Auxiliary Antenna Research Articles

Integrated 4G/5G Multiservice MIMO Antenna for Hand-Held Devices

A novel compact monopole antenna with integrated services for 4G/5G application has been proposed in this manuscript. The 4G services such as Long Term Evolution (LTE) and GSM 850/900 is provided by the primary antenna of size 45 × 15 mm. The 5G communication services are supported by the auxiliary antenna of size 19 × 15 mm. The monopole radiator with the combination of multi-branch stubs and meandered structures in the primary radiator introduces the resonance at the desired operating frequency. The impedance bandwidth of the primary antenna is 170 MHz (0.8–0.97 GHz) and 900 MHz (1.8–2.7 GHz) for LTE and GSM applications. The impedance bandwidth of the auxiliary antenna is 7 GHz (13–20 GHz) for 5G application bands. To achieve the desired operating bands, the length and width of the stubs are used as the tuning parameters. The large ground plane of size 200 × 150 mm is used as the mock-up system for the proposed antenna structure. To enhance the coverage of the handheld devices, the primary and auxiliary antenna is integrated in the mock-up system. The efficiency and gain of the antenna are in the range of 3–5 dBi and 70–96%. The simulated and measured results are correlated with each other.

GNSS yaw attitude estimation: Results for the Japanese Quasi‐Zenith Satellite System Block‐II satellites using single‐ or triple‐frequency signals from two antennas

The Japanese Quasi-Zenith Satellite System (QZSS) constellation has added three new Block-II satellites, which broadcast ranging signals from their main L-band antenna together with augmentation signals from separate, auxiliary antennas. After determination of the baseline vector between main and auxiliary antenna, differential processing allows for an estimation of the satellite's yaw attitude with an accuracy of less than 1°. Differential carrier-phase center variation maps have been derived. Yaw estimation results are presented for periods of special interest, for example 360° yaw rotations, orbit correction maneuvers and the satellite's eclipse period, where a special pseudo-yaw steering attitude mode is applied. The second part of the paper introduces a new concept using triple-frequency signals from two different antennas for attitude determination. This method is demonstrated with QZSS measurements but is also applicable to other satellite navigation system, like the enhanced GLONASS-M satellites with L3 signal capabilities.

On Cancellation Capability of Full-Duplex RF Self-Interference Cancellation Schemes

In this work, we study the self-interference cancellation (SIC) capability of two basic radio frequency (RF) SIC schemes: auxiliary antenna cancellation and multireconstruction-path (MRP) cancellation (including particular two-reconstruction-path balun cancellation), and derive their cancellation capability in detail. Theoretical results show that auxiliary antenna cancellation capability and balun cancellation capability are related to the ratio of bandwidth to carrier frequency, the latter is further related to an angle ratio; that is, the ratio of the angle between the self-interference vector and the first fixed delay vector to the angle between the two fixed delay vectors, and common MRP cancellation capability is essentially related to the channel response of self-interference and the canceller frequency response. Numerical results confirm a perhaps obvious intuition: MRP cancellation outplays auxiliary antenna cancellation to cancel self-interference, especially when multiple self-interference paths exist, and MRP cancellation with more reconstruction paths achieves higher cancellation capability.

Deep, Broad Null Formation for Canceling Moving RFI in Radio Astronomical Arrays

Radio frequency interference (RFI) is rapidly becoming a major issue for many applications. It is especially problematic for radio astronomy, where signal-to-noise ratios (SNRs) are less than unity. Antenna array systems such as phased array feeds (PAFs) and interferometric imaging arrays are able to cancel RFI through adaptive projection-based spatial notch filtering techniques. Current methods for formulating these projection operators suffer from an unfortunate trade-off. They must sacrifice integration time when calculating the sample spatial correlation matrix in order to track RFI motion, but this consequently increases sample estimation error and reduces null depth. In this work, we propose a new way to process spatial correlation matrices to form a broad null that reliably cancels moving RFI without increasing sample estimation error due to insufficient integration. Additionally, when assisted by an RFI-tracking auxiliary antenna, this approach also reduces the total data rate coming out of a spatial correlator, thus making broad-null-based RFI cancelation more computationally efficient and practical for real-time active array-based RFI mitigation systems.

