Tian Hong Loh

Electrically Small and Low Cost Smart Antenna for Wireless Communication

A compact low-cost low-power smart antenna has been proposed in this paper. To reduce the cost and power consumption, it employs the structure of an Electronically Steerable Parasitic Array Radiator (ESPAR) antenna. To reduce the size of the antenna, a top-disk loaded monopole and six folded monopoles are employed as the driven element and parasitic elements, respectively. The proposed antenna is called “folded monopole ESPAR antenna”. The heights of the top-disk loaded monopole and folded monopoles are reduced to be less than . Furthermore, the radius of the folded monopole ESPAR antenna is reduced by using capacitive loading technique. An equivalent circuit model is proposed for analyzing the antenna. To validate the concept, a prototype is developed and the antenna operates from 2.3 GHz to 2.55 GHz. The measured results confirm that the folded monopole ESPAR antenna can achieve electronically beam scanning in horizontal plane over a 360 range. The prototype antenna achieves a gain of 4.0 dBi and a front-back ratio of 20 dB. The parasitic elements are loaded by varactors and beam forming is achieved by controlling the DC voltages applied to the varactors.

Measurement of electrically small antennas via optical fibre

Electrically small antennas for wireless communications applications are prone to excite common mode currents on cables connected to them for measuring their performance. A miniature RF-optical transducer enables an optical fibre connection to the antenna, thereby eliminating the large distortion associated with the unwanted radiation from a coaxial cable. This opto-electric field sensor system operates from 300 kHz to 10 GHz. Results of a small UWB monopole antenna with coaxial cable and with optical fibre are compared.

Small Director Array for Low-Profile Smart Antennas Achieving Higher Gain

A small director array (SDA) is an antenna gain enhancing section of the low-profile smart antenna which can be used as a fixed array or reconfigurable array using switched parasitic elements. Gain improvements up to +10 dBi are achieved in the SDA through a Yagi-Uda configuration using parasitic elements with a large diameter. The array height is reduced by 50% comparing with the standard Yagi-Uda antenna. The reconfigurable SDA used an electronically steerable switched parasitic arrangement so that the beam can be steered from 0° to 360° in the horizontal plane. The height of the reconfigurable SDA is 0.2 λ. The measurements proved that the reconfigurable SDA can increase the antenna gain by 3 dB. The front to back ratio showed significant improvement. The proposed SDA also had the advantages of low cost and low power consumption, thus promising for applications in small satellites, unmanned aerial vehicles and mobile terminals.

Compact MIMO Antenna With Frequency Reconfigurability and Adaptive Radiation Patterns

A frequency-reconfigurable antenna for a multiple-input-multiple-output (MIMO) system with electronically steerable radiation patterns in azimuth plane is proposed in this letter. For MIMO systems, the steerable radiation patterns are able to reduce the correlation between signals and increase the channel capacity. There are two folded-monopole electronically steerable parasitic array radiator (FM-ESPAR) antennas in the proposed MIMO antenna system in this letter. The radiation pattern of each FM-ESPAR antenna is steerable in azimuth plane from 0 to 360 . Its frequency is reconfigurable between 2.3 and 2.6 GHz. A top-disk loaded monopole and folded monopoles are employed to reduce the height of each FM-ESPAR antenna to 12 mm (λ/10 at 2.4 GHz). The FM-ESPAR antennas are separated from each other by using a 30-mm-long sleeve ground plane. The measured results confirm that the MIMO antenna comprising two FM-ESPAR antennas achieves good isolation at any angle between the main lobes of the FM-ESPAR antennas. The proposed MIMO antenna has compact size, electronically steerable beams, and frequency-agile capability.

Compact Dual-Band Antenna With Electronic Beam-Steering and Beamforming Capability

A low-cost compact dual-band antenna that can achieve electronic beam steering in the horizontal plane across a range from 0° to 360° and adaptive beamforming is presented. Multiple radiation patterns can be generated by the antenna for interference canceling. To reduce the size and cost, the antenna employs the configuration of electronically steerable parasitic array radiators (ESPARs). The parasitic elements are 12 folded monopole antennas, which surround a short monocone antenna. The short monocone antenna serves as the driven element. Each folded monopole is loaded with a p-i-n diode, and by controlling the dc voltages applied to the p-i-n diodes, the antenna can achieve electronic beam steering and adaptive beamforming. To prove the concept, a prototype antenna was developed whose frequency bands are 1.8-2.2 and 2.85-3.15 GHz. The height of the antenna has been reduced to 0.12 λ at 1.8 GHz.

