Transfer Learning Based Rapid Design of Frequency and Dielectric Agile Antennas

In this paper, a frequency agile Vivaldi antenna with enhanced gain is presented. By using PIN diodes four narrowband modes and UWB mode can be selected. The agility of the antenna is attained by switching of three pairs of circular slots which are carefully printed in the ground plane of the Vivaldi antenna. In order to improve the gain of the Vivaldi antenna a dielectric director with elliptical shape and with 10.2 of permittivity is coupled to the antenna aperture. An elevated gain about 11 dB is attained at different frequencies. This antenna is an excellent answer for multi wireless applications needing UWB and frequency agile antennas with ameliorated gain such as cognitive radio.

The design of a frequency agile microstrip patch antenna is described that is readily interfaced with differential RF transceivers. By integrating three pairs of varactor diodes with the patch antenna, and tuning them in unison, frequency tuning ratios approaching 2 are possible with the design. This is made possible by the intrinsically broadband nature of the differential feeding scheme used. An intuitive equivalent circuit for predicting the port characteristics of the antenna is presented. Moreover, the circuit is shown to be highly accurate in predicting losses produced by the varactor diodes and the consequent radiation efficiency of the antenna. To the best of the authors' knowledge, this is the first time a detailed analysis of the effect of varactor diode losses has been undertaken in frequency agile antennas using an equivalent circuit. The equivalent circuit model is subsequently validated using full-wave simulations and experimental measurements of an antenna operating in the 2-4 GHz range.

Multiplexing and Multiple access technologies are becoming vital components for high-performance wireless communication system. Whereas multiplexing techniques employing either multiple antennas or multiband/wideband antennas for multiplexing are commonly used, these techniques have inherent drawbacks. A feasible solution to this is to employ frequency reconfigurable or frequency agile antennas. This approach has advantages from both multiple antenna and multiband/wideband antenna designs. In this paper, a hardware implementation of a proposed biasing and control circuit/system for wireless multiplexing that utilizes a frequency reconfigurable or frequency agile antenna is reported. The device comprises a microcontroller, DAC, CMOS oscillator, power module and a USB interface for communication with a custom-built software installed on a PC. The device has functions for control, digital signal processing and de-multiplexing. The device is fed with an input multiplexed signal, and the de-multiplexed output signals are extracted and displayed on the graphical user interface of the software. Due to the re-configurability and programmability of the device, it presents a flexible, cost effective solution for a variety of real-world applications.

A new techniques for designing the frequency agile annular ring microstrip antenna (ARMSA) is presented. The frequency agility is achieved by loading the MOS capacitor on annular ring microstrip antenna. Instead of controlling the resonance frequency by changing the radii of annular ring microstrip antenna, it is also possible by means of changing the gate bias voltage of MOS capacitor without altering the radii of annular ring microstrip antenna. The investigations based on cavity model are carried out for the various thickness of oxide (Si3N4) layer from 100 Å to 400 Å. It is found that the maximum frequency agility 51.56% (1.65 GHz) is obtained for 100 Å and minimum frequency agility 30.31% (0.97 GHz) is obtained for 400 Å.

A dual polarized high gain dielectric lens antenna with frequency agility from 20.8 GHz to 25.4 GHz is proposed. A plano-convex dielectric lens is used to focus the beam from the patch antenna in the forward direction resulting in higher realized gain. Co-pol and cross-pol separation of 15 dB for both polarizations is reported in the forward direction. In this antenna design, variable capacitors are implemented along the four corners of the patch to tune the operational frequency in the K-band while still maintaining the radiation pattern symmetry with respect to both the feeding ports.

A frequency agile antenna is proposed with its ground plane having a semicircular shaped slot which is capable of switching the frequency to different bands, one at a time, in the wide frequency range of 5.33 GHz to 9.90 GHz. To achieve frequency agility, switching of six RF PIN diodes which are placed along the slot length is done in various combinations. Frequency tuning ratio of about 1.85 : 1 can be achieved using this design. Results such as return losses, gain, bandwidth, and radiation patterns are presented in this paper.

In this paper, a compact frequency and polarization agile patch antenna is presented. The antenna comprises a square patch with truncated corners along with a triangular slot etched at the center of the patch. Pin diodes are used to bridge the gap between the truncated corners and center triangular region with a radiating square patch. By appropriately biasing the pin diodes the antenna achieves frequency and polarization diversity. The antenna achieves five distinct states with three linear polarization (LP) states operating at three different frequencies and two circular polarization (LHCP/RHCP) states operating at the same frequency. The antenna gives a −10 dB impedance bandwidth of 95 MHz (1.825–1.92 GHz) in the GSM band for LP state 1, 115 MHz (2.365–2.48 GHz) in the ISM band for LP state 2, 145 MHz (2.08–2.225 GHz) in UMTS band for LP state 3, 100 MHz (2.1–2.2 GHz) UMTS band for CP state 4 and 5. The antenna attains a measured peak gain of ∼4.8 dBi at LP states and ∼4.54 dBi at CP states in its operating band.

