Reducing mutual coupling between elements of an antenna array is one of the main topics in array designs. The use of electromagnetic band-gap (EBG) structures built by microstrip technology is an attractive way to mitigate the mutual coupling problem. This letter describes a novel configuration of uniplanar compact electromagnetic band-gap (UC-EBG) structures to reduce mutual coupling between the radiating elements. The idea is to use the UC-EBG structures placed on top of the antenna layer. The main objective is to reduce both the element separation and the mutual coupling between the patch antennas, which in turn increases antenna directivity. The proposed configuration eliminates drawbacks of similar structures presented in previous works.

Mutual Coupling Reduction in Patch Antenna Arrays Using a UC-EBG Superstrate

The work presented in this paper concerns a theoretical study on frequency selective surfaces (FSS) with application to artificial magnetic conductors or high-impedance surfaces (HIS). Current realizations of HIS are based on a planar FSS at the interface of a metal-backed dielectric slab either including vertical vias or not. A stable resonance was found for the case of series-resonance grids without vias in the slab. The resonance turns out to be unique in theory for all angles of incidence and both polarizations of plane waves illuminating the HIS. It was shown that vias destroy the stabilization effect and introduce a frequency shift. The analytical model was validated by HFSS simulations.

High-impedance surfaces having stable resonance with respect to polarization and incidence angle

The relatively high dielectric constant of the low-temperature cofired ceramic (LTCC) substrate materials can reduce the antenna gain and increase the mutual coupling in antenna arrays due to the increased surface-wave power. We present a design of a uniplanar-compact electromagnetic band-gap (UC-EBG) structure on the Ferro A6-S LTCC tape system operating in the 60-GHz frequency band. The UC-EBG design is used with an aperture-coupled microstrip-line-fed patch antenna (ACMPA) and with a 16-element array to increase the antenna gain. The UC-EBG is also used to reduce the mutual coupling between antennas in the E- and H-planes. The performance of the antennas with and without UC-EBG are evaluated with the probe-station and radiation-pattern measurements. In addition, the reflection from the UC-EBG surface is measured using a WR-15 waveguide excitation. Good agreement is achieved between the simulations and the measurements. An increase of up to 4.5 and 2.3 dBi is achieved in the gain for a single element and for a 16-element array, respectively. A reduction of up to 11.8 dB is observed in the E-plane coupling between two patches. The presented design is suitable for electromagnetic shielding, reduction of coupling in integrated LTCC modules, and providing high gain antennas for low-cost millimeter-wave applications.

UC-EBG on LTCC for 60-GHz Frequency Band Antenna Applications

This article presents a unique technique to enhance isolation between transmit/receive radiating elements in densely packed array antenna by embedding a metamaterial (MTM) electromagnetic bandgap (EMBG) structure in the space between the radiating elements to suppress surface currents that would otherwise contribute towards mutual coupling between the array elements. The proposed MTM-EMBG structure is a cross-shaped microstrip transmission line on which are imprinted two outward facing E-shaped slits. Unlike other MTM structures there is no short-circuit grounding using via-holes. With this approach, the maximum measured mutual coupling achieved is -60 dB @ 9.18 GHz between the transmit patches (#1 & #2) and receive patches (#3 & #4) in a four-element array antenna. Across the antenna’s measured operating frequency range of 9.12 to 9.96 GHz, the minimum measured isolation between each element of the array is 34.2 dB @ 9.48 GHz, and there is no degradation in radiation patterns. The average measured isolation over this frequency range is 47 dB. The results presented confirm the proposed technique is suitable in applications such as synthetic aperture radar (SAR) and multiple-input multiple-output (MIMO) systems.

/pdf/mutual-coupling-isolation-using-embedded-metamaterial-em-2bqr88p6xh.pdf

Mutual-Coupling Isolation Using Embedded Metamaterial EM Bandgap Decoupling Slab for Densely Packed Array Antennas

In this paper, the effect of Electromagnetic Bandgap (EBG) Superstrates on return loss of the Probe-Fed Microstrip Antenna (PFMA) has been examined. Originally the EBG superstrate layer made by Frequency Selective Surface (FSS) layers is used to increase the directivity of the PFMA, but to increase the efficiency of the whole structure including the PFMA and EBG superstrate it is necessary to have suitable impedance matching. In this paper the EBG superstrate as a resonance load to the primary radiation source (PFMA) and then by choosing the appropriate geometrical parameters of the structure we can obtain suitable impedance matching beside the directivity enhancement of the primary radiation source.

/pdf/using-electromagnetic-bandgap-superstrate-to-enhance-the-21akamn0aw.pdf

Using Electromagnetic Bandgap Superstrate to Enhance the Bandwidth of Probe-Fed Microstrip Antenna

This paper reviews recent advancements in the research and development of Uniplanar Compact Photonic Bandgap (UCPBG) structures for microwave and millimeter-wave applications. These planar periodic structures are particularly attractive and have been intensively investigated due to their easy fabrication, low cost, and compatibility with standard planar circuit technology. In this paper, basic properties of UC-PBG will be studied such as the slowwave effect, distinct stopband and passband, leakage suppression of surface waves, and realization of a magnetic surface. Owing to the different features of UC-PBG, these structures have been applied to microwave circuits to improve microstrip filters and patch antennas, to perform harmonic tuning in power amplifiers, to suppress leakage in conductor-backed coplanar waveguide, to realize TEM waveguides, and to implement low-profile cavity-backed slot antennas.

/pdf/analysis-and-applications-of-uniplanar-compact-photonic-2siia0tqe2.pdf

Y. Qian

Papers

Analysis and Applications of Uniplanar Compact Photonic Bandgap Structures