This paper presents a compact quad-band multilayer antenna operating at 6 GHz, 8 GHz, 28 GHz, and 38 GHz, designed for point-to-point communication links. Utilizing aperture-sharing techniques, the antenna integrates a 2×2 dual-band slotted aperture-coupled microstrip patch array for the 6 GHz and 8 GHz bands with a dual-band slotted aperture-coupled element operating at 28 GHz and 38 GHz. The overall stack has a compact vertical profile with dimensions of 1.01λ× 1.12λ× 0.039λ (λ= free space wavelength at the lowest frequency). Full-wave simulations demonstrate excellent impedance matching and isolation between bands, with bandwidths of 1.3%, 0.6%, 7.18%, and 7.15% at 6 GHz, 8 GHz, 28 GHz, and 38 GHz, respectively. The antenna exhibits broadside gains of 11.54 dBi, 13.76 dBi, 10.47 dBi, and 8 dBi, with isolation levels exceeding 20 dB, 33 dB, 25 dB, and 40 dB at the respective bands.
