A circularly symmetric high-impedance surface (HIS) is used as a ground plane in the design of a low-profile two-arm spiral antenna It is shown through simulations that an HIS with circular periodicity provides 16 $\%$ and 113 $\%$ greater operational and fractional bandwidths, respectively, for spiral antennas compared to canonical rectangular HISs It is also observed that with the aid of a circular HIS ground plane, the gain of the spiral antenna increases for 25 dB compared to when a rectangular HIS is used as a ground plane Measurements are performed to validate the simulations; a very good agreement is indicated

Gain and Bandwidth Enhancement of a Spiral Antenna Using a Circularly Symmetric HIS

A dual-port, dual-band, and circularly polarized (CP) radio frequency identification reader antenna is designed to operate at both ultrahigh frequency (UHF) and lower ultra-wideband (UWB) bands for indoor positioning systems. In conjunction with a properly selected quadruple feed network, a shared aperture using the concept of hybrid mode is utilized for broadening the antenna bandwidth. The concept is demonstrated to achieve a high gain, wideband, and CP operation within a low profile. The measured overlapping 3-dB axis ratio (AR) bandwidth and 10-dB impedance bandwidth for the UHF band ranges from 0.918 to 0.926 GHz with a minimum in-band antenna gain of 9 dBic. The measured overlapping 3-dB AR bandwidth and 10-dB impedance bandwidth covers from 3 to 5.2 GHz with a minimum in-band gain of 9 dBic in the lower UWB band (i.e., 3.1–4.8 GHz). The gain suppression near the two wireless local area network bands (i.e., 2.45 and 5.8 GHz) is more than 20 dB. The isolation between two ports is larger than 25 dB over the UHF and lower UWB bands, respectively.

Dual-Band Shared-Aperture UHF/UWB RFID Reader Antenna of Circular Polarization

In this paper, performance enhancement in a shorted polygonal archimedean spiral antenna has been proposed by backing it with a hybrid reflector. In the proposed work, two arms of the polygonal spiral antenna are shorted at an outer octagonal conductive ring aiding in size reduction of the polygonal spiral. The shorted polygonal spiral antenna with the advantages of low profile and the good axial ratio at lowest frequencies of operation is backed by a hybrid reflector that utilizes combination ferrite layer which tapers towards the center to a PEC layer. The hybrid reflector helps to improve the gain of the antenna significantly at low frequencies without compromising the gain of the antenna at high frequencies. The antenna operates from 0.6 GHz to 6.5 GHz with a minimum boresight gain of 0.2 dBic at 0.6 GHz and an average gain of 6 dBic from 2.2 GHz. The antenna also demonstrates a good axial ratio of ≤3 dB over the VSWR bandwidth in a low-profile dimension of 0.13 λ0 × 0.13 λ0 × 0.04 λ0. The proposed work thus presents a novel idea to develop a compact high-performance spiral by shorting the arms of a polygonal spiral with a conductive ring and backing the same by a hybrid reflector and cavity.

Performance enhancement of shorted polygonal archimedean spiral antenna using hybrid reflector

This paper presents a method to improve the circular polarization of an Archimedean spiral antenna placed over a radial Artificial Magnetic Conductor (AMC). Results have been compared with the same radiating element over a more classical AMC reflector. A prototype of an Archimedean two-wire spiral antenna has been built to operate from 0.5 GHz to 6 GHz. Measurement results with this radial AMC give a relative bandwidth of 79 %, in which the broadside RHCP gain is improved. In this bandwidth the axial ratio of Archimedean spiral antenna placed over a radial AMC is less than 2 dB whereas it is higher than 3 dB with a classical cartesian shape of AMC reflector.

Axial ratio improvement of an Archimedean spiral antenna over a radial AMC reflector

The aim of the present contribution is to show that metasurfaces such as reactive impedance surfaces (RIS) and artificial magnetic conductors can be efficiently used in the design of low-profile circularly polarized L-band antennas. We present the design and simulation of the compact and low-profile antennas. The solution based on RIS will be compared to a circularly polarized microstrip patch antenna using the same materials in order to prove the benefit of metasurfaces. The engineered metasurfaces allow increasing the bandwidths with few modifications on the thickness and the overall antenna size.

Low-profile metamaterial-based L-band antennas

A wideband reflector’s antenna based on quasi-artificial magnetic conductor is proposed. To validate the design, an Archimedean spiral has been backed to this new reflector. In comparison to classical solution using absorbent material, the prototype presents a very low thickness of λ/15 at the lowest operating frequency and an improved gain over a 2.4:1 bandwidth. The whole methodology to design this reflector can be applied to other wideband antennas.

Wideband QAMC reflector’s antenna for low profile applications

In this letter, the maximal achievable bandwidth of an Archimedean spiral antenna above a reflector is investigated. This bandwidth is defined by the frequency range where the gain in the broadside direction is higher than the case without a reflector. To determine this theoretical bandwidth, we propose an analysis consisting in replacing the Archimedean spiral antenna by a bidirectional elliptical plane-waves source above an infinite reflector. Thanks to this approximation, it is possible to evaluate this bandwidth with a simple analytical expression, which is defined by constructive interferences between two plane waves. The maximal bandwidth obtained from this formula is equal to 5:1 for a metallic reflector. Simulations and measurements are then presented in order to confirm this result.

Maximal Bandwidth of an Archimedean Spiral Antenna Above a Reflector

This paper presents the benefits of a Perfect Electric Conductor (PEC) used as a reflector for an Archimedean spiral antenna. Such a configuration can improve the broadside gain of 3dB over a theoretical relative bandwidth of 133%, with a thickness of only λ/12 at the lowest operating frequency. A prototype of an Archimedean two-wire spiral antenna has been built to operate from 1GHz to 10GHz and placed 10 mm above a conducting plane reflector. Measurements results gave a relative bandwidth of 110%, in which the broadside RHCP gain is improved.

Wideband reflector for Archimedean spiral antenna

This paper presents the advantages of a Perfect Electric Conductor (PEC) used as a stepped reflector for an Archimedean spiral antenna. Such a configuration is used to improve the broadside gain over a relative bandwidth of 145%.

Stephane Mallegol

Papers

Wideband QAMC reflector’s antenna for low profile applications

Axial ratio improvement of an Archimedean spiral antenna over a radial AMC reflector

Maximal Bandwidth of an Archimedean Spiral Antenna Above a Reflector

Wideband reflector for Archimedean spiral antenna

Wideband stepped reflector for Archimedean spiral antenna