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2022-06-19 PIER C Vol. 120, 275-291, 2022. doi:10.2528/PIERC22040202

Research on Resonant Wireless Energy Supply Double-Layer Receiving Coupler for Portable Electronic Equipment

Weihua Chen, Kun Qian, and Xiaoheng Yan

In order to reduce the electromagnetic interference on the receiving side of electronic equipment in the process of wireless energy supply, a magnetic coupling resonant wireless energy supply system for portable electronic equipment with double-layer PCB coil structure is designed under the condition of 100 kHz. Firstly, the circuit principle is analyzed, and the compensation circuit model of LCC-P is established; Then, the coil model is constructed and optimized, the effects of turns and wire diameter on the coil self inductance and coupling coefficient are analyzed. The best parameters are selected, and the magnetic field distributions of the three coil structures at different distances are simulated and studied. Finally, an experimental platform is built to study the transmission efficiencies of different receiving coils at different spacings. The magnetic field intensities at different positions are compared to further verify the performance of double-layer coils. The experimental results show that when the coil spacing is in the range of 4-16 mm, the efficiency can reach 40%-71%. The central magnetic field of the coil is increased by 16%, and the external magnetic field is reduced by more than 20%. The temperature rise of one hour charging is 5.34˚C, which is only 0.78˚C higher than that of other coils

2022-06-14 PIER C Vol. 120, 265-274, 2022. doi:10.2528/PIERC22040104

Design and Electromagnetic Loss Analysis of High Speed Permanent Magnet Synchronous Motor for an Air Compressor

Xiaojun Ren, Ming Feng, and Jinliang Liu

Air compressors are widely used in various industrial fields. The motor of air compressor requires high power and high speed. This paper focuses on the structural design and loss analysis method of highspeed permanent magnet synchronous motor in air compressor. The structure of motor is designed. The key parameters are calculated. The influence of structural parameters on motor loss is analyzed. The analytical and design results are verified by finite element method (FEM). Finally, the prototype of motor has been manufactured. The performance of the motor is verified on the prototype.

2022-06-13 PIER C Vol. 120, 253-263, 2022. doi:10.2528/PIERC22040103

Model Predictive Control of Permanent Magnet Synchronous Motor Based on Parameter Identification and Dead Time Compensation

Xin Liu, Yanfei Pan, Lin Wang, Jian Xu, Yilin Zhu, and Zhongshu Li

A model predictive control method for permanent magnet synchronous motor based on parameter identification and dead time compensation is proposed to solve the problems of poor parameter robustness and large current errors. In this method, the prediction model is firstly established based on the mathematical model of the permanent magnet synchronous motor. After that, the current error caused by the parameter change in the prediction model and the current harmonics caused by the dead time effect are basically analyzed theoretically. Then, the adaptive linear neural network algorithm is proposed to identify the motor parameters and applied to the prediction model, and the harmonic components are filtered out using the adaptive linear neural network algorithm. The recursive least squares algorithm is used to quickly update the system weights to improve the dead time compensation control effect. Finally, the effectiveness and correctness of the proposed algorithm are verified on the experimental platform. The experimental results show that the predictive control method of permanent magnet synchronous motor model based on parameter identification and dead time compensation can effectively reduce the current error of the control system and accelerate the dynamic response of the speed.

2022-06-11 PIER C Vol. 120, 243-252, 2022. doi:10.2528/PIERC22031603

Design of a Wideband ME Dipole Antenna with Wide Beamwidth

Haoyu Fang, Jianfeng Sun, Hao Zhang, Yiqing Liu, and Zhuopeng Wang

A wideband and widebeam magneto-electric (ME) dipole antenna is designed in this paper. Based on the conventional magneto-electric dipole antenna, a bent vertical metal plate is added to the electric dipole, and the impedance bandwidth (IBW) and beamwidth of the antenna are widened together. Inclined metal walls are added on both sides of the metal ground to improve the gain at high frequency and make the antenna gain more steady in the operating bandwidth. To further broaden the IBW of the antenna, the conventional Γ-shaped feed is changed into a branch structure. The IBW of the finally designed antenna reaches 56.8% (2.91-5.22 GHz). In the whole operational bandwidth, the radiation pattern in E-plane realizes the half power beam width (HPBW) of more than 110°, and the H-plane radiation pattern realizes the HPBW of more than 160°. The maximum width of E-plane HPBW is 175°, and the maximum width of H-plane HPBW is 229°.

