high isolation diplexer with novel matching network

This paper reports a new kind of matching network for microstrip diplexer. By properly adjusting the input admittance of the matching network, each channel of the diplexer can be designed independently. The diplexer can be easily realized by the connection of different bandpass filters without further tuning. The matching network is comprised by some open- and short-circuited transmission lines, and source-load coupling can also be conveniently introduced. Moreover, the proposed matching network occupies little place, and thus the size of the diplexer is mostly determined by the filters. To illustrate the concept, a diplexer has been designed, fabricated and measured. Simulated and measured results are found to be in good agreement with each other.

A Differential Filtering Microstrip Antenna Array With Intrinsic Common-Mode Rejection

A differential third-order Chebyshev filtering microstrip antenna array with high common-mode (CM) rejection is presented. The feeding structure consisting of one line resonator and one H-shaped resonator as well as the microstrip antenna elements together provide the three stages in the bandpass filter design. Under differential-mode excitation, the H-shaped resonator can be effectively coupled with the line resonator, and thus differential signals can be radiated. However, under CM excitation, the H-shaped resonator cannot be excited so that the CM suppression can be achieved. A prototype antenna array with center frequency at 3.5 GHz has been designed and fabricated to experimentally validate the principle and design approach. Experimental results exhibit that the proposed differential filtering antenna array features high CM rejection, low cross-polarization level, and good filtering response.

Novel Broadband Filtering Slotline Antennas Excited by Multi-Mode Resonators

A novel type of slotline antenna excited by multimode resonators are proposed in this letter. To widen the impedance bandwidth, two types of resonant modes are excited, including slotline mode and stub-loaded resonator mode. An equivalent multipoles filtering network is given for providing a physical insight into the in-band property. Two prototype antennas are finally designed and fabricated to experimentally validate the principle and design approach. Experimental results exhibit that proposed antennas feature not only broad impedance bandwidth but also good filtering response such as flat gain frequency response, sharp band-edge characteristic, as well as high stopband suppression.

Design of Wide-Stopband Bandpass Filter and Diplexer Using Uniform Impedance Resonators

This paper proposes a simple and effective method to designing wide-stopband bandpass filters and diplexers using uniform impedance resonators. Microstrip terminated parallel coupled lines are utilized to generate the filtering functions. By adjustment of the electrical lengths of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be obtained. Appropriate positioning of these zeros enables the suppression of spurious frequencies. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for both homogeneous and inhomogeneous mediums are given in detail. Different combinations of the frequency position of the transmission zeros can provide various characteristics. To extend the stopband bandwidth, one or more transmission zeros can be distributed on different harmonic frequencies. To demonstrate the proposed method, two bandpass filters and a diplexer are designed and fabricated. The measured results are in good agreement with the simulated ones. The first filter provides a high attenuation of 40 dB up to 6.8 times the fundamental frequency (f0) and the second filter provides a lower attenuation of 28 dB, but this time extending up to 14.9 f0.