A novel multi-mode frequency reconfigurable MIMO and an ultrawideband (UWB) MIMO antenna design for cognitive radio applications is proposed in this paper. The antenna structure contains two modified triangular-shaped printed monopole antenna elements and a combination of varactor and PIN diodes. The proposed antenna has three operating modes: UWB mode for spectrum sensing, a frequency reconfigurable MIMO mode for communication over different frequencies, and UWB antenna operating in MIMO configuration. The UWB mode and reconfigurable communication mode are obtained by utilizing different switching ON/OFF states of PIN and varactor diodes. In the UWB mode, the antenna can cover the spectrum from 1 to 4.5 GHz, while it achieves the frequency reconfigurability over a wide range from 0.9 to 2.6 GHz using varactor diode tuning in the reconfigurable communication mode. The proposed antenna has a compact and planar structure with overall dimensions of 120 × 60 × 1.5 mm
 3
. The proposed design also exhibits good MIMO performance; the minimum isolation measured is 12.5 dB, while the envelope correlation coefficient (ECC) of less than 0.19 is achieved for the whole operating band. To validate the proposed concept, the prototype of the antenna system is fabricated and measured. The simulation results are in good agreement with the measurement results.

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A Reconfigurable MIMO/UWB MIMO Antenna for Cognitive Radio Applications

In this paper, two designs of an ultra-wideband antenna with reconfigurable band notches are presented. The first design is based on several nested complementary split-ring resonators, whereas the second has two identical split-ring resonators. Electronic switches mounted across or along these resonators serve to activate or deactivate their corresponding band notches, thus leading to band-notch reconfigurability. Prototypes of the two designs are fabricated and tested, and their results are compared.

A reconfigurable frequency-notched UWB antenna with split-ring resonators

The main motive of this paper is to discuss a design of compact five-port integrated ultrawideband (UWB) and narrowband (NB) antennas system for cognitive radio applications. The proposed system composes of one UWB antenna for spectrum sensing and four NB antennas for communication. The UWB and NB antennas are printed on a very compact FR-4 substrate of dimensions 40 mm $\times36$ mm $\times1.6$ mm. The UWB antenna coupled with port 1 is designed to sense the complete UWB spectrum of 3.1–10.6 GHz approved by Federal Communications Commission in 2002. The four NB antennas operate at different single or dual bands to cover the complete UWB spectrum. In particular, the first NB antenna allied with port 2 achieves a single operating band ranges from 8.7 to 9.92 GHz. The second NB antenna associated with port 3 also covers a single band from 9.82 to 10.74 GHz. The third NB antenna linked to port 4 yields dual bands from 3.06 to 4.23 GHz and 6.33 to 8.83 GHz. The fourth NB antenna accessed at port 5 operates in a single band from 4 to 6.37 GHz. Isolation between the antennas is less than 16 dB over the antennas operating bands. Finally, the proposed integrated structure is fabricated and verified. Experimental results have a good agreement with the simulated results.

A Five-Port Integrated UWB and Narrowband Antennas System Design for CR Applications

This paper initially discusses lumped equivalent models of narrowband (NB) antennas and then presents a technique to enhance isolation between UWB and NB antennas of the three antennas system. The proposed models are able to yield similar S-parameter performance as that of NB antennas at their resonant frequencies. Also, a good match is observed at other frequencies between the HFSS and AWR results. This paper reports an isolation enhancement technique using microstrip lines. The proposed approach enhances a minimum isolation of 11 dB at respective resonant frequencies. This paper also reports lumped equivalent models of dual band reject filters (DBRFs). Proposed geometry is fabricated and tested. Experimental result shows an agreement between the simulated and measured results.

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Lumped Equivalent Models of Narrowband Antennas and Isolation Enhancement in a Three Antennas System

Radio frequency energy harvesting (RF-EH) is a potential technology via the generation of electromagnetic waves. This advanced technology offers the supply of wireless power that is applicable for battery-free devices, which makes it a prospective alternative energy source for future applications. In addition to the dynamic energy recharging of wireless devices and a wide range of environmentally friendly energy source options, the emergence of the RF-EH technology is advantageous in facilitating various applications that require quality of service. This review highlights the abundant source of RF-EH from the surroundings sources, including nearby mobile phones, Wi-Fi, wireless local area network, broadcast television signal or DTS, and FM/AM radio signals. In contrast, the energy is captured by a receiving antenna and rectified into a working direct current voltage. This review also summarizes the power of RF-EH technology, which would provide a guideline for developing RF-EH units. The energy harvesting circuits depend on cutting-edge electrical technology to achieve significant efficiency, given that they are built to perform with considerably small current and voltage. Hence, the review includes a thorough analysis and discussion of various RF designs and their pros and cons. Finally, the latest applications of RF-EH are presented.