2022-06-07 PIER C Vol. 120, 223-241, 2022. doi:10.2528/PIERC22041401

Optimal Design of a Circularly Polarized Antenna for LTE Bands 42/43 Applications

Saja Alaa Gheni and Dhirgham Kamal Naji

In this paper, an optimized circularly polarized (CP) antenna is proposed for operating in the LTE bands 42/43 applications. This CP antenna comprises three sections, the meander-line and L-shaped strip structures modeled on the front side of a Roger 3003 substrate, and on the back side a rotated H-shaped ground plane is printed. In order to further increase the antenna common bandwidth (CBW), that is the voltage standing wave ratio bandwidth (VRBW) and axial ratio bandwidth (ARBW), an offset-fed line on the front side and a shorting pinare used. A feasible solution of the optimized CP antenna with compact size is achieved by applying an optimization design methodology with a fitness function that takes into account the antenna performance parameters, CBW or both the VRBW and ARBW in addition to the realized gain (RG). Two programs are operating in synchronous fashion for finding the optimal geometric antenna parameters, a particle swarm optimization (PSO) for implementing the fitness function in MATLAB and a CST MWS simulator tool for extracting the antenna performance parameters. The optimized antennas without and with shorting pin are obtained with a broadest CBW and feature of CP operation and an acceptable RG across the desired LTE 42 (3.4-3.6 GHz) and LTE 42/43 (3.4-3.8 GHz) band, respectively. The proposed two designed antennas, with and without shorting pin, are fabricated, and the measured results are in good agreement with the simulated ones. From measured results, a -10 dB-S11 impedance bandwidth (IBW) of 220 MHz (3.38-3.60 GHz) and 460 MHz (3.37-3.83 GHz), a 3-dB ARBW of 200 MHz (3.4-3.6 GHz) and 390 MHz (3.42-3.81 GHz) with respective maximum RG of 2.26 and 2.39 dBic are exhibited by the antennas without and with pin, respectively. The obtained 3-dB ARBWs and -10-dB IBWs make the proposed antennas entirely cover the LTE 42 or LTE 42/43 frequency bands.

2022-06-04 PIER C Vol. 120, 209-222, 2022. doi:10.2528/PIERC22041402

Design and Analysis of Multiband Fractal Reconfigurable Antenna Using PIN Diodes for Smart Wireless Communications

Iqra Masroor, Jamshed Ansari, Amrees Pandey, and Piyush Kumar Mishra

Fractal and reconfigurable antennas are the need of modern wireless communication systems that operate under dynamic scenarios catering to the diversified needs of modern wireless applications. In this dissemination, a novel multiband Fractal Reconfigurable Antenna (FRA) has been presented and discussed using two RF PIN diodes as switching elements for electronic reconfiguration. It is analyzed using equivalent circuit concept and investigated in terms of various antenna performance parameters. The proposed FRA can operate in various frequency bands resonating at four different frequencies with switchable bandwidth and gain. The highest gain is observed to be about 8.37 dB at 9.68 GHz while the highest bandwidth is about 540 MHz in the X-band. The simulation and measurement results obtained are found to be in agreement. The multiband characteristics of the proposed FRA make it useful for smart wireless communication applications in the S (2-4 GHz), C (4-8 GHz) and X (8-12 GHz) microwave bands.

2022-06-04 PIER C Vol. 120, 195-208, 2022. doi:10.2528/PIERC21110501

An Efficient Modeling Method of the Ballistic Target for Monostatic/Bistatic Observations

Zaihuan Sun, In-O Choi, Se-Won Yoon, Sang-Bin Cha, and Sang-Hong Park

This paper proposes an efficient method to simulate the micro-Doppler (MD) frequency of a ballistic warhead by considering a real flight scenario in monostatic and bistatic observations. The radar signal is difficult to obtain by changing the observation angle as the conventional electromagnetic software does obtain the reflected signal for a fixed target, so we transformed the pose of the model engaged in micro-motion in a local coordinates, to the pose on the trajectory, by constructing the transformation matrix. Then we obtained the radar signal by using the point scatterer model and the high frequency estimation method, physical optics, and compared the MD results by using the short-time Fourier transform. In simulations for various observation scenarios, MD signatures were successfully obtained, and scattering characteristics were accurately analyzed.

