An X-band phased-array antenna unit with harmonic suppression is formed on the basis of a printed dipole antenna by integrating a low-pass filter with a transformed radial stubs(TRS) fed by stripline. The antenna with harmonic suppression is only 2.44mm higher than the antenna without harmonic suppression. The measured results of the 8×8 small test array show that the suppression of the fundamental wave with respect to the second harmonic is at least 15 dB, and the average can reach 20dB.

In this brief, the design methodology of an antenna calibration network using multi-layer stripline-slotline coupling is proposed. A multi-layer coupler and a two-stage Wilkinson power divider are designed to ensure the basically stable amplitude-phase characteristics of coupling and achieve the wide frequency band. To minimize phase imbalance, the lengths of channels should be kept equal to the maximum extent possible. In addition, the transmission line conversion structure is applied at each port for integration with the antenna array. Aiming at the problems of signal crosstalk and mutual coupling, the isolated via holes are installed near the lines and metal spacers are placed over the ports. By using the semi-closed structure, part of substrates is dug out to expose the resistor welding position. A semi-closed calibration network in series-parallel-fed is fabricated to verify the design methodology. In 8–16 GHz, the amplitude-phase characteristics are considerable, in which the coupling is 37–44 dB and phase deviation is below 8°. The isolation between ports T1-T16 is greater than 33 dB and voltage standing wave ratio (VSWR) of them is lower than 1.8.

Based on backward transformation method (BTM), the probe distance error analysis in z ‐axis for phased array calibration is described. When BTM is employed in phased array calibration to obtain the electric field over the radiation aperture of antenna, the Taylor expansion of probe distance error is used for analyzing the accuracy of reconstructed aperture field. It is found that probe distance error less than 1/35 of a wavelength is recommended. To verify this conclusion, the measured results demonstrate the validation of this analysis, which is helpful in the near‐field calibration for phased array.

Based on the passband characteristics of frequency selective surface (FSS), a wideband transmitarray (TA) with linear polarization rotation at W-band is proposed. The middle layer of the unit cell is a pattern of arrow-shaped structure, which can rotate the incoming wave by 90°. A pair of parallel strip polarizers is employed to enhance the polarization conversion efficiency. The prototype of $25\times 25$ -element TA is fabricated by the standard PCB technology. Within the 3 dB gain bandwidth of 20%, the measured peak gain of 28.7 dB with the corresponding aperture efficiency of 38.2% is achieved. The error analysis is also conducted by comparing the simulation and measurement. The performance of the proposed TA demonstrates that it is a suitable solution for wideband and low-cost applications in the millimeter-wave spectrum.

In view of the problem that the existing energy-frequency selective surface（ EFSS） is very sensitive to incident angle or the frequency selective features are unsatisfactory,an angular insensitive EFSS is designed,consisting of three layers of metal screens. The upper and lower layers are square metal patches and ground metallized holes,and the middle layer is etched Jerusalem cross gap. The upper and lower layers of the metal patches and the metallized holes are connected via PIN diodes. Finally,the method is verified to be effective via the simulation.

A 45° linear-polarized phased array operated over P- to L-band with a maximum of ±45° scan volume in azimuthal plane is proposed, the array is composed of microstrip-fed antipodal Vivaldi antenna elements. The active reflection coefficients and the spatial polarization characteristic (SPC) of the array with various scanning angles were simulated and optimized with the help of metal baffles as the parasitical parts of the array. For demonstration, a prototype of 45° linear-polarized array is fabricated and measured. The measurement results indicate a wide-band wide-scan performance and the spatial polarization characteristic keeps much stable.

In this article, a novel differential bandpass filter based on periodic spoof surface plasmon polaritons (SSPPs) is proposed. It consists of a pair of double-layer SSPPs using double-sided parallel-strip line (DSPSL), a pair of single-layer SSPPs, and a 180° phase inverter. The transmission characteristics of the proposed SSPPs’ structure are analyzed by the differential-mode and common-mode method, and also applied to design the differential filter. To validate the design concept, a differential filter sample has been designed, fabricated, and measured. The simulated and measured results indicate a 3-dB fractional bandwidth of 25.5% (frequency 5.5 GHz), and a wide 20-dB common-mode suppression from 2.9 to 8 GHz can be achieved for the differential filter.

A wideband planar dipole array based on artificial magnetic conductor (AMC) surface is presented for phased array applications. One wideband in-phase hexagonal AMC cell is realized firstly. An X-band planar dipole is modified by employing a detached H-shaped patch and four L-shaped stubs for impedance bandwidth enhancement. The active VSWR with different scanning angles and the radiation pattern of center element in small array are simulated. For demonstration, a prototype of 45 degrees linearly polarized array with the elements of 4 x 32 is fabricated and measured. From the measurements, it can provide a stable gain over the entire scan range of +/- 45 degrees within 8-11 GHz. Meanwhile, the difference of two orthogonal polarization components keeps less than 3.5 dB below 11 GHz as the beam scanning. It shows good performance in low-profile and low cost phased array antennas.

A novel single-layer band-pass frequency selective surface (FSS) is proposed in this letter. The unit cell is composed of eight rotationally symmetrical fishbone-shaped structures surrounded by a modified octagonal loop. This fishbone-shaped FSS exhibits stable resonant frequency while the incident angle ranges from 0 degrees to 60 degrees for both TE and TM polarizations, which means that polarization insensitivity and angular stability are well demonstrated on the proposed FSS. A prototype is fabricated and measured in an anechoic chamber, and good agreements are obtained between measured and simulated results.

