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2021-07-12 PIER Letters Vol. 98, 155-163, 2021. doi:10.2528/PIERL21052902

Compact Four-Band Cactus-Shaped Antenna for 5G and WLAN Applications

Juan Zhang, Xiaoming Liu, Chen Wang, Lu Gan, Ye Wang, and Lijun Sun

A low-profile coplanar waveguide fed four-band compact antenna for 5G and WLAN applications is presented in this letter. Multiple bands are generated using a cactusshaped patch, which consists of several inverted L-shaped slots and branches. The proposed antenna provides 150 MHz (2.10 GHz-2.25 GHz), 400 MHz (3.25 GHz-3.65 GHz), 1022 MHz (4.42 GHz-5.44 GHz), 1400 MHz (5.60 GHz-7.00 GHz) bandwidths of 10 dB return loss, corresponding to the target N1/N78/N79 5G bands and 5.8 GHz WLAN band, respectively. Moreover, the proposed antenna has a low profile of 21 mm × 29 mm × 1.6 mm, while maintaining tolerable gain in these operation bands. In addition, monopole-like radiation patterns are obtained, which is suitable for wireless communication. In order to verify this design, a prototype has been fabricated and measured. The measured results show satisfactory agreement with the simulated ones.

2021-07-06 PIER Letters Vol. 98, 145-153, 2021. doi:10.2528/PIERL21051402

Four-Element Low-Band MIMO Antenna for Mobile Phones with Small Clearance

Harri Varheenmaa, Rasmus Luomaniemi, Anu Lehtovuori, Pasi Yla-Oijala, and Ville Viikari

This letter presents a four-element MIMO phone antenna with a metallic rim and 2-mm ground clearance that operates in the low-frequency band. Characteristic mode analysis is used to design the metallic rim so that the structure supports four resonating modes that can be excited separately to obtain MIMO operation in the desired frequency range below 1 GHz. Four exciter elements with matching circuits are designed so that the coupling between the ports is moderate. The prototype is manufactured, and measurement results are shown to corroborate the increased capacity compared to traditional two-element MIMO solutions.

2021-07-01 PIER Letters Vol. 98, 139-144, 2021. doi:10.2528/PIERL21053003

A Compact Negative Group Delay Circuit Topology Based on Asymmetric Coplanar Striplines and Double-Sided Parallel Striplines

Zhongbao Wang, Yu Bai, Yuwei Meng, Shao-Jun Fang, and Hongmei Liu

An innovative negative group delay (NGD) circuit topology based on asymmetric coplanar striplines (ACPSs) and double-sided parallel striplines (DSPSs) is proposed. The original NGD circuit topology consists of two sections of ACPS, one section of open-circuited DSPSs, a connecting hole, and a group of grounding holes. The NGD characteristic is achieved by the open-circuited DSPS combined with the connecting hole. To verify the proposed NGD circuit topology, a prototype is designed, fabricated, and measured. From the measured results, an NGD time of -2.42 ns at the center frequency of 1.577 GHz is obtained with an NGD bandwidth of 36 MHz (1.561-1.597 GHz). The insertion loss is less than 4.75 dB with the return loss larger than 11.7 dB in the NGD band.

2021-06-28 PIER Letters Vol. 98, 129-137, 2021. doi:10.2528/PIERL21050601

Analysis and Design of Miniaturized Wideband Rat-Race Coupler with Improved Phase Performance

Hongmei Liu, Yao Wang, Tielin Zhang, Shao-Jun Fang, and Zhongbao Wang

In the paper, a miniaturized wideband rat-race coupler with improved phase performance is designed and analyzed. Flat output ports phase differences are obtained by utilizing a component-loaded T-type transmission line (CLT-TL) with a stub-loaded short-circuited coupled line (SLS-CL). Let the CLT-TL and SLS-CL sections be equivalent to uniform 90° and 270° transmission lines, respectively. Design equations are derived, and an optimization is proceeded to obtain the circuit parameters. For validation, a prototype is designed, fabricated, and measured. Including the feeding lines, the circuit size is 0.31λg × 0.31λg. Under the criterion of return loss (RL) > 10 dB, the measured bandwidths for ports 1 and 3 excitations are both reach 48%. For amplitude imbalance (AP) < 0.5 dB, the overlap relative bandwidth is 46.88%. The measured bandwidths with 2° phase imbalance are 49.58% and 54.01% for ports 1 and 3 excitations, respectively.

