Zhihao Tian

Efficient and Accurate Measurement of Absorption Cross Section of a Lossy Object in Reverberation Chamber Using Two One-Antenna Methods

The averaged absorption cross section of a lossy object can be measured in a reverberation chamber (RC). Conventionally, the measurement is conducted in the frequency domain and it requires two antennas with known efficiency. In this paper, the two one-antenna methods are presented-one is in the frequency domain and the other is in the time domain. In the frequency domain, by using the enhanced backscatter effect, the measurement setup is greatly simplified and only one antenna with known efficiency is required. In the time domain, the measurement can be conducted rapidly and accurately using just one antenna and the source stir technique by considering the robustness of the chamber decay time; moreover, the RC can be replaced by a suitable electrically large conducting cavity, which will greatly reduce the hardware requirement. It is found that the time-domain approach is superior to the frequency-domain approach in many aspects. The new measurement methods are efficient and accurate, while the system requirements and setup are simpler than the conventional ones.

A Modified Two-Antenna Method to Measure the Radiation Efficiency of Antennas in a Reverberation Chamber

A modified two-antenna method is proposed to measure the radiation efficiency of antennas in a reverberation chamber. By combining the conventional reference antenna method and the one-antenna method, and introducing a virtual antenna, the proposed method does not need a reference antenna with known efficiency and can be applied to highly lossy antennas, which could be problematic for the existing methods. Measurements are conducted to verify the effectiveness of the proposed method. The proposed method can be regarded as a generalized form of the two-antenna method and is compared to the existing reverberation chamber methods. The advantages and limitations of the proposed approach are also discussed.

Shielding Effectiveness Measurement of an Electrically Large Enclosure Using One Antenna

A new method is proposed to measure the shielding effectiveness (SE) of an electrically large enclosure. Traditionally, the SE measurement requires at least two (in an anechoic chamber) or three antennas (in a reverberation chamber). In this paper, only one antenna is needed in the whole measurement procedure. There is no requirement to use a reference antenna. It is interesting to note that if the aperture of the enclosure under test (EUT) can be covered (by using a conductive sheet or aluminum foil), the SE can be measured quickly by comparing the Q factor or the decay time of the covered and uncovered EUT. Measurements have been conducted to evaluate and verify the proposed method. The results are compared with those obtained using the nested reverberation chamber method; limitations of the proposed method are also discussed and identified. It is found that when the EUT is well shielded, the uncertainty of the proposed method could be relatively large. Nevertheless, the proposed method does offer a new simple and efficient approach to measure the SE of an electrically large enclosure.

The Limit of the Total Scattering Cross Section of Electrically Large Stirrers in a Reverberation Chamber

The total scattering cross section (TSCS) has been proven to be an effective quantity to characterize the performance of stirrers in a reverberation chamber (RC). It is shown in this letter that the maximum TSCS is a quarter of the stirring surface area, and it is equal to the absorption cross section (ACS) of the same area with perfect radio absorbers. The mathematical proof is presented and measurements are performed to validate this limit. It is also shown that the TSCS and ACS are statistical dual quantities; related dual quantities are also given. The TSCS can be used to characterize how well a stirrer is designed or how close an RC is to a perfect RC.

Extract the Decay Constant of a Reverberation Chamber Without Satisfying Nyquist Criterion

The decay constant of a reverberation chamber is an important fundamental parameter to characterize the performance of the chamber and is used in many measurement applications. Normally, it is extracted from the inverse fast Fourier transform of the measured S-parameters. It is generally accepted that aliasing in the time domain should be avoided, thus it requires a very high sampling rate in the frequency domain and a huge amount of measured samples. This limits the bandwidth in each measurement and also takes excessive measurement time. In this letter, we show that the Nyquist criterion does not have to be satisfied in the full bandwidth of the measurement and the sampling interval can be larger than the coherence bandwidth. A new criterion is presented for the decay constant estimation. Examples are given to demonstrate the validity and efficiency of the proposed criterion.

