Allen L. Davidson

Measurement of building penetration into medium buildings at 900 and 1500 MHz

The propagation loss into ten medium-sized buildings in Schaumburg, IL, has been measured. At 900 MHz, the mean penetration loss in the lower enclosed floors at or near ground level was found to be 10.8 dB with a standard deviation of 5.8 dB. At 1500 MHz, penetration loss was found to be 10.2 dB, and the standard deviation was 5.6 dB. Data was also taken up to 12 floors (with a higher concentration of data on the first five floors) to show higher elevation trends in the penetration loss. The measured building penetration loss was combined with data from other references, and the slope of a best fit curve as a function of frequency is found to be -7.9 dB per decade.

Mobile antenna gain at 900 MHz

A program has been initiated to investigate the effect of the urban multipath environment on mobile antennas at 900 MHz. The program involves the constructuion of several mobile antennas, careful measurement of these antennas on an antenna range to determine their characteristics in a controlled environment, then measurement of their characteristics in the multipath environment of cities. Measured results are compared to computed results to permit generalized conclusions to be reached. This paper presents the results of the first phase of the program; measurements made in the controlled pattern range environment.

The impact of digital technologies on future land mobile spectrum requirements

Key advances in digital signal processing (DSP) enabling technologies are bringing about a paradigm shift in private land mobile radio (PLMR). Efficient digital modulation and information compression, made possible by advances in semiconductors, are providing the bandwidth reduction necessary to bring visual communication services like fax and video to the land mobile market place. The emergence of these advanced technologies will be fueled, largely, by the availability of adequate radio spectrum. The authors extend the work of K. Crisler and A. Davidson (IEEE 1990 Int. Symp. Electromagn. Compat. Symp. Record, pp. 401-405. 1990) and examine the impact of semiconductor advances on the context of PLMR.

Mobile antenna gain in the multipath environment at 900 MHz

A program has been completed that investigated the effect of the urban multipath environment on mobile antennas at 900 MHz. The program involved the construction of several mobile antennas, careful measurement of these antennas on an antenna range to determine their characteristics in a controlled environment, and measurement of their characteristics in the multipath environment of cities. Measured results were compared to computed results and pattern range results were compared to field data to permit generalized conclusions to be reached. The results of the second phase of the program, measurements made in the mobile multipath environment, are presented. Analysis of this data shows that gain antennas have significantly less gain in areas where multipath propagation predominates and that the increased aperture of the gain antennas provides no significant smoothing of the received signals in the multipath environment.

High gain omnidirectional land mobile base station antenna

Measurements and computations made on a 1.5-GHz 5.6-m (18.5-ft) aperture 2 degrees vertical beamwidth antenna with an omnidirectional horizontal pattern are presented. The gain is greater than 16 dBi over a range of 70 MHz. Good agreement between measured and computed patterns provides confidence that the elevation pattern can be used to predict the received field when the antenna is used in an urban multipath propagation environment.<<ETX>>

Measurement and analysis of corner reflector backlobe levels

Pattern range and real world measurements have been made on a corner reflector antenna to determine the effect the environment has on the back lobe protection. Side and back lobe augmentation can be implemented which provides 37 dB average front-to-back protection on the pattern range. Without augmentation, the average front-to-back protection on the pattern range was 25 dB, and in the real world it was 24 dB. Analysis of these measurements and other data which will be presented permits us to conclude that scattering objects in the main lobe of the antenna when on a good site in the real world limit the average front-to-back protection to about 33 dB. Therefore, the scatterers do not present a limitation when the augmentation techniques are not used, but do set a limit on the ultimate protection which can be provided.

Omnidirectional transmitter combining antenna

Historically, it has been difficult to combine transmitters which are closely spaced in frequency onto the same omnidirectional antenna. Two principal techniques have been used: cavity combining and transmission line hybrid combining. When using cavities, the minimum separation is limited by the amount of insertion loss that is acceptable and by the frequency stability of the cavities. In the 800- MHz land mobile frequency band, cavity combining has been used to combine transmitters as closely spaced as 0.5 MHz with 3 dB of insertion loss. When combining transmitters separated less than 0.5 MHz, hybrid combining has been used. When two transmitters are combined using this technique, half of the power of each is dissipated into a matched load. Further, each time the number of transmitters being combined is doubled, an additional 3 dB is added to the insertion loss. A new technique has been developed which utilizes transmission line hybrids to combine the transmitters, but which does not suffer from large insertion loss. The power that was previously dissipated in the resistive load is radiated in a manner that produces an omnidirectional pattern. The antenna and network that accomplish this combine signals with 90° phase shifts. Measurements show that it is possible to combine eight transmitters arbitrarily close in frequency with 35 dB of isolation between adjacent channels, less than 0.5 dB insertion loss, and with horizontal pattern circularity better than ±3 dB. Additionally, this technique can be combined with cavity combining to maintain high isolation between additional tranmitters.