2021-06-24 PIER Letters Vol. 98, 121-127, 2021. doi:10.2528/PIERL21041104

A Novel Planar Filtering Magic-T

Jun-Mei Yan, Hai-Ying Zhou, and Liangzu Cao

This paper presents a planar filtering magic-T with a simple structure. It consists of four half-wavelength microstrip resonators with one loaded with a shorted microstrip stub at its central location. The resonator loaded with a shorted microstrip stub has the even-symmetry resonant mode. Other three resonators have the odd-symmetry resonant mode. The planar filtering magic-T has four ports, which all adopt a tapped line structure. Its novelty lies in the simple structure. Compared with previous works in the literature, its inter-resonator coupling zones are apart away and have no influence on each other, which means a simple design. Furthermore, a different-properties coupling is not needed, and its filtering response can be easily extended to the high-order case. The operational mechanism and design method are introduced in details. A planar filtering magic-T with center frequency of 920 MHz was designed and fabricated. The measured results show that, at the center frequency, the return losses (S11/S44) is less than 20/12 dB; an isolation degree of 25 dB (S41) can be observed; the insertion loss of the difference port (S21/S31) and sum port (S24/S34) are 4.5/4.7 dB and 4.3/4.6 dB; the phase unbalance is 8˚/7˚(Σ/Δ). Totally, these results can verify the effectiveness of the proposed novel planar fiiltering magic-T.

2021-06-24 PIER Letters Vol. 98, 113-120, 2021. doi:10.2528/PIERL21051205

Plastronic Circular Line Matched Dipole Antenna

Gildas Bengloan, Anne Chousseaud, Bruno Froppier, Jacques Girard, Marc Brunet, and Eduardo Motta Cruz

A compact 3-D, circular line matched dipole (CLMD) antenna is presented in this paper. The realization of the antenna is based on Laser Direct Structuring (LDS) plastronic technology, enabling metallization on plastic parts. Cylindrical holder is chosen to carry the dipole, which implies high bending constraints on the antenna. Miniaturization of the radiating element is obtained by an effective use of 3-D space, resulting in a very low profile length dimensions of 0.14λ × 0.14λ × 0.05λ operating at 868 MHz. Specific attention is paid to the input impedance change due to conformation. An equivalent circuit model is proposed to take into account the conformation and design the matching line. Both simulated and measured results demonstrate good performances, with a 30 MHz bandwidth (i.e., a relative bandwidth of 3.5% with S11 < -10 dB) around the working frequency. The LDS prototype achieves a maximum gain of 1.2 dBi with a quasi-omnidirectional radiation pattern. This compact and conformed design presents a real interest for pervasive highly integrated ISM band IoT sensors.

2021-06-22 PIER Letters Vol. 98, 105-111, 2021. doi:10.2528/PIERL21051207

Surface Mounted Microstrip Antenna Using Ball Grid Array Packaging for mmWave Systems Integration

Xi Wang, Xiubo Liu, Wei Zhang, Dongning Hao, and Yanyan Liu

In this letter, two cost-effective surface-mount patch antenna elements for millimeter-wave (mmWave) systems using ball grid array (BGA) packaging are presented. A single-layer substrate based on FR4 is used to meet the low-cost requirements. The BGA packaging makes the proposed antenna element compact and easy to integrate. A U-slot is added to the patch to improve the impedance bandwidth of the patch antenna, and a vertical transition is designed to transmit the excitation signal by using a plated through-hole (PTH). The design process of the antenna is illustrated in detail. The antenna prototype has been simulated, fabricated, and measured to validate the design. The size of the fabricated prototype is 5 mm × 5 mm × 1.3 mm, which is very suitable for integration into a mmWave system.

2021-06-22 PIER Letters Vol. 98, 95-103, 2021. doi:10.2528/PIERL21051203

A Low-F/D Wideband Transmitarray Antenna

Yan-Fang Liu, Lin Peng, Bo Wang, Wei-Sheng Yu, Tian-Cheng Zheng, and Xing Jiang

In this paper, a wide 3-dB gain bandwidth transmitarray (TA) antenna with low focal length to diameter ratio (F/D) is presented. The TA comprises four identical metasurface layers, and the metasurfaces are printed on thin dielectric substrates, which are separated by air gaps. The unit cells of the metasurfaces are constructed by etching slots on the metal layers, which include a serrated crevice and two disjunct slots. The F/D of the TA is designed as 0.48 to accommodate the applications required low profiles. A TA is constructed by arranging high transmission elements at the center and the other elements in the external of the aperture. A transmitarray antenna (TAA) operating at 9~13 GHz is designed by applying a horn antenna to the TA, which achieves a measured 1-dB gain bandwidth of 10.5% (3-dB gain bandwidth of 23.3% and measured maximum gain of 22.48 dBi at 10.5 GHz) and a maximum measured aperture efficiency of 38.4%. Compared to the reported works, the proposed TA has outstanding F/D and wide 3-dB gain bandwidth.

