Series-fed beam-scanning array antenna comprising multi-stage configured microstrip antenna with tunable reactance devices and open stubs

We previously proposed a series-fed beam-scanning array antenna employing MUSCAT (MUlti-Stage Configured microstrip Antenna with Tunable reactance devices) (Honma, N. et al., Proc. 2003 Asia-Pacific Microwave Conference $APMC´03, vol.2, p.953-6, 2003). To abate losses which occur at higher frequencies, we now propose a MUSCAT array employing open stubs that are placed at both ends of the rectangular microstrip antennas and connected to tunable reactance devices. The results of the analysis and measurement at 5 GHz indicate that our new configuration reduces the insertion loss by 1.3 to 1.6 dB in the unit element group compared to the configuration employing the tunable devices directly attached between the microstrip and the ground. Also, the undesired radiation from the stubs only slightly affects the radiation performance of the unit element array. We have analyzed the MUSCAT array antenna with five unit element groups to evaluate the beam-scanning performance, and we find that the MUSCAT array with the open stubs improves the beam scanning range by 2.5 times compared to the previous configurations. Based on the analyses and measurements, we find that the newly configured MUSCAT array offers wide beam scanning and easy operation with low loss.