2022-06-03 PIER C Vol. 120, 179-193, 2022. doi:10.2528/PIERC22031707

Slotted Patch Based Multiband Antenna with Multiple DGS Effect to Suppress Cross Polarized Radiation

Rajib Kumar Dash, Puspendu Bikash Saha, and Dibyendu Ghoshal

A defected ground structure (DGS) loaded slotted patch antenna is proposed in this article to achieve multiband response with minimization of cross polar radiations in both the radiation planes. Besides, the antenna in this work achieves reduction in cross polar radiation at all its resonating bands with a simple inset feeding mechanism. Loading of identical U-shaped slots in the patch helps the antenna to achieve dual resonance characteristics and also leads to minimize the orthogonal E-field components. Along with the slotted patch, implementation of DGS results in multiple current paths leading to additional resonances in lower frequency range and also suppresses the strong leakage current in the ground plane. Moreover, three identical slots are loaded at the edges of the ground which balance the strong E-field components in opposite direction improving the reflection coefficient at the different resonating bands. The proposed antenna achieves multi-resonance characteristics operated in 2.44-2.56, 5.45-5.52, 6-6.13, 7.43-8.04, and 8.99-9.17 GHz. Minimization of orthogonal E-field components and suppression of leakage current are responsible for obtaining minimum cross polar radiation from the antenna as -39.08 and -41.01 dB in E- and H-planes, respectively.

2022-06-02 PIER C Vol. 120, 159-177, 2022. doi:10.2528/PIERC22021103

Distributed RSS-Based 2D Source Localization System in Extended Indoor Environment

Tunguturi Sridher, Achanta Dattatreya Sarma, Perumalla Naveen Kumar, and Kuruva Lakshmanna

The evolution of computing and network technologies which involve thousands of devices that are connected wirelessly to serve variety of applications in Internet-of-Things (IoT) draws significant interest in locating the indoor objects. In our paper, we focus on developing a hybrid source positioning technique with off-the-shelf hardware modules. A rectangular corridor with a multipath environment is considered in our work. For better localization accuracy, the corridor is classified into segments with threshold RSS values. Based on the measurement data segment-wise logarithmic regression models are developed, and the performance in terms of Correlation Coefficient (R2) and Root Mean Square Error (RMSE) is evaluated. For localization, basically trilateration is used. However, to overcome the adverse issues due to the indoor environment such as flip ambiguity, uncertainty in range measurements, circumscribing the circle's scenarios, two circle intersection, dynamic circle contraction, and expansion methods are used. Relevant Pseudocode algorithms are presented. The proposed hybrid method significantly improves the localization accuracy. The standard deviation of errors in x and y directions are about 16.75 cm, 66.24 cm in the first segment and 19.75 cm, 60.16 cm in the second segment. The analysis and results are useful in establishing state of the art IoT and future generation 5G networks.

2022-05-22 PIER C Vol. 120, 145-157, 2022. doi:10.2528/PIERC22030503

Effect of Temperature on the Properties of Omnidirectional Mirror One Dimensional Photonic Crystal

Olfa Nasri, Jihene Zaghdoudi, and Mounir Kanzari

In this work, we present numerical results regarding the effects of temperature on the omnidirectional photonic band gap (OPBG) of ternary 1DPC containing metal (Ag) layer or graphene layer. By periodically introducing layer metal (Ag) or graphene into 1DPC, the width of OPBG has been increased. As the temperature increases, the photonic band gap of the OPBG becomes wider. Compared to the conventional OPBG in ternary 1DPC containing Ag, the OPBG in 1DPC containing graphene with temperature T = 1000˚K is greatly broadened by 2.04 times. The theoretical basis of our study adopts the transfer matrix method TMM. In fact, these broad omnidirectional and thermally tunable OPBGs will offer many prospects for omnidirectional mirrors, temperature sensing device, optical filters, polarizer, and other optical devices.

