A Reconfigurable Stacked Microstrip Patch Antenna for Satellite and Terrestrial Links

A reconfigurable stacked microstrip patch antenna is proposed. The antenna operates at an upper frequency f(u) with a broadside pattern, 7.5-dBi right-hand circularly polarized gain, and 15.8% bandwidth. At a lower frequency f(1), the antenna operates as a planar inverted-F antenna (7.3% bandwidth and 3.9-dBi peak gain) with the main beam directed close to the horizon. Switching between the two regimes of operation is achieved using p-i-n diodes. antenna operation in the upper frequency hand is suitable for low-earth-orbit or medium-earth-orbit satellite communications, and in the lower frequency band, the antenna is useful for terrestrial land-mobile or other wireless applications

Threshold Power of Canonical Antennas for Inducing SAR at Compliance Limits in the 300-3000 MHz Frequency Range

A study of the specific absorption rate (SAR) in an exposed body induced by canonical antennas is presented, with the aim of determining an upper bound for the antenna transmit power that demonstrates that a product is inherently compliant with internationally accepted radio frequency (RF) exposure limits. Starting from the fundamental limits in antenna quality factor (Q) and the corresponding bandwidth, several antenna sizes are selected, and their SAR distributions are computed using the method of moments (MoM) and finite-difference time domain (FDTD) method in the frequency range 300-3000 MHz. The threshold powers are then determined, below which the peak 1-g and 10-g averaged SAR would not exceed the limits specified in international exposure standards. From the data, simple expressions are derived to estimate the threshold power over a wide range of antenna sizes, frequencies, and distances from the body. It is demonstrated that the results presented in this paper are conservative in comparison with the measured SAR data of real products as well as other published data

Correlating Threshold Power with Free-Space Bandwidth for Low-Directivity Antennas

This paper develops a threshold power rationale that can be used to demonstrate inherent compliance for portable wireless devices with specific absorption rate (SAR) limits over the 300-6000-MHz frequency range. This is achieved first by understanding the relationship between basic antenna parameters (bandwidth, operating frequency, and distance to the body) and SAR. From this, an upper limit is determined for the power transmitted by a portable wireless device such that the SAR will not exceed the compliance limit. Based on the presented computational and measured data, an empirical formula is developed for the threshold power as a function of the aforementioned parameters. It is demonstrated that the derived threshold power is conservative for all of the low-directivity antennas studied. Computed results are also compared against practical device data (mobile telephone data collected from the manufacturers) to show that the predicted threshold power data using the proposed formula are conservative. The limitations of the proposed formula are also discussed

A Miniature Spiral Diversity Antenna System with High Overall Gain Coverage and Low SAR

A miniature spiral diversity antenna system operating at 1.85 GHz is proposed. Two 10 mm 6.25 mm antennas were placed at two corners of a printed circuit board at a height of 7 mm from the ground plane. Each antenna achieves nearly 7% bandwidth within 6 dB return loss. The mutual coupling between the two antennas is less than 10 dB. The proposed diversity antenna scheme exhibits high overall gain performance in all three principal planes compared to a single antenna solution. Computed specific absorption rate (SAR) data against a specific anthropomorphic mannequin (SaM) phantom and a hand model show that the diversity antenna system induces low SAR compared to a single antenna