With the trend of the miniaturization, broadband, and integration of multisystems of wireless communication terminals, a new ultrawideband planar inverted-F antenna (PIFA) with capacitive ground plane is proposed in this paper. The capacitive ground plane is composed of a sheet of metal islands, which makes a major contribution to ultra-wideband from 2.3 GHz to 9.0 GHz by applying the capacitive compensation for input impedance of the PIFA in high-order modes frequency bands. The effect of geometric parameters of capacitive ground plane and antenna height on antenna performance is analyzed. It is found that the radiation pattern in free space and the gain of the proposed antenna also meet the demands of the wireless communication terminals. The reported antenna was fabricated and measured, and the experimental results are in good agreement with the simulation results.
To expand the capacity of communication system or achieve a multimode communication, a real communication system is required to be implemented with multiband or wideband characteristics. Therefore, it is important to develop a wideband antenna for wireless communication terminal equipments which are usually limited in a confined space for antennas. A compact wideband mobile handset or wireless data card multiple-input multiple-output (MIMO) antenna for long term evolution (LTE) applications especially has been a challenging problem. A planar inverted-F antenna (PIFA) is widely used in mobile devices because of its advantages of compact size, low profile, and easy integration with portable devices. However, the narrow impedance bandwidth of a conventional PIFA is difficult for wideband and ultrawideband applications. Hence, it is most desirable to find methods which can improve the bandwidth of the PIFA antenna for multiband or wideband applications. A tapered-type radiating patch [
In this paper, we propose a novel ultrawideband PIFA with capacitive ground plane which consists of a sheet of periodic metal patches. By applying the capacitive compensation for the input impedance of the PIFA in higher frequencies, the proposed PIFA has a broad working frequency band. The effect of geometric parameters of the periodic metal patches and antenna height on antenna performance is analyzed. It is found that the radiation pattern in free space and gain of the proposed antenna also meet the demands of the broadband wireless communication terminals. Good agreement of the measurement with simulation results can be observed.
Figure
Geometry of a conventional PIFA.
Capacitive ground plane composed of a sheet of periodic metal square patches.
Parametric studies were performed to analyze the effects of the capacitive ground plane structure parameters on the antenna performance. It is worth pointing out that the radiating patch and the positions of feeding point and short pin are kept constant. Here we only pay attention to the contribution from the proposed capacitive ground plane. Figures
Parametric analyses of the effect of capacitive ground plane on the return loss of the PIFA. (a) Period
Furthermore, we analyzed and compared the input impedance characteristics of and between the proposed PIFA and conventional antennas, as shown in Figure
Comparison of the input impedance characteristics of the conventional PIFA with solid ground plane and the proposed ultrawideband PIFA with capacitive ground plane.
Figure
Radiation patterns of the ultrawideband PIFA: (a) 2.5 GHz, (b) 4.0 GHz, (c) 6.0 GHz, and (d) 8.5 GHz.
According to the designed parameters, the proposed PIFA was fabricated and shown in Figure
Fabricated ultrawideband PIFA antenna, (a) capacitive ground plane, and (b) PIFA antenna.
Comparison of measured and simulated
Furthermore, we apply the ultrawideband PIFA to a wireless mobile phone platform, as shown in Figure
(a) Capacitive ground plane is locally embedded into the PCB, (b) ultrawideband PIFA on the mobile phone platform.
Comparison of measured and simulated
This paper proposed a new ultrawideband PIFA antenna with a capacitive ground plane which is composed of a sheet of metal periodic patches. By applying the capacitive compensation for input impedance of the PIFA in high frequency bands, the proposed PIFA can work from 2.3 GHz to 9.0 GHz, and the relative bandwidth is up to 118%. The effect of geometric parameters of capacitive ground plane and antenna height on antenna performance was analyzed in detail. It is found that the radiation pattern in free space and the gain of the proposed antenna also meet the demands of the wireless communication terminals. Due to the small dimension of the capacitive ground plane, the proposed ultrawideband PIFA is easily integrated with other systems of wireless communication terminal applications. Simulation and measurement results verify that the proposed PIFA antenna has good ultrawideband characteristics.
This work is supported partly by the Program for New Century Excellent Talents in University of China, the National Natural Science Foundation of China under Contract no. 61072017 and no. 61072021, the National Key Laboratory Foundation, the Fundamental Research Funds for the Central Universities, and Foundation for the Returned Overseas Chinese Scholars, State Education Ministry and Shaanxi Province.