2022-05-11 PIER C Vol. 120, 135-144, 2022. doi:10.2528/PIERC22032201

Dual-Band Dual-Polarized Slotted Coaxial Waveguide Antenna

Wei Yu, Lei Sun, Long Li, and Hong-Bing Sun

This paper presents a dual-band dual-polarized antenna including one L-band vertically polarized antenna, four C-band horizontally polarized subarrays and four C-band vertically polarized subarrays. Both the L- and C-band radiation elements are designed based on the concept of slotted coaxial waveguide antenna. The coaxial waveguide structure is in rectangular shape which is suitable for multi-element integration. And bending stripline inside the waveguide cavity plays the role of inner connector for the coaxial waveguide and exciter for radiating slots on the waveguide. Results show that impedance bandwidths of 14.9% for L-band and 5.9% for C-band are obtained with good port isolation. The antenna also exhibits good radiation performance with the low cross-polarization. The results indicate that the proposed antenna is suitable for synthetic aperture radar applications.

2022-05-10 PIER C Vol. 120, 119-133, 2022. doi:10.2528/PIERC22022402

A Novel Antipodal Vivaldi Antenna with Quad Band Notch Characteristics for UWB Applications

Vikas Kumar Rai, Mithilesh Kumar, and Shyama Prasad Chakraborty

This work presents a design and analysis of a high gain Antipodal Vivaldi Antenna (AVA) with quad band notch characteristics for Ultra-Wideband (UWB) applications. The proposed AVA is designed on a 1.2 mm FR4 substrate with dielectric constant 4.3 and loss tangent 0.025. Initially, the AVA parameters are optimized in a full wave simulator to get the required UWB performance. The UWB performance is further improved significantly by cutting a C shaped slot from the AVA flares. The C shaped slot introduces an extra resonance that widens the initial bandwidth. The band-notched filtering characteristics are achieved by - adding a Sun Shaped Slot (SSS) on the top and bottom flares of the AVA, inserting a hexagonal shaped Complimentary Split Ring Resonator (CSRR) on the ground plane of the AVA and finally by inserting vias on either side of the feed line. The first designed notch band is from 2.2-2.7 GHz, covering the Bluetooth region. The second notch band is designed from 3.3-3.6 GHz, corresponding to WiMAX applications, and the third notch band is from 4.6-5.7 GHz corresponding to the WLAN band. Finally, a notch is fashioned from 8.8-9.5 GHz, corresponding to ITU applications. The simulated and measured return loss plots show that the antenna achieves an impedance bandwidth of 1.15-14 GHz with a reflection coefficient less than -10 dB, except at the four eliminating bands. To the best of the authors knowledge, the proposed technique is novel, and it allows good narrowband rejection over the UWB regime.

2022-05-09 PIER C Vol. 120, 105-117, 2022. doi:10.2528/PIERC22031604

Wideband Diversity MIMO Antenna Design with Hexagonal Slots for 5G Smart Mobile Terminals

Hatim S. Alhaqbani, Mohammed M. Bait-Suwailam, Maged A. Aldhaeebi, and Thamer S. Almoneef

In this paper, we propose a wideband polarization diversity multiple-input multiple-output (MIMO) antenna array for 5G smart mobile devices. The proposed MIMO antenna array consists of 8-ports dual-polarized L-shaped lines that highly excite radiating slots, where the elements are placed at four-corners of a compact mobile unit of size 75×150 mm2. The uniqueness of the proposed MIMO antenna structure comes from the deployment of octagon-shaped resonant slots within the metallic ground plane, i.e. the octagonal-slots are etched from the bottom (ground) layer of the main mobile board. Due to the unique slots in the ground plane, wideband impedance has been achieved (3.38-3.8 GHz at -6-dB threshold). The proposed smart phone 8×8 diversity MIMO antenna is designed to support the spectrum of commercial sub-6 GHz 5G communications and cover the frequency range of around 3.5 GHz band with high decoupling between antenna ports. The proposed array is designed, numerically simulated, fabricated and tested. Good agreement between simulated and measured results was achieved. The MIMO antenna has a satisfactory far-field performance along with very low envelope correlation coefficient (ECC) < 0.055, high diversity of more than 9.95, and very low specific absorption rate (< 1 W/Kg for a 10-g human tissue).

