SIW Cavity-Fed Millimeter-Wave Circularly Polarized Filtenna Enabled With Custom-Designed Patches

In this letter, a millimeter-wave circularly polarized filtenna enabled with custom-designed patches is presented. The configuration of the filtenna is simple, which consists of an I-shaped substrate integrated waveguide (SIW) cavity, four square patches etched with cross slots, L-shaped stubs that are connected to the square patches, and regularly arranged shorting vias. The filtering response with controllable radiation nulls is facilitated by the I-shaped SIW cavity. The regularly-arranged shorting vias play a crucial role in the creation of an axial ratio (AR) minimum for the filtenna. Four square patches etched with cross slots contribute to the generation of the other two AR minima in the passband. Thus, a wide AR bandwidth is achieved. The gain value of the filtenna is ultimately enhanced by the introduction of L-shaped stubs, which alters the current distributions of the top patches. A prototype of the developed filtenna is fabricated and measured for validation. The measured results demonstrate an overlapped fractional bandwidth (where |<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l1</sub>| ≤ −10 dB and AR ≤ 3 dB) of 11.2% [(24.1 to 26.95) GHz] and a peak realized gain value of 10.4 dBi.