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Radio Frequency Energy Harvesting Technologies: A Comprehensive Review on Designing, Methodologies, and Potential Applications

In recent years, the demand for spectrum continues to increase with the advent of various wireless communication applications. However, it is a limited resource and cannot be made available beyond a certain extent. Many of the times, licensed spectrum is free due to its inefficient utilization. So, it can be utilized for other applications to mitigate the problem of limited spectrum availability to some extent. Among the many ways of performing this task, one approach is to use the frequencies in statically licensed spectrum through continuous sensing, which is popularly known as cognitive radio technology. In this model, UWB antennas are employed to monitor the radio environment and narrow band (NB) antennas are adopted for communication. This paper discusses various kinds of planar monopole antennas for cognitive radio applications. They are divided into three categories on the basis of different antennas used in cognitive radio environment. In the first category two separate antennas, which include one UWB antenna and one frequency reconfigurable NB antenna are employed for spectrum sensing and communication, respectively. In the second category, a single port frequency reconfigurable UWB/NB antenna is used. However, it requires an appropriate switching mechanism to switch between the UWB and NB modes. The third category includes dual-port integrated antennas systems, in which one UWB antenna and one frequency reconfigurable NB antenna are integrated on a single substrate. Finally, this paper discuss an opinion of designing multi-port integrated UWB and NB antennas systems to overcome the drawbacks of reconfigurable antennas and to further enhance the spectrum utilization efficiency.

A Survey on Planar Antenna Designs for Cognitive Radio Applications

Design and analysis of a moon slotted circular planar monopole UWB (ultra-wide band) antenna is discussed. The proposed antenna operates within a frequency spectrum of 2.62GHz to 12.63GHz, which includes the unlicensed band 3.1GHz-10.6GHz approved by FCC in 2002. It achieves a maximal peak gain of 4.85dBi at 9.75GHz and highest radiation efficiency of 95.94% at 3.1GHz. This antenna is mounted on a FR 4 substrate having dimensions 30mm×19mm×1.6mm. This paper initially reports a systematic way of conventional circular planar monopole UWB antenna design and then presents a step-by-step design process to obtain the proposed UWB antenna from the conventional one. In this process transmission line equivalent models for different design steps are also discussed. These models are basically derived from the conventional assumption of copper elements interms of R, L and C. Then after, it reports a comparison study of the two UWB antennas. Finally, the proposed UWB antenna geometry is fabricated and tested. Experimental result shows an agreement with the simulated result.

Moon slotted circular planar monopole UWB antenna design and analysis

State-of-art design aspects of wearable, mobile, and flexible antennas for modern communication wireless systems

In modern wireless communication, microstrip antennas are widely equipped in mobiles, laptops and other portable devices due to their advantages like small size, light weight, low cost and easy integration with planar structures. Moreover, the research evolution in these antennas, which are required for portable wireless communication system applications, is advancing day by day. So, it is essential to notice the research and improvements happening in the area of microstrip antennas for the intended applications. The main objective of this paper is to discuss numerous microstrip antennas for GSM, Wi-Fi and Wi-MAX 2500 applications. The GSM applications cover GSM 900, GSM 1800 (DCS 1800) and GSM 1900 (PCS 1900) bands while the Wi-Fi applications cover 2.4GHz and 5.8GHz bands. Sometimes, these antennas also operate in various bands of GPS, LTE 2300, LTE 2600, UMTS and Wi-MAX 3500 along with the GSM, Wi-Fi and Wi-MAX 2500 bands. This paper initially presents various conventional microstrip antennas that include single, dual, triple and multi band antennas. Then, it reports frequency reconfigurable narrow band antennas and finally multi-port microstrip antennas. It also explains merits and demerits of all antenna categories. Finally, this paper helps to explore and design suitable microstrip antennas for the required applications.

Anveshkumar Nella

Papers

A Five-Port Integrated UWB and Narrowband Antennas System Design for CR Applications

A Survey on Planar Antenna Designs for Cognitive Radio Applications

Moon slotted circular planar monopole UWB antenna design and analysis

State-of-art design aspects of wearable, mobile, and flexible antennas for modern communication wireless systems

A survey on microstrip antennas for portable wireless communication system applications