In this brief, a balanced dual-band bandpass filter (BPF) using quad-mode ring loaded resonator (RLR) is presented. The resonance characteristics of the proposed quad-mode RLR are analyzed and the design graphs of the electrical lengths and the four resonant modes are given. Based on the above analysis, four resonant modes are applied to achieve two differential-mode (DM) passbands. U-shaped microstrip lines and stepped impedance microstrip/slotline (MS) transition structures are employed to achieve good common-mode (CM) rejection without affecting DM ones. In addition, an additional transmission pole is realized in the lower passband due to the stepped impedance slotlines. Meanwhile, six transmission zeros (TZs) are generated due to the horizontal transmission interference of the resonator and new coupling path, which improves the selectivities of the passbands. Furthermore, based on the proposed filter, a balanced dual-band filtering power divider (FPD) is designed for miniaturization. By loading isolation resistors on the slotline, the output ports isolation is improved. To verify the theoretical design, two proposed designs have been manufactured and measured. The measured and simulated results are presented with a good agreement.

An Improved Differential Evolution (IDE) algorithm is proposed for optimization problems. With the novel mutant operation adopting sub-optimal individual, the convergence of Differential Evolution (DE) algorithm is accelerated without increasing the risk of premature. Five typical test functions are minimized using DE and IDE algorithms, and the results show the superior performance of IDE algorithm. Furthermore, the algorithm is applied to pattern synthesis of two antenna arrays. Broad nulls are formed in radiation pattern of a linear array to suppress broad-band interferences. In a microstrip patch array, the sidelobe level of array is decreased about 12.9 dB and the mainlobe can scan to the desired angle.

In this letter, a leaky-wave antenna (LWA) based on double-layer (DL) slow-wave structure, possessing high scanning rate and wide scanning angle features is investigated. The DL unit structure consists of a top layer structure with cross-shaped unit and a bottom layer structure with slot-shaped unit. The DL units realize the property of controlling the cut-off frequency and slope of dispersion curves independently by independently changing the unit slow-wave property of top and bottom layers. The radiation of LWA is achieved by triangularly modulating the cross-shaped units of top layer. Due to the existence of the slot-shaped units of bottom layer, strong slow-wave property is introduced to increase the growth rate of period phase shift, thus achieving high scanning rate. Meanwhile, the n = −2 space harmonic (SH) of the LWA is separated from the fast-wave region of n = −1 SH, thus enlarging scanning angle in forward quadrant. A prototype of the proposed LWA is fabricated and measured. The LWA can achieve a wide scanning angle from −68 ° to +74 ° in a narrow frequency band of 9 to 10.75 GHz.

A balanced filtering directional coupler (BFDC) based on slotline is designed in this paper. The proposed coupler is composed of balanced microstrip/slot (MS) transition feed structures, three-line cross-finger-coupled resonant structures and asymmetric parallel loaded branch. The MS transition feed structure is adopted at the input and output ports to make the differential mode (DM) response independent of the common mode (CM) one and achieve a good CM suppression. Two transmission zeros (TZs) are generated and controlled by the coupling of three-line cross-finger-coupled resonant structure, thereby the out-of-band selectivity can be enhanced. Asymmetrical parallel loaded branch can effectively improve the flatness of the coupler. In order to verify the design strategy, the coupler was designed, fabricated and measured, and the measurement results are in good agreement with the simulation ones. The DM operating band of the designed coupler covers 4.2 GHz to 5.3 GHz (FBW=24%) with 15 dB return loss. Isolation is better than 15 dB and CM suppression is better than 40 dB.

The brief presents a quasi-design about balanced wideband Schiffman phase shifters based on slotlines, which can achieve phase shift with relatively small phase equiripple and high common mode (CM) rejection. The proposed balanced phase shifters are mainly composed of a microstrip/slotline transition structure and a C-section coupling slotline. C-section coupling slotline consisting of two long parallel coupling slotlines and two short parallel coupling slotline can achieve the phase shift function. The microstrip/slotline transition structure is employed as a balanced port, so that the differential mode (DM) response and CM one are independent of each other. Different from the traditional Schiffman phase shifter: two methods are used to compensate the different phase velocity between the odd and even modes. In order to decrease the DM transmission loss, sandwich structure is also employed in this design. To the best of authors’ knowledge, the balanced wideband Schiffman phase shifter based on slotline may be the first ever reported. Finally, 45∘, 90∘ and 180∘ phase shifters with a central frequency at 2.37 GHz are achieved to verify the design method. The measured results agree well with the simulation.

Conformal antenna arrays often have many elements with different radiation patterns and much cross‐polarisation. Those factors make synthesising radiation patterns a difficult problem. In this study, the authors propose a balanced dynamic differential evolution (BDDE) algorithm to suppress the cross‐polarisation in conformal arrays. To increase the probability of the inferior group participating in the mutant, a suboptimal individual is adopted in the mutant operation. Parameters are dynamically updated to accelerate the convergence speed. We adjust the cross‐rate to its maximal value every few generations to increase the diversity in the population. Two conformal arrays are modelled to verify the ability of BDDE to synthesise the radiation pattern and polarisation simultaneously. To avoid increasing the number of unknowns caused by dual‐feed antennas, circular polarised patch antennas with one feed are used to compose the conformal arrays. Embedded element patterns are used in the synthesis to take into account the influence of mutual coupling between the elements and their environment. We compare BDDE with other popular DE algorithms, and simulation results show that the proposed algorithm achieves lower sidelobe levels and cross‐polarisation reliably and efficiently.