Page 98 - Antennas for Base Stations in Wireless Communications

Base Station Antennas for Mobile Radio Systems 71

TABLE 2.3 Typical Mechanical Details Illustrating Good Design Principles
Detail Practical Imperfections Preferred Detail Example
1
(a)
(b)
Strip conductors joined to one Contact pressure at circled point is not defined.
another or to ground. Loss, power rating, and PIM are uncertain. (b) Can also be achieved by
Impedance changes if contact point moves. bending or pressing strip end(s).
2

Right angle connection Any lack of square or deflection of the joint Move the fixing closer to the
between flat conductors. displaces the contact point: loss, PIM, unstable Z. bend, or press the flange to
define the contact point.
3
Most thermoplastic materials creep under pressure,
so the joint integrity is lost and heating occurs.
Brittle material may be fractured if joint is over-
Connection through a tightened. Add a sleeve over the fastener to
dielectric layer. remove stress from the dielectric
and to form a stable current path.
4
The problems are the same as those of the
preceding example, but this is worse because the
pressure under the fastener is higher for a given
Clamping through a joint closure force. Add a sleeve and a washer to
dielectric layer. reduce pressure: also observe
precautions as in (1).
5
This is particularly to be avoided. It shares the
problems of (3), and the point of current flow
between the screw and the upper conductor is
undefined. Don’t rely on current flowing from a
screw into the threaded component.
Current path relies on contact Defined current path.
through thread.
6
These examples are exaggerated to show clearly
what is happening.
Spring plug contact is Current path is incorrect: impedance uncertain and Contact is at entry to hole. it is
smaller than hole. current density at contact point is high. Plug will stable and less dependent on
overheat. spring temper.

chosen. If the reasons for avoiding the details in the left-hand column are
understood, a variety of good solutions may often be found. This kind of
improvement in design details is not costly and the rewards are of value
both to the antenna manufacturer and the user: There will be fewer fail-
ures in post-production VSWR and PIM tests, together with improved
stability in performance and higher levels of lifetime reliability.

2.3.8 Use of Computer Simulation
The increasing power and affordability of computing resources has led
to the development of a range of electromagnetic simulation programs
that can be used to accelerate the design of base station antennas.