Wideband Compact Triangle-Slot Antenna with Out-of-Band Rejection

A wideband and compact triangle-slot antenna with out-of-band rejection is proposed. The antenna covers the whole C-band (4-8 GHz) including the 5.8 GHz ISM and sub-6 GHz band of 5G. First, a right-angled triangle-slot antenna is developed from a rotated square-slot antenna with a 50% size miniaturization. Then, a defected ground slot (DGS) and a thin microstrip line section are integrated into the antenna to improve the out-of-band rejection. This prevents the noise and unwanted interference to the receiver and effectively suppresses the high-order harmonics from the transmitter. Importantly, the added DGS and thin microstrip line increases the bandwidth up to 5.51 GHz (82.7% fractional bandwidth) and reduces the antenna size. Finally, by adding matching elements using stacked rectangular slot principle, the antenna size is reduced furthermore, leading to a total 60% reduction in size. The final ground size is 32 × 32 mm, which is suitable to be integrated into portable devices. The return loss is measured up to the third harmonic of the highest working frequency and compared with the reference triangle-slot antenna to validate the rejection concept. The out-of-band return loss remains smaller than 1.2 dB up to 26.5 GHz. The maximum improvement of return loss is 33.3 dB at 26.4 GHz, from 34.4 dB of the reference antenna to 1.1 dB of the proposed antenna.