Ahmet Kenan Keskin

Partially Dielectric-Loaded Ridged Horn Antenna Design for Ultrawideband Gain and Radiation Performance Enhancement

In this letter, a partially dielectric-loaded double-ridged horn antenna (PD-DRHA) that operates at 1-18-GHz frequency band is proposed for ultrawideband applications. The partially dielectric loading technique using a small lens inward the aperture has been implemented to enhance the gain of the standard double-ridged horn antenna (DRHA), without changing the physical dimensions. Approximately 5 dB gain increment level is achieved from 5 to 15 GHz with slight changes on return loss characteristics. Moreover, the pattern distortion of DRHA typically between 12-18-GHz band is improved. The antenna gain, radiation pattern, and input reflection performance measurements are presented with comparisons.

Ultra wide band TEM horn antenna designs for ground penetrating impulse radar

This paper deals with ultra-wide band (UWB) TEM horn antenna types, which are suitable for hand-held and vehicle mounted impulse GPR systems. On this scope, conventional, dielectric loaded, Vivaldi form, multi-sensor adaptive and array configurations of the TEM horn structure are designed, simulated and measured. Vivaldi shaped TEM horn fed ridged horn and parabolic reflector antenna prototypes are proposed to reach hyper-wide band impulse radiation performances from 300 MHz up to 20 GHz for multi-band GPR operation that can provide high resolution imaging. The gain and input reflection performances are demonstrated with measurement results.

Design of an ultrawide band low noise microstrip amplifier using 3D sonnet- based SVRM with particle swarm optimization for space applications

In this work, a determinististic, efficient design methodology is put forward to design a wide-band, low-noise microstrip amplifier, where the microstrip widths, lengths {W^→,ℓ^→} of the input/ output matching networks are obtained accurately and fast for a substrate {ε_r, h, tanδ} using the cost-effective 3D EM- based Support Vector Regression Machine (SVRM) microstrip model provided that ensuring the stable source Z_S(ω) and load Z_L(ω) terminations for the compatible {Noise F(ω) ≥ F_min(ω), Input VSWR Vi(ω) ≥1, Gain G_Tmin(ω)>G_T(ω)≥G_Tmax(ω), Bandwidth B} quadrates of the employed transistor. The 3D EM- based SVRM microstrip model provides the accurate and fast characterization of the equivalent transmission line in terms of the characteristic impedance Z₀ and the dielectric constant ε_eff within the continuous domain of {0.1mm ≤ W ≤ 4.6 mm, 2 ≤ ε_r ≤ 10, 0.1mm ≤ h ≤ 2.2mm, 2GHz ≤ f ≤ 14GHz} in an efficient manner. In the modeling process, the substantial reduction (up to %64) is obtained utilizing sparseness of SVRM in the number of expensive fine discretization training data with the negligible loss in the predictive accuracy using the quasi-TEM microstrip synthesis formulas as the coarse model that allow to identify the regions of the design space requiring denser sampling. Moreover, the multi-objective amplifier design problem is reduced into the two single-objective design problems of the input(IM)/ output (OM)matching networks to provide the source Z_S(ω) and load Z_L(ω) terminations to the transistor, respectively. Finally the design methodology is applied to the design of typical wideband low-noise amplifiers of the transistor NE3512S02 within 3GHz and 8GHz using T-, II- L types of microstrip matching circuits satisfying the maximum gain provided the available minimum noise and a permitted amount of input mismatching at each operation frequency. In the design optimization of the IM/OM networks, a Memetic Algorithm (MA) in which a simple local optimizer called Nelder-Mead (NM) algorithm is used along with the global optimizer Particle Swarm (PSO) algorithm is used. Furthermore, typical T-T designed amplifier is validated using the Circuit Simulator AWR and 3 D EM Simulator SONNET.

Front-end design for Ka band mm-Wave radar

In this paper front-end design for a Ka band milimeter wave (MMW) radar which consists of an antenna, a low noise amplifier (LNA) and a band pass filter is presented. The operation frequency of the designed system is between 24-25 GHz in Ka band. A high gain axially displaced elliptical (ADE) dual reflector antenna is employed on the antenna structure. ADE sub-reflector with 5 cm diameter is illuminated by a feeder horn and a main reflector 30 cm diameter parabola focuses incoming waves from the ADE sub-reflector. According to the simulation results narrow half power beam width (HPBW=30) and high gain (G=35 dBi) are obtained with good efficiency (%58). An HJ-FET that has low noise figure (NF<;1 dB) and high gain (>13 dB) is utilized to design a LNA. Double transistors are connected as cascaded to achieve higher transducer gain (Gt>19 dB). Matching circuits and feeder resonators are designed by microstrip lines to obtain low input and output VSWR (Vin<;2.1, Vout<;2.1). A microstrip band pass filter (BPF) is designed to receive required signals and to suppress other bands. The BPF is formed by combination of a radial stub low pass filter (LPF) and a short stub high pass filter. Low insertion loss (S21>-2.5dB) and low return loss (S11<;-15 dB) are aimed to take signal as lossless as at pass band. The simulated designs are manufactured and measured. It is seen that there are good agreements between measurement and simulation results.