2021-06-21 PIER Letters Vol. 98, 85-94, 2021. doi:10.2528/PIERL21051107

Design of Low-Profile and Safe Low SAR Tri-Band Textile EBG-Based Antenna for IoT Applications

Wissem El May, Imen Sfar, Jean Marc Ribero, and Lotfi Osman

A coplanar tri-band wearable antenna combined with an electromagnetic bandgap (EBG) structure is described for sub-6 GHz 5G and wireless local area network (WLAN) applications. The proposed antenna is fully implemented in textile materials thus offering a robust, compact, and discreet solution to meet the requirements of wearable applications. The addition of the EBG structure increases the textile antenna performance in terms of radiation patterns in the presence of the human body. The experimental results show that the proposed design exhibits tolerance to various bending conditions as well as loading by body tissues. In addition, to ensure the safety of the design for human health, the values of the specific absorption rate (SAR) have been reduced by more than 95%, which complies with the international standard. This design could thus be considered as a good candidate for IoT applications compared to the current state of the art while having a tri-band behavior and smaller volume.

2021-06-18 PIER Letters Vol. 98, 75-84, 2021. doi:10.2528/PIERL21032516

Design of Tri-Band Hybrid Dielectric Resonator Antenna for Wireless Applications

Lavuri Nageswara Rao, Govardhani Immadi, and Madhavareddy Venkata Narayana

In this article, a compact dielectric resonator antenna (DRA) with partial ground plane for wireless applications is examined. The exhibited structure is fed by a microstrip line. To demonstrate the functionality of a tri-band, a circular dielectric resonator antenna with concentric circular rings is created. The developed antenna parametric analysis has been performed on HFSS platform. The configured design operates at three frequency bands, i.e. 1.98-2.59 GHz (ISM), 3.24-3.85 GHz (Wi-max), and 4.85-5.85 GHz (WLAN), with the fractional bandwidths of 26.6%, 20.4%, and 18.67%, respectively. The customized concentric rings are placed onto the substrate to reinforce the antenna appearance and also miniaturize the size. The measured outcomes are strongly in accordance with the simulated results. The designed model can be customized with certain attributes to wireless applications.

2021-06-16 PIER Letters Vol. 98, 69-74, 2021. doi:10.2528/PIERL21051601

Compact LTCC Filter with 7th-Order Harmonics Suppression for 5G N77 Band Applications

Lan Luo, Huanyan Tie, Qiang Ma, and Bo Zhou

A compact dual-mode band-pass filter (BPF) with 7th-order harmonics suppression is proposed. The proposed dual-mode BPF is designed using a three-section stepped-impedance-variable feeding line (SIVFL) and a square resonator. The high-order harmonics suppression is achieved by the SIVFL structures, and the size reduction is achieved using meandered lines and a resonator with two degenerate modes. The proposed BPF has a wide stopband up to 7th-order harmonics and a compact size of only 7 x 7 x 0.3 mm. The proposed BPF is suitable for the fifth-generation (5G) N77 band applications due to its working frequency, compact size, and good performance. Comparison and discussion are implemented as well.

2021-06-15 PIER Letters Vol. 98, 61-68, 2021. doi:10.2528/PIERL21042901

Bandpass Filters Based SIW Square Cavity with Novel Feeding and Coupling Schemes

Bo Yin, Qianqian Huang, and Xiangyu Shi

This paper presents two novel different feeding and coupling schemes to solve the problem of generating transmission zeros (TZ) in lower stopband and their applications to design single-band filters. The designed two filters are based on substrate integrated waveguide (SIW) square cavity with orthogonal ports. In the design of Filter A, two L-shaped stubs are introduced to form an addition coupling path between two ports, which cause the generation of one TZ. Other two TZs are formed due to the resonance characteristics of L-shaped stubs and ports offset. Two metal vias are used to adjust center frequency slightly. In the design of Filter B, other two stubs are designed to form two additional coupling paths, thus forming a total of three coupling paths with the original path. Two TZs are obtained by utilizing the phase difference between different paths, and one TZ is generated for the resonance characteristics of the proposed stub 3. Simultaneously, an L-shaped slot is used to adjust center frequency. Both designed filters use the coplanar waveguide (CPW) structure to control bandwidth. Two filters are set to operate at 14.4 GHz with bandwidth of 800 MHz. Both filters are fabricated and measured. The simulation results of two filters are in good agreement with the measured ones.

