Bandwidth enhancement of low-profile microstrip antennas using tightly coupled patch arrays

A tightly coupled patch array (TCPA) is introduced to realize small-size and low-profile microstrip antennas with enhanced bandwidth performance. Past approaches have used electromagnetic band gap (EBG) structures or frequency selective surfaces (FSSs) as substrates (i.e. in passive mode) to realize low-profile antennas. In contrast, the proposed TCPA employs an FSS aperture as the radiating element (i.e. active). In this paper, a small-size finite array is designed along with a very thin and compact feeding network. The proposed TCPA operates around 1.95 GHz with 17.3% impedance bandwidth (|S11| <; -10dB), 4.8dB realized gain (94% efficiency) and 30% gain bandwidth (3dB drop). Of importance is its thickness, with overall dimensions being λ₀/3.3 × λ₀/3.3 × λ₀/25.5 at 1.95 GHz. A preliminary TCPA antenna prototype was fabricated and tested. Both simulated and measured data show enhanced bandwidth as compared to the microstrip patch antennas of the same size on conventional substrates or EBGs.