SLM Printed Wideband Filtering Antenna With Low Sidelobe and Controllable Bandwidth for K-Band Multibeam Applications

In this communication, we have implemented the filtering functions and low sidelobe level (SLL) simultaneously into a wideband multibeam antenna design to suppress the radio frequency interference (RFI) from spatial and frequency domain for the first time. The double ridge waveguides (DRWGs) not only perform the wideband feeds with a miniaturized size, which is helpful to obtain a wider steering range without grating lobe, but also functions as a high-pass filter (HPF), which enables the whole design more compact. Combining the high-pass response of DRWG and the low-pass response of the shorted stubs, the band-pass response is realized. The lower and upper cut-off frequency is independently defined, allowing for controllable bandwidth. An efficient estimated power-ratio formula to design unequal power divider is proposed to effectively guide the design of the nonuniform feed networks. Furthermore, the method of spline function as the profile curve fitting is introduced to replace the traditional Chebyshev transformer in the design of CTS antenna with smooth wall spline profile, reducing the requirement for machining precision. The whole antenna structure integrated the parallel plate waveguide (PPW), DRWG with coaxial feeding together, thus several special transitions are designed for field transformation and impedance matching. Finally, the prototype is fabricated with selective laser melting (SLM) printed technology, realizing an integral machining without welding or bonding. The measurements indicate that the antenna exhibits wideband bandpass response. In the operating band of 21-27 GHz, the antenna is capable of ±35° beam scanning range in H-plane, together with reduced E-plane SLL below-20 dB.