2021-06-07 PIER Letters Vol. 98, 55-60, 2021. doi:10.2528/PIERL21050203

Surface-Mount PIFA Using Ball Grid Array Packaging for 5G mmWave

Xi Wang, Xiubo Liu, Wei Zhang, Dongning Hao, and Yanyan Liu

In this letter, a surface-mount planar inverted-F antenna (PIFA) is proposed for the 5G mmWave system using ball grid array packaging (BGA). To meet the requirement of cost-effectiveness, the proposed antenna element is designed on a single FR4 layer to achieve low cost. To achieve a compact size, the BGA packaging is used on the proposed antenna element. Finally, the size of the antenna prototype is only 4.5 mm × 4.5 mm × 1.3 mm. Besides, the surface-mount feature allows the proposed antenna to be integrated with other devices in the same system package. The simulation and measurement results are discussed in detail. The measurement results show that the impedance bandwidth of - 10 dB is 15.3 % (24.7-29.6 GHz), and the peak gain is 5.85 dBi at 28 GHz. The proposed PIFA can be used in the 5G NR bands N257 (26.5-29.5 GHz), N258 (24.25-27.5 GHz), and N261 (27.5-28.35 GHz).

2021-06-02 PIER Letters Vol. 98, 49-54, 2021. doi:10.2528/PIERL21031303

Synthesis of in-Line Fully Canonical Response Filters with Frequency-Variant Couplings

Angel Triano and Pedro de Paco

A direct synthesis approach is presented to realize in-line topology filters with adjacent frequency-variant couplings implementing a transmission response with the same number of finite transmission zeros as poles. The proposed method starts with an N-order fully canonical filter response definition. A non-resonant node (NRN) is incorporated into the transversal network to make room for an extra coupling, and as a consequence of the extended similarity transformation applied, the NRN is transformed into a resonant node. The result is a network with N poles and N transmission zeros implemented with N+1 resonant nodes and N FVC, being able to describe a fully canonical response with an inline network without cross couplings.

2021-05-30 PIER Letters Vol. 98, 41-48, 2021. doi:10.2528/PIERL21031108

Gain Enhancement Using Modified Circular Loop FSS Loaded with Slot Antenna for Sub-6 GHz 5G Application

Anubhav Kumar, Asok De, and Rakesh Kumar Jain

In this paper, a modified circular loop FSS with a slot antenna is proposed for sub-6 GHz 5G applications. The proposed FSS reduces the resonant frequency to towards lower bands of conventional circular FSS without change in its size. The operating bandwidth (-10 dB) of proposed antenna loaded with polarization insensitive single-layer FSS varies from 3.6 GHz to 6.1 GHz with an average gain of 7-7.5 dB and a maximum realized gain of 7.87 dB. An FSS superstrate is loaded onto a slot antenna to increase the realized gain of 4 dB, where the FSS shows desirable electromagnetic wave reflection characteristics over operating bandwidth and can be used in 5G sub-6 GHz band applications.

2021-05-29 PIER Letters Vol. 98, 33-40, 2021. doi:10.2528/PIERL21041701

A Low-Loss Dual-Band Negative Group Delay Circuit with Flexible Design

Yuwei Meng, Zhongbao Wang, Yu Bai, Shao-Jun Fang, and Hongmei Liu

A low-loss dual-band negative group delay circuit (NGDC) with a flexible design is proposed. The proposed NGDC consists of a transmission line coupled asymmetrically with two step-impedance open-loop resonators. The negative group delay (NGD) times and center frequencies of the lower and upper bands can be tuned independently. To verify the design concept, two dual-band NGDC prototypes I and II are fabricated and measured. The measured NGD times of prototype I are -4.9 ns and -4.8 ns at the center frequencies of 1.949 GHz and 2.054 GHz, respectively. The insertion loss is lower than 2.7 dB and the return loss larger than 11.2 dB in both NGD bands. For prototype II, the NGD times at 1.949 GHz and 2.086 GHz are -4.7 ns and -3.3 ns, respectively. The measured insertion loss is better than 2.4 dB with the return loss larger than 11.9 dB.

