Compact Dual-Band Filtering Antenna With Wide Stopband Characteristics Using Proximity-Coupled Feeding at 28 GHz and 38 GHz

A new class of via-less dual-band wide-stopband filtering antenna is proposed. The proposed topology is based on a stacked patch antenna structure, which is excited using a proximity-coupled line. The antenna structure is composed of a square patch, capacitive parasitic elements, radiating parasitic elements, and a parallel strip line (PSL). To maintain compactness, the proposed antenna design utilizes multifunctional capacitive parasitic elements. These elements radiate at 28 GHz and generate two radiation nulls at 31.5 GHz and 55.5 GHz for interference suppression. To improve the selectivity and out-of-band rejection performance of the filtering antenna, additional nulls are introduced via the PSL and parasitic elements. Prototypes of a single element and a 1 × 4 antenna array are fabricated and measured for validation. The measured results of the single element confirm a −10 dB impedance bandwidth of 27.8 GHz to 29.7 GHz and 37.2 GHz to 39.7 GHz. The realized gain is ascertained to be 6.32 dBi and 5.66 dBi at 28 GHz and 38 GHz, respectively. The suppression levels between the operating frequency bands and upper stopband are better than −18.4 dB and −17.4 dB, respectively. The measured 1 × 4 antenna array achieves a peak gain of 9.8 dBi at 28 GHz and 10.8 dBi at 38 GHz, respectively.