LTE MIMO Closed Slot Antenna System for Laptops With a Metal Cover

This paper presents an LTE MIMO closed slot antenna system for laptops with a metal cover. Its main and auxiliary antennas have the same structure that measures 130 × 3 mm 2 . They are configured in a manner of reflection symmetry on the display metallic ground plane and are 5 mm away from the hinge. The distance between the two antennas is 20 mm, and the profile height of the MIMO antenna system is only 3 mm. This LTE closed slot antenna is excited by an exciter of 30 × 3 mm 2 to cover the LTE eight-band operation (LTE700/GSM850/900/1800/1900/UMTS/LTE2300/2500). The exciter is a simple planar inverted-F antenna (PIFA) structure loaded with reactive matching elements, which can enhance the impedance matching in the desired frequency bands. This LTE MIMO closed slot antenna system has good isolation of at least 16 dB without adding any additional isolation elements. The measured antenna efficiency of the MIMO antenna system is larger than 40% in the low-frequency band and 50% in the high-frequency band, meeting the practical application requirements.

Low-profile switchable LTE/WWAN MIMO antenna system

ABSTRACTThis study proposes a low-profile switchable LTE/WWAN multi-input and multi-output (MIMO) antenna system for laptops. The main and auxiliary antennas, mirror-imaged of each other, are configured on the left and right sides of the top edge of the display ground plane. The two antennas are each a planar inverted-F antenna (PIFA) having the size of 102 × 5 × 3 mm3. The PIFA structure is matched in impedance with a set of reactive chip elements to increase the antenna operating bandwidth, and is combined with a set of switchable circuits to change the low-frequency resonant path in accordance with the switch status, ON or OFF, thus allowing the low-frequency modes to cover the LTE700 and GSM850/900 bands. Without any isolation element, an isolation of 15 dB or more can be achieved in the MIMO antenna system. The measured realized antenna efficiency is also 48% or greater.

An Auxiliary Antenna Based Inter-User Interference Mitigation Approach in Full-Duplex Wireless Networks

When a full-duplex (FD) base station (BS) serves an uplink and a downlink half-duplex (HD) users, the uplink user would produce the inter-user interference (IUI) on the downlink user. In this letter, an IUI suppression scheme is proposed based on the auxiliary antenna at the downlink user. A problem of maximizing the sum achievable rate of the uplink and downlink is formulated by adjusting the weighted vector at the downlink user with limited uplink and downlink transmit power. This problem is solved by two steps. First, the optimal weighted vector at the downlink user is derived. Second, the optimal downlink power is given for a fixed uplink power and the optimal uplink power is obtained by a search method. The single-cell simulation results show that the average achievable rate of the proposed IUI suppression scheme significantly outperforms the existing schemes especially when the cell radius is small and can nearly approach the performance of the ideal FD case with IUI perfectly suppressed.

Aperiodic Switched Array for Line-of-Sight MIMO Backhauling

A switchable aperiodic array solution is proposed to increase the minimum channel capacity of a multiple-input–multiple-output (MIMO) backhauling system over an extended line-of-sight communication range. The objective is to propose a low-complexity design solution that is cost-effective in regard to the manufacturing, installation, and its design process. It is shown that by adding only one switch and one auxiliary antenna per base station, a ${4 \times 4}$ MIMO system can be realized that is capable of minimizing the capacity loss that both regular and aperiodic arrays suffer from as a function of the link distance.

Spatial Interference Cancellation in MIMO Systems Using Side Lobe Canceller Structure

In this paper, a new MIMO receiver structure is proposed in which interferences are suppressed using a canceller operating in the spatial domain. The method presented in this paper is based on the assumption that a MIMO system with a certain number of antennas at the transmitter and receiver side is available. Distance between the antenna elements is subject to various factors and is selected in such a way that fading between different antenna pairs is independent of each other. In the proposed structure, without imposing additional restriction on the size of the array on the receiver, some auxiliary antennas are placed between every two adjacent elements to create antenna sets. Adaptive nulling is performed in each set to place nulls in the direction of the interferences. Then, the MIMO receiver processing is done such as is required in the conventional MIMO receiver without auxiliary antennas. In other words, the proposed structure added some auxiliary antennas to the MIMO receiver to cancel interferences that are separable in the spatial domain. To evaluate performance of the proposed structure, bit error rate (BER) of the conventional MIMO receiver and the proposed structure are compared in the space–time block-coded (STBC) MIMO system. Simulation results show that, in comparison with the conventional STBC technique, the proposed method has a better performance in the presence of interference.

