Direct sequence code division is used to enhance an ultrawideband impulse modulated communication system using a photoconductive switch-based receiver. Experimental results show an aggregate processing gain of 44 dB using a 750 MHz spreading bandwidth

GaAs photoconductive switches are proposed as front-end elements in ultrawideband wireless impulse communications systems. A theoretical discussion of receiver architectures is presented favoring a matched filter approach that leads to a simple architecture. Experimental results at 38 Mb/s show the resistance of impulse modulation to a narrowband interferer. Design of the photoconductive switches for efficiency is important, and some device measurements are reported showing trigger energies below 100 pJ.

We present the first demonstration of a new receiver for digital time-hopped spread-spectrum wireless communications. The time-hopped system is based upon the transmission of short radio frequency (RF) pulses with bandwidths exceeding 200 MHz. The new receiver used photoconductive switching to perform front-end correlated reception. This type of receiver was designed to provide a large dynamic range in the presence of noise and interference. Results show a bit error rate of better than 10-7 at a 250-kB/s data rate

We demonstrate an impulse radio architecture which employs a GaAs photoconductive switch in performing correlated reception. Results show a bit-error-rate of better than 10/sup -8/ at 38 Mb/s and excellent interference rejection.

Spread-spectrum (SS) wireless links offer many distinct advantages including the ability to share the RF spectrum among many users, interference rejection, signal hiding, and low probability of intercept. On the transmit side, an information signal with bandwidth, B is spread into a larger RF bandwidth, BRF. On the receive side, the signal is typically correlated with a matched signal, collapsing it back to its initial bandwidth, B. Hence, the receiver's output signal to noise ratio (SNR) can be increased over the input SNR. These generation and gating capabilities form the basis of our impulse-modulated timehopped SS communications system

Proven properties of spread-spectrum (SS) RF communications such as interference rejection and large information carrying capability have led to the increased use of SS signaling schemes in RF wireless communications systems. Whether the system engineer seeks to increase the information carrying capability or operate in a low signal-to-noise ratio environment, communications with a broadband RF signal can increase the performance. One might envision an RF bandwidth that is greater than 50% of the RF center frequency. However, in practice, spreading bandwidths are often only a few percent of the center frequency or carrier frequency. A larger spreading bandwidth brings with it the problem of designing directional antennas that will faithfully transmit and receive the SS signal. Photonic beamsteering using true-time delay can be a viable solution to the beam-squint problem. We focus on an interesting approach to generating, transmitting, and steering the broad-band burst mode signals.

We describe a new RF spread-spectrum communications system. The system exploits the proven capability of picosecond conductivity to serve in both generation and sampling of precisely timed RF bursts. We also present initial results from a proof-of-principle system.

A mode-locked laser is used to synchronize jitter-free ultrawideband (UWB) pulse generation at an array of UWB antenna elements. The jitter-free pulses radiated by each element add together in free space to produce a radiated field pattern that is steerable via optical true-time-delay techniques. The results from a three element array experiment are presented and used to develop a model for an N-element phased array. A transmission-line model is presented for a single array element, which includes the functions of energy storage, as well as UWB pulse generation and radiation.

We have developed a novel opto-electronic transceiver designed to provide a jam-resistant, high-security, low-power rf communications link. By employing picosecond photoconductivity and a time-hopped spread-spectrum architecture, the transceiver can realize multi-octave instantaneous rf bandwidth. The design is capable of processing gains well above those of existing spread-spectrum communications systems. Hence, significant jam resistance is achievable with a minimum of rf power. The transceiver is particularly well suited to serve as the physical layer of a packet radio system and can be packaged in a hand-held unit with Q-switched diode laser technology. We present results from an opto-electronic digital spread-spectrum data link that demonstrate some of the capabilities of this approach.

An optically controlled spread-spectrum RF data link architecture was demonstrated. The data link used a time-hopped optical pulse train derived from a mode-locked laser to synchronize transmission and correlated reception of wideband RF pulses. This was the first demonstration of an optically controlled time-hopped RF spread-spectrum link.

Photoconductive switches are used to trigger an array of three pulsed ultra-wideband antennas. The jitter-free pulses radiated by each antenna add together in free space to produce a radiated field pattern that is steerable via true optical time-delay techniques. This technique can be applied to an N-element phased array for increased radiated power and beam-steering capabilities.<>

We examine the advantages of using photoconductive switches in the jitter-free linear mode of operation. We show that the jitter-free property of a linear-mode PC switch can be used to coherently add power in a free-space ultra-wideband radiation system. This approach allows PC switches to be operated at reasonable power levels where operation is very reliable.

We have demonstrated the generation and radiation of an ultra-wideband (UWB) radiation using a high TC superconductor (HTS) laser triggering fast opening switch, a transmission line pulse forming network, and conical monopole transmitting and receiving antennas.

Jitter-free photoconductive (PC) switching is employed to generate a jam-resistant, time-coherent ultra wideband (UWB) pulse train. The power from multiple PC switch triggered antenna elements is combined in free space to produce a steerable UWB beam.

A new method of generating ultra-wide-band electromagnetic pulses using a Tl2Ba2CaCu2O8 high T(c) superconductor as a fast laser activated opening switch is presented. The superconductor is used as an opening switch with a current charged transmission line pulse forming network to produce jitter-free triggered square pulses which are radiated by an ultra-wide-band conical antenna. We report radiation and reception of pulses with center frequencies near 3.5 GHz and a bandwidth in excess of 80%. We also discuss how this technique can be used to assess various wide-band antenna designs.

A high Tc superconductor opening switch controlled inductive energy storage pulsed power system (IESPPS) has been demonstrated. A 500 Hz pulse train of jitter-free 75-318 ps electrical pulses was produced. We also show that the IESPPS produces a pulse compression ratio of 6-10. Compared with previous results, we have reduced the pulse width by a factor of ten and increased the repetition rate by a factor of 500 while reducing the laser trigger energy from 1 mJ/pulse to 20 muJ/pulse.

: One of the necessary pieces of equipment needed for ultra-wideband (UWB) radio effects measurements is a suitable UWB field probe and radiating antenna. The conical monopole antenna (CMA) is an easy-to-fabricate, inexpensive, and useful UWB device that can be used for both of these applications. In this report we present information that should allow both antenna designers and users to quickly assemble a custom CMA to meet their design goals. A subjective explanation of the theory of operation is presented along with analytical expressions that predict the radiated and received pulse shapes. Experimental results are presented to verify the CMA theory of operation; these results also serve as an example of how UWB radiation can be monitored with a CMA during field measurements. Wide bandwidth probe, UWB antenna, Conical monopole antenna.