A Low-Loss Butler Matrix Using Patch Element and Honeycomb Concept on SISL Platform

This paper proposes a low-loss Butler matrix using patch element and honeycomb concept on substrate integrated suspended line (SISL) platform. The SISL Butler matrix is composed of four couplers, two crossovers, and four phase shifters. Both the coupler and crossover are implemented using patch elements for ease of fabrication and low conductor loss. We adopt the honeycomb concept to integrate all the required components together to form the Butler matrix as an integrated whole. Every component is assigned with an individual cavity, and via holes are designed between the adjacent cavities to form the via fence, which makes these components isolated from each other. All the components are embedded inside the air cavity of the self-packaged SISL multilayer structure with electromagnetic shielding property, and the radiation loss can be reduced to minimum. Double-metal layers with via-hole connection are adopted to reduce the conductor loss. The dielectric loss is further reduced by using patterned substrate. The proposed SISL Butler matrix is fabricated using the standard printed circuit board process with low cost. From 24.5 to 26.5 GHz, the measured insertion loss of the Butler matrix is around 1.1 dB, and the measured phase error is within 8°. An SISL antenna array is integrated with the Butler matrix for verification of its switch-beam property. The proposed SISL Butler matrix has advantages such as low loss, low cost, high integration, and self-packaging.