Performance evaluation of the adaptive sidelobe canceller system with various auxiliary configurations

In practical radar systems, the conventional adaptive sidelobe canceller (SLC) works very well as long as the input signal-to-interference-plus-noise (SINR) ratio is low or when the desired signal is known to be absent during certain time intervals. However, under high SINR, attenuation in the direction of the desired signal is inevitable. In this paper, the conventional sidelobe canceller is improved by replacing the separate auxiliary antennas by a number of existing elements of the main antenna array. This modification makes the proposed SLC different from the conventional one because the desired signal components of the main channel and auxiliary signals may be correlated. Such correlation may cause serious attenuation in the desired signal especially when the number of reused elements from both of the main array and auxiliary antenna is increased. The resulting malfunctioning of the desired signal cancellation is eliminated by adjusting the weights of the reused elements to produce a specific cancellation pattern. The required cancellation pattern should have two main features: first, it should have a level equal to that of the main array pattern at the interferer direction. Second, it should have a very low level or a null at the direction of the desired signal. The simulation results show that good performance for interference cancellation, maintaining a distortionless response for the desired signal, and low sidelobe level can be obtained by using the proposed technique. Besides the simplicity and low cost, the other advantage of the proposed SLC is that it can work effectively regardless of the strengths of the desired signal.

Multi-Element Phased Array Calibration Method by Solving Linear Equations

In this paper, we propose a new phased array calibration method that measures all antenna element excitations simultaneously. The method has the minimum number of measurements among the known similar methods. The auxiliary antenna used for measurement is placed in either near-field or far-field region to receive the complex array signals during the change of the antenna element phase settings. According to the superposition principle of electromagnetic field, a set of linear equations concerning the element signals are created with the measured array signals. With the scattering parameters between the measurement probe antenna and the element antennas prestored or simplified, we calculate the excitations of the antenna elements by solving the linear equations. The coefficient matrix of the linear equations determines the antenna element phase settings for the array signal measurements. The principles for the selection of the coefficient matrix concerning accuracy, complexity, and hardware requirements are presented. A recursive matrix-forming method is presented for the matrix selection in this paper. Numerical simulations and experiment results validated the effectiveness of the proposed method.

Virtual Multipath Attack and Defense for Location Distinction in Wireless Networks

In wireless networks, location distinction aims to detect location changes or facilitate authentication of wireless users. To achieve location distinction, recent research has focused on investigating the spatial uncorrelation property of wireless channels. Specifically, differences in wireless channel characteristics are used to distinguish locations or identify location changes. However, we discover a new attack against all existing location distinction approaches that are built on the spatial uncorrelation property of wireless channels. In such an attack, the adversary can easily hide her location changes or impersonate movements by injecting fake wireless channel characteristics into a target receiver. To defend against this attack, we propose a detection technique that utilizes an auxiliary receiver or antenna to identify these fake channel characteristics. We also discuss such attacks and corresponding defenses in OFDM systems. Experimental results on our USRP-based prototype show that the discovered attack can craft any desired channel characteristic with a successful probability of 95.0 percent to defeat spatial uncorrelation based location distinction schemes and our novel detection method achieves a detection rate higher than 91.2 percent while maintaining a very low false alarm rate.

Switchable Long-Term Evolution/ Wireless Wide Area Network/ Wireless Local Area Network Multiple-Input and Multiple-Output Antenna System for Laptop Computers

This paper introduces a multiple-input and multiple-output (MIMO) antenna system for deployment in the closed hinge slot region of notebook computers for long-term evolution (LTE)/wireless wide area network (WWAN)/wireless local area network (WLAN) applications. This antenna system was placed in the closed hinge slot region formed by the full metal cover, metal ground plate, and metal hinges. The MIMO antenna system, includes a main antenna (Ant 1), an auxiliary antenna (Ant 2), and an isolation element. The main and auxiliary antennas were integrated with the metal surrounding them and were used to excite several resonance modes of the closed hinge slot. Excellent antenna efficiency was achieved using the small antennas. Although Ant1 and Ant2 are only 25 mm $\times5$ mm in size, they could cover LTE/WWAN or WLAN operating bands by switching feed points in the same antenna pattern. The isolation element—a 10 mm $\times6$ mm metal sheet—was placed at the center of the closed hinge slot region, and enhanced isolation by more than 7 dB. The isolation levels exceeded 18 dB for LTE700/2300/2500 bands and 15 dB for 2.4/5.2/5.8 GHz WLAN bands.

A New Rectenna Using Beamwidth-Enhanced Antenna Array for RF Power Harvesting Applications

This letter presents a new rectenna using beamwidth-enhanced antenna array for RF power harvesting applications. Based on an example of a 1 × 4 patch antenna array, the beamwidth-enhancement method is demonstrated. By maximizing the power transmission efficiency between the 1 × 4 antenna array and two auxiliary antennas, the optimal excitation distribution that leads to an enhanced beamwidth can be determined. In comparison to the same antenna array fed by the uniform amplitude and phase, the beamwidth of the designed antenna array at the H-plane is about two times wider. A high-efficiency rectifier is designed to convert the harvested RF power into dc power and is then combined with the 1 × 4 antenna array to form the proposed beamwidth-enhanced rectenna. Measurement results show that the rectenna's efficiency is more than 50% when the wave incident angle is between −38° and 35° at the H-plane under the power density of 1276 μW/cm2.

