A compact planar log-periodic dipole array (LPDA) antenna operating from 0.55 to 9 GHz with high measured gain is proposed to be implemented in a reverberation chamber as a source antenna. To minimise the total size of the LPDA antenna, variants of top-loading techniques are utilised, and a much smaller spacing factor is opted to specify the spacing between the elements. However, miniaturisation of the LPDA antenna limits the antenna's wideband characteristics over the desired range of frequencies. Hence, a feedline meander and a trapezoidal stub are incorporated into the design as impedance matching techniques to effectively enhance the bandwidth performance especially for the lower band of the antenna's operating frequency range. The LPDA antenna exhibits radiation patterns with and without a radome having the measured gain ranging from 2.48 to 7.89 dBi and from −1.20 to 7.94 dBi, respectively.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2016.0611

Compact log-periodic dipole array antenna with bandwidth-enhancement techniques for the low frequency band

In this letter, a log-periodic dipole array (LPDA) antenna operating between 1.1 and 13.8 GHz with and an average peak realized gain of 5.2 dB is presented. It is suitable for GPS (L1-L5), PCS, IMT-2000, Bluetooth, WLAN, WiMAX, UWB, and X-band applications. The antenna is designed by introducing a subsectional tapered feedline instead of standard microstrip feeding, which leads to a remarkable lower-frequency performance. The upper-frequency performance of the antenna is improved by adding a feeding point patch. The group delay is also examined for the final design, and maximum 1.5 ns deviation is observed in UWB. By using ordinary and simple dipoles with this modified feedline approach, a superior antenna performance is obtained over a very wide frequency band, and it is validated by the comparison of three fabricated antennas. Additionally, the antenna size is also reduced without using complicated and/or top-loaded dipole structures.

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Subsectional Tapered Fed Printed LPDA Antenna With a Feeding Point Patch

A wideband microstrip series-fed magnetic dipole array antenna is proposed. The five-element dipole array antenna is designed to achieve both wide bandwidth and high gain because of its microstrip series feeding structure. The low-profile low-cost array is suitable for applications such as wideband high-gain wireless communications. Measured and simulated results are in good agreement. The measured impedance bandwidth of the array is enhanced up to 28.6% (5.0–6.7 GHz). The radiation patterns show its advantages of high gain (about 10 dBi), endfire radiation and vertical polarisation.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/el.2014.3434

Wideband microstrip series‐fed magnetic dipole array antenna

A novel broadband endfire dipole array antenna is presented in this letter. With a novel impedance matching method, this antenna is realized as a series-fed structure and four dipole elements on the same printed circuit board. The bandwidth of the antenna is increased by staggered tuning of the dipole elements. The measured results show that the antenna has an impedance bandwidth of 70.5% for voltage standing wave ratio ( $\mathrm{VSWR)} , a gain of 3.43–6.78 dBi and endfire radiation pattern. The total size is $0.595\times 0.977\; \lambda _o^2$ ( $\lambda _o$ is the free-space wavelength at the center frequency). The studies of the dipole length and distributed capacitor are also performed to verify the design theory. The advantages of broad bandwidth and unidirectional radiation pattern make this antenna favorable in wireless communication systems.

Design of Novel Broadband Endfire Dipole Array Antennas

A wideband and high-gain uniform circular array with calibration element for smart antenna application is presented. This letter focuses on the feasibility of substituting calibration element for calibration network to achieve wide bandwidth and high gain. The proposed array antenna with 15 array elements and a calibration element is designed and fabricated. Good agreement between simulated and measured results is observed. Simulation and measurement results reveal that the proposed array element can provide an impedance bandwidth of 38.3% (3.95-5.82 GHz) and a radiation pattern bandwidth of 12.8% (4.4-5 GHz). The impedance bandwidth of the calibration element is 15.4% (4.39-5.12 GHz). Additionally, within the pattern bandwidth, the radiation pattern of the array element has horizontal deviation angles in E-planes ranging from - 5 ° to 6 ° , 3-dB beamwidths in E-planes from 25 ° to 35 ° , and element gains from 7 to 7.9 dBi. Compared to the conventional array, the proposed method can be able to increase the average array gain of 1.2 dB and to decrease the average normalized sidelobe level (SLL) of 4.2 dB. In addition, over the operating band, the phase and amplitude matching of the coupling coefficients between the calibration element and 15 array elements are from 3 ° to 7.2 ° and 0.6 to 1.2 dB, respectively.

Wideband and High-Gain Uniform Circular Array With Calibration Element for Smart Antenna Application

A new balun used for feeding a planar log-periodic dipole array antenna (PLPDA) is proposed. This balun, which is based on mode conversion, converts gradually the transmission mode from quasi- TEM (coaxial cable) to full TEM (balanced line), with an accessible excitation current property (ECP), which is not achievable in classical feeding techniques (infinite or self balun). To validate this approach, an ultra-wideband (UWB) PLPDA antenna was designed with these balun structures for operating in the L and S bands (1-4 GHz) and the results were compared in terms of reflection coefficient and radiation pattern. A PLPDA antenna with a mode converter balun was fabricated. Results show that the proposed balun is a low length (10 mm) frequency-independent (4.5 GHz based on |S11|<-10 dB) device useful for feeding the UWB PLPDA antenna. Moreover, antenna's ECP can be modified, which is necessary for phase centre variation compensation.

M.I. Mirzapour

Papers

Ultra-wideband planar LPDA antenna with mode converter balun