Some Compact Low-profile Patch Antennas Based On Metamaterials And Novel Structures

Patch antennas are widely used in modern military and commercial wireless systems.As the rapid progress of radio technology and increasing requirement of wireless applications in the future, low profile patch antennas are facing challenges in both miniaturization and bandwidth enhancement. Based on patch antenna theories, miniaturization and bandwidth enhancement of patch antennas and their use in designing MIMO wireless terminal antennas are studied in cooperation with novel mechanisms of metamaterials and some novel structures. Theoretical predictions, numerical simulations and measurements have been conducted.Based on metamaterials, two miniaturized patch antennas have been proposed. One is based on the TM0 surface wave with very large phase velocity at low frequencies in the infinitely long DPS-ENG bi-layer parallel waveguide. Resonant cavities associated with patch antennas with proper boundaries have been designed and patch antennas of approaching sub-wavelength miniaturization with inherent high radiation efficiency have been proposed, when the dispersion of the ENG metamaterial is taken into account. The other is that TM020 mode of patch antennas with broadside radiation has been achieved, or broadside radiating TM030 mode has been miniaturized, based on the flip of the derivative of electric field on the boundary of DPS-DNG or DPS-MNG blocks.With the dispersion of the DNG and MNG metamaterial taken into account, dual-band broadside patch antennas on the DPS-DNG and DPS-MNG juxtaposed blocks have been proposed. Compared with the commonly used dual-band designs, the proposed dual-band patch antennas have the advantages of good broadside radiation properties, pure polarization, no grating lobes and design versatility.To overcome the inherent drawback of narrow bandwidth of low profile patch antennas, a bandwidth enhancement approach mainly based on multi-resonance has been proposed. Three resonances are introduced to form a broadband by directly coupling threeλ/4 slits. With improvement of the feeding probe and optimization of the location of the radiator, an E-shaped antenna structure in 2.4 GHz has been proposed as an example. A bandwidth of approaching 20%, which is three times of that of the previously reported conventional patch antenna with the same antenna height, has been achieved, and the largest scale of the antenna is less thanλ/4 and the height of antenna is as low as 0.0029λ. Detailed design procedure has been described and several key parameters have been discussed, which are useful for designing antennas at other frequencies with this bandwidth enhancement approach. Combined with recently emerging and fast developing MIMO technology, two designs based on compact low-profile patch antennas, have been proposed for MIMO wireless terminals. One is a two juxtaposed low profile X/4 patch antenna system. With the space diversity technique, a novel structure for reducing mutual coupling of the radiators has been proposed. Mutual coupling of less than-20dB and good MIMO properties have been achieved when the inter-antenna space of two low profile X/4 patch antennas is only 0.024λ. The other is a first proposed compact planar co-located MIMO antenna system, composed of a square ring patch antenna and aλ/4 patch antenna. Based on the polarization diversity technique, mutual coupling of less than-20dB, low antenna co-relation and relatively high gain have been achieved when the total lateral size is less than 0.28λand inter space of two radiators is only 0.008λ.