2021-05-19 PIER Letters Vol. 98, 25-31, 2021. doi:10.2528/PIERL21040207

Optimization of the Wheeler Cap Technique for Efficiency Measurement of RFID Antennas Matched to Complex Loads

Nadeen Rishani, Jean-Marc Laheurte, Stephane Protat, and Raed Shubair

This paper proposes an improved mathematical formulation of Johnston's approach to measure the radiation efficiency of an antenna, based on the Wheeler Cap (WC) technique. The proposed modifications allow the measurement of the radiation efficiency of small antennas matched to complex loads implemented on Radio Frequency IDentification (RFID) tags. The studied structure is a low-cost, silver-printed, differentially-fed RFID dipole antenna. The antenna is printed on a flexible PET (polyethylene terephthalate) paper that is conformable on various objects. Link budget measurements validate the accuracy of the formulation, which can be applied to any dipole antenna matched to an RFID chip with a complex input impedance.

2021-05-17 PIER Letters Vol. 98, 17-24, 2021. doi:10.2528/PIERL21022501

Orbital Angular Momentum Orthogonality Based Crosstalk Reduction

Unaiza Tariq, Hiva Shahoei, Guang Yang, and Duncan L. MacFarlane

We report a reduction in crosstalk between a transmitting antenna and an adjacent receiving antenna due to the use of radiation patterns with different orbital angular momentum (OAM). This crosstalk reduction is based on the orthogonality between different OAM modes. To generate OAM beams, patch array antennas are designed using High frequency simulation software (HFSS). The designed antennas are fabricated and characterized. An experiment is carried out to determine the amount of crosstalk reduction achieved due to the OAM nature of the signals transmitted. The variation of this crosstalk reduction with the distance between the transmitting and receiving antennas is also studied. The results obtained are verified through theoretical analysis using simulations in HFSS. A maximum theoretical crosstalk reduction of 3.6 dB has been obtained, and a crosstalk reduction of 2.6 dB has been realized experimentally. The results may benefit full-duplex communication links.

2021-04-29 PIER Letters Vol. 98, 9-16, 2021. doi:10.2528/PIERL21022603

Mechanisms and Influence Factors of Dynamic Behavior of Water Droplets on the Composite Insulator Surface Under AC Electric Field

Wen Cao, Hua Feng, Hao Xue, Wei Shen, Long Zhao, and Hao Yang

The deformation behaviors of a droplet on surface of composite insulator can strengthen local electric field, which could finally lead to flashover. Both experiments and numerical simulations for dynamic behaviors of a droplet on the surface of a composite insulator under applied AC voltage are investigated in this paper. Experiments are performed to study the influences of water droplet's volume and conductivity on the dynamic behaviors. Two critical parameters are proposed to describe the morphological change process of water droplet, and it is shown that the process can be divided into three stages. Moreover, these motion laws are explained by establishing theoretical factors and physical influence models. In addition, we perform computer simulation to study the dynamic behaviors of a water droplet under AC field, and the findings are in good consistency with our experimental results, proving the rationality of the theoretical physical model. It is found that the vibration frequency of droplet changes regularly with at different stages under the AC electric field.

2021-04-21 PIER Letters Vol. 98, 1-8, 2021. doi:10.2528/PIERL21032401

A Dual-Band 8-Element 4/5G Printed MIMO Antenna Using Open Slot Radiators

Mohamed Morsy

This paper presents a dual-band eight-element multiple-input multiple-output (MIMO) antenna for 5G applications. The 8-element antenna is formed into two 4×4 MIMO systems that operate at 2500-2600 MHz and 1800-2200 MHz bands. The antenna elements are mounted along the perimeter of a rectangular ground plane with a total size of 110 × 80 mm2 and are printed on both sides of a low-profile PCB material. Elements radiate through open rectangular slots etched on the antenna's ground conductor. The open slots are excited by T-shaped microstrip lines fed by 50-Ω coaxial connectors. The size of the ground plane's slots, and the T-shaped radiators control the resonance of the antenna's elements. The proposed design employs orthogonal elements to mitigate mutual coupling. The isolation between ports is less than -10 dB. The radiation efficiency ranges from 40% to 65% across operating frequency bands.