Download this article in .PDF format
This file type includes high resolution graphics and schematics when applicable.

Figure 9 shows a prototype of the fabricated antenna. Its impedance characteristics were measured with a model 37269A vector network analyzer (VNA) from Anritsu Co. The measured impedance bandwidth is 66 MHz (2421 to 2487 MHz) and two separate resonant frequencies at 2441 and 2480 MHz with return loss values of 41.6 dB and 22.2 dB, respectively (Fig. 10). The measured antenna performance shows excellent agreement with the simulated return-loss curve. A few shifts in the bandwidth and positions of resonant frequencies are due to the fabrication tolerances.

Microstrip Antenna Maintains Low Profile, Fig. 9

The measured and simulated normalized radiation patterns at the first and second resonant frequencies are plotted in Fig. 11, where the “Co(S),” “Co(M),” and “Cross(M)” stand for simulated co-polarization, measured co-polarization, and measured cross-polarization, respectively. The proposed low-profile antenna exhibits good broadside radiation patterns in the E-plane (x-z plane) and H-plane (y-z plane) at each resonant frequency.

Microstrip Antenna Maintains Low Profile, Fig. 10

Microstrip Antenna Maintains Low Profile, Fig. 11

In the E-plane, the measured 3-dB beamwidth is 83 deg. at 2441 MHz and 84 deg. at 2480 MHz. It can be seen that the beam peaks of the E-plane are slightly shifted from the z-direction due to the feeding position on the main patch. In the H-plane, the measured 3-dB beamwidth is 93 deg. at 2441 MHz and 86 deg. at 2480 MHz. Symmetrical radiation patterns are obtained in the H-plane due to the bilateral symmetry of the antenna configuration. In addition, it is obvious that low cross-polarization levels are obtained in the two orthogonal planes. The antenna gain versus frequency was also measured, with measured peak gain of 5.6 dBi at 2.45 GHz.

Microstrip Antenna Maintains Low Profile, Table 1

Microstrip Antenna Maintains Low Profile, Table 2

As is well-known, the impedance bandwidth of a conventional microstrip antenna with a thin substrate (less than 0.01λ0) is quite narrow. To enhance its impedance bandwidth, a U-shaped parasitic patch was employed, and summaries of conventional and modified (with patch) microstrip antennas can be compared in Tables 1 and 2. Table 1 shows that the modified antenna provides a wider operating bandwidth than a conventional microstrip antenna—as much as 2.747 time greater. But Table 2 shows that the modified antenna exhibits similar radiation patterns to those of the conventional antenna, except with a slight decrease in gain. The modified U-slot antenna obtains maximum gain due to a larger ground plane. The proposed low-profile antenna is well suited for conformal communications terminals.

Zhifeng Yao, Lecturer


College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling 712100, People’s Republic of China

Mintong Li, Associate Professor


College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling 712100, People’s Republic of China

Chen Lin, Engineer


The 723 Institute of CSIC, Yangzhou 225001, People’s Republic of China

Dong Wang, Ph.D.

College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling 712100, People’s Republic of China

Download this article in .PDF format
This file type includes high resolution graphics and schematics when applicable.