Impedance Transformer for Recessed Ground Patch Antenna at 60 GHz

This letter presents the concept of tapered recessed ground (TRG) below the microstrip feedline to transform the source impedance (50 Ω) to the edge impedance (Z
_in
) of the recessed ground microstrip patch antenna. The dimensions of tapering parameters, including its length, width, and depth, are studied in detail to match Z
_in
. The use of this method overcomes the fabrication challenges of narrow slots of inset-feed technique, especially on high-indexed substrates. Prototypes of 60 GHz recessed ground patch antennas, using inset-feed (A
₁
) and TRG techniques [A
₂
and A
₃
(with different tapering dimensions for each)], are fabricated on a 0.127 mm thick alumina substrate (ε
_r
. = 9.8) as a proof of concept. The measured results indicate a -10 dB impedance bandwidth of 7.5% (A
₁
) and 7% (A
₂
and A
₃
) with return loss better than 30 dB at 60 GHz. The measured gain and radiation efficiency of antenna A
₂
are more by 2.35 dB and 8.3%, respectively, than antenna A
₁
. The measured and simulated results agree reasonably well and validate the concept of TRG.