Compact-size Electronically Steerable Parasitic Array Radiator antenna

In this paper, a compact Electronically Steerable Parasitic Array Radiator (ESPAR) antenna that covers the frequency band from 2.4GHz to 2.5GHz is proposed. The top-disk-loaded monopole and folded monopole structure are employed to reduce the height of proposed ESPAR antenna. The height of top-disk-loaded monopole and folded monopole have been reduced to be lower than 1/8 wavelength, much smaller than 1/4 wavelength, i.e. the height of traditional ESPAR antenna. Furthermore, the distance between the driven element and parasitic elements, i.e. the radius of the ESPAR module, is also reduced. The proposed ESPAR module achieves a gain of 4.01dBi and a front-back ratio of 13.9dB despite its compactness. The beam forming is achieved by tuning the reactive load of the varactors series whose parasitic elements surround the central driven element.

Compact Smart Antenna With Electronic Beam-Switching and Reconfigurable Polarizations

This paper presents a compact-size, low-cost smart antenna with electronically switchable radiation patterns, and reconfigurable polarizations. This antenna can be dynamically switched to realize three different polarizations including two orthogonal linear polarizations and one diagonally linear polarization. By closely placing several electronically reconfigurable parasitic elements around the driven antenna, the beam switching can be achieved in any of the three polarization states. In this design, a polarization reconfigurable square patch antenna with a simple feeding network is used as the driven element. The parasitic element is composed of a printed dipole with a PIN diode. Using different combinations of PIN diode on/off states, the radiation pattern can be switched toward different directions to cover an angle range of 0° to 360° in the azimuth plane. The concept is confirmed by a series of measurements. This smart antenna has the advantages of compact size, low cost, low power consumption, reconfigurable polarizations, and beams.

New facility for minimally invasive measurements of electrically small antennas

Present and emerging wireless communications technologies present measurement and calibration problems that are not adequately catered for by existing facilities. Our aim in this research work is to construct, test and report a new antenna facility for minimally invasive measurements of electrically small antennas. This facility will allow antenna designers and system users to be able to evaluate and calibrate small and smart antennas and will help to remove current technical and commercial barriers that are being caused by a lack of traceability, which leads to measurement discrepancy. The small-antenna test range and electro-optic (EO) transducer employed for this new facility are described and the capability of the EO transducer is explored.

A Cost-Effective Direct Magnitude Measurement Methodology for Smart Antennas

In this paper, a novel measurement methodology is presented for characterizing smart antennas prior to incorporation of the transceiver that includes forward-error correction (FEC) coding and modulation. Using this method, the signal-to-interference ratio (SIR) is plotted as a function of the separation angle between the desired signal and the interference according to different required link margins (RLMs). This parameter gives the system developers, network designers, and users a clear idea about whether a smart antenna will suit their wireless communication system. The radiation pattern of the smart antenna can also be obtained from the measured interference signal. A low-profile wideband electronically steerable parasitic array radiator (ESPAR) smart antenna is used for the comparison of the proposed method with the traditional method. Compared to traditional methods that measure smart antennas together with transceivers, the proposed method is simpler and can improve the measurement repeatability and reduce the measurement time.

Low-cost beam-switching circularly-polarised antenna using tunable high impedance surface

This paper presents a low-cost beam-switching method for circularly-polarised (CP) patch antenna. By fabricating a switchable single feed circular patch antenna over a properly designed electronically tuneable high impedance ground plane, its radiation pattern can be steered. The feeding network in this design is also simplified. To demonstrate the concept, an antenna prototype with right hand circular polarisation (RHCP) at C band is developed, simulated and described in this paper. Using the electronically tuneable approach on both the antenna feed and high impedance ground plane the proposed antenna is able to cover 360° in azimuth at an elevation angle of 45° with an axial ratio lower than 3 dB. Furthermore, it reports a gain of 7.9 dBi at 4.8 GHz. The antenna is shown to be capable of achieving the beam-switching by tuning the high impedance surface electronically. The beam-switching is achieved without the use of array antenna, microwave phase shifters or beam-switching feed networks such as the Butler Matrix. Hence the proposed beam-switching CP antenna has compact size and low-cost, and is promising for small satellites applications.