On this page we present some notable concepts, prototypes and theoretical results of our research. Only very brief descriptions are given, for more info please refer to publications.

Patch antenna array with enhanced impedance and radiation bandwidth

In this work, a novel design of patch antenna with two symmetrical slits and two closely spaced resonances is proposed. Novel patch antenna demonstrates a great flexibility in impedances adjustment at both resonances that is of a great importance in the design of series fed antenna arrays with a large number of radiating elements. Printed antenna with two linear arrays consisting of 16 serially fed patches is designed and fabricated. Measured results agree very well with simulations. Antenna operation frequency range is 15.6-17.3 GHz that is 10.3% of a relative bandwidth. The measured antenna gain is 19.5 dBi with a small variation of 1.2 dB within the whole operating bandwidth, sidelobe levels are below -22 dB in H-plane and -11.5 dB in E-plane. Half power beamwidth is less than 8° and 40°, in H- and E-planes, respectively. Antenna array exhibits the enhanced impedance and radiation bandwidth in comparison with similar antenna structures and is very suitable for various radar applications, notably for compact, low-cost frequency modulated continuous wave systems.

  • N. Boskovic, B. Jokanovic, M. Radovanovic, and N. S. Doncov, “Novel Ku-Band Series-Fed Patch Antenna Array With Enhanced Impedance and Radiation Bandwidth,” IEEE Transactions on Antennas and Propagation, vol. 66, no. 12, pp. 7041–7048, Dec. 2018.

Frequency Scanning Antenna

A novel design of the 1-D frequency scanning antenna array with enhanced scan sector, frequency sensitivity, and sidelobe suppression was designed and manufactured. The antenna is intended for the direct imaging radar sensors. Modified pentagonal dipoles with impedances ranging from 120 to 1070 Ω are used as radiating elements to provide the required sidelobe suppression. For the antenna design, new types of phase shifters are considered, with respect to their insertion loss, frequency band- width, phase shift, and manufacturing simplicity: the double-cell left-handed shifter and its right-handed counterpart. Four linear arrays with eight pentagonal dipoles are combined to obtain the antenna array with higher gain and narrower main beam with respect to constituent linear arrays, but with almost identical H-plane scanning properties. The proposed antenna array was manufactured, and the measured results show an increased scan sector of 55°, high frequency sensitivity of 14.25°/100 MHz, gain of 15.5–17 dBi, and low sidelobe levels of around 20 dB in the whole scanning frequency range. Measured results are in very good agreement with simulations.

  • N. Boskovic, B. Jokanovic, and M. Radovanovic, “Printed Frequency Scanning Antenna Arrays With Enhanced Frequency Sensitivity and Sidelobe Suppression,” IEEE Transactions on Antennas and Propagation, vol. 65, no. 4, pp. 1757–1764, Apr. 2017.

High-gain Microstrip Patch Array

We designed and built high gain printed antenna array consisting of 420 identical patch antennas intended for FMCW radar at Ku band. The array exhibits 3 dB-beamwidths of 2° and 10° in H and E plane, respectively, side lobe suppression better than 20 dB, gain about 30 dBi and VSWR less than 2 in the frequency range 17.1 - 17.6 GHz. Excellent antenna efficiency that is between 60 and 70 % is achieved by proper impedance matching throughout the array and by using series feeding architecture with both resonant and traveling-wave feed. Enhanced cross polarization suppression is obtained by anti-phase feeding of the upper and the lower halves of the antenna. Overall antenna dimensions are
31 λ0 × 7.5 λ0.

  • N. Boskovic, B. Jokanovic, F. Oliveri, and D. Tarchi, “High gain printed antenna array for FMCW radar at 17 GHz,” in 2015 12th International Conference on Telecommunication in Modern Satellite, Cable and Broadcasting Services (TELSIKS), 2015, pp. 164–167.

Antenna Canceller

Transmitter leakage cancellation method was proposed, based on the antenna image impedance, i.e. the passive network synthesized to replicate the antenna impedance in the band of interest. The concept is verified for the patch antenna array operating in the Ku band, where the achieved isolation is measured to be better than 35 dB in the 17-17.4 GHz range. This method can provide great benefit for single antenna CW radar applications.

  • V. Milosevic, M. Radovanovic, B. Jokanovic, O. Boric-Lubecke, and V. M. Lubecke, “Tx leakage cancellation using antenna image impedance for CW radar applications,” in 2016 46th European Microwave Conference (EuMC), 2016, pp. 425–428.