This paper presents a frequency and polarization reconfigurable UHF RFID patch antenna based on a switchable feeding network. For best integration of the antenna, its size and ground plane are much smaller with respect to the canonical patch antenna design, however the proposed design is able to cover the EU and US frequency bands of the RFID standard. State-of-the-art CMOS switches are employed as key element for selecting the desired polarization and proper matching network. The switches provide also a simple solution for high power applications in contrast to concepts based on PIN diodes or varactors. Simulated results have shown good performance. Considering its flexible and inexpensive structure, the proposed system is a promising alternative to aperture tuning and circular polarized antenna approaches.

Microstrip patch antennas mainly draw attention to low-power transmitting and receiving applications. These antennas consist of a metal patch (rectangular, square, or some other shape) on a thin layer of dielectric/ferrite (called a substrate) on a ground plane. Microstrip antennas have matured considerably during the past three decades, and many of their limitations have been overcome. As the size of communication devices is decreasing day by day, the demand for miniaturized patch antennas is growing. Many methods of reducing the size of antennas have been developed in the past two decades. The recent trend in this direction is to use fractal geometry. The design of an antenna for a specific resonant frequency requires the calculation of the optimal value of various dimensions. This is a hard task for fractal antennas because the accurate mathematical formulas leading to exact solutions do not exist for the analysis and design of these antennas. The use of bio-inspired computing techniques is gaining momentum in antenna design and analysis due to rapid growth in the computational processing power, and the main techniques are Artificial Neural Network (ANN), Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Bacterial Foraging Optimization (BFO), and Swine Influenza Model-based Optimization (SIMBO), etc. In the area of antenna design, the ANNs are employed to model the relationship between the physical and electromagnetic parameters. The trained ANNs are effectively used for the analysis and design of various types of antennas. Bio-inspired optimization techniques have been used by researchers to calculate the optimal parameters of various patch antennas and for the size optimization of antennas. Also, the hybrids of ANN and optimization techniques are proposed as effective algorithms for many applications, especially when the expressions for relating the input and output variables are not available. The presented research has addressed these recent topics by designing miniaturized fractal antennas using bio-inspired computing techniques for various low-power applications, thus, providing costeffective and efficient solutions.

Analysis of equivalent antenna based on FDTD method

In order to aid in the design of frequency agile antennas used for beam scanning purposes a design method based on dispersion-like frequency diagrams is proposed in this paper. This method results from a reinterpretation of the workings of both slotted waveguide antennas and leaky wave antennas. In this way it is shown that antennas based on periodic structures can be described in a general manner by expressing the phase difference between antenna elements in terms of a frequency dependent and a frequency independent component which may have a different periodicity as that of typical beam scanning antennas. In consequence, based on this methodology it is possible to predict the behavior of beam scanning antenna arrays based on any type of radiating elements, by independently adjusting the periodicity of the radiating elements and the phase delay between them.

Frequency agile antennas based on aluminum nitride ceramics

This paper introduces the design of a new frequency-reconfigurable ultra-high frequency radio frequency identification (UHF RFID) antenna, demonstrating an innovative approach that enables dynamic adjustment of its resonance frequency. The proposed antenna design features a central dipole structure, enhanced by two hexagonal split-ring resonators (H-SRR) at each end. A T-match network is integrated into the center of the dipole, which is essential for achieving impedance matching between the antenna and the Alien Gen2 H4 RFID microchip. The antenna is designed using a Rogers 4350B substrate, a high-performance dielectric material ideal for RFID applications. With dimensions of 68×32.6×1.524 mm3, the compact antenna maintains full UHF band (860 MHz to 930 MHz) coverage compliant with International Telecommunications Union (ITU) RFID standards. This ensures that the antenna can be used in different regions around the world, offering broad compatibility with various RFID systems. The antenna's frequency reconfigurability is achieved through the integration of localized capacitors with variable values, which plays a key role in enabling precise adjustments to the antenna's center frequency across the entire UHF band. Extensive simulation results validate the effectiveness of this reconfigurable design, demonstrating that the antenna can dynamically adjust its frequency while maintaining excellent performance metrics, including impedance matching, radiation efficiency, and bandwidth. This makes the proposed antenna an ideal choice for modern RFID applications.

In the current work we examine the application of Nematic Liquid Crystals (N-LCs) to frequency-agile antennas. A patch antenna design with a liquid crystal base is proposed. N-LCs are anisotropic and their electrical properties are determined by the macroscopic orientation of their molecules (director tilt-angle). However, these depend on the applied electric field, which means that the electric properties of the N-LC base can be effectively controlled. The above described problem is governed by a coupled system of PDEs. It is solved iteratively using a finite-difference scheme with relaxation. Once the director field is obtained, the dielectric properties of the material are determined for each value of the bias voltage. The proposed antenna is then simulated using HFSS. The return loss and resonant frequency are computed for each of value of the applied voltage. It is shown that the antennas under consideration can be tuned using relatively low applied voltages. This demonstrates the potential of liquid crystal based antennas in frequency-agile antenna design.

The design of an aperture-coupled microstrip antenna with switchable polarisation and frequency agility is studied. Switching between two orthogonal linear polarisations (LPs) is realised by mounting two switching pin diodes on the antenna. To achieve multi-operating frequency (frequency agility) on one of the LPs, a voltage-controlled varactor diode is loaded between the top-loaded square patch and the ground plane. From the measured results, a good cross-polarisation level is observed when operated in both linear states at around 2 GHz.