Two novel classes of high-selectivity input-reflectionless bandpass filters (BPFs) with narrow- and wide-band characteristics and out-of-band transmission zeros (TZs) are presented. These input-reflectionless BPFs, which are based on a complementary-duplexer approach, respectively, exploit inter-coupled short-/open-ended dual-behavior resonators (DBRs) and coupled line/T-stub two-path transversal filtering stages in their main BPF channel. Their absorptive auxiliary channel is made up of a resistively terminated dual-band bipath transversal filtering cell, whose dual passbands are allocated in the stopband regions of the main BPF channel. Thus, the RF-input-signal energy that is not transmitted by the main channel in its attenuated bands is dissipated by the loading resistor of the auxiliary one. Hence, input-reflectionless properties are attained in the whole BPF architecture. The theoretical design principles of the conceived narrow- and wideband input-reflectionless BPF approaches are described. Furthermore, their experimental usefulness is verified through the development and characterization of two microstrip sharp-rejection BPF prototypes centered at 2 GHz.

A novel compact dual-band balanced coupler with differential-mode power division, broadband common-mode, and common-to-differential-mode conversion suppression is proposed. In these double-functionality balanced-coupler architectures, double-sided parallel-strip line 180 degrees phase inverters are used to realize the broadband common-mode rejection. Moreover, the frequency is tunable by changing the characteristic impedance of the transmission line. For practical verification, a balanced couplers (epsilon(r) = 2.65, h = 0.5 mm, tan(delta(D)) = 0.003) operation at 0.9/1.8 GHz is constructed in microstrip technology and tested.

A wideband planar dipole based on dual-layer artificial magnetic conductor (AMC) is designed. First, the size of dual-layer AMC is reduced by more than half, and the in-phase band is wider than the single-layer AMC. Then, the improvement of large scan angle can be obtained by the offset between two layers of AMC in two directions. At last, a wideband planar dipole with 24.5% bandwidth is achieved.

Wideband MIMO antennas using decoupling network are presented, which are based on the transversal signal-interference concept. The directional coupler was designed and optimized to make up the decoupling network. Compared with the coupled antennas without the decoupling network, the isolation is more than 15 dB within 1.8-2.7 GHz. For demonstration, an integration of two antennas with the decoupling network was prototyped and measured. Good agreement between simulation and measurement is observed.

A novel dual-wideband bandpass filter with controllable bandwidths is presented in this article. Two passbands for the WLAN band are realised based on a multimode resonator with three open stubs. The bandwidth of the two-order passbands with even or odd mode can be adjusted by appropriately selecting the characteristic impedance of the multimode resonator. A planar microstrip dual-wideband bandpass filter prototype with a 3-dB fractional bandwidth of 16.7% and 9.2% is designed and fabricated. High selectivity and good in-band performance can be achieved in the dual-wideband bandpass filter.

In this letter, a miniaturized microstrip patch antenna with enhanced bandwidth is presented. Based on the transversal signal-interference concept, the dual feedline structure is employed to reduce the nonradiating side of the antenna element. In order to extend the impedance bandwidth, an additional T-shaped stub resonator is introduced. Compared to a typical rectangular patch antenna, 32% size reduction and 17.0% impedance bandwidth (S-11 < -10 dB) enhancement are achieved, respectively. Good agreement between simulation and measurement can be observed.

Two high selectivity fifth-order wideband bandpass filters (BPFs) with multiple transmission zeros based on transversal signal-interaction concepts are proposed in this paper. Two transmission paths consisting of a shorted stub and two open coupled lines are used to realize signal transmission from Port 1 to Port 2. Two fifth-order wideband passbands with six and ten transmission zeros from 0 GHz to 2 f 0 ( f 0 is center frequency of the passband) can be achieved respectively due to the superposition of signals of the two transmission paths. Two prototypes with 3-dB fractional bandwidths of 61.7% (2.07-3.92 GHz) and 48.2% (2.3-3.76 GHz) are designed and fabricated for demonstration. Good agreement can be observed between simulated and measured performances.

In this paper, a novel miniaturization method for filter implementation is presented and validated. According to frequency response transformation, the filter structure has the wideband bandpass response in the required frequency band which is lower than the operation frequency. The in-band and out-of-band characteristics are also improved to realize wide passband and stopband responses. For demonstration, three filters are designed based on the proposed ideas. The efficient circuit area is reduced by 56.8%-64.7% compared with the conventional wideband filter, indicating significant miniaturization using the proposed method. Another advantage of our work is that the stopband is extended to more than 9 f 0 than other wideband filter structures. Good agreement between simulation and experiment is obtained.

A compact dual-wideband bandstop filter based on transversal signal-interference concept is proposed in this paper. Two transmission paths with a half-wavelength open stub and two open coupled lines are used to realize two wide stopbands for WLAN bands. Second-order stopband with two transmission poles near each stopband can be easily realized by the two transmission paths. A planar dual-wideband bandstop filter with 3-dB fractional bandwidths of 54.2% and 23.6% is designed and fabricated. The theoretical and measured results are in good agreement and show good in-band filtering performance and high selectivity.