Large Aperture Antenna Array Research Articles

Wide-Angle Frequency Scanning Metasurface Antenna Fed by Spoof Plasmonic Waveguide

We propose novel wide-angle frequency scanning metasurface antenna and antenna array fed by spoof plasmonic waveguide. The spoof plasmonic waveguide adopts the ultra-thin corrugated metallic strip which can support and propagate spoof surface plasmon polariton (SSPP) with high efficiency. By compensating the momentum difference between SSPP and free-space propagation modes via constant phase gradient, metasurface antenna can exhibit wide-angle and continuous radiation property according to the Generalized Snell's law. A prototype is designed, fabricated and measured, which consists of a wideband polarization rotating transmissive phase gradient metasurface (TPGM) placed a certain distance above spoof plasmonic waveguide. Such antenna works in a wideband range from 6.8 to 14.0 GHz, and the main beam can continuously scan from the forward direction to the backward direction with high efficiency. The measured results show that the scanning angle can reach 55°, which agree well with the simulated and theoretically calculated results. Furthermore, the proposed metasurface antenna can be combined easily as an antenna array with a simple feed network. Compared to single metasurface antenna, the antenna array exhibits the pencil-shaped directional radiation property, and the average gain of antenna array is obviously enhanced. The proposed frequency scanning metasurface antenna is of great value in the design of conformal antenna and the large aperture antenna array, especially on curved faces.

On Dimensions of OTA Setups for Massive MIMO Base Stations Radiated Testing

The development of base stations (BSs) with large aperture antenna arrays, enabled partially by the utilization of cmWave and mmWave frequency bands, will require radiated testing in fading conditions. In this paper, the objective is to investigate the suitable measurement distances and physical dimensions of the over-the-air setups for the performance evaluation of massive multiple-input multiple-output (MIMO) BSs in anechoic chambers with multiple probes. Setup dimension is the major cost factor in the test systems and is thus the key issue to be investigated. The purpose is to determine whether the conventional far field criteria must be followed when determining the range of the setup or if they can be relieved. The impact of limited test setup dimension on various metrics, e.g., far field criteria, field performance within the test area, system link budget analysis, direction of arrival estimation algorithm as well as multi-user MIMO sum-rate capacity are investigated to determine the range of the test setup. It was found that the link budget does not support for the measurement distances claimed by the Fraunhofer distance. Most of the utilized metrics, especially the sum rate capacity, indicate that smaller setup sizes can still yield reasonable measurement accuracy. Simulations were performed at 2.6, 3.5, and 28 GHz frequencies.

Null Steering Approach With Minimized PCV and GD for Large Aperture Vertical Antenna Arrays

A novel null-steering method that minimizes the effect of radio frequency interference (RFI) and the effect of antenna phase center variation (PCV) and group delay (GD) is proposed. PCV and GD are important to characterize for global navigation satellite system (GNSS) antenna arrays used in satellite based landing architectures, since they directly affect the pseudo-range and accumulated Doppler observables. The proposed method is denoted as the beam subtraction method (BS). The BS method is compared against a conventional null-steering (CNS) method applied to a large aperture antenna array. Simulation results reveal noticeable improvement in both the PCV and GD curves as a function of azimuth and elevation angles when using the BS method compared to the CNS thus reducing the error on the range measurements as well as improving system availability in the presence of RFI.

A Relative Technique for Characterization of PCV Error of Large Aperture Antennas Using GPS Data

The Federal Aviation Administration's (FAA) local area augmentation system (LAAS) is a code-based differential global positioning system (DGPS) to be used for guidance of aircraft during the approach and landing phase of flight. Code-based multipath error was a limiting factor in the LAAS meeting category III accuracy requirements for this phase of flight. Consequently, a large aperture antenna was proposed for use at each ground-based DGPS reference site to reduce the impact of code-based multipath error to less than 0.25 m. The large aperture antenna accomplishes this task at the expense of providing limited coverage in the vertical plane (0-35/spl deg/). An ancillary high-zenith antenna is then necessary to track satellites from 35-90/spl deg/ in elevation. Phase center variation (PCV) has been observed to be a significant source of GPS error when translating the accumulated carrier phase (ACP) and pseudorange (PR) data between the two aforementioned antennas to a common phase center. This paper presents a relatively simple method for reducing the error caused by the PCV of a large aperture antenna. This is done by comparing the GPS ACP data from a large aperture vertically polarized dipole array antenna with undesirably large PCV (more than 20 cm), with similar data from a right-hand circularly polarized high-zenith antenna with small PCV (relative to physical center of array). A triple-differencing technique of the ACP data between the two antennas across successive epochs is used to characterize the PCV of the large aperture antenna as a function of elevation angle. The PCV correction factor is applied to the ACP data from the large aperture antenna array. The ACP data from the two antennas are then combined in software to appear as one antenna with minimal offset from PCV. A field test that employed this technique is described and test results are provided. This technique confers an advantage over other methods for PCV determination, which require precision mounting and/or robotic motion capabilities, or the use of an antenna range.

Measurements on the wavefronts of ionospherically propagated HF radio waves made with a large aperture antenna array

The wavefronts of high-frequency (HF) radio waves received after reflection from the ionosphere exhibit both spatial nonlinearities and temporal variations which may limit the performance of large aperture antenna arrays. An experimental investigation has been undertaken in which the phase and amplitude of ionospherically propagated signals have been measured at several widely spaced antennas and the measurements have been interpreted in terms of the reflection process. Signals were received over a 122 km path for which pulsed soundings were available and from several European broadcast transmitters. The received signals exhibited widely differing behaviour and this is interpreted in terms of their modal content. For predominantly single moded signals, the observations indicate that for midlatitude paths any random components normally contribute less than 10% of the received power.

The effects of an ionospherically induced partially coherent wavefront on the performance of a thinned random antenna array

Very large aperture antenna arrays are being planned for future military applications. It is known that due to irregularities in the ionosphere, where the reflection process takes place, the wavefront across such apertures becomes less coherent as the aperture size is increased. The main thrust of this study is to examine the degradation in the antenna gain and pattern characteristics of a thinned linear array, with 100 elements randomly spaced with a Hamming spatial taper, over a baseline of 10 km, for frequencies from 6 to 30 MHz. These results are then compared with those for a filled linear array having 400 Hamming amplitude-weighted elements and a baseline of 10 km. It is found that the effects of a partially coherent wavefront on the thinned array are comparable to those for the filled array in that the loss in gain and main-beam broadening are similar.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>