Diversity Gain Measurement in a Reverberation Chamber Without Extra Antennas

This study aims to simplify the diversity gain measurement in a reverberation chamber since the conventional method requires two extra antennas: a transmitting antenna and a reference antenna with known radiation efficiency. By incorporating the one- or two-antenna method for the radiation efficiency measurement in a reverberation chamber and taking advantage of the enhanced backscattering effect, the proposed method in this letter does not need extra antennas, and only the antenna under test is enough to complete the measurement. A virtual antenna is introduced to help understand the proposed method. The measurement results obtained from the proposed method show a good match with the results obtained from the conventional method; preconditions and limitations of the proposed method are also identified and discussed.

A Novel Reconfigurable Metal Rim Integrated Open Slot Antenna for Octa-Band Smartphone Applications

In this paper, a novel reconfigurable open slot antenna has been proposed for LTE smartphone applications to cover a wide bandwidth of 698–960 and 1710–2690 MHz. The antenna is located at the bottom portion of the mobile phone and is integrated with metal rim, thereby occupying a small space and providing mechanical stability to the mobile phone. Varactor diode is used to cover the lower band frequencies, so as to achieve a good frequency coverage and antenna miniaturization. The operational principles of the antenna are studied and the final design is optimized, fabricated, and tested. It has achieved the desired impedance bandwidth and the total efficiency of minimum 50% in free space throughout the required bands. The antenna performance with mobile phone components and human hand is also been studied. Furthermore, the SAR in a human head is investigated and is found to be within allowable SAR limits. Finally a multiple-input multiple-output antenna configuration with high isolation is proposed; it has an identical reconfigurable open slot antenna integrated at the top edge of the mobile phone acting as the secondary antenna for 698–960 and 1710–2690 MHz. Thus the proposed antenna is an excellent candidate for LTE smartphones and mobile devices.

Two Alternative Methods to Measure the Radiated Emission in a Reverberation Chamber

One of the most important applications of a reverberation chamber is for radiated power measurement. Two new alternative methods are proposed to measure the radiated power of equipment under test in a reverberation chamber in this paper. Traditionally, as stated in IEC 61000-4-21 standard, this measurement requires two antennas, a signal generator and a spectrum analyzer or receiver. However, it is found that if a signal generator is not available, a vector network analyzer can be used to complete the measurement. Furthermore, if only one antenna is available, by taking advantage of the enhanced backscattering effect, the measurement can still be completed. By incorporating the one- and/or two-antenna methods, the radiation efficiency of antennas is also considered. Measurements have been conducted to verify the proposed methods, the results from these three methods are compared, and a very good agreement is obtained. It is found that the two proposed methods are simpler than the conventional method.

A Shoelace Antenna for the Application of Collision Avoidance for the Blind Person

A shoelace antenna for the application of collision avoidance for the blind person is proposed for the first time. A thin flexible metal wire is used to fabricate the antenna, which can run along with the shoelace without destroying the shoe or adding extra big structures. According to the investigations, to put the feeding probe at the bottom of the cross point is better than the locations around the string bowknot. To make the shoelace tighter or looser will influence the performance with an affordable variation. The effect of the biological tissues has been taken into account during the performance evaluation of the antenna. The measured fractional bandwidth is 11% with a resonance of 2.43 GHz in the ISM Band. The main lobe of the antenna points to the upper front direction with an angle of about 20°, which is suitable for the detecting of the anterior obstacles when walking. The measured results indicate reasonable performance for the shoelace antenna to serve as a tool for the blind person.

Average Absorption Coefficient Measurement of Arbitrarily Shaped Electrically Large Objects in a Reverberation Chamber

It is shown in this letter that the average absorption coefficient (AAC) of an object under test (OUT) can be obtained by comparing the measured absorption cross section (ACS) of the OUT with the ACS value of a perfect absorber of the same shape. The ACS of an arbitrarily shaped electrically large perfect absorber can be obtained numerically. Measurements are performed to demonstrate the proposed method. Results show that the AAC is not sensitive (but not independent) to the shape and size of an electrically large absorber. The procedure proposed in this letter can be used to characterize the electromagnetic wave absorptive and scattering ability of arbitrarily shaped objects. A system-level AAC could be very useful for many applications.