In this paper, a dual circularly-polarized (CP) multi-beam antenna is proposed for future vehicular radar applications. The antenna is composed of two pillbox reflector beamforming networks (BFNs) and a series-fed microstrip line based dual CP leaky-wave antenna (LWA) array, which has a symmetrical structure and can obtain both left hand circular polarization (LHCP) and right hand circular polarization (RHCP) by switching the exciting current direction of the microstrip line. Besides, a shorted stub is loaded in the LWA to suppress the open-stop band (OSB), and thus achieve the broadside radiation and good impedance matching of the LWA. To realize the dual-polarized radiation characteristic with low-cost passive beam scanning capability, two pillbox BFNs are connected at both sides of the LWA to share the LWA aperture. The two different BFNs can excite different CP radiation patterns. A prototype of the proposed antenna is fabricated in the frequency band 23.5–24.5 GHz, and the measured results approve that the proposed antenna can realize ±36° beam scanning range with −4.0 dB crossover level, and the gain is higher than 17.7 dBi in the operating band. The advantages of the proposed antenna, including low-profile, low-cost, passive beam scanning ability, and dual circular polarization, make it an attractive choice for low-cost millimeter-wave radar applications.

In this article, a dual-polarized multibeam antenna is proposed. Two orthogonally polarized slotted waveguide antennas (SWAs) are cross-placed as the main radiator, which is designed based on ridged waveguides (RGWs) to reduce the width of the waveguides and obtain a wider steering range. The two SWAs are fed by two pillbox reflector beamforming networks (BFNs), and a special impedance transition is designed to reduce the reflection between the quasi-TEM wave in the parallel-plate waveguide (PPW) to the TE10 wave. By exciting different feeding patches in the focal planes of the pillbox reflectors, the SWA achieves different beams. In order to further increase the crossover level, the single-port excitation (SPE) and the dual-port excitation (DPE) method are used together to increase the equivalent source number in the compact area of the focal plane. Besides, the DPE method can also reduce the sidelobe level (SLL) of the beams excited by the side ports. A prototype is designed at the operating frequency of 10 GHz and fabricated by the 3-D-printed technology and computer numerical control (CNC) technology. The measured results show that the proposed antenna achieves ± 36° beam scanning in the multibeam plane with the minimum crossover level of −2.1 dB. The cross polarizations are below −20.0 and −15.9 dB for the horizontal polarization (H-P) and the vertical polarization (V-P), respectively. The advantages of dual polarization, high aperture efficiency, low cross polarization, wide beam scanning range, and low crossover level make this antenna a very appropriate choice in multibeam radars and communication systems.

In this brief, a dual-polarized multi-beam antenna is proposed based on substrate integrated waveguide (SIW) pillbox beamforming networks (BFNs). By using a rotationally symmetrical frequency scanning leaky-wave antenna (LWA) array and four SIW pillbox BFNs, the 2-D beam steering capability is realized for two polarizations. Due to the rotationally symmetrical geometric characteristic of the LWA, the orthogonally placed BFNs can excite orthogonally polarized beams. A stable gain with a wide beam scanning range in the limited bandwidth is realized, where only the backward to broadside scanning region of the LWA is used, and the forward radiation is compensated by the axisymmetric BFN. Moreover, the stacked layout of the multi-layer antenna structure greatly helps realize miniaturization. The proposed antenna can provide ±35° beam scanning range by switching 7 ports in the multi-beam plane and ±31° frequency beam scanning range within the bandwidth of 21 GHz to 27.5 GHz. The advantages of the proposed antenna, including dual-polarization, 2-D beam scanning, low profile, compact size, and low cost, make it a very appropriate choice in millimeter-wave multi-beam radars systems.

In this letter, a compact wideband substrate integrated waveguide (SIW) monopulse comparator is proposed. The TE ₁₀ and TE ₂₀ modes of an SIW transmission line are used to generate in-phase and out-of-phase excitation fields for the sum and difference beams without complex phase shift network. The monopulse comparator can realize maximum 0.4-dB amplitude balance, 3.6° phase balance for both sum and difference ports, and −37.0-dB isolation coefficient within the operating bandwidth of 9.43–10.65 GHz. In addition, to integrate the monopulse comparator with a low-cost beam scanning capability, six monopulse comparators are used as the sources to excite a flat Luneburg lens. The experimental result demonstrates that ±58° beam coverage range with around −20.0-dB null depth and 15.0-dBi gain can be realized. The advantages of the proposed monopulse multibeam antenna, including low profile, low cost, wide beam scanning range, and wide operating bandwidth, make it a very promising solution for low-cost monopulse radar systems.

In this letter, a compact wideband multi-beam pillbox antenna is proposed based on differential feeding technology. The proposed design focus on extending the operating frequency bandwidth of the leaky-wave antenna (LWA) array with a fixed broadside beam, since the bandwidths of the existing pillbox antennas are always limited by the radiators, especially considering the standard printed circuit board (PCB) technology with limited layers. To overcome this limitation, a differentially fed LWA is used as the radiator. The two sub-arrays of the LWAs are excited with oppositely propagating waves through a coupled slot, generating two oppositely directed beams whose combination can produce a fixed broadside beam over a wide operating bandwidth. A fourteen-element LWA array is fabricated with a pillbox beamforming network (BFN) to verify its design theory. The simple feeding structure of the LWA makes the LWA array can be stacked on the top of the pillbox BFN, achieving antenna miniaturization. The measured results show that the proposed antenna can achieve the -10 dB impedance matched bandwidth from 14.0 GHz to 16.0 GHz and seven beams with ±34° beam scanning range. The broadside beam has a gain variation range of 16.8 dB to 20.2 dB over the operating band.