2022-05-07 PIER C Vol. 120, 93-103, 2022. doi:10.2528/PIERC22031706

Minimizing Grating Lobes in Large Arrays Using Clustered Amplitude Tapers

Jafar Ramadhan Mohammed

One of the common ways to design large arrays is by designing a small subarray known as cluster and using it as a repeating element throughout a large array. In this paper, the genetic algorithm is used to optimize the clustered amplitude tapers such that the final array pattern has minimum grating lobes and controlled sidelobe level. The formulation of the synthesis problem includes the minimization of the excess magnitude of the grating lobes or peak sidelobes which are usually higher than a given allowable limit. Moreover, two clustered configurations based on increased/decreased number of elements per cluster around the array center are introduced. Correspondingly, their clustered sizes increase/decrease as they approach the center of the array. Simulation results show that the proposed method has capability to optimize clustered linear and planar arrays without noticeable appearance of undesirable grating lobes. The analysis for an array composed of 20 elements with clusters of different cluster sizes M = 10, 8, 5, 4 and different numbers of elements per cluster Ns = 2, 3, 4, 5 elements found that the complexity reductions were 50%, 60%, 75%, 80%; peak sidelobe levels were -29 dB, -23.6 dB, -21.3 dB, -19.15 dB; and the directivities were 25.53 dB, 25.64 dB, 26.33 dB, 26.32 dB, respectively.

2022-05-07 PIER C Vol. 120, 77-92, 2022. doi:10.2528/PIERC22032401

A Modified Construction Method of Blended Rolled Edge and Its Application

Yongquan Jiang, Hongcheng Yin, Chongjiang Mo, and Dewang Kong

It is of great practical value to study the blended rolled edge of reflector used in Compact Antenna Test Range (CATR). Taking a rectangular aperture reflector as the benchmark, a reflector with ideal blended rolled edge is obtained by means of parameter iterative optimization after accurately establishing the position relationship between the local and global coordinates where the blended rolled edge is located, precisely deriving the geometric equation of the main reflector zone and blended rolled edge zone in the local coordinate, and optimizing continuity condition of curvature radius. On the basis, a blended rolled edge reflector with minimum operating frequency of 0.8 GHz and quiet zone size of 2 m is designed. The simulation results show that the performance of the reflector with blended rolled edge obtained by the proposed method is better than that obtained by the traditional construction method, and the designed reflector has excellent performance. The work in this paper provides a theoretical support for the optimal design and engineering application of the blended rolled edge reflector.

2022-05-06 PIER C Vol. 120, 61-75, 2022. doi:10.2528/PIERC22012903

Efficient Indoor Wireless Monitoring of Long-Term Ill/Post Operative Patients with Implants

Samuelraj Chrysolite and Thomas Anita Jones Mary Pushpa

In the medical world, the continuous monitoring of patients having a long-term illness is mandatory. The usual monitoring systems placed around the patients are bulkier and costly. Moreover, the movement of those patients is limited as they are connected to the monitoring devices with probes. To enable the locomotion of the patients a miniaturizedimplantable antenna sensor with the dimension 2.5 x 7 x 0.25 mm3 is proposed to monitor arterial pressure. The proposed antenna sensor is fabricated and verified for its performance metrics. Radiation analysis for the implants is carried out through a metric called Specific Absorption Rate (SAR). Deviation of pressure in the patient is measured through the rate of change of resonant frequency through an external reader coil. Communication established between the Transmitter (patient with implant) and the Receiver for better monitoring is verified through field strength calculated at various locations inside the hospital rooms in order to allocate rooms for the post-operative/long term ill patients efficiently.

2022-05-06 PIER C Vol. 120, 45-60, 2022. doi:10.2528/PIERC22032003

UWB Filtenna with Reconfigurable and Sharp Dual-Band Notches for Underlay Cognitive Radio Applications

Yousif Mohsin Hasan, Abdulkareem S. Abdullah, and Falih Mahdi Alnahwi

In this paper, a compact UWB antenna with a reconfigurable and sharp dual-band notches filter to cancel the interference with some critical applications (5G WLAN, and X-band satellite downlink) is proposed for underlay cognitive radio (CR) applications. The dual notched bands are produced by coupling a pair of π-shaped resonators on both sides of the feed line and by etching a U-slot inside the feed line of the antenna. The proposed UWB filtenna in this configuration has a surface area of 22×31 mm2 and produces simulated (measured) reconfigurable notched frequencies at 5.466 GHz (5.7 GHz) and 7.578 GHz (7.44 GHz) with an impedance bandwidth of 3.024-10.87 GHz (2.825-10.74 GHz). Three PIN diodes are used to switch the presence of the dual-band notch. Two PIN diodes turn ON-OFF simultaneously (D1A & D1B) are inserted within a pair of π-shaped resonators to control the 5G WLAN band notch, and a single diode (D2) is embedded within a quarter wavelength resonator which is located inside the feed line of the antenna for controlling the X-band band notch. The simulation and measured results reveal that the proposed filtenna effectively covers UWB with controlled cancellation for the interference with the intended bands. The realized gain is 4.5 dBi through the passband except in the notched frequencies, where it is decreased to less than -11 dBi in both notch frequencies. In other words, the proposed filtenna has a very high VSWR of greater than 20 at the notched frequencies.

