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In this letter, a multibeam leaky-wave antenna (LWA) based on a modified Luneburg lens (LL) beamforming network is proposed. The antenna performs a simple structure and low profile with 2-D beam scanning. First, the modified LL serves as a beamforming network since its variation range ratio of refractive index can be determined by the relative permittivity of the substrate. This can be simply achieved using a printed circuit board technique rather than the square root of two of conventional LL. Then, the relationship between the input port angle and the multibeam angle is analyzed using the geometric-optical method. Finally, a high-scanning-rate LWA array based on spoof surface plasmon polaritons is designed, and its open-stopband is effectively suppressed. A prototype is simulated and fabricated. The measured results show that the proposed antenna has a multibeam range of −42° to 40° in the E-plane and a beam scanning range of −53° to 44° in the H-plane within 8–10.5 GHz, which agrees well with the calculation and simulation.

In this letter, a dual circularly polarized periodic leaky-wave antenna based on spoof surface plasmon polaritons (SSPPs) with linearly sweeping beams is proposed. The antenna can simultaneously radiate left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) beams. Single-arm Archimedean spirals serve as radiators and are designed. Based on linearity analysis and curve fitting, SSPPs structure with potentially linear scanning ability are selected. Finally, the axial ratio (AR) and S-parameter for the proposed SSPPs antenna with spiral radiators are optimized around the broadside frequency using longitudinally asymmetric analysis. A prototype is fabricated and measured results show that the proposed antenna achieves a relative 3 dB AR bandwidth of 31.6% (8–11 GHz) with the same LHCP and RHCP scanning range of 65° and linearly sweeping ability.

In this brief, cross-shaped resonators (CSRs) are integrated in spoof surface plasmon polaritons (SSPPs) unit, and a novel compact single-conductor SSPPs transmission line (TL) with bandpass feature is proposed. In this design, a unit structure based on classical SSPPs structure embedded with a CSR is proposed. To analyze the proposed unit structure, scattering parameters and ABCD-matrix theories are used. After the theoretical analysis, a SSPPs TL with bandpass filtering property is designed. The simulated passband is from 7.9 to 12.2 GHz with a relative bandwidth of 42%. A prototype is fabricated and measured. The measured results are in agreement well with the simulated ones. This proposed structure is attractive and useful for the design of high integrated SSPPs circuits.

In this letter, a method of tunable gain microstrip antenna for compact pattern-reconfigurable array is proposed. The tunable gain element is realized by integrating a switchable resistive attenuator, which is composed of a RF SP4T and four loading resistors. The method is demonstrated on a six-element sidelobe reconfigurable array operating at 2.45 GHz, which consists of three kinds of tunable gain elements with different gains. The measurements have a good agreement with the simulations and show the first sidelobe level range from −14 to −20 dB of the array at 2.45 GHz in H-plane is achieved based on the tunable gain range from 5 to 1.9 dBi of the elements.

In this brief, a broadband $9\times9$ Butler Matrix (BM) and its extension for multibeam antenna array (MAA) application are presented. Based on the configuration of $3\times3$ beamforming network (BFN) comprised of three couplers and two 90° phase shifters, the topology of $9\times9$ BM is built, which can provide in-phase signals at output ports. And a broadband $9\times9$ BM is implemented to verify the design by adopting broadband components. The results indicate that the designed broadband $9\times9$ BM achieves equal power division and 9 uniformly distributed progressive phases (PPs) between output signals in a relative bandwidth of 40% when the 9 input ports are excited, respectively. And the fabricated $9\times9$ BM is applied in MAA for producing 9 beams including a boresight beam. In addition, according to the design method of $9\times9$ BM, the topology of the extended $27\times27$ BM is built and presented, which validates that an extended BM with higher order can be realized by the design method, and the extended BM can also provide in-phase signals at output ports.

In this article, a new approach to designing a modified $N^{2} \times N^{2}$ Butler matrix (BM) based on an $N$ -way directional coupler (NWDC) is presented. First, by introducing phase shifters and ingeniously arranging the input and output ports, the topologies of $9 \times 9$ BM based on a three-way directional coupler (3WDC) and $16 \times 16$ BM based on a four-way directional coupler (4WDC) are built. Next, according to the design method of $9 \times 9$ BM and $16 \times 16$ BM, the topology design of modified $N^{2} \times N^{2}$ BM based on NWDC is developed. Considering whether there are progressive phase differences (PPDs) of 0° at output ports, the two cases in which $N$ is odd and even are discussed. Finally, in order to verify the design method, a prototype of microstrip $9 \times 9$ BM working at 5.5 GHz is designed, fabricated, and measured. The results show that the designed microstrip $9 \times 9$ BM achieves equal power division and nine different PPDs among the output signals when the nine input ports are excited, respectively, which meets design expectations. And it is used as a beamforming network (BFN) for a multibeam antenna array (MAA) to generate nine radiation beams. And then, the design method of modified $N^{2} \times N^{2}$ BM is validated by the implementation of microstrip $9 \times 9$ BM. And the design method of the modified $N^{2} \times N^{2}$ BM provides a novel approach for BFN technology when massive input and output ports are required.

A new topology of modified Butler matrix (BM) based on three-way directional coupler (TWDC) is proposed in this brief. The two TWDCs are regarded as two submatrices, by alternately arranging the output ports of the two submatrices and introducing a front network consisting of 3dB/90° hybrid couplers, 3dB power divider and phase shifters, a topology of modified five-input six-output ( $5 \times 6$ ) BM is constructed. In order to verify the design method, a prototype of microstrip $5 \times 6$ BM operating at 5.5 GHz is implemented and it is used as a beamforming network (BFN) for multibeam antenna array (MAA) to generate five radiation beams including a boresight beam. The measured and simulated results coincide well with each other. And according to the design method, a topology of extended $9 \times 12$ BM is designed based on the $5 \times 6$ BMs, which validates the capacity of building a modified BM with a higher number of the input and output ports.