1. Sommaire
A Compact UWB Sub-nanosecond Pulse Generator for Microwave Radar Sensor with Ringing Miniaturization
Younes Ahajjam a,c , Otman Aghzout a,b , José M. Catalá-Civerac , Felipe Peñaranda-Foixc , Abdellah Driouach a
a Dept. of Physics, Faculty of Science, Abdelmalek Essaadi University, Tetouan, Morocco.
b Electronics & Microwave Group, TITM Department, ENSA, Tetouan, Morocco
C Instituto ITACA. Universitat Politècnica de València. Valencia, España.

2. CERCUIT DESCRIPTION AND DESIGN RESULT AND DISCUSIONS CONCLUSIONS
Topics
INTRODUCTION
CERCUIT DESCRIPTION AND DESIGN
RESULT AND DISCUSIONS
CONCLUSIONS

3. Introduction
A Compact UWB Sub-nanosecond Pulse Generator for Microwave Radar Sensor with Ringing Miniaturization

4. CIRCUIT DESCRIPTION AND DESIGN
The circuit schematic of the proposed pulse generator has been constructed by two principle parts:
1- Avalanche transistor circuit .
2- SRD pulse sharpener circuit.
Circuit diagram of the proposed Gaussian pulse generator

5. Avalanche Transistor Circuit
The first part of the generator consists of Q, C1, R1, C2 and R2.
The transistor Q operates as common-emitter switch, and generates a negative voltage pulse with sufficient power and speed to drive an SRD.
The driving waveform passes through a coupling capacitor C2 to the SRD pulser.
The discharge current of the avalanche transistor circuit flows from the capacitor C2 through the avalanche transistor and the resistor R3
Layout and Circuit designed of the avalanche transistor circuit

6. Avalanche Transistor Circuit
. With the aim to reduce possible parasitic inductive effects in the discharge circuit, we have made the discharge path as short as possible; which leads to a great minimization of the ringing in the output waveform.
Short discharge path of the avalanche transistor circuit
Layout and result before the made the disharge path short .
Layout and result after the made the discharge path short.

7. SRD Pulse sharpener circuit
Photograph of circuit designed of SRD pulse sharpener
During the forward bias condition, a large amount of charge is injected into the diode making the impedance low. In case of reverse biasing, the device continuous as low impedance until all charge is totally removed, at the point where the diode rapidly switches from the low a high impedance
The ability of the SRD to store charge and change its impedance level rapidly is used to sharpen the slow waveform edges in the nanosecond region.
Layout and circuit designed of SRD pulse sharpener circuit

8. SRD Pulse sharpener circuit
In order to increase the rise-time of these pulses, it’s a necessary to have accuracy in the simulation results, since the crucial role of SRD in the circuit, unfortunately there is not an advanced model of SRD in Simulators as AWR Microwave office and Multisim. This reason leads us to propose a new model.
After studying existing models in literature; A voltage-switch model for SRD and its equivalent circuit are presented .
(a) SRD of AWR Microwave Office. (b) New model of a step recovery diode (SRD).
Rejection levels are enhanced when distance d1 is decreased, corresponding with an increase in the effective capacitive value provided by the gap between the antenna and the SRR loading element.
In the circuit, Rs indicate the nonlinear impedance, Cj the nonlinear capacitance, Ls and Cp are the parasitic parameters of the SRD component. The SRD used in the generator is MA T of M/A-COM Corporation, which has a reverse capacitance of 1pF, a minority-carrier lifetime of 10 ns, a minimum transition time of 150 ps, a reverse breakdown voltage of 30 V, forward bias current 50 mA and a SOD323 package

9. SRD Pulse sharpener circuit
(a) Output waveform before the application of new model of SRD
(b) Output waveform and after the application of new model of SRD.
It’s clear to see the great difference between the output waveform of the circuit before and after to the new model of SRD has been applied.

10. Results and discusions
Circuit Final of Ultra-short pulse generator
Rejection levels are enhanced when distance d1 is decreased, corresponding with an increase in the effective capacitive value provided by the gap between the antenna and the SRR loading element.
The designed Pulse generator is fabricated on FR-4 glass Epoxy substrate having a relative dielectric constant of 4.34 and thickness of 1, 53 mm .

11. Results and discusions
Simulated Gaussian pulse generator response.
Measured Gaussian pulse generator response.
Gaussian pulse with maximum amplitude of 6.4 V, rise-time of 440ps and with a pulse repetition frequency of 100 KHz. The pulse has also a FWHM (Full-Width at Half-Maximum) of about 620 ps. It is possible to decrease the FWHM by shorting the delay line length, but the output amplitude decrease also.
 However, and unlike others generators, our pulse transmitter has the advantage of producing pulses with low ringing levels (3.6% OVERSHOOT) and reasonably high output amplitude.
Rejection levels are enhanced when distance d1 is decreased, corresponding with an increase in the effective capacitive value provided by the gap between the antenna and the SRR loading element.

12. Conclusions
A compact, low-power and low-cost design of an ultra-short pulse transmitter ultra-wideband microwave radar is presented
A good agreement is demonstrated between measurement and simulation results for fabricated ultra-short pulse transmitter prototypes.
With the modeling of the Step recovery diode (SRD) and make the discharge path very short, a good output waveform has been obtained highlighted with 6.4 in amplitude and 440 in fall-time with a minimum ringing of 3.6 in overshoot
The Gaussian pulse generator circuit is completely fabricated on the micro-strip structure, which has the feature of low-cost, compact and small size. Simplicity and performance properties of the circuit, makes its attractive for various UWB radar and communications systems.
Thursday, April 14, 2016

13. A Compact UWB Sub-nanosecond Pulse Generator for Microwave Radar Sensor with Ringing Miniaturization
a Dept. of Physics, Faculty of Science, Abdelmalek Essaadi University, Tetouan, Morocco.
b Electronics & Microwave Group, TITM Department, ENSA, Tetouan, Morocco
C Instituto ITACA. Universitat Politècnica de València. Valencia, España.