Although the high gain and multi band antenna design discussed in this paper has small size and light weight, it can receive and transmit GPS and WLAN signals, and can cover the three bands of WLAN. For small antennas, high gain is usually not obtained.

However, in satellite communication applications, the antenna must be small and light, and can provide beamforming, broadband and polarization purity. In the antenna design for multi band global positioning system (GPS) and wireless local area network (WLAN), it is possible to design an antenna with polarization diversity, high gain, small size and light weight.

For example, for GPS applications, one antenna may be required to handle both the low band of 1.226ghz and the high band of 1.575ghz. For IEEE 802.11a/b/g WLAN applications, the antenna must operate in two frequency bands of 2.4GHz and 5GHz, and the bandwidth must support data rates of 11 Mbps and 54 Mbps.

Other applications include planned Air Force Satellite Systems in the 1.8GHz and 2.25GHz bands. For a single antenna covering multiple wireless bands, the coverage range of 1.8GHz to 2.1GHz should also be considered for the third generation (3G) cellular system.

Polarization is an important characteristic for a successful antenna design. For space applications, circular polarization (CP), such as right-handed circular polarization (RHCP) or left-handed circular polarization (LHCP), is usually used for transmission, reception and multiplexing in the same spectrum range to increase the system capacity. Although most WLAN systems require linear polarization, the use of circular polarization will eventually become an advantage of mobile systems.

Some theoretical limitations determine how small the antenna can be when providing the required gain and bandwidth. For space-based (satellite) applications, the antenna is required to adapt to a certain waveform coefficient. The polarization direction of the antenna is circular polarization and works on 1.8GHz uplink (satellite reception frequency) and 2.25GHz downlink (satellite transmission frequency).

Beamforming capability is also a key requirement, which allows satellites to maintain communication at different positions and angles. The antenna must be strong enough to withstand shock and vibration, temperature environment (usually between - 40 ℃ and + 70 ℃) and power flicker shock.

Several options are considered in the design, including helical antenna, four leaf helical antenna (qfha) and various microstrip patch structures. The initial analysis and electromagnetic (EM) software simulation results show the difficulty of realizing the required performance on a small physical size.

After considering several non-traditional methods, the ring radiator technology is selected as a possible solution. Compared with other schemes, the resonant structure is adopted to effectively prolong the path length of radiation current (achieve high gain), while the antenna is reduced by 25% to 35%.

This technology can not only meet the requirements of waveform coefficient, but also achieve higher gain than the larger microstrip patch antenna or resonant cavity helical antenna.

Compared with the more understandable design and analysis methods for microstrip patch antennas, the design and analysis of ring antennas require very empirical design (and empirical speculation). Fortunately, by performing a detailed initial design and analysis process and carefully studying the EM simulation results, the design risk of the ring antenna can be reduced regardless of its complexity.

In a simple rectangular patch antenna, two notches at both ends of the patch can be used as radiation sources, with an interval of about half the wavelength. If the length of each notch is about half the wavelength, a 2.1dbi gain can be obtained. Any such two antennas working as binary arrays can theoretically provide an additional 3dB gain.

Therefore, a simple patch antenna should be able to achieve 5.1dbi gain. With some improvements, even better gain or waveform may be obtained, depending on the type of ground plane or resonant mode.

The ring antenna can be designed as a multi harmonic structure, and these resonators can be separated or coupled to be suitable for multi frequency or broadband applications.

By adjusting the phase of each secondary mode, they can work in a predetermined way. In this way, high gain and beamforming can be realized through phase superposition and cancellation in the far field in the appropriate direction. In most cases, these structures may achieve 9dbic gain (theoretical value) and 17% bandwidth.

Theoretically, corresponding to the voltage standing wave ratio (VSWR) of 1.50:1, 2.0:1 and 3.0:1 respectively, the bandwidth of 15%, 20% and 30% can be realized accordingly. Unfortunately, it is impossible to find a system design method that can meet the required physical and electrical performance on all frequencies.