ENZ Waveguide

Tuning Resonances in ENZ Waveguide

We presented novel methods for both simultaneous and separate tuning of the ENZ waveguide resonant frequencies using short slots. We investigate the influence of slot offset in longitudinal slots and slot angle in inclined slot on frequency tuning of the ZOR and FP resonances, respectively. Two longitudinal slots cut at the channel inputs can tune both the ZOR and FP resonances toward lower frequencies. Interesting results are obtained if a single slot is placed in the middle of the channel. Namely, by keeping the slot in the longitudinal form one can manipulate the position of the tunneling frequency merely by changing the slot offset.

In addition, if the slot is rotated with respect to the channel centerline, only the position of the FP resonance is changed. It is shown that the longitudinal offset slot can be represented using an equivalent shunt capacitor, while the rotated slot can be represented using an equivalent series inductor. Based on the extracted equivalent capacitance of the tuning slots, we proposed closed-form expressions that predict very precisely the longitudinal slot capacitance versus frequency for different slot offsets.

ENZ channel with two longitudinal slots
ENZ channel with single longitudinal slot
ENZ channel with a centered inclined slot
  • N. Vojnovic, B. Jokanovic, M. Radovanovic, F. Medina, and F. Mesa, “Modeling of Nonresonant Longitudinal and Inclined Slots for Resonance Tuning in ENZ Waveguide Structures,” IEEE Transactions on Antennas and Propagation, vol. 63, no. 11, pp. 5107–5113, Nov. 2015.

ENZ Filters

Third Order Dual-Band Filter

We presented a novel design of the third order dual band filter operating in the frequency band 10-15 GHz. The filter consists of two rectangular cavities filled with foam dielectric and connected by an ultra-thin waveguide channel, which mimics the epsilon-near-zero (ENZ) metamaterial. Each resonator is designed to support two propagating modes - one per each passband. By changing the filter dimensions for which we have derived analytical expressions, it is possible to change the center frequency of both passbands, their fractional bandwidths and the position of the transmission zero between passbands.

  • M. Radovanovic and B. Jokanovic, “Dual-Band Filter Inspired by ENZ Waveguide,” IEEE Microwave and Wireless Components Letters, vol. 27, no. 6, pp. 554–556, Jun. 2017.

Tunable ENZ Filter

A novel tunable filter based on ENZ waveguide technology is presented and discussed. This kind of filter utilizes the possibility of independent tuning of two types of resonances that occur in ENZ waveguides using short slot cuts in the ENZ channels. By forming a dual-channel configuration, a second-order bandpass filter can be obtained using zero-order-resonance (ZOR) from one channel and Fabry-Perot (FP) resonance from the other one (whose frequency is slightly different from ZOR). Both resonances can be simultaneously and equally tuned by changing the respective slots’ lengths. The maximum observed passband shift is 900 MHz or 8.3%. During filter tuning, 3 dB-bandwidth varies between 330 MHz (3.4%) and 470 MHz (4.4%) as the length of the tuning slots decreases. Maximum insertion loss observed is 1.8 dB.

  • N. Vojnovic, B. Jokanovic, M. Radovanovic, and F. Mesa, “Tunable second-order bandpass filter based on dual ENZ waveguide,” in 2015 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), 2015, pp. 316–318.

Reconfigurable Multiband Filter

Reconfigurable composite triple split-ring resonator filter was designed and built. Reconfigurability is achieved by means of the de-tuning technique that enables obtaining different dual-band and single-band composite resonators from one triple-band topology. Seven different configurations are possible: one triple-band, three dual-band and three single-band. PIN diodes are used as switching elements, which are placed on the vertical branches of split-ring resonators so that the filter insertion loss does not increase. Measurements showed excellent agreement with the theory.

  • M. Ninic, B. Jokanovic, and P. Meyer, “Reconfigurable Multi-State Composite Split-Ring Resonators,” IEEE Microwave and Wireless Components Letters, vol. 26, no. 4, pp. 267–269, Apr. 2016.

Bianisotropic Effective Parameters

To model asymmetric metamaterial transmission lines, bianisotropic effective medium was used. Corresponding parameter retrieval procedure was developed, and validity was confirmed by performing “reverse” procedure, i.e. by simulating effective medium slab and comparing the scattering data.

  • V. Milosevic, B. Jokanovic, and R. Bojanic, “Effective Electromagnetic Parameters of Metamaterial Transmission Line Loaded With Asymmetric Unit Cells,” IEEE Transactions on Microwave Theory and Techniques, vol. 61, no. 8, pp. 2761–2772, Aug. 2013.

More to come…