Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China
lycloud1978@163.com*
Abstract—A novel 3-bit frequency-reconfigurable antenna (FRA) with miniaturized dimensions is realized with a meander line. The frequency reconfiguration of the antenna is achieved by introducing N RF p-i-n diodes into the meander line. The related parts of the meander line with different lengths are bypassed or included into the antenna by switching on or off the diodes, resulting in 2Nswitchable size lengths of the antenna and equally spaced operating frequencies. A 3-bit meander-line reconfigurable antenna (N=3) is designed, and the simulated and measured results agree well. The antenna provides 23=8 independent switchable states, with the operating frequencies covering a wide switchable frequency range from 1.04 GHz to 1.51 GHz and the working bandwidths varying from 80 MHz to 150 MHz. The number of working states is optimally large, considering the number of switches used. Besides, this work has an acceptable peak gain of 1.59 dBi regarding the miniaturized total dimension of 0.17 λ × 0.07 λ (λ is the wavelength of the lowest working frequency), which is more compact than many published FRAs.
Introduction: With the rapid development of modern wireless communication systems, RF front-ends are required to operate at multiple frequency bands, and the number of integrated antenna and total dimensions is highly increased. To solve the problems, reconfigurable antennas have been extensively studied recently.
Reconfigurable antennas can be classified into three types, namely, frequency-reconfigurable antennas (FRAs) [1]-[10], polarization-reconfigurable antennas [11], and radiation pattern reconfigurable antennas [12]. Among them, FRAs have attracted substantial attention and been intensively studied. The frequency of an FRA can be continuously tuned using varactors [1]-[5] or discretely switched using RF-switches [6]-[10]. Frequency reconfigurability has been achieved on various types of antennas, such as microstrip patch antennas (MSAs) [1], [2], [9], dipole antennas [3], patch-slot antennas (PSAs) [6], microstrip monopole antennas (MMAs) [7], microstrip slot antenna (MSA) [8], and planar inverted-F antennas (PIFAs) [10]. Majority of FRAs tune/switch the resonant frequencies by reconfiguring the current flow path on the antenna or reshaping the antenna structure, changing the equivalent electrical lengths of antennas in addition.
Nonetheless, many of these published FRAs fail to take miniaturization into account, which is critical especially when FRAs are used in handheld devices. Typically, antenna miniaturization is accomplished by folding the radiation branch of the antenna [13], [14], by selecting an antenna patch loaded with a specialized shape [15] or a shorting wall [16], and by introducing metasurfaces [17] or metamaterial structures [18]. The most common method of antenna miniaturization is to use a meander line. In [14], a miniaturized monopole chip antenna with meander lines on the first and third layers is presented, greatly reducing the antenna’s size at lower and upper bands.
Furthermore, many published FRAs load too many switches while only providing a limited number of operational states. Fortunately, binary reconfiguration can successfully resolve this problem by realizing 2N switchable states with N switches. A 3-bit binary reconfigurable PIFA with eight independent states covering a working frequency range from 1.52 GHz to 2.25 GHz is developed by using three MEMS switches in [10]. The presented FRA is miniaturized by the meander line in [7], and only three states are achieved using two diodes.
In this study, a miniature 3-bit frequency-reconfiguring monopole antenna with a meander-line is proposed. It employs three switches to achieve 23 states, which is the maximum number of states. The structure can be extended for achieving binary FRA with larger number of bits.