Basically, a 4 × 4 Butler matrix (BM) connected to an antenna array allows to have four beams, each oriented in a specific direction depending on the excitation port. In this paper, an almost continuously steerable beam system based on a conventional 4 × 4 BM with adjustable phase shift is presented and demonstrated. Here, varicap diodes are used instead of an additional phase shifter. Under different bias levels applied to the couplers throughout these varicap diodes, an output variable phase difference was obtained. A prototype of the proposed tunable BM integrated with an antenna array operating at 3.5 GHz was fabricated and tested. The experimental results show a good agreement with those simulated. A reflection and isolation coefficient better than −15 dB over the entire desired frequency band and an amplitude imbalance lower than ±1.5 dB were achieved. The measured radiating beam under different DC biasing can be oriented from ±6° to ±18° when port 1 or 4 is excited and oriented from ±32° to ±43° for ports 2 and 3.

This paper details the design and development of a planar switched beam network using 4 × 4 Butler matrix (BM) over a thin and flexible type biocompatible substrate. Four mils thick liquid crystal polymer (LCP) is used as a substrate here (ϵr = 2.92, tanδ = 0.002). The proposed design is centered at 28 GHz, targeting commercial millimeter-wave applications. Floral-shaped antenna with defective ground structures has been implemented as basic radiating elements. The whole structure is based on microstrip line configuration. The architecture occupies an area of 23.85 × 19.20 mm2 over the LCP substrate. Individual components of the BM are detailed here, followed by a system analysis of the whole integrated structure. The present work also covers the electrical equivalent circuit modeling of the whole beam-forming network. The fabricated prototype offers better than 18 dB return losses at each input port for the desired frequency band with 6 dBi (max.) peak gain and 500 MHz bandwidth around the center frequency. Port-to-port isolation of better than 15 dB is achieved with this topology. Experimental and simulated results are in good agreement in all aspects. A comparative study is also chalked out to highlight the significance of the current research work with respect to alike earlier reported structures.

This article presents the modeling and realization of a compact substrate integrated coaxial line (SICL) based butler matrix operating at 5 GHz for beam-forming applications. The proposed 4 × 4 butler matrix is developed using SICL-based hybrid coupler, crossover, and phase shifter. A compact 90∘ coupler comprising of center tapped unequal stubs is designed to enhance the size reduction as well as to extend the out of band rejection. Wideband SICL-based crossover operating from DC to 10 GHz is conceived for the proposed butler matrix using a plated through hole as transition. The SICL crossover features very high measured isolation of 65 dB owing to the reduction in coupling between the two signal paths within a lateral footprint of only 0.034 $\lambda_g^2$. A meandered SICL-based line is used in order to provide the necessary 45∘ and 0∘ phase shift to realize the butler matrix. The fully shielded and self-packaged compact 4 × 4 SICL-based butler matrix is fabricated and experimentally validated to operate at 5 GHz.

An 8 × 8 butler Vivaldi beam-steering antenna array is introduced for X-band application. Circularly polarized array is made of eight Vivaldi elements with 1×8 platform and an 8×8 beam feeding network. Vivaldi radiating element is used in array form to enhance impedance bandwidth and overall efficiency such as gain. Using microwave passive components, for instance, 3 dB branch line couplers and crossover help to have orthogonal modes for feeding each of the elements, hence circular polarization property is achieved. Extracted results show that the array has an impedance bandwidth over 7–12.7 GHz (~58%) for VSWR≤2 and an axial-ratio bandwidth of 3.15 GHz that is between 8.15 and 11.3 GHz (~33%). The peak gain of antenna array is 18 dBi at 10 GHz. The proposed beam-steering antenna with compact size and good operation is capable to cover an angle range from −42 to 55 degree in whole operation frequency.