# Dual-Band Shared-Aperture Antenna with Pattern and Polarization Diversity
## 1 Introduction  
To adapt to various applications and scenarios, the rapid development of modern wireless communication systems requires the antenna to have multiple functions. It is better to integrate dual bands, polarization, and pattern diversity with a single antenna. The combination method in realizing an aperture-shared antenna is suggested as an effective way. The antenna conceives a novel structure that integrates a Sub-6 GHz modified magneto-electric (ME) dipole antenna and a millimeter wave (mmW) inclined-plane horn antenna in [1] and achieved dual impedance bandwidths (IMBWs) for S11 \(<\) -10 dB of 40.9% and 58.2% for the Sub-6 GHz and mmW bands, respectively. In [2], the combination of a 2.4/5 GHz stacked patch and the mmW-band magneto-electric dipole is realized. In [3, 4], a dielectric resonant antenna (DRA) is combined with other antennas to achieve dual bands with a large frequency ratio. Apart from the combination method, some other structures can also be utilized for large frequency ratio antenna designs. In [5, 6], mmW-band substrate-integrated waveguide (SIW) leaky wave antenna array is employed as the resonators of the microwave antenna to realize a large frequency ratio. In [7], a slotted SIW is introduced to a microstrip line to realize microwave and mmW-band radiation at the same time. Another novel design in [8] can radiate independently in two separate bands by introducing a monopole mode to a planar Yagi-Uda antenna. Vivaldi antenna based on a partial structure-reuse mechanism is proposed for dual-band design, which can also improve space utilization at the same time [9, 10]. In [11], two Vivaldi antennas are placed in a compact orthogonal position to achieve two beams by sharing the same metasurface, butthe gain is below 9.6 dBi, and the bandwidth is 27-30 GHz which is not wide enough. In [12], four evenly separated concentric regular pentagon slot antennas are fed by two feeding structures to achieve multiple bands, covering 1.4-1.58 GHz, 1.82-2.14 GHz, 2.48-2.9 GHz, 3.1-3.8 GHz, 4-4.5 GHz, and 27.8-28.3 GHz. Due to the limited gain of combining two single antennas, the shared-aperture technique can also be used in antenna arrays [13; 14; 15; 16; 17; 18; 19]. In [13], a substrate-integrated waveguide slot array is placed above a patch antenna to realize dual bands at 3.5 and 60 GHz, with dual bands of 2.3% and 5.3%, respectively. W-band sparse array antenna is inserted into the Ka-band horn antenna [14], exhibiting dual IMBWs of 16% and 28.6%. In [15], a frequency selective surface (FSS) structure is placed between the Ku- and Ka-band, which realizes the function of improving isolation without affecting their radiation performance. In [16], 4 \(\times\) 4 X-band elements and 4 \(\times\) 4 Ku-band elements are interleaved on a single aperture to constitute an 8-port shared-aperture antenna array, but its radiation pattern is only directional, and it maintains bandwidths of 10.0-10.35 GHz and 13.0-13.9 GHz. In [17], the 7.35 GHz radiation patch is placed inside the 2.35 GHz radiation ring to realize an aperture-shared antenna array. Although it realizes a high gain of 8.832 and 15.58 dBi at 2.45 GHz and 7.35 GHz, respectively, its bandwidth is only 23 and 135 MHz. Another study [18] investigated the use of a 3 \(\times\) 3 metasurface (MS) as a radiator at the S-band, while the same 3 \(\times\) 3 MS is discretized into 9 \(\times\) 9 sub-cells to function as an FSS at the K-band for the slot array. Most studies focus on realizing two linearly polarized (LP) by the shared-aperture antenna. However, circular polarization (CP) is needed in some scenarios to improve the signal robustness. Recently, the reused MS has been used as an effective way for dual-band antenna design [20; 21; 22; 23; 24; 25]. As described in [20], an antenna is designed to achieve dual bands by integrating a shared surface combined S-band metasurface and Ka-band partially reflective surface (PRS), which also contributed to a reduced antenna size.