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A wideband circular polarized (CP) switched-beam patch antenna array is presented in this communication. The switched-beam system consists of four two-section branch-line couplers, two wideband 45 phase shifters and 1 × 4 proximity-coupled L-probe feeding CP microstrip patch antenna array. With such an arrangement, the proposed array can obtain a wide axial ratio (AR) bandwidth than that of conventional switched-beam CP antenna array. Measured results showed this array has an impedance bandwidth over a frequency range of 4.04-5.78 GHz (~36%) for |S11

An ultrathin and broadband radar absorber comprising single-layer resistive frequency selective surface (FSS) is investigated in this letter. The resistive FSS layer constructed from resistive/low-conductivity treble-square loops is backed by a grounded foam material. Numerical results show that the proposed absorber can provide a 10-dB radar cross section (RCS) reduction for the conducting plate over the frequency range of 10.7-29 GHz, which is equivalent to a relative bandwidth of 92.2%. Moreover, the structure has the thickness of 2 mm (only 0.071 to 0.193 at lowest and highest frequencies, respectively). The equivalent circuit model is then used to introduce the working principles of the proposed absorber.

A novel phased array is presented to extend array scanning range by using pattern reconfigurable antenna elements and weighted thinned synthesis technology in this paper. The pattern reconfigurable microstrip Yagi antenna element is used as a basic element in array and it is capable of reconfiguring its patterns from broadside to quasi-endfire radiation by shifting states of the PIN diode switches integrated on parasitic strips. A weighted thinned linear array synthesis technique is analyzed and some interesting conclusions have been made. A linear array composed of eight pattern reconfigurable antenna elements is manufactured to demonstrate the excellent performance of the array. The active element pattern of each element is measured and pre-stored. Based on active element patterns and weighted thinned linear array synthesis technique, the pattern scanning performance of the novel array is synthesized. The results indicate that the array can scan its main beam from φ = -60° to φ = 60° in H-plane with gain fluctuation less than 3 dB while maintaining low side lobes, and the -3 dB beam width coverage is about from φ = -68° to φ = 68°. The performance is superior to the traditional phased array made of wide-beam elements.

A circularly polarized switched-beam patch antenna array with butler matrix is designed and experimentally demonstrated in this letter. With suitable rotation technique, circular polarized radiation can be improved for beam steering. Also, this technique enhances the axial-ratio (AR) bandwidth within its scanning angle. Measured results showed this array has an impedance and AR bandwidth over a frequency range of 5.75-6.2 GHz when the main beam of array is scanned to different directions. Good agreement is observed between simulation and measurement.

A hemisphere dielectric resonator pattern reconfigurable antenna (DRA) is proposed in this paper. The proposed antenna element can operate in four states (SI∼SIV) and correspondingly reconfigure its patterns in four directions. A thinning linear array by non-uniform spacing with the element is constructed to scan its main beam from θ = −77◦ to 77◦ in E-plane with 3-dB beam coverage from θ = −90◦ to 90◦ by changing two states and progressive phases.

An ultralow-profile antenna based on a typical magnetic metamaterial unit cell, i.e., complementary electric resonator (CELC) structure, is introduced in this paper. The antenna behaves with an attractive performance of operating in induced “TM120 mode” as the fundamental resonance mode, which is much lower than TM100 mode. Compared to the reported miniature microstrip antennas based on slotting patch/ground technologies, the proposed antenna shows advantages in terms of low profile, high radiation efficiency, and low cross polarization. According to our investigation, even though the relatively strong backward radiation is accessorily caused due to the inherent complementary meander line (CML) slotting as a drawback for this type antenna, the peak gain in the broadside is much higher than a slot antenna with approximately the same dimensions.

In this paper a microstrip parasitic-dipole antenna is proposed and an array is constructed by the proposed antenna on conformal conical surface. The proposed antenna has a good impendence bandwidth, lower cross-polarization. The proposed array exhibits excellent impendence bandwidth of 28.5% and can scan its patterns with lower cross-polarization compared with a conventional conformal microsstrip patch array.

A weighted thinned linear array with pattern reconfigurable antenna elements is proposed to overcome the disadvantages of traditional millimeter wave phased arrays, such as, narrow scanning range, high grating lobes. The developed array can scan its main beam from φ = -76° to 76° in H-plane and has 3 dB beam coverage from φ = -88° to 88° with low grating lobes by shifting two operating states of the elements and adjusting the feed phases.

A single-fed compact circularly-polarised (CP) microstrip antenna is designed and experimentally demonstrated. By embedding the symmetric-slit in the radiation patch and protruding a pair of perturbation elements at the boundary of the centre square slot, the proposed antenna can obtain good CP performance with effective size reduction at a fixed frequency operation. Meanwhile, an impedance transformer is utilised for impedance matching.

The authors investigate in this study using PIN attenuator diodes to reduce the radar cross-section (RCS) of a microstrip patch antenna. A simple design guideline and a useful loading scheme are developed. In the investigation, PIN diodes are equivalent to capacitances and resistances when diodes are reverse-biased and forward-biased, respectively. According to the magnitude distribution of the induced electric field under the patch for a specific incidence angle, the loading positions of PIN diodes are selected near to where the maximum electric field appears. First, three typical incident angles are separately considered. As a result, RCS reduction for the microstrip patch antenna is realised by utilising the variable resistance characteristic (energy dissipation) of PIN attenuator diodes. Secondly, the loading positions for that three incident angles are combined to realise RCS reduction over a large angular spatial region and within a wideband frequency range, and thus an electronically controllable low RCS status can be successfully realised. The proposed design guideline is demonstrated. It is worth mentioning that, by real-time adjusting the bias status of each PIN diode, the antenna realised gain as well as the relative bandwidth is well maintained when the antenna is at work.

A defected ground structure (DGS) is used to suppress mutual coupling between elements in a microstrip array and eliminate the scan blindness in an infinite phased array. Two kinds of DGSs, namely back-to-back U-shaped and dumbbell-shaped DGSs, are analysed and compared. The analysis indicates that the back-to-back U-shaped DGS is better at suppressing propagation of surface waves in microstrip substrate. A two-element microstrip array with back-to-back U-shaped DGS is designed and the array characteristics against different element distances are studied. The results show that the degree of the mutual coupling suppression is increased when the element distance is reduced. However, compared with the traditional array, a higher gain and lower side lobes are obtained when a larger element spacing is selected. The scan blindness of an infinite microstrip phased array in E-plane is studied by simulation, and the calculation demonstrates that the scan blindness can be eliminated by applying a back-to-back U-shaped DGS to the infinite phased array.

A novel pattern reconfigurable patch antenna with a microstrip configuration is proposed. The antenna consists of a disc patch, a ring and eight radially symmetrically distributed microstrip monopoles. The patterns are reconfigured by shifting the states of the eight switches and eight reconfigurable states are available. Each conical pattern around the broadside of the antenna has a wide beam width in the azimuth plane and the eight reconfigurable patterns can cover continuously the space in the horizontal plane. The performance is very advantageous for smart antenna applications on future mobile terminals.