Millimeter wave short range radar system design

In this paper, a 24 GHz millimeter wave (mm-wave) short range radar system is presented. In the designed radar system, there is one transmitter and one receiver channel. The transmitter channel has +9 dBm output power and 24 GHz output carrier signal is modulated with 20 ns square wave by SPDT switch. At the receiver channel, there are two LNAs, which have totally 40 dB gain, a microstrip band pass filter (BPF) and a double balanced IQ mixer. The designed radar system is measured using an oscilloscope at output of IF channel. According to the results, it is seemed that 200 mV and 50 mV reflection levels are received from metal and human target, respectively, at 2 meters without IF amplifier. ADE reflector antennas and horn antennas are utilized for transmitting and receiving.

Quasi TEM-Horn antenna array for rescue radar buried victims under rubble

In this paper, it is presented that quasi TEM-Horn antenna array to rescue buried victims under rubble. Designed antenna array, which consists of 4 elements, is operated between 400 MHz and 2 GHz. In order to penetrate electromagnetic wave into rubble, lower frequencies like 400-500 MHz should be used, because of attenuation of the concrete. Besides, it is required that ultra-wide band operation for good resolution while searching a buried victim. As an element of the array, quasi TEM-Horn antenna is utilized. Total dimensions of the array antenna are 14 cm × 27 cm × 57 cm. Distance between each element is 14 cm and also there is a reflector behind the antennas. Antenna gain is started from 8 dBi at 400 MHz and is increased till 14 dBi at 2 GHz. Furthermore, VSWR of the antenna is mostly fewer than 2 at the operation band, but at some frequencies it reaches 3. Reflector, which is placed 6 cm behind the array, is not only providing gain enhancement, but also reducing back lobe radiation at lower frequencies and shielding. Moreover array elements could be employed to understand which way the target is using A-scan data.

Genetic Algorithm applied to microstrip implementation of matching circuits for a UWB low- noise amplifier

In this paper, design of the input and output matching microstrip circuits subject to the transistor potential performance is completed to meet an ultra-wide band front-end requirements. For this purpose, the performance characterization of a microwave transistor is implemented to design a microstrip amplifier so that geometry of all the matching microstrip elements on a selected substrate (W?, ℓ?, T, εr, H, tanδ) where {W?,ℓ?, T} and {εr, H, tanδ} are the subvectors including widths, lengths and thickness of the microstrip lines and relative dielectric constant, height and loss of the substrate, respectively, can be obtained from the output subject to the transistors potential performance. Thus, a microstrip, Ultra-Wideband (UWB) amplifier realizable as a Microwave Integrated Circuit (MIC) is designed as a worked example using Genetic Algorithm for the maximum gain along an available wideband, simultaneously ensuring the available minimum noise and the permitted small constant mismatching at each operation frequency. Finally, the resultant amplifiers performance is verified by both the microwave circuit and 3-D full-wave EM-simulators.

Quasi horn antenna array for Ku band monopulse radiation

In this paper, a quasi-horn antenna array, which is combination of 4 × 4 slot array and its flares, is designed for Ku band monopulse radiation. The slots are fed by waveguide power divider. In order to obtain sum and difference radiation pattern, a magic T is utilized end of the waveguide feeder. Slot dimensions and distance between each slot are adjusted and optimized to get high gain and low return loss using 3D EM simulation. Short depth flares are added to aperture of each 4 × 1 slots to enhance gain of the array. According to the simulation results, gain of the array at the sum port is 21.9 dBi. At the difference port, monopulse radiation pattern have 19.3 dBi maximum gain and -32 dB null. Return losses at the sum and difference port are lower than -6 dB in the operation band. Total dimensions of the 4 × 4 array are 8.36 cm × 8.4 cm × 7.06 cm.

Avalanche transistor short pulse generator trials for GPR

This paper presents impulse generator for ground penetrating radar (GPR) transmitter based on multiplication effect of avalanche transistor. Different impulse generators are designed using single and multiple avalanche transistors. Circuits with multiple transistors used both serial and parallel connections of transistors. 100 kHz signal with 2.2 V and 3 ns pulse width was used as a trigger signal. 280 V DC bias voltage required for single and triple cascaded transistor circuit. Bias voltage for double and quadruple transistor circuit was 370 V DC. Maximum 150 V output with 1.5 ns pulse width was obtained. Circuit schematics and results are demonstrated.

Ultra-wide band antenna designs and numerical system modelling for forward-looking GPR

This paper presents ultra-wide band (UWB) horn feeder and parabolic reflector antenna designs, which are considered highly suitable for forward-looking vehicle-mounted ground-penetrating radar (GPR) systems and time-domain numerical modelling of impulse GPR signal radiation, wave propagation and target scattering. In this context, the partial dielectric-loaded Vivaldi shaped TEM horn (PDVA), TEM horn fed double-ridged horn (PDTEM-RHA) and their compact versions are investigated, designed simulated and measured. An offset parabolic reflector antenna prototype with a compact PDTEM-RHA feeder is proposed to reach hyper-wide band impulse radiation performances from 500 MHz up to 15 GHz for a multi-band forward-looking GPR operation that can provide deep subsurface detection with high-resolution imaging, due to a big advantage of narrowed beam widths. The antenna gain and radiation pattern performances are demonstrated with measurement results.