Low‐profile millimetre‐wave wideband microstrip antenna with parasitic patch arrays

A millimetre‐wave low‐profile wideband microstrip antenna is proposed. To widen impedance bandwidth and achieve stable large gain simultaneously, coplanar parasitic patch arrays are arranged on both sides of a microstrip patch fed by a coaxial probe. Double slots are etched on the microstrip patch to reduce H‐plane cross‐polarization levels. Zero‐phase‐reflection analysis with Floquet‐port model is proposed to predict resonant frequency of the parasitic patch arrays. Resonance modes excited is verified according to input impedance with an ideal probe. Two adjacent broadside resonances respectively dominated by the quasi‐TM10 mode of the microstrip patch and quasi‐TM30 of the parasitic patch array are excited in turn. The proposed antenna with a dimension of 1.06 × 1.06 × 0.024 λ03 (λ0 is the wavelength of 29 GHz in free space) realizes 15% (27–31.35 GHz) impedance bandwidth for |S11| ≤ −10 dB. Realized peak gain is up to 9.26 dBi and 2‐dB gain bandwidth is 15.7%. H‐plane cross‐polarization levels within 3‐dB beamwidth are less than −14 dB, and back radiation levels are less than −17.9 dB.