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Low-profile microstrip end-fire antennas based on metamaterial substrates

University of British Columbia

The development of microstrip technology has introduced a range of revolutionary antenna designs that provide a low-cost, easily integrable antenna in a low-profile, planar form factor. Typical microstrip antennas have either a broadside or an omnidirectional radiation pattern. This study investigates the design of a low-profile end-fire microstrip antenna based on the use of metamaterial substrates. A 900 MHz dipole antenna is placed above two types of high impedance surfaces (HIS): a single-layer HIS and a double-layer HIS. The patches forming the HIS were designed to produce a radiation pattern with main lobes as close to 90° from normal as possible. Our simulation results show that a single-layer HIS design with thickness of 0.06λ₀ and length and width of 1.1λ₀ by 1.1λ₀ has a main lobe at 56° from normal and an efficiency of 28%. A double-layer HIS design with a thickness of 0.03λ₀, a length of 1.1λ₀, and a width of 2.15λ₀ produces a main lobe at 40° from normal with an efficiency of 50%. In order to produce a radiation pattern closer to end-fire, we propose a compact microstrip patch antenna that uses a negative permittivity substrate to achieve an end-fire radiation pattern. The antenna is designed to operate at X-band frequencies and has a footprint of 42 mm². Loading a narrow patch with a negative permittivity substrate introduces an effective inductance that resonates with the strong fringing capacitance of the patch. The electric field is vertically polarized and nearly uniform across the patch with negative permittivity ensuring a uniform phase distribution. This introduces nulls in the transverse direction that improve the directivity of the antenna. The negative permittivity substrate is implemented using a thin-wire medium with four vias spread across the patch. The fabricated antenna is matched using a quarter-wavelength transformer to 50 Ω at 10.8 GHz with a peak return loss of 30 dB and a peak directivity of 11.3 dBi. The operating frequency appears between two parallel resonances and has a 10-dB impedance bandwidth of 4%. The efficiency is simulated to be approximately 85%.

Text

2018-01-15

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/64371

Electrical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/