A low-power consumption, small-size smart antenna, named electronically steerable parasitic array radiator (ESPAR), has been designed. Beamforming is achieved by tuning the load reactances at parasitic elements surrounding the active central element. A fast beamforming algorithm based on simultaneous perturbation stochastic approximation with a maximum cross correlation coefficient criterion is proposed. The simulation and experimental results validate the algorithm. In an environment where the signal-to-interference-ratio is 0 dB, the algorithm converges within 50 iterations and achieves an output signal-to-interference-plus-noise-ratio of 10 dB. With the fast beamforming ability and its low-power consumption attribute, the ESPAR antenna makes the mass deployment of smart antenna technologies practical.

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Fast beamforming of electronically steerable parasitic array radiator antennas: theory and experiment

A novel ground-plane shape to improve the horizontal gain for electrically steerable passive array radiator (ESPAR) antennas is investigated. The peak directivity of a monopole antenna with a finite ground plane, such as a circular or rectangular ground plane is at a higher angle from the horizon. Thus, the horizontal gain is lower than that of a dipole antenna. Using a circular ground plane of a half-wavelength radius with a skirt of a quarter wavelength wound around it, the angle of the peak directivity and the horizontal gain for the ground-based communication system were improved. For an ESPAR antenna - one of the monopole arrays - the horizontal gain was also improved. It was confirmed that it was possible to form the main-beam radiation and a beam null in the horizontal plane, each in an arbitrary direction, by changing the control voltage to the passive element. This was shown by an experiment with an ESPAR antenna with a finite reflector, a feed element, and seven passive elements.

Electrically steerable passive array radiator (ESPAR) antennas

The design of an optimized electronically steerable passive array radiator (ESPAR) antenna is presented. A genetic algorithm using a finite element based cost function optimized the antenna's structure and loading conditions for maximal main lobe gain in a single azimuth direction. Simulated gain results of 7.3 dBi at 2.4 GHz were attained along the antenna's elemental axis. The optimized antenna was fabricated and tested with the corresponding experimental gain better than 8 dBi. The 0.7 dB error between simulated and measured gain was constant for numerous structures and therefore did not affect the optimization. The optimized antenna reduced average main lobe elevation by 15.3/spl deg/ to just 9.7/spl deg/ above the horizontal.

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Seven-element ground skirt monopole ESPAR antenna design from a genetic algorithm and the finite element method

An array with pattern-reconfigurable elements is used to generate a digital modulation by switching the elements for every symbol. This technique is known as directional modulation. Because the modulation is generated at the antenna level, it gives control over the directions in which data is sent, unlike baseband modulation which transmits the same data in all directions at different power levels. A procedure for determining how to switch the elements to transmit only in a specified direction is outlined. Results indicate that compared to a traditional reconfigurable array, the directional modulation array allows information to be sent over a narrower beamwidth. Additionally, the method provides more selectivity in the possible transmit angles. Measured and calculated results from a four-element reconfigurable array are presented.

Beamsteering in Pattern Reconfigurable Arrays Using Directional Modulation

A novel dielectric embedded electronically steerable passive array radiator (ESPAR) (DE-ESPAR) antenna array for mobile wireless communication terminal is developed by finite element method based numerical modeling technique. The size reduction of the seven-element monopole antenna was accomplished by embedding the array in a cylindrical rod of FIK ceramic complex with a relative permittivity around /spl epsiv//sub r/=4.5. Dielectric embedded prototypes of a seven-element ESPAR antenna array were modeled and experimentally characterized. Experimental and numerical results are in good agreement. The optimized antenna produced a horizontal directivity of 5.1 dBi and return loss of 19 dB at 2.48 GHz. An overall volume reduction of 80% and footprint reduction of 50% were achieved.

/pdf/dielectric-embedded-espar-de-espar-antenna-array-for-58gycc3ceb.pdf

Dielectric embedded ESPAR (DE-ESPAR) antenna array for wireless communications

Simulation results showing the frequency characteristics and radiation patterns of the electronically steerable passive array radiator (ESPAR) antenna are presented. Three software packages (NEC2, HFSS and XFDTD) were used to obtain the results. Five different loading cases optimised at 2.4 GHz provided main lobe direction ranging between 0/spl deg/ and 360/spl deg/ azimuth. All five cases had minimum S/sub 11/ values between 2.35 GHz and 2.4 GHz resulting in a resonant frequency variation of 2.2%. S/sub 11/ response was found to be better than -9 dB in all cases, with 4 cases exhibiting results better than -11.90 dB. -10 dB S/sub 11/ bandwidths in these cases were greater than 200 MHz. Highest gain variations in the H field between the cases was 1.5 dB, with maximum gain values ranging from 4.46 dBi to 5.99 dBi. Gain variation 100 MHz either side of resonance was smaller than 0.44 dB. Radiation patterns taken over the 200 MHz (8.4%) bandwidth were only slightly different from the resonant patterns.

T. Ohira

Papers

Seven-element ground skirt monopole ESPAR antenna design from a genetic algorithm and the finite element method

Frequency characteristics of the ESPAR antenna