This communication presents a new approach to implement planar antipodal Vivaldi antenna design. A nature fern inspired fractal leaf structure is implemented here. Impedance bandwidth (−10 dB) of the proposed antenna is around 19.7 GHz starting from 1.3 to 20 GHz. The lower operating frequency of this antenna is reduced by 19% with the second iteration as compared to the first iteration of fractal leaf structure. The prototype antenna is fabricated and tested in frequency as well as in time domains to obtain various transfer characteristics along with common antenna parameters. Experimental results show that good wideband feature, stable radiation pattern, and promising group delay of less than 1 ns signatures are obtained, which agree well with the simulated data. The miniaturized proposed antenna structure becomes an attractive choice in microwave imaging applications because of its ultrawide fractional bandwidth at 175%, high directive gain of 10 dBi, and finally appreciably large fidelity factor above (>90%).

A Fern Fractal Leaf Inspired Wideband Antipodal Vivaldi Antenna for Microwave Imaging System

A compact antipodal Vivaldi antenna (AVA) with the dimension of $42 \times 36 \times 1.6~\hbox{mm}{^3}$ is proposed in this letter. Structural modifications in the radiating fins have increased the electrical length thereby reducing the lower operating frequency from 5.2 GHz to 3.7 GHz. Proposed antenna maintains $-20~\hbox{dB}$ copolarization to cross-polarization ratio throughout the operating bandwidth. The prototype is fabricated and the measurement results are presented to validate the performance of the proposed AVA.

A Compact Antipodal Vivaldi Antenna for UWB Applications

A continuous-time (CT) radio frequency (RF) antenna array beamformer and analog circuit based on a discrete-space-continuous-time (DSCT) 2-D fan-filter having transfer function HF,A(zx,sct) is derived. The proposed transfer function is based on a 2-D FIR discrete domain fan filter. The discrete domain prototype is converted to the proposed mixed-domain DSCT analog filter by replacing unit sampled delays with CT analog first-order all-pass networks corresponding to the bilinear transform. First-order all-pass network Φ(st) is a poor approximation to a CT delay exp(-sT) . To address this, a novel broadband pre-warping method is proposed to exactly compensate for such “bilinear warping”. A 65 nm CMOS VLSI circuit for Φ(st) is proposed and an example fan filter with axis oriented at θ0=35°, half-fan-angle e = 5° and maximum frequency Fu = 2.6 GHz is simulated employing closed-form expressions, an ABCD parameter based model and 65 nm CMOS simulations in Cadence. A stop-band interference rejection of 38 dB is verified by BSIM4 based simulations. The proposed circuit for Φ(st) operates at 3.7 mA from a 1.2 V supply. The beamfomer is shown to operate correctly in the presence of PVT variations of Φ(st).

RF Analog Beamforming Fan Filters Using CMOS All-Pass Time Delay Approximations

In this paper, a new, complete, and comprehensive breast phantom measurement system is presented. A side slotted vivaldi antenna is used for breast phantom measurement. The radiating fins are modified by etching six side slots to enhance the electrical length and produce stronger directive radiation with higher gain. This approach reduces the lower operating frequency and increases the gain and efficiency without compromising the size of the antenna. The overall size of the antenna is 8.8 ( ${L}$ ) $\times7.5$ ( ${W}$ ) cm $^{{ {2}}}$ or approximately $0.4\lambda \times 0.5\lambda $ at the first resonant frequency of 1.79 GHz. The results show that the antenna has a fractional bandwidth of approximately 127% from 1.54 to 7 GHz for return loss less than 10 dB with a directional radiation pattern. The average gain of the proposed prototype is 8.5 dBi, and the radiation efficiency is approximately 92% on average over the operating bandwidth. The fidelity factor for face to face is 0.98, and that for side by side is 0.4479, which proves the directionality and lower distortion of the signal. The prototype is successfully simulated, fabricated, and analyzed. The radiating fins of the proposed prototype are optimized to achieve the desired properties for breast phantom measurement. The antenna is used as the transceiver in a breast phantom measurement system to detect unwanted tumor cells inside the breast. An automated electromechanical imaging system with the necessary data post processing makes it an easy and suitable tool for microwave imaging to detect breast tumors.

Microwave Breast Phantom Measurement System With Compact Side Slotted Directional Antenna

A 16‐modified antipodal Vivaldi antenna array for microwave‐based breast tumor imaging applications

A type of antipodal Vivaldi antenna is designed in this paper, which can be used for pulse radiation in UWB communication. Vivaldi antenna is a special tapered slot antenna with planar structure and is easy to be integrated with transmitting elements and receiving elements to form a compact structure. The antenna designed has good performance in the band 3.1GHz to 10.6GHz, which is assigned to Ultra Wide Band (UWB) wireless communication by FCC. The antenna proposed can radiate or receive UWB pulses with little distortion and a good directivity and a high efficiency.

Analysis and Design of UWB Vivaldi Antenna

When high power microwave is propagating in Rain, Elcctrommagnctic wave will be induced attenuation and depolarization for absorbency and dispersion of nonspherical raindrops, with the hoist of frequency, the attenuation and depolarization will become worse and worse . In the paper CPA of rainfall in correlation area based on factual metrical rainfall condition is advanced reckoned, and inclination angle of raindrops is considered, which amend old formula for calculating XPD, finally produce the model of microwave propagation which can avoid the effect of rainfall depolarization.

Analyse of Model of Rainfall depolarization Based on Factual Metrical Rainfall Condition

http://or.nsfc.gov.cn/bitstream/00001903-5/344825/1/1000014499152.pdf

Theoretical and experimental investigation of air breakdown on single high power microwave based on the mixed-atmosphere propagation model

When high power microwave propagates in atmosphere, sand and dust caused by battlefield explosion would attenuate energy of HPM considerably. This paper derives equivalent complex permittivity constant of mixture of wet sands according to Garnet formula, gives distribution function of sand and dust particle diameter and formula of permittivity constant of sand and dust, deduces engineering algorithm of sand and dust attenuation finally.

Analysis and Calculation of Sand and Dust Attenuation Model

Considering electron temperature arising time, new concepts of safe pulse length threshold and safe amplitude threshold are put forward. Combined with electron kinetic equation, electron energy equation and Maxwell equations, a FDTD method is proposed to analyze the nonlinear propagation characteristics of high power microwave in lower ionosphere. And also, the relationship of safe pulse length threshold, safe amplitude threshold with frequency, electron number density and collision frequency are discussed.

Nonlinear Propagation of High Power Microwave in Ionosphere

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