An important aspect of using stub matching at high frequency: Investigation with measured results of a ku-band planar array antenna

In this paper, an interesting observation that is seen when stub matching is implanted in a planar array antenna is explained. An 8×8 Ku-Band planar array antenna with a common aperture and radiating element fed with different feed networks for two frequencies is designed, fabricated and tested for its performance at a compact antenna test range. Measured gain at one of the frequency is about 8 dB less than the expected value. An investigation is carried out to understand this anomalous behavior of the antenna. Simulations carried out in a CAD tool revealed that the stub used for impedance matching indeed is radiating with a gain of more than 7 dBi and this is the reason for the reduction of gain in the required polarization. The design is now modified without the stub and successfully tested.