Improved Measurement Method of Circularly-Polarized Antennas Based on Linear-Component Amplitudes

An improved measurement method of circularly-polarized (CP) antennas based on linear-component amplitudes is proposed in this paper. By utilizing two sets of orthogonal linear polarization (LP) amplitudes, measurement on axial ratio (AR) of CP antennas can be realized without phase information. However, the rotation sense of the co-polarization cannot be determined due to the absence of the phase information. Above problem is discussed here for the first time, and a solution is presented to determine the rotation sense of the co-polarization by using common auxiliary CP antennas. In addition, there will be some particular cases with large errors in actual measurement. Here a corresponding solution method is given. Finally, co-polarization and cross-polarization patterns can be further obtained from AR results. To verify this improved method, a self-developed CP microstrip array was measured. The measured results are in agreement with the simulated results, which prove this method is correct, effective and practical.

High-Linearity 3-Bit Frequency-Tunable Planar Inverted-F Antenna for RF Applications

A compact planar inverted-F antenna (PIFA) has been designed, fabricated, and characterized to work either for receiving or transmitting applications. The antenna center frequency can be tuned from 1.52 up to 2.25 GHz, using switched auxiliary strips. Ohmic contact radio frequency microelectromechanical system (RF-MEMS) switches are used to connect and disconnect the auxiliary strips, maintaining both efficiency and antenna linearity (power handling capability). The measured PIFA efficiency for all states in an anechoic chamber is between 52% and 95%. The antenna linearity has also been measured using an adjacent channel power ratio test bench, showing 42-dB dynamic range up to 28-dBm input power.

Antenna Pattern Measurement of the Large-Size Radio Telescope by Correlation Techniques and GNSS

It is a challenge to measure the antenna pattern of a large-sized radio telescope with a high resolution because it hardly rotates. This letter presents a simple and efficient method to measure the large-sized radio antenna pattern based on correlation techniques and the Global Navigation Satellite System (GNSS). We estimate the normalized pattern function of the electric field by utilizing correlation properties of the navigation signal in the auxiliary antenna and the radio antenna. The method avoids obtaining a large number of accurate pseudo-code information. Compared to the traditional methods based on the energy detection, the proposed method extends the measurement range and improves the measurement accuracy of the antenna pattern. At the same time, the method also has a better performance in anti-variation of channel and anti-interference.

LTE MIMO Antennas on Variable-Sized Tablet Computers With Comprehensive Band Coverage

A two-antenna system with comprehensive coverage on 690–960-MHz and 1710–2690-MHz Long Term Evolution (LTE) bands is proposed for uses on tablets of different sizes. Two different antenna configurations are employed to reduce coupling. The main antenna is based on an inverted-F structure. Lumped element loadings are used to enhance bandwidth performance. The auxiliary antenna adopts the capacitive coupling element technique to minimize the antenna footprint and reduce its clearance distance to the ground. Implementation issues such as fabrication difficulty, design transportability across platforms, and antenna diversity gain are looked into. Measured results show moderate efficiency and good isolation characteristics with acceptable return loss in LTE bands. Its superior diversity performance is validated with measured effective diversity gain, which confirms that the proposed design is suitable for LTE multiple-input–multiple-output (MIMO) uses.

Methods of measuring the parameters and fault diagnosis phased antenna array in the near field without the use of mechanical positioners

The problem of measuring the parameters of phased antenna arrays without mechanical displacements of the test and / or the auxiliary antenna. Examples demonstrating the high efficiency and practical importance of this approach to measurement.

A distributed localization in wireless sensor networks utilizing AOD estimation and synthetical uniform circular array

The localization of wireless sensor nodes is one of the key technologies in wireless sensor networks (WSN). Recently, a distributed localization method has been proposed based on a novel concept of angle of departure (AOD) estimation, which can be employed by e.g., the single antenna sensors to estimate the angle information and achieve localization. Based on the AOD estimation, in this paper, we introduce a synthetic uniform circular array (SUCA) synthesized by a rotary antenna on anchor to get the distributed localization of the sensors in multi-path environments. The rotated operation of antenna could create the SUCA with a larger aperture to deal with AOD of multipath components (MPCs) and relax the condition that array aperture should be greater than the number of MPCs. This new localization method only relies on radio transceivers without requiring extra measuring equipments, and the sensor nodes conduct localization in a completely distributed manner instead of centralized processing, which is suitable for large-scale WSN. Meanwhile, the influence of carrier frequency offset (CFO) between the transceivers is also considered and it is eliminated by utilizing the signal emitted from an auxiliary antenna.