Tian-Ling Zhang

A Bidirectional Dual-Frequency Retrodirective Array for Full-Duplex Communication Applications

A bidirectional dual-frequency retrodirective array is presented, which uses intermediate frequency (IF) phase conjugation as the design concept. The proposed array has the ability of working at two different interrogating frequencies. For each interrogating signal, the frequency is converted to the other. This array contains the attractive features of simultaneously achieving bidirectional dual-frequency retrodirectivity and high isolation between the receiving and retransmitting signals. It is suitable for a full-duplex communication system. The proposed array is fabricated and demonstrated. Monostatic and bistatic measurements have been done to validate the performance of the system.

Triband Frequency-Selective Surface as Subreflector in Ku-, K-, and Ka-Bands

A novel triband frequency-selective surface (FSS) is designed to be a subreflector for reflector antennas. The element of the proposed FSS structure consists mainly of two identical layers of a square loop combined with a hexagonal ring and a hexagon. The designed FSS reflects electromagnetic waves in Ku-band (12-15.2 GHz), but transmits electromagnetic waves in K-band (18-21.6 GHz) and Ka-band (29.3-32 GHz). Moreover, such an FSS has the merit of stable performance for various incident angles within 50° for both TE and TM polarizations. Simulated results show that the insertion losses in K-band are less than 0.5 dB when the incident angles vary from 0° to 45°, and less than 1 dB for the incident angles from 45° to 50°. In Ka-band, the insertion losses are less than 0.5 dB when the incident angles vary from 0° to 30°, and less than 1 dB when the incident angles are from 30° to 50°. For both TE and TM polarizations, the incident angle is up to 50° with S21 less than -15 dB in Ku-band. Both designed procedure and measured results of the FSS are presented and discussed.

Design of broadband orthomode transducer based on double ridged waveguide

A Ku broadband OMT for satellite communication applications is designed. This OMT consists of a stepped double ridged waveguide junction, a power combiner and an axial branch. It is similar to that of B⊘ifot junction, but has no septum and pins which increase the complexity of the structure. The OMT with a size of 42×44×100mm3 can cover from 10.44GHz to 14.93GHz (35.4% bandwidth). The return losses are better than 27dB and the isolation is greater than 70dB. The OMT has excellent performance and can be easily manufactured. In this design, the mode matching technique is used to optimize the components of the OMT.

Design of a Dual-Frequency Retrodirective Array

A dual-frequency retrodirective array is proposed. By using two separated antenna arrays and double balanced passive mixers, the proposed system can achieve dual-frequency retrodirectivity in a bidirectional way. The low-frequency interrogating signal can be retransmitted at the high frequency, and it can also work in a reverse order. The proposed array has the advantages of low cost and high isolation between interrogating and retransmitting signals. The bidirectional characteristic can make it very useful in the two-way communication system. A four-element prototype is designed and fabricated. Measured results show good retrodirective performance.

Design of a Broadband Frequency Offset Van Atta Array

A novel broadband Van Atta array operating in a broadband with frequency offset characteristic is proposed. A single sideband mixer is introduced to achieve sideband choice without utilizing filters which make this array have excellent performance and wider applications than the conventional Van Atta array. The simulated results of the amplitude and phase of the array show that this antenna array can achieve retrodirectivity with frequency offset and good isolation in a broadband. The experimental performance of the array is observed within the frequency range from 2.8GHz to 3.4GHz.

BROADBAND AND LOW-PROFILE SLOT ANTENNA WITH AMC SURFACE FOR X/KU APPLICATIONS

A low-profile and broadband slot antenna with artificial magnetic conductor (AMC) surface is designed for X and Ku communications. Loaded with evolved C-shaped branches, the proposed coplanar waveguide (CPW)-fed slot antenna, which consists of two radiating slots, exhibits wide impedance frequency band performance. The presented AMC, the unit cell of which is made up of two central hexagonal circles with six rectangle branches, operates in a wide in-phase reflection frequency band ranging from 6.0 to 13.94 GHz (79.64%) at the reference plane 4mm above the AMC surface. An AMC surface composed of 8 × 10 AMC unit cells is located under the slot antenna with a distance of approximately 0.107λ (λ denotes the free-space wavelength at 8.0 GHz), which improves the radiation and impedance match properties of the broadband slot antenna while maintaining low profile. A prototype of the proposed slot antenna with AMC surface is fabricated and measured. Measured results show that the composite antenna achieves a wide impedance bandwidth from 7.64 to 14.58 GHz (62.47%). The measured peak gain is up to 10.26 dBi, and the maximum cross-polarization level is −17.5 dB for both E and H planes. Good agreements between the measured and simulated results validate good performance of the presented slot antenna within the desired frequency band.

BROADBAND AND GAIN ENHANCED BOWTIE ANTENNA WITH AMC GROUND

A low-profile wideband bowtie antenna backed by artificial magnetic conductor (AMC) ground is presented for gain enhancement. The proposed bowtie antenna, loaded with an open stub in the upper layer, has broadband property. By using an AMC reflector, consisting of 6×9 metallic patches, the bidirectional radiation of the bowtie antenna is changed to unidirectional radiation. The distance between the bowtie antenna and the AMC surface is only λ/10 at 3.75 GHz. Both the bowtie antenna and the AMC surface are fabricated and measured. The measured results demonstrate good and stable performances, including maximum gain of 8.27 dBi, and flat gain response with variation of 0.6 dB in the wide impedance matching (S11 < −10 dB) band from 3.05 GHz to 4.35 GHz (35.1%). Furthermore, the maximum cross-polarization level is −17 dB for both E and H planes, and the measured front-to-back ratios are more than 18 dB. Good agreement between the simulated and measured results validates the proposed design approach.

An iteration method of sidelobe suppressing of unequally spaced array

An iteration method is presented for unequally spaced array. In every iteration process, the adjacent element spacing is optimized by Differential Evolution with Global and Local neighborhoods algorithm (DEGL) to suppress the sidelobe level. Then the radiation patterns of the elements are updated once in every iteration step after the array model is reconstructed including the dimension of element and the distances between adjacent elements according to the optimization results and simulated by HFSS. The method dispenses with the time consuming of full wave analysis, taking the effects of the mutual coupling between the elements including both the radiation pattern and VSWR of the element in the array into account. A 16-element array is designed and fabricated to validate the proposed method.

Synthesis of an unequally spaced array using DEGL algorithm

An unequally spaced linear array used in retrodirective array is proposed in this paper. The synthesis is carried out using Differential Evolution with Global and Local neighborhoods (DEGL) algorithm. A 16-element array with two layer antenna element is implemented to validate the numerical results. The simulation results show that the maximum sidelobe level is basically below −20 dB in the range of 4.4 GHz-5 GHz.