2022-05-05 PIER C Vol. 120, 27-44, 2022. doi:10.2528/PIERC22020402

Design of Tri-Band Textile Fractal Antenna Using Three Different Substrate Materials for Wi-Fi Applications

Asit Rajakathar Kittur and Loganathan Balaji

The purpose of this study is to embed an antenna on very thin textile materials. A rectangular Fractal Antenna is chosen for this application. This antenna radiates for three different frequencies viz. 2.4 GHz, 4.2 GHz and 5.9 GHz. The substrate materials used for three antennas are Poly Viscous, Poly Cotton and Linen which are easily available. Instead of using traditional method applying copper plate or copper layer on substrate material, a simple process of pasting carbon conductive ink on substrate materials is used. On each textile antenna above mentioned frequencies are radiated. Performance parameters of all three antennas are simulated and matched with practical results. The optimum antenna having the best result is used for Wi-Fi Applications.

2022-04-30 PIER C Vol. 120, 11-26, 2022. doi:10.2528/PIERC22022501

Design and Implementation of Wearable Antenna Textile for ISM Band

Hasri Ainun Harris, Radial Anwar, Yuyu Wahyu, Mohamad Ismail Sulaiman, Zuhanis Mansor, and Dwi Andi Nurmantris

Wearable antenna is one component needed for mid-range communication. It can be integrated into clothing, bags, or any other item worn. This paper presents the structure and performance of a wearable antenna used in place of the ESP8266 Wi-Fi module antenna in dresses. With a higher gain than 2 dBi, this replacement will provide greater signal coverage than the existing Wi-Fi antenna module. The proposed geometry utilizes rectangular patches with the inset feed method in the feedline segment, constructed using copper foil tape, 2.85 mm thick polyester as a substrate with a permittivity (εr) of 1.44, and Defected Ground Structure (DGS) technique. The operating frequency of the proposed antenna is at 2.4 GHz in ISM (Industrial, Scientific, and Medical) band. The whole process was used to optimize the structure, fabricated, and measured. As determined by simulation, the proposed antenna's return loss is -13.89 dB, whereas the measured value is -13.253 dB. The measurements scenario for the substitute and existing antenna are divided into two categories: line-of-sight (LoS) and non-line-of-sight (NLOS). Each of them experiences vertical and horizontal position of antenna. In LOS conditions, the vertical position has an average coverage of 9.84 meters more than the antenna module and the horizontal position is 13.84 meters. In NLOS conditions, the horizontal position has an average coverage of 9.22 meters more than the EP8266 antenna module, which in the vertical condition is about 17.06 meters. The obtained data successfully demonstrated that the proposed antenna could significantly increase the coverage of the ESP8266 module.

2022-05-05 PIER C Vol. 120, 1-10, 2022. doi:10.2528/PIERC22021503

A Novel Miniaturized Reconfigurable Microstrip Antenna Based Printed Metamaterial Circuitries for 5G Applications

Hayder H. Al-Khaylani, Taha Ahmed Elwi, and Abdullahi Abdu Ibrahim

A novel reconfigurable sub-6 GHz microstrip patch antenna operating at three resonant frequencies 3.6, 3.9, and 4.9 GHz is designed for 5G applications. The proposed antenna is constructed from metamaterial (MTM) array with a matching circuit printed around a printed strip line. The antenna is excited with a coplanar waveguide to achieve an excellent matching over a wide frequency band. The proposed antenna shows excellent performance in terms of S11, gain, and radiation pattern that are controlled well with two photo resistance. The proposed antenna shows different operating frequencies and radiation patterns after changing the of photo resistance status. The main antenna novelty is achieved by splitting the main lobe that tracks more than one user at same resonant frequency. Nevertheless, the main radiation lobe can be steered to the desired location by controlling the surface current motion